marine propulsion for small crafts

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Marine

ropulsion

•

n

Small raft

TECHNICAL

PAPER FOR:

THE

SOCIETY

OF NAVAL

ARCHITECTS

AND MARINE ENGINEERS

SOUTHEAST SECTION

A POWERBOAT SYMPOSIUM

AND

SECTION MEETING

Miami Beach

February 19 and 20 1985

By :

DAVID F. BUTLER

BUTLER MARINE TECHNOLOGY

INC.

600 SOUTHEAST FIFTH COURT

POMPANO

BEACH FLORIDA

33060

305-781-7458



SECTION

TABLE

OF CONTENTS

I ••••• INTRODUCTION

II

FOUR CYCLE

GASOLINE

ENGINES

I l l TWO CYCLE

GASOLINE

ENGINES

IV TWO

CYCLE DIESEL ENGINES

V FOUR

CYCLE DIESEL

ENGINES

VI

TRANSMISSIONS AND

DRIVE

SYSTEMS

LIST

OF

ILLUSTRATIONS

FIGURE NUMBER

1

TITLE

1900 GASOLINE ENGINE ••

14

HORSEPOWER

2

4

5

6

7

1957 GASOLINE ENGINE •• 6 HORSEPOWER

TABLE

OF ENGINE SPECIFICATIONS

SECTION

II

1985

V 8

GASOLINE ENGINE •• 32 HP

MERCURY

475

TURBO

RACING

ENGINE

HAWK 511 ENGINE WITH P 1000

EXHAUST

MERCURY

5

EFI

RACING

ENGINE

CARNOT

ENGINE

CYCLE

9

1

11

12

ACTUAL

ENGINE CYCLE 3 5 CU INCH ENGINE

ENERGY DISTRIBUTION 3 5 RAW WATER

COOLED ENGINE WITH STERNDRIVE

ENERGY DISTRIBUTION 454 FRESH WATER

COOLED ENGINE SYSTEM

FUEL ECONOMY CURVES FOUR CYCLE



LIST OF ILLUSTRATIONS

CONTINUED)

fiGURE NUMBER

If

ITLE

13

TABLE OF TWO CYCLE ENGINE SPECIFICATION

SECTION

l l

14 TWO

CYCLE ENGINE DESIGN

15

ENGINE CYCLE

FOR TWO

CYCLE DESIGN

16

TABLE

OF

TWO


SECTION

IV

17

TWO

CYCLE SYTEM

OF

OPERATION

18

TURBOCHARGED

TWO

CYCLE DIESEL ENGINE

19

MARINE FOUR CYCLE DIESEL ENGINES

2

VOLVO TMD

4

DIESEL ENGINE

SECTION V

21 DETROIT DIESEL 8 2 LITER ENGINE

22

PERFORMANCE CURVES

8 2

LITER 28

BERTRAM)

23

CATERPILLAR

32 8 TA

CONSTRUCTION

24

MTU 6V-396 FOUR CYCLE DIESEL

25

MARINE TRANSMISSION -

GAS

26

VOLVO STERNDRIVE CONSTRUCTION

SECTION VI

27

ELEMENTS OF A MARINE DIESEL

28

ARNESON DRIVE



INTRODUCTION

At the turn of the 20th century, sail

and

steam were the only

motive power of significance on

the

yachting

scene and of these, sail

was

the overwhelming

choice. While powerful, fast steam yachts were

in

existance,

their numbers

were extremely

small. There were some

steam launches

with

small single-cylinder engines and simple upright

boilers, and

a

very

few

fast curisers

with tandem or

triple expansion

steam power

plants.

New types of propulsion were appearing in small

runabouts

- the

Naptha powerplants

an

offshoot

of steam

engine designs)

and

the infant gasoline engines.

There

was no

question

that sail dom

inated

the

yachting scene, far overshadowing

all

other means

of

propul

sion.

At the turn of the century

gasoline engines

for small launches

were typified by

the

Easthope

one

and two cylinder gasoline engines.

A

single-cylinder

model

is

shown in FIGURE ONE. The inlet

and

exhaust valves are driven by external push rods driving off the cam

shaft.

The

distributor is driven by exposed bevel

gears,

and

the

direct drive transmission is the ultimate in simplicity.

The

engines of

the

period were

typified

by long strokes, and

this

tended

to limit maximum RPM. This

engine

had a 3. 875

bore and

a 5-inch stroke. Displacement was 59 cubic inches, and maximum

power was

14 horsepower at

9

RPM.

The engine could also

idle

at

100 RPM which is incredibly slow. Specific power output was

1/4

horsepower per cubic

inch.

Some of the new racing

engines

discussed

later turn out 1. 4 horsepower per cubic inch while

screaming

away at

5 400 RPM.

World War I provided a tremendous push to engine technology •

By the

end

of

the

war,

water-cooled military aircraft

engines

had

become amazingly modern in concept and construction. Mercedes

with a straight

six and Hispano-Suiza

with a

V-8 both

had

reliable



engines over 3 horsepower. The Liberty aircraft engines in the

United

States

found

their way

into

racing boats, and the new

speed

records

and publicity did much to

popularize speedboats

in the

1920 s.

During

the

1930s

intense research

in

diesel

technology

took

place with the

development of powerful locomotives to replace

the

steam engines. Since steam locomotives

are

non-condensing,

the

overall

system efficiency was less than five

percent,

and the

potential

cost

savings

with diesel locomotives was enormous. By the beginning

of World War

II,

two and four cycle diesel engines in the sizes needed

for

landing craft

and submarines had

been developed

and were in low

volume production. World War

II gave

a

tremendous

push in all areas

of diesel technology,

and

many improvisations

were

required. General

Motors had

an

outstanding diesel in

the six

cylinder 71 series engine,

but many applications

required

more power.

Arrangements

were created

with

two and even four 6-71 engines driving a single transmission, and

by 1947

the

twin installations were able

to provide 4

HP

at

2000

RPM

for

yachting

applications.

In the post World War II

period

the

gasoline

engines specifically

designed for

marine applications were

gradually

dropped in favor of

the

new

overhead valve

automotive

engines

available

for

marine

con

versions.

These

engines were built in new, highly automated

plants

in

large production

volumes,

and

provided much higher power outputs

at reasonable cost

than

the older designs.

Diesel technology for yachts was pretty well dominated by

naturally aspirated designs in

both

two and four

cycle until

the early

1970s. The Detroit Diesel SV-71-TI and the Cummins

VT-370

became

popular engines for yachts in the

4

to 55 foot size, and pointed the

direction of

future development.

During

the past

decade, intense

research has lead to a flood of turbocharged diesel engines in many

configurations, ranging from turbocharged six-cylinder designs attached

to

sterndrives

up

to the

complex

turbocharged

and aftercooled V-12

and

V-16

diesels

available in the

9

to 2630 Horsepower range.



MODEL

4 6

MARINE ENGINE

14

Hp

at

900

Rpm

Easthope

has

been

designing

and manufacturing marine engines

since

1897. As one

of the

oldest engine

manufacturers in

the world our sole

aim

.237

Hp

has been

to build

engines as

basic

and

reliable

as

possible. All our

engines

undergo

the most

thorough

examination both during and

after

construction so

that

we

can

confidently

say that all the boat

owner has to do is

install

the

engine

and

enjoy it. Easthope engines

are

completely

handbuilt

n

and

designed to give a lifetime

of

service

with

the

minimum of maintenance

19

Gasoline Engine

1 ::::=====-1-



FOUR CYCLE GASOLINE ENGINES

The

small

gasoline

engine

shown

in

the

introduction

is

still

manufactured today with one important area of

change.

The ignition

systems at the

turn

of the century were a major source of unreliability,

and the little

Easthope

has a modern ignition system

and

alternator.

The

dampness

of the

marine

environment caused many serious

problems.

Rolls

Royce

in the famous Silver Ghost

series

went

to

two totally

independant ignition

systems

with two spark plugs per

cylinder.

Marine

engines were

also

available

with

this system, and the Easthope

Model 8-14

twin cylinder can

still be ordered with

both magneto

and

distributor

ignition

with two spark plugs per

cylinder.

Careful

maintenance

and good

ventilation

were

the

best

recommendations for

reliable

service

on

these

early

engines. The

Easthope

single-cylinder

developing

14

horsepower at 900 RPM is typical of the period.

This

little engine

could idle

at 100 RPM and the specific

power output,

at .237

HP

per cubic inch,

was

very modest. If

more

power was

required, a two cylinder model was available, providing

38

horsepower

at

1200 RPM. This was a later design which enclosed the valve

push

rods

inside

the

basic

engine

castings. The

engine

was

still

designed

with a common cast iron

sump which

provided the

line

of

strength

from the engine through the transmission, and the flywheel was huge

to

allow

idling

at 150 RPM. The

specific power

output

was

considerably

higher

at

.

32 HP

per

cubic

inch. These small economical engines

powered

thousands of launches

and

small runabouts early in

the

century.

They

were

far lighter and more fuel efficient than the steam powered

plants of the period and

eliminated

the

need for

a licensed steam engineer

and the need for shoveling

coal

to

stoke

the boiler on

a

hot summer's day.

A typical

marine engine used

from the mid-1930s

up into the

1960s is

shown

in FIGURE TWO. This is a Chris-Craft Model B of

1957 providing 6 horsepower at 3200 RPM. This type of engine

was



Chris Craft 6 0 h p marine

Here's a nother power-packed Chris-Craft 60-hp engine.

You'll find the Model B

w ll

deliver the power and econ

omy that you expect in ll Chris-Craft marine engines.

Satisfied users

of

Chris-Craft marine engines can tell

you about the remarkable performance they've been

getting. One boat designer says, "Several years ago I

designed a fast fishing boat that was powered with a

Chris-Craft marine engine. After serving 14 years, this

engine was removed

and

installed in another

boat-

60 Hp at

3200

133 u In

.45

and s still going strong

And,

he says, "the economy of upkeep and oper

ation of Chris-Craft marine engines has been truly

remarkable. For many years now,

at

my own boat yard,

I have installed Chris-Craft marine engines in new boats

and as replacements. None has ever given any trouble."

For

smooth, dependable power, low upkeep, long

life, boat owners all over the world have chosen this

Model B marine engine.

1957

Gasoline

Engine

2 ~



MARINE FOUR CYCLE GASOLINE ENGINES

ENGINE

DISPLACEMENT

HORSEPOWER

MAX

RPM

HP/CU INCH

EASTHOPE

MODEL

11 6

59 9

237

EASTHOPE

MODEL 8 111

118 38

12 322

CHRIS CRAFT

B

133

6 32 •

45

CHRIS

CRAFT

K

23

95

32 • 41

CHRIS

CRAFT

KFL

236 6

131 38

55

CHRIS CRAFT MCL

339 2 175

34 52

CHRIS

CRAFT WB

404 3

2 32 • 49

CRUSADER 22

3 5 2 5 44

• 67

MERCRU ISER 26

35

245

44 700

CRUSADER

35

454

32

44 705

MERC 475 TURBO

454

1175 52 1 05

HAWK

511 511

57 54

1

12

MERC 500 EFI

1196

7 6

1 52

3



FOUR CYCLE GASOLINE ENGINES

very

widely

used

In

the

small

Mahogany

Runabouts.

For

larger yachts

60

horsepower

was simply not

sufficient even

with the modest demands

of forty years

ago.

The

line

of engines

included a

six-cylinder

companion the Model K at 95

horsepower

with a very similar output

at

111 HP per cubic inch.

Cabin

cruisers

and high speed

runabouts

required still

more

power

and

this

need was met

by 1 increasing

maximum

RPM above

the

3200 limit

2

increasing displacement up to the maximum practical

limits in

six cylinders

The

model

WB

had

11011 cubic inches

or

67

.II

cubic

inches

per cylinder. 3

Use

of

multiple carburetors on the

engines. These fifty year

old

designs used Updraft

carburetors

with

a

vertical plate-type

flame

arrestor as

shown in FIGURE TWO,

and

a

pair

could

be mounted side by side feeding into a split intake manifold.

There was a V-8 monster available at about 7 liters capacity

but it was such a specialized engine it was too

expensive

for

normal

applications.

Most

large

yachts used

two

of the

175

or

200

horsepower

six

cylinder

engines and for the larger yachts over

fifty

feet three

engines were often installed.



VEE

EIGHT MARINE ENGINES

During the 1960s and 1970s the marine gasoline engines

changed from the In-line blocks designed as marine engines to

the conversion of the new powerful

overhead

valve

vee-eight

engines developed for automotive uses. Most of the current marine

engines

are based

on the

General Motors

series of

blocks

of

305

cubic inches

up to 454

cubic

inches. For race boat

applications,

heavy-duty

454 blocks with

the

four bolt main

bearing

design allow

horsepower outputs up into the astronomical

range.

Often these

engines

are

re-worked

with

oversize bores and

special

crankshafts

to

further

increase the

displacement to

the 500

cubic inch

range.

A comparison

of

the standard and high-performance vee-eight engines

is given below in the lower half

of

FIGURE THREE.

The

power outputs on the chart show the current

state of

the

art

with the large, strong automotive

blocks.

The Crusader 220

the Mercruiser 260 and the Crusader 350 are the standard models

used

in

90

percent of

the

inboard

cruisers

built today, and these

same

basic

engines are

used

in most of

the

stern

drive·

models. Typically,

the

305 and

350 blocks are used in

yachts under

30 feet,

and the

big

454 block is the workhorse for cruisers over 30 feet and in

performance

racing boats in

stern drive

configuration. All

of

the standard

engine

designs

give a

specific power output of about

•

70

horsepower per

cubic inch

of

displacement.

This is three times as

high

as the typical

engine

of

1900 and

55 higher than

the 1957 engine shown in FIGURE TWO.



TURBO-CHARGED GASOLINE ENGINES

The design

of a

turbo-charged gasoline engine based

on

the

454

cubic

Inch block Is shown In FIGURE FIVE. This model is

built

by the HI Performance

Division of

Mercruiser and provides

a power

output

of

just over one horsepower

per

cubic

inch of

displacement.

This is accomplished

by

mounting a turobcharger at

the end

of

each exhaust

manifold

and using the

two turbines

to power air

compressors, boosting the

incoming

air

in

the intake

manifold.

Turbocharging is

highly

successful

in

aircraft gasoline engines

and

in

marine diesels, but has really not been competitive

in

marine

gasoline engines. Aircraft

engines are designed

from

scratch to

meet

the stresses

of turbocharging,

and the 325 horsepower Continental

opposed

six,

for

example

can

stand

39 inches

of

mercury boost on

take

off

which

puts the pressure

in

the intake

manifold

at

almost

34

pounds per

square inch psia).

Such pressures

would blow a

con

ventional marine gasoline engine to

bits,

fracturing pistons, bending

rods and causing cracked heads and bearing failures.

The turbocharged

Mere

475

must

compromise

on

Intake boost

for

these

reasons, and the turbos cause restrictions

in

the exhaust

gas path.

TUNED EXHAUST

Another approach

is

to concentrate

on

getting

the

maximum

amount of

air

through

the

engine.

This

is

illustrated by the HAWK

511

engine in FIGURE

SIX.

·To

achieve the

54

brake horsepower,

all

the

passages in

the

cylinder

heads are carefully polished

with

rotary

grinders

to smooth

the

air flow oversize

intake

and

exhaust



475T

75

Hp

at

5200

5 Cu

Inches

1 05 Hp/Cu In

HI :·:PERFORMANCE PRODUCTS

2521 Bowen Street •

Oshkosh

WI 54901

Telephone (414) 231-9180. Extension 331. or 353

Tu rboc ha rged

SPECIFICATIONS

Horsepower

475

Cylinders V-8

Displacement

454

Cu. ln.

Bore Stroke 4.2Sx4.00

Compression Rallo

7:1

Induction Single 4 Barrel

Fu

II

Throllle Range 5200

Drive Unit TRS

MC II SSM

or MC Ill

SSM

A BRUNSWICK

COMPANY

783

Gas Engine

~ 5 ~



TUNED EXHAUST (CONTINUED)

valves

are fitted

and

special matched

sets

of

pistons

and

machined-

-over connecting rods are assembled

to

special crankshafts.

This

power output

can be

further

raised to 570

brake

horsepower by the

use of

Stelling

exhaust headers. An

engine

and transmission

set up

in full racing dress

costs about

27,500 due to the tremendous

input

of skilled

hand labor and

the very expensive materials used In

con

struction.

TUNED INTAKE SYSTEM

About the highest power

output

per cubic inch of displacement

in marine gasoline engines is achieved using the approach shown in

FIGURE SEVEN. Four tall stacks bring the air smoothly into

each

of

two huge

Holley

carburetors.

The exhaust would

be

similarly

treated

with

huge

cast aluminum exhaust manifolds capable of handling the

exhaust gas with the absolute minimum pressure

drop.

This is done

with

large

polished

passages and

a

short

large-diameter path

for

the exhaust gas

directly

aft

and

through the

transom.

In this

illustration

the exhaust

headers

have

been removed to show the double

carburetor

and

intake air

configuration.

The exhaust

headers

would

be similar

to

FIGURE

SIX.

In the racing

classes

of engines each

engine

has a huge input of skilled mechanical

effort

and this includes

Individual

dynamometer

testing of each engine. The

700

horsepower

rating

means a guarantee of

over

700 brake horsepower

centrified

with

each engine. This

amounts

to

over

1. 5 horsepower

per

cubic inch

or

in the

current

technology

nearly 90

horsepower per liter of dis

placement.



DOUBLE ENDED HOLLEY CARBURETOR

WATER CONNECTION TO PORT

EXHAUST S Y S T E M ~

PORT EXHAUST MANIFOLD ..;

ENGINE LUBRICATING OIL

f i tTER

TO

STARTER 12 VOLT)

COOLING LINES

HIGH VOLTAGE WIRES TO SPARKPLUCS

TYPE HIGH VOLTAGE COIL

TYPE SPECIALLY BALANCED DISTRIBUTOR

ARRESTOR

~ F ~

PUMP VENT LINE

DISTRIBUTION MANIFOLD

COOLING WATER HOSE TO EXHAUST MANIF

LINES ·TO BOTH ENDS OF

THE

CAR

ALUMINUM

VALVE

ROCKER COVER

S

CAST ALUMINUM WATER COOLED

EXHAUST MANIFOLD

FUEL SUPPLY FROM PRESSURE CO

SEA WATER PUMP DRIVING COOLIN

WATER INTO ENGINE

WATER LINE TO

OIL

COOLER

H WK

NGIN S

TYPE

FUEL

PUMP

HIGH CAPACITY OIL PAN

WITH INTERNAL BAFFLES

ST RBO RD

SIDE

Jo



EFI

700•

Hp

at

6000

496 Cu Inches

1 43 Hp/CU In

HI

: :PERFORMANCE PRODUCTS

2521 Bowen Street • Oshkosh WI 54901

Telephone {414) 231-9180. Extension 331.

or

353

SPECIFICATIONS

Horsepower 700

Cylinders

V·8

Displacement 482/496

Cu. ln.

Bore Stroke 4.375x4.0/

4.440x4.0

Compression Ratio

12:1

lnducllon Eleclronic

Fuel Injection

Full Throtl le Range 6000

Drive Unll MC

Ill

SSM

i i

:tiH :9

MARINE

A BRUNSWICK COMPANY

78

Mercury 5 EFI

~ 7



CHANCEABLE CYLINDER

HEAD WHICH IS {

1)

HOT

2) INSULATING 3) OLD

q) INSULATING

PISTON,

WHICH

IS A

FIT IN THE CYLINDER

•

si

COMPRESSION STROKE

DI B TIC COMPRESSION

WITH NO HEAT TRANSFER

arnot

EXPANSION STROKE

lNG MEDIUM HEATED

BY HOT CYLINDER HEAD

CONSTANT TEMPERATURE )

EXPANSION STROKE

NO

TRANSFER

WORKING MEDIUM COOLED

BY COLD CYLINDER HEAD )

Volume •

Engine ycle

s

PERFECTLY SMOOT

CYLINDER WALLS W

ARE LSO PERFECT

INSULATORS { NO



THERMODYNAMIC EFFICIENCY (CONTINUED}

efficiency of 24 does not seem too good and leads to the need for

a

fundamental

look at

the

operating

principles of the

4-cycle gasoline

engine.

The

most

efficient possible cycle for

a

piston engine

was

postulated by

a

Frenchman,

Nicholas

Carnot,

in 1820.

The

Carnot

Cycle is shown in FIGURE EIGHT and is described

as

follows:

A

cylinder

contains

a

working

mixture .

Starting at

point

a in

the cycle,

the

gas

is at

pressure

P1 and temperature T 1

•

The cylinder head

is a hot

surface at temperature T1,

and

the

heat

transfer

is so instantaneous and so

perfect

that T 1 is

maintained

as

the piston

moves from

point a

to

point

b doing mechanical

work

on

the

piston.

At

point

b

the hot cylinder head

is

suddenly replaced by

a perfectly insulated head, and

the

cylinder walls

and piston are

also

perfectly insulated. While the process

a-b

is ISOTHERMAL

(constant temperature} the process b-e

is ADIABATIC.

The gas

has

continued

to

do

useful work on

the piston

and

the

mechanical

energy

is

represented

by a drop in

the

internal energy of the gas

in

the cylinder.

At

point

c

a cold cylinder head

at

a

temperature

T 2 is

suddenly placed

on

the engine, and as the piston compresses the

gas,

the

cold

head

absorbs energy

so

that

the

work

of

compression

is far less

than that of

expansion.

This

is

another

ISOTHERMAL

process.

At

point d an insulating head

is

put

on

the

cylinder

and the gas

is

compressed

adiabatically

back

to

point a .



ACTUAL OPERATING CYCLES

The operating

cycle

of

a

typical

3 5

cubic

inch V-8

marine

engine is

shown

in FIGURE NINE The

curve

shown is built on

the best

available check

point

from

laboratory dynamometer

data,

but the shape of the

curves

have been

simplified

to

make math

ematical analysis

easier.

COMPRESSION STROKE

The

compression

stroke

swoops smoothly

upward to peak

pressure

and

temperature

in

the

Carnot cycle. In

real

life

the

performance is very different

due

to

massive

heat

transfer

from

the compressed charge

to

the cold

cylinder

walls.

Theoretically,

a

compression

ratio of B 5 to 1 would achieve a

pressure

of 250

PSI, and a

thermature of

750

degrees.

With a real engine,

there

is

massive

heat

transfer

as 43 cubic inch

charge

is crammed

into

a

1

/2-inch

high

space

at

the

top

of the

cylinder,

and

actual

pressures

of

about

175

PSI

and temperatures of

5

degrees are

achieved

in

an

engine in

good

mechanical

condition.

POWER STROKE

About

2 degrees before

the

piston

reaches top

dead

center

TDC).

the spark plug fires.

The

combustion process burns the

charge

to a pressure of

about

850 PSI, and the central flame tem

perature is at about 2500 degrees. Both the temperature and

pressure

are much less than theoretical calculations

due

to

massive

heat

transfer.

Thermodynamically, the

flame is

burning

in a large

diameter

chamber

only 1

/2-inch

high with ice cold

walls. The

heat

transfer possibilities

are

enormous.

The cylinder

and

heat

must

be



VOLVO TMD

4 TURBOCHARGED DIESEL

ENGINE

PRE COMBUSTION CHAMBER DETAIL

FIGURE

2



soo

·

• 6 0 0 \

I

....

UOT

Pressure \1

v ~ ~ ~ ~

4

00

1 \.. -1----

p

s I

I ' - , ~ . ' 0

.... ~ X P A

NSION . .

~ . . . , .I ·e.-

'

,..

. t o ' r ~ t -

'I FSI

e s h ~ _

= r

~ - ~ - = - - ' . J - ~ ~ ' f . . . . C ' • •=-·::.-.,.

--....;;

F l ' f e ~ l •

_ _ •

THO• •

- - L - - - 1

P

1

' -

1-_Z - ~ --' j-e .I= I ·

s

1

-

J:N.TA

0

5

10

IS

Volume

20

25 SO

'35 ..co

4S

Cubic Inches •

O·F·IS

"'as

Pressure-

Volume

Curves

4 Cycle

' - ---- ----



POWER STROKE CONTINUED)

kept

so

cold

since

a raw

water

cooled

engine cannot

allow

the

salt

water

to

get over

150

degrees or the

salt starts to

precipitate out

of

solution.

The

20

degrees of travel

between spark plug firing

and top

dead

center

occurs in less than a millisecond at 400 RPM. With

typical

flame

speeds

of 150 feet

per

second, the burning occurs

basically

with

the piston near top dead center, and FIGURE NINE

shows

a

straight

pressure

rise

to simplify

calculations.

If

the

fuel

is

not

of high enough octane, there will be detonation which is

easy

to

hear

in a car

and far more

difficult to

detect

in a marine

engine.

Fortunately, knock will rarely cause mechanical damage

to an engine and

is easily solved

by

1

proper

grade

of leaded

fuel; 2 retarding

the spark ignition

closer

to

top dead

center.

Pre-ignition is an entirely different story. If hot spots

develop

in a chamber, the

compressed

charge may light

off

before

the

plug

fires.

Flame

speeds of

1000

feet

per

second

give

no

audible

warning, but

can

cause severe engine destruction. The

flame

fronts

and pressures are building

at

sonic velocity

as

the

piston

is still

coming

up

and peak

pressures go so

high that damage is inevitable.

Good

engine

cooling

and avoidance

of long maximum RPM operation

are

the best

preventatives.

EXHAUST STROKE

On a normal marine

engine

the exhaust valve opens about

50 degrees before bottom

dead center BDC). On

racing engines this

is moved

back

toward

80 degrees

before BDC.

The

remaining pressure



6

EXHAUST STROKE CONTINUED)

drives the gas through the exhaust

valve opening

at

sonic velocity

and with the exhaust typically at 1500 degrees, the opportunity for

heating

the

exhaust valve is tremendous.

The pressure

remains well

above atmospheric during

the

entire exhaust stroke, and pumping the hot exhaust

gas

through

the

slot around the

exhaust

valve represents negative work

and

another

loss

in the

operating

cycle. The exhaust valve closes

about

15 degrees

after

top

dead

center.

INTAKE STROKE

About 15 degrees

before top dead

center

the

intake valves

open, resulting

in about a 30° period when both intake and exhaust

valves are

open.

With

tuned intake and exhaust

systems,

the

moving exhaust

gas

and intake air columns continue to move properly,

even

with

both valves open.

The

entire induction system of the gasoline engine operates

below

atmospheric

pressure. A vacuum

gauge

in

the intake

manifold

would show up

to

15 inches of mercury

under

low

demand

operation

2000 RPM

but

only 2 - 4 inches of

mercury

when

the engine

is

running

wide

open at

4400 RPM. The critical operation it

at

wide

open throttle where

only

a small pressure differential

must

provide

huge

air flows through the carburetor. With a Rochester

Quadrijet

4-barrel carburetor, 387 cubic feet

per

minute

will flow

even

at

low

differentials. The large

Holley models can move 1050 CFM

of

air

through four barrels in a

racing engine.

At the end of the intake

stroke, there is a

cylinder

full

of

air at

ambient temperature and

at

a pressure of 12.7

pounds

per

square

inch

absolute.



HEAT LOSSES

IN AN

ENGINE

There

is

a

serious

limitation

to

the

thermal

efficiency

of

an engine even using a CARNOT cycle. When all the

thermal

and

friction losses are taken away,

the

operating cycle

shown

in FIGURE

NINE is much

less

efficient.

The overall

distribution

of

the thermal

energy

burned

in a

raw-water cooled

305 cubic engine

is shown in FIGURE TEN.

The

source

of energy

is

the 201 gallons of

gasoline

burned

per

hour at wide

open throttle.

With fuel at 18 900 BTU

per gallon

there is

enough total

energy

to

deliver 926 horsepower

if

it all

could

be

utilized. Unfortunately, only 25 of it comes out

as

useful work

at the

engine

flywheel.

The largest

loss

is the huge

thermal loss

in

the

hot

exhaust

gas.

The

hot

expanded gas in the cylinder at

72

PSI and 1500°F

represents 35

of

the total thermal energy

available in

the

fuel.

The

other

gigantic loss is the 32 or 300

horsepower)

lost to

the

cooling

water. Ideally,

the cylinder walls would be

kept at about

1500°F and the gasoline injected

at the

end of the compression

stroke

as

in a diesel. In thermodynamic terms,

the

cooling water at 140°F

is ice cold and the gasoline is

wasting

most of its energy maintaining

a ball of hot gas

surrounded

by a deep

freeze

of cylinder

walls,

piston and cylinder

head.

After these huge exhaust and cooling losses, 309 horsepower

remains

for

useful

work.

Seventy-five horsepower is lost in friction

in the

engine, and a

further

14 horsepower in

the

bearings and

gears

of

the transmission.



'

900

800

~ ~ o o i

W

i

I I

6-soo;

o l

~ ~ 4

ol

HE T

LOST

TO

EXH

AtiST

GRS 35

'3'21 HP

HEAT

LOST

- ENE:R GV

L O S S E S

.

RAW

WATER

.

COOLED

G S

E N G I N E W I T H

OUTD < : \Ve

TO C.OO

LING

WATei'C. '3'2

300 HP

o:

H E ~ T

I ~ 3 Q CONTENT

T ~ A N S M I S S I O N

LOSS

14

HP

I

o 9 3 6 ~ p

I

200

I

\00

THRUST T o MoVE

6oAT

154

HP

=

I Ocro

Burt er?..

.... 8

Losses-

Raw

Water

ooled

as

11 10

l



HEAT LOSSES IN AN ENGINE CONTINUED)

The

effective shaft horsepower of the overall system is 220.

With a propulsive efficiency of 70 ,

this

gives

5 horsepower

to

actually push the

boat

through the water.

EFFICIENCY OF FRESH

WATER

COOLED ENGINES

The

highest

efficiency achieved in the

marine

gasoline power

plants was found

in

fresh water cooled, pressurized

coolant

systems

running

at temperatures of 190 to 200°. This approach minimizes

the

heat

transfer

from

the operating gases

to the coolant. When

this

approach

is

combined

with

carefully calibrated

carburetors, improved

efficiencies are achieved.

The overall results

are still

poor, as

shown in FIGURE ELEVEN.

The fuel rate

of

25.11 gallons per hour provides sufficient thermal

energy

for

12311 horsepower

at 100

efficiency.

Thirty-five percent

of

this

heat

is

lost

in

the exhaust gas; the

same percentage

is in

the

raw

water

cooled

engine.

With the big

block

engine, this amounts to a

staggering

32

horsepower. The heat

lost

to the cooling water is reduced from 32 to

30

but still accounts for

a whopping

367

horsepower.

Heat

lost

to friction is 100

horsepower

or

8 , and the marine

transmission

loss is

35

horsepower.

This figure

is much larger than

on the raw

water

cooled engine due to the transmission characteristics.

The small

engine has

been shown with a stern drive which

uses

cone

clutches,

while the

fresh

water cooled engines are almost always used

in

inboard engine installations. These transmissions have multi-disc

clutches with much

higher

transmission losses.



HE'AT

CoNTI N T

O FUEL

1200

1000

l

800

U

3

0 OO

Q

U

Ill

l

400

0

: t

200

1'2

HP

HEAT

LOST TO

EXHAUST

GAS

35 -=432HP

I I E ~ T

.

LOST

To

CoOLING-

WATeR.

= :,aoHP

P o P o L . SIVE LoSS aSHP

(33 OF SHP

T H ~ ~ S T TO H o V e

YACHT

190

HP =

t5%

E N E ~ G (

LOSSES

F ~ e S H

W T E ~

Cocn

.

ED

G S O L I N E

I N 8 o A ~ D

b.F.B

8'i -8S'



EFFICIENCY OF FRESH WATER COOLED ENGINES CONTINUED)

The shaft

horsepower

available

is 300,

or 24

oy

the

thermal

energy of the fuel. with a 70 propulsive efficiency we

have

17

of

the energy

content of

the

fuel

available to

thrust

the boat

through

the water.

FUEL CONSUMPTION CURVES

Fuel

consumption curves

for a typical 305 cubic inch marine

engine

is

shown

in FIGURE TWELVE.

The

gallons

per

hour

are

shown

in the

lower

solid

line.

At

idle

the engine

burns

about

gallons

per hour and consumption rises to 201 gallons per

hour

delivering

220

brake

horsepower at 4400 RPM.

A curve of

fuel economy

is shown

in

the upper curve on

the left-hand side. Fuel economy Is measured in pounds of fuel

required

per

brake horsepower-hour.

Thus

at 1000 RPM it requires

2.27 pounds of fuel for each

brake

horsepower for an hour. In the

most

efficient

range from 2500 to 3500 RPM, the engine requires only

6/10 pound

of fuel per brake horsepower-hour.

At wide-open throttle

the fuel consumption

rises

to about . 65 lb. per horsepower hour to

deliver

about 200 shaft horsepower

at

4400 RPM.



Fuel

20

Gal

5

Hour

•

5

0

0

FUEL

ECONOMY- MAIZ.INE V-S

305

1N3

8 45:

I c R ENGINe:

Z:l T

•

-

,69

2oo

Shaf

ISO

H P

100

50

----

·

0

5

1 0 0 0 1500

zooo

2500 ~ 0 0 0 3500 ~ 4 5 0 0

Engine R.P.M. •

Fuel

Economy Curves

o e

1 2



FUTURE TRENDS

Future trends in four-cycle gasoline engine technology are

visible today

in

the

automotive

developments

in

the

United

States,

Japan and

Europe.

FOUR VALVE DESIGNS

Extremely high power outputs are being achieved

by

designing

with four valves per cylinder. As heads manufactured this way become

available in automotive

engines, they

will move

over

into marine

very quickly. If effect, the four valve design opens up

the

intake

and

exhaust flow allowing specific outputs to exceed

horsepower per

cubic inch in

standard engines.

TURBOCHARGING

Turbos are being added to small displacement

automotive

engines

today. When larger

displacement engines

are

designed to handle

the

higher maximum

pressures

developed by turbochargers, they will be

adapted

for

marine

use.

LIGHT WEIGHT ENGINES

Considerably higher

power

outputs will be available in the

future

with

the

same

external engine size. The

new

lost

foam

casting process

gives

very

accurate

block

castings

with typical

cylinder

wall

thicknesses of

• 230 inches.

Larger bores,

more

efficient

water passages and higher weight are

coming from

this

casting technique, particularly when

used

with OSTEO-STENETIC

heat

treatment

procedures

for machined

castings,

such

as connecting

rods

and crankshafts.



FUTURE TRENDS · CONTINUED)

FUEL INJECTION

Another area

is

to increase the burning

efficiency

by reducing

the fuel-air

ratio. Intense

research in this area is yielding excellent

results. Electronic sensors

are being

mounted

in

the engines to

monitor

operating conditions. The use of

fuel injection

systems

monitoring

individual cylinders performance are in the works in

automotive

applications

and

when

this

is

combined

with

knock sensors

which

adjust

the timing of the spark plugs

for individual

cylinders

we

are

pretty close

to optimum efficiency.



TWO

CYCLE

MARINE

GASOLINE

POWER

.ENGINES

The two cycle marine gasoline engine was first applied

as

a

small,

low-powered

outboard

motor to propel

rowboats

at

low speed.

The intent

was

to

replace

hours

of

hard

work

rowing

with

a small

portable

engine which would accomplish the same purpose. Many

inventors participated around the turn of the

century,

but the

Evinrude

system turned

out

the

best, and these

heavy,

low-powered,

single-cylinder

motors became widely used. In the 1920s, the emphasis

shifted to more

powerful

opposed piston

twin-cylinder

models.

By

mounting the cylinders opposite

each

other, the vibration was consid

erably

reduced

and

higher power

with lighter

weight was achieved.

Eighty years

of development has resulted in huge improvements

in compression

ratios,

fuel economy, reliability, smoothness and power

to

weight ratios.

A

table of

current

engines

is shown in FIGURE

THIRTEEN. The OMC SAIL DRIVE is a specialized small

engine

designed

to drive heavy

loads

at low speed. t is included in the

chart since it

shows

that when current two-cycle

technology

is

applied to a workboat -type design problem, the maximum RPM

and

power

output per

cubic

inch

are cut

way back in

the

interest

of dur

ability

and

reliability

in

handling heavy loads.

The

maximum

engine

RPM

and

the specific power output are

typical

of engines of

forty

years ago.

Normally,

outboard

engines as a class are utilized on the

lightest and

smallest classes of

recreational boats.

The basic

designs

have

been

adjusted for this

with extremely high

power

to weight ratios

and high

specific

power outputs. The Johnson 75 horsepower engine,

for example, weighs 540 pounds, where a s imilar _power level in a

four

cycle

stern drive or inboard engine configuration weighs

almost

exactly

double this weight. The price is paid in durability. In commercial

service

fishing

outboard motors

are

often

replaced

yearly.

In fresh

water,

outboard

engines

last for

many years and in the modest hourly

usage of

many salt

water boats careful flushing of the engines after

use

results in

adequate service

life.



DISPLACEMENT

ENGINE

CUBIC

INCHES HORSEPOWER

MAX

RPM HP/CU

IN

OMC SAIL

DRIVE

31.8 15 3300

• 47

MERCURY 60 49.8 60

5800

1.20

JOHNSON 120 110 120 6000 1. 09

JOHNSON 275 220 275 6000

1. 25

EVINRUDE V 8

FORMULA ONE 214

400 10

000

1. 92

MARINE TWO CYCLE GASOLINE ENGINES

~ 1 3



TWO

CYCLE MARINE GASOLINE

POWER

ENGINES (CONTINUED)

The highest

power

output in outboard engines is

achieved

in

the

newest Formula One

engines typified by

the Evinrude model

shown

last

on FIGURE THIRTEEN. The heart of

the

engine is a

214 cubic

inch

V-8 block specially manufactured and hand

assembled.

Racing

pistons in

matched

and balanced

sets

are assembled to racing

rods

and the assembly topped off

with a

two-barrel

carburetor for

each

cylinder.

When mounted on a Formula One hydroplane, typically

one built of wood and

weighing

under 400 pounds, these engines can

drive the boat to

15

miles per hour. The engines alone

run about

22,000 a

copy

and

must

be

torn

down

and rebuilt

after

about seven

hours of running

at

full

racing

speed.

TWO CYCLE ENGINE DESIGN

The

basic

assembly of

a two

cycle

outboard is shown in

FIGURE FOURTEEN. The

fresh

charge is

drawn

into the crankcase

through a one-way reed valve during the movement of the piston

upward. There are

free-flowing

carburetors,

often one

per cylinder,

on

the high output engines and the crankcase serves as a receiver

for

the fresh charge.

As

the

piston

drives down

on the

power

stroke, the reed valves close and pressure builds up under the

piston. This

positive

pressure is used to scavenge the old combustion

gases

from the

cylinder as

the

piston

approaches bottom

dead

center.

This

configuration, with a vertical

crankshaft,

has been developed

over the years

into

a

very

specialized form of engine design.

The

gas dynamics become very critical to success. The time

for

the

exhaust gases

to

be

swept out and

replaced by

a

fresh

charge

are

VERY short, and

the

pressure differentials available to accomplish

the flows

are quite

low. At full

speed,

the

racing engine

is turning

at

10,000 RPM, or

167

times a SECOND.

This

means that from the time

the

exhaust port is uncovered until bottom

dead

center is one millisecond

( 1/1000

second).

Even a

regular outboard,

such

as

the 275

horsepower

model, at 6000 RPM has only 1/350 second for the entire exhaust and



RIDGE O TOP OF PISTON

TO

HELP CYLINDER

SP RK PLUG

EXHAUST C S

EXHAUST M N I FOLD

FRESH MIXTURE FLOWING

CYLINDER

CRANKCASE

FILLED

WITH

COMPRESSED GASOLINE AIR

MIXTURE

VENTURI

REED

TYPE

CHECK

VALVES

CONNECTING ROD

r Two

Cycle Engine Design

4

AIR

INTAKE

FOR

ENGINE



2 4

TWO

CYCLE MARINE GASOLINE POWER ENGINES CONTINUED)

recharging of

the cylinder. In a

camera

this

is

considered a fast

shutter speed, but in these engines it is the

total

time allowed

for

complete

purging

of

the cylinder.

It is small

wonder

that

about

1/4 of

the

incoming charge

mixes

with

the

exhaust and is

lost

during

this

very rapid transfer.

PRESSURE-DISTANCE CURVES

The pressure-distance relationships in a

modern

two-cycle

outboard are shown in FIGURE FIFTEEN. The

cylinder

volume is

27

cubic inches

with

the

piston

at

bottom

dead

center.

During

the

compression

stroke,

fresh

fuel-air

mixture flows

into

the cylinder

from the compressed charge in the crankcase. At a volume of about

22 cubic inches the intake port is cut off. The

piston

continues

upward and some of the

fresh

charge inevitably moves out the exhaust

port until it

is closed

off

when

17 cubic

inches

of cylinder volume

remains. The

trapped or

effective

volume is

the swept

volume

between 17 cubic inches and the 2.4 cubic inches

remaining at

top

dead

center.

During this

compression

period, the charge compresses

toward a theoretical 270

PSI; however,

the

spark plug

fires before

top dead

center

is reaches and

the

pressure

rises

quite rapidly as the

piston gets near TDC.

POWER

STROKE

Theoretically the

charge

would

burn to

a pressure

close to

900

PSI,

but this

theoretical

peak is

chopped

way down by the

burning rate of the

fuel

and heat

transfer

in

tiny space above

the

piston. It is amazing that the engines work at all, since the

game

is

to build

a 2500

degree fire

in a

chamber

1/4-inch

high with

a cold

cylinder

head above and a cold piston below.

Whether

the

piston

is

at

150

or

300 degrees

makes little

difference when the

fire

is

2200

degrees hotter.

The

losses to

heat

transfer have to

be

enormous.



TOP

DEAD

CENTER

PRESSURE IN

CYLINDER

POUNDS/INCH

2

P S I

THEORETICAL PEAK

/

I

I

PRESSURE

ACTUAL

PEAK

PRESSURE

BLOV1DO>WN

EXHAUST PORT

t11

BOTTOM

DEAD

CENTER

IGNITION

;.. -

SCAVENGE

POINT

PRESSURE

l i j 7

PSIA

CHAMBER

v LUME

0

Two

I

TRAPPED OR

1

EFFECTIVE

-----...,

VOLUME

EXHAUST PORT

CLOSES

INTAKE PORT

OPENS

PORT

CLOSES

<? 40

I

CUBIC

INCHES 17.0

CUBIC

INCHES

27 0

I

J

I

SWEPT VOLUME

CYLINDER VOLl JME

CUBIC INCHES

olume

6on tg:

Btr

T . O . f < I ~ I · O H C

Cycle

Pressure Distance

15



TWO

CYCLE MARINE GASOLINE

POWER

ENGINES CONTINUED)

During

the

power

stroke, the

useful work

is

done

by

the gas

shoving

the piston downward.

At

the

beginning of the

stroke,

the

force exceeds two tons, and

by

the end of the stroke

just

before the exhaust port opens,

the force is typically

about

1/2

ton.

EXHAUST STOKE

When the

piston reaches

a swept volume

of 7 cubic inches

the

exhaust

port

opens, and the

remaining

gas pressure

blows

down

into

the

exhaust manifold. With careful gas dynamics tuning the

remaining

pressure is slightly over atmospheric when

the

intake port

is uncovered.

Obviously,

if the remaining pressure is too

high,

the

exhaust gas

will blow

into the intake system and the

column

of gas

will develop a

dynamic

motion in the wrong direction.

The trick

is

to have the exhaust system

pressure

down just about even with the

compressed

intake

charge when

the port opens.

As

the exhaust

pressure

continues

to

decline,

the

compressed

incoming

charge

starts

to flow

into

the cylinder, sweeping up one

cylinder

wall and driving

the remaining

exhaust

gas ahead

into the exhaust

manifold.

The fresh

charge continues to flow in past bottom

dead

center and until the

intake port is

cut

off by the rising

piston,

The cycle then continues,

cutting

off

the exhaust port

and

compressing the charge until the

spark plug fires.

Modern two cycle

engines

represent some of the most

sophisticated

gas dynamics in

any

engine technology

today.

The

entire intake and exhaust systems are

tuned

to take advantage

of the

kinetic

energy of the

moving

gas

column

and achieve gas

flow

rates which are incredible in the time spans available.

These

modern

two

cycle designs provide extremely high power outputs

for

the engine

weight, and also

very high power

outputs

for

the engine displacement.



TWO


The main booster

of

the two cycle diesel principle for small

craft has been the General Motors

Corporation

with the

Detroit

Diesel

line

of

marine engines

and

the Electromotive

Division which

manufactures mid-sized

diesels

for

locomotives

and

commercial vessels

over

8 feet in length.

During World War II

thousands

of the Detroit Diesel

six-cylinder

71-series engines were installed in small landing craft. For larger

ships dual

engine

installations

driving a single shaft were developed

and when

even

more power was needed

an arrangement consisting

of

four

six-cylinder

engines

driving

a common

transmission

was

developed. By 1959 this concept had been refined so

that

the dual

engines

could

provide

47

horsepower and

special

Quad units using

HV 8 injectors could supply 1008 Brake Horsepower for yachting

use.

Transmission losses

were

fairly

high with this complex

arrange

ment and the weight was also

high at six

tons.

In

the

1960s

the

basic line-up of

two-cycle Detroit

Diesels

was

built

on

the

71

series engines

ranging

from

two-cylinder

to

sixteen-cylinder

models.

The

basic

workhorse 6-71 engine

was

available in a turbocharged

version

with a

power

output of 310

horsepower at 2300 RPM. This represented a 25 percent increase

in

power

and

this engine

in

both naturally

aspirated and turbocharged

versions

became popular in

cruisers

of forty feet and up.

In

the early

1970s

the power outputs had risen slightly

and a new series of

smaller

53 cubic

inch

per

cylinder

engines had

been

added

to the

line. The

8V-53-N

became

a

very

popular engine

for yachts in the

thirty-five

to forty-five foot range. A

powerful

turbocharged engine had been

added

in the 8V-71-T providing

425

HP and this became a widely used engine in yachts of the forty to

fifty-five

foot range.



TWO

CYCLE DIESEL

ENGINES

DISPLACEMENT

MAXIMUM

ENGINE

CUBIC INCHES

HORSEPOWER RPM

HP/CU

IN

ENGINES OF

THE

196

PERIOD:

6 71 N 426

235

23

.55

6 71 T

426 31

23 .73

12V 71 N

852

5 4

23 .59

16V 71 N

1136

66

23

.58

ENGINES OF

THE

EARLY 1970s:

DETROIT

DIESEL

BV 53 N

424

256

28 • 6 4

DETROIT DIESEL

BV 71 N

568

35

23 • 616

DETROIT DIESEL

BV 71 TI 568

425

23 • 748

DETROIT DIESEL

12V 71 N

852

525

23 • 616

ENGINES OF

THE

MID

198 s:

6V 53 T I 318

3 5

28

.96

6V 92 TA

552

475

23

.86

12V 71 TI

852

9

23

1 6

12V 92 TI

11 4

1 5

23

.95

16



TWO CYCLE DIESEL ENGINES CONTINUED)

TWO CYCLE DIESEL ENGINE OPERATION

A two

cycle diesel works on

a slightly different

method

than

the

outboard

engines. The

basic principles are shown in

FIGURE SEVENTEEN. Four

exhaust valves are installed

in

the

cylinder head, with a fuel injector mounted in the center. The

left-hand

illustration shows the intake and exhaust phase. A

powerful

roots

blower

is

gear-driven

from the camshaft

and

provides

a

positive

pressure

in

the

intake

manifold. When

the

piston gets

close

to bottom dead center

(BDC),

the exhaust valves

open and

the remaining pressure

in

the

cylinder

blows down into

the exhaust manifold.

The

incoming air enters

through

a ring of

ports around the bottom of the cylinder, and the positive pressure

in the intake manifold is used to give a

torrent

of air

rising

vertically

to

clear

the

cylinder. The time

for

clearing

the

cylinder

is

about 5

milliseconds

at

2300 RPM, far longer than

the

time

for

change in an

outboard engine 1-1/2 milliseconds). The cylinder in a

Detroit

Diesel is

also

far

larger than the outboard designs. Since

this is

a diesel, the incoming

air

has no fuel

and excess

air simply blows

and causes no

losses.

The middle illustration shows the piston rising on

the

com-

pression

stroke, and

at 17

to 1 compression, this

results

in a pressure

of

about 600 PSI at top dead

center. About

2 degrees before top

dead

center, the

fuel

injector

starts blasting in a fine mist of fuel

oil

at

about

1150

PSI.

The

injection

stroke

typically

continues

for

3

degrees

at

full load and would be

cut

off early

under part

load

operation. With

the

two

cycle

diesel,

each

downward

stroke of the

piston is a power stroke, and this has allowed the very high power

outputs developed in recent

years. Power

outputs of •86 to 1. 6



Exhaust

and Intake

Stroke

Compression

Stroke 2

Power

TWO CYCLE DIESEL OPER TION

1 7



CAMSHAFT WITH ACCESSORY

DRIVES ON BOTH ENOS

PUMP CIRCUL TING FRESH WATER

THROUGH BLOCK AND HEADS

ACCESSORY DRIVE

BELTS OFF

urbocharged

wo

Cycle

IR

COMPRESSOR

DRIVEN BY

TURBOCHARGER

ENGINE DRIV EN COMPRESSOR

WITH

COUNTERWEIGHTS

HEAD WITH

EXHAUST VALVES

UN

IT

INJECTORS

6

PSI

INPUT

115 PSI INJECTION TO CYLINDER

PISTON IN REPLACEABLE

C ST

IRON

CYLINDER

ASSEMBLY

Diesel

Construction

8



TWO CYCLE DIESEL ENGINES CONTINUED)

FUEL AND AIR QUANTITIES CONTINUED)

130 degrees is cut in half to 5 cubic

feet

per pound

and the

velocity

of gas in

single 8-inch

tubes is

down to 98 feet per

second.

EXHAUST GAS TEMPERATURES

Diesel

engines

are

very

efficient compared

to gasoline

particularly at

part

loads.

While

the

gas engine

must have

a fuel

air mixture within specific

limits

at

all speeds

the diesel can run

extremely lean at low speeds providing just enough energy to

over

come

internal

friction.

This can be

seen in some

tests

run

with

a

Detroit

Diesel

8V-92-TI engine.

TEMPERATURE OF

EXHAUST GAS COOLING WATER JUST

ENGINE RPM TEMPERATURE BEFORE DUMPING

IN

EXHAUST

OF

OF

520 250 130

800

420 128

1000 520

124

1400

625

122

1800

670 120

2300 710

109



FOUR-CYCLE DIESEL ENGINES

In contrast

to

the two-cycle

diesels,

there are many

manufacturers

offering four-cycle

engines.

A few of the most

popular engines are shown in FIGURE NINETEEN.

VOLVO TMD 4

AND

TAMD

4

In the 1970s, Volvo introduced a series of six-cylinder

diesels suitable for

small

boats,

all

based

on

an in-line

block

of

219 cubic inches. The Volvo engines were available either with

conventional

transmissions

or

sterndrives, and

are

used

in many

small

yachts

in the 2 to 35-foot

range. The

design

of

the

engine

is

shown

in FIGURE TWENTY, together

with

the pre-combustion

chamber . The

engine

is shown with a turbocharger

and

intake

air compressor mounted at the aft end of the block,

and

the illus

tration

also

shows

a

clever transmission approach.

The

inboard

transmission is built from the basic gear

and

clutch assemblies from

the Volvo

sterndrive,

thus

giving

a

high

commonality

of parts

between

inboard

and

sterndrive installations. The

engines were offered in

naturally aspirated versions at 85

SHP,

turbocharged at 13

HP,

and turbocharged/aftercooled

at

165

HP.

The turbocharged versions

have become very popular in small boats in the 2 to 30-foot lengths.

PRE-COMBUSTION CHAMBER

The pre-combustion chamber, shown in the small insert, is

a system

used

on many small diesels,

such as

the

Mercedes automotive

engines.

It

provides

quieter operation

and ease

of starting

at

a small

trade-off

in efficiency. Basically, the piston

rams

the compressed

air

into the small

anti-chamber,

which is

fitted

with

both

a fuel injector

and

a glow plug .

To

start the engine, a heavy, 12-volt electrical

current

is applied to the glow plug which becomes red

hot.

As

the

engine is



MARINE

FOUR CYCLE

DIESEL ENGINES

DISPLACEMENT MAX

HORSEPOWER

ENGINE

CUBIC INCHES

HORSEPOWER RPM PER CU IN

VOLVO TAMD 4

219

165 3600 .75

CUMMINS VT 370

785

37 3 .47

CUMMINS VT 555M 555

32 3000 .576

DETROIT DIESEL

8.2

LITER

5 8

24

3200

• 47

PERKINS

T 6. 3544 M)

354

24

2800 .68

CATERPILLAR

3208 TA

636

375

2800

.59

MTU VEE TWELVE 2892

1960

2100 .68

12V

396

TB 93

========= 9===========



PRE-COMBUSTION CHAMBER CONTINUED)

cranked, the compressed

air flows

over the plug and is

heated,

and

the

injector blasts the fine mist of

fuel

directly on

the

plug.

The compact chamber gives

a small

volume for the

combustion

to

take place

efficiently,

and

as

the pressure rises, the

gas flows

out of the cavity and drives the piston

downward.

There is a

small loss of

efficiency

due

to gas

friction

and heat transfer

as

the charge

flows in and out of

the chamber

at

very high

speed.

DIESEL INJECTOR TECHNOLOGY

The

technology

of fuel injection, particularly on small

diesel

engines

is

just short of incredible.

An 8 Kilowatt

Onan generator,

for example

is powered by a small 14 horsepower four

cycle

diesel.

Turning

at a steady 1800 RPM

hour after hour

it burns

.90 gallons

of

fuel per hour. This must be

divided up

into 162,000 separate

injections

of 1/1800 Ounce

apiece.To

measure such

microscopic quan-

tities, pressurize the

fuel

to

2000

PSI,

and

inject

in a

period

of

less

than 3

milliseconds .

0028

seconds)

takes

incredible precision.

The

typical four cycle

fuel

injector works

with

far larger

quantities. A

Caterpillar

3208 TA at wide open

throttle burns just

under 2 gallons per hour to develop

375

horsepower. This

works

out to 2 pounds per

minute,

which must be split up

into

11,200

separate injections

at

2800 RPM. Each full throttle

injection meters

1/338

ounce .

003

ounce), pressurizes it,

and

injects into

the

cylinder

in

about

a

15

degree

rotation

of the crankshaft. The

time

for

this

cycle

is shown

in

typical

figures in

the Illustration below.

The overall

injection

starts about 18 degrees before top dead center TDC), but since the



DIESEL INJECTOR TECHNOLOGY CONTINUED)

TYPICAL FUEL INJECTOR PRESSURE TIME CURVE

PRESSURE RISE

FULL THROTTLE

PRESSURE RISE

PART LOAD

10°

TYPICAL

IGNITION .__.w-

DELAY

18

DEGREES BTDC

PEAK

PRESSURE 1150 PSI TO

4500 PSI DEPENDING

ON

DESIGN

3000 TO 3500° TRANSIENT

TEMPERATURES

COMBUSTION

45 DEGREES AFTER TDC

Injector

plunger

Is

cam driven there

Is

a pressure buildup In the

system during the

cam

rise. The bulk of the

fuel Is

Injected

between

1

degrees

before

TDC, and shortly

after

TDC. On part throttle

operation the

metering system Is designed to

cut

off early,

truncating

the

Injection cycle. Peak pressure

vary

widely. Detroit Diesel, with

the

unit

Injector

system has a cam driven rocker arm driving on top

of

the

plunger, and

with

such

a

short

system

pressures

as

low

as

1150

PSI

are used.

Four cyCle designs

usually

have long fuel

injection lines

from the pump

to

the injector,

and

pressures

of 25 PSI to 4500 PSI

are

typically

used

to

give fast injection, and compensate for the

slight

expansion of the steel lines

under

impact

pressure.



CUMMINS VT-370 FOUR CYCLE DIESEL ENGINE

In

the

early 1970s there

were very

few turbocharged diesel

engines available. One outstanding

engine

was the Cummins

VT-370

which provided 370 horsepower at

3000 RPM. Installed in large

yachts

such as the

Chris-Craft

47-foot Commanders, these engines provided

high power output

with

relatively quiet operation. Sound level

tests

in

the Salon

above

the engine

room

showed decibel readings

8 dBA

quieter

than competitive engines and

on

a long

cruise, this

made a

tremendous difference. Fuel economy in turbocharged

four-cycle

diesels

is

good, and

many

of

these

47-foot

yachts

are

still in

steady

operation,

prized

by their

owners

for

an

excellent balance

of

power,

quiet

operation,

relative economy and durability. One advantage of

the turbocharged

diesels was the ability

to

run

comfortably

all day

on

a cruise

RPM

about 200 below maximum, giving a cruise

speed

in the

25 MPH range.

CUMMINS VT-555M SERIES ENGINE

In

the

1970s Cummins

brought

out a series

of

555

cubic inch

engines

for yachts in the

30

to 40 foot range. Over the past

decade,

these

engines

have grown

from

the original

205 horsepower naturally

aspirated

version

to the Big

Cam

turbocharged current

models

providing 320

HP

at 3000 RPM, for a specific power output of

.576

HP/cubic inch.

This

represents

a

growth

of over

55

in

power output

over the .37 HP/cubic inch available on the original engines.

DETROIT DIESEL

8.2

LITER ENGINES

The 8.

2 liter engine

represents

the

first

small four-cycle

Detroit

Diesel engine in

many years. Originally

offered in

the

early

1980s as a naturally aspirated engine

at

just over 200

HP, it is

in the



HE T EXCH NGER

T NK

COMPRESSED

DJUST BLE

FRONT

MOUNTS

FRESH IR

SUPPLY

LTERN TOR

TURBOCH RGER ND

IR COMPRESSOR

EXH UST M NIFOLD

RE R ENGINE MOUNTS

ETROIT IESEL

8 2

LITER ENGINE

2



DETROIT DIESEL 8.2 LITER ENGINES CONTINUED)

growth stage with

several

turbocharged marine conversions by

distributors

offered in 1982. The current

engine

factory built

with a single

centrally mounted

turbocharger is

shown

in FIGURE

TWENTY ONE.

The

performance of

a

pair

of

prototype

B. 2

liter

engines in

a Bertram

28

is

shown

in FIGURE TWENTY TWO. A set of curves in

this

format should

be

developed for every new engine installation

in

a

yacht. The

plot

of

MPH

vs

RPM

covers the cruising range

when

the

yacht

is fully up on

plane and

gives the

owner valuable range

vs

speed

information. Since hull friction varies as the square of the

speed

it is

not

too surprising to

see

that

the best

fuel economy

will be

achieved at

the lowest planing speed. In this case it is

1. 9 MPG in the 1600 to 1900 range. In an interesting parallel test

with

this

same model yacht

the diesel

fuel economy was 50

better

than

the

performance

with a

pair

of the 235 HP two

cycle gasoline

engines. In both cases I ran each boat over a 60-mile course

similarly

loaded over a

weekend. The outboard engines gave

a

higher

top speed

but the

diesels

really

shine

in

the

field of fuel economy.

PERKINS T 6,3544 (M) SIX CYLINDER DIESEL

An

example

of the results of a

long

development

and refinement

process

is the

Perkins

line of six

cylinder diesels.

A

rugged

354

cubic

inch

block is the

heart

of

the

engine and

the

basic version with a

Brog-Warner transmission

provides

135

horsepower at

2800 RPM.

After

a

decade of development and refinement the

latest

versions can

pour

out 77 more horsepower through turbocharging the

integration

of

large

capacity coolers and careful design of

the

induction and exhaust

air

flow. From a

specific

output of •38 HP

/cubic

inch the power has

grown

to

.68

HP/cubic inch

In

the

T 6.3544

(M}

model



E

o

CD

m

~

CD

,)

c:::

o

E

0

Q

a



TURBOCHARGER

COMPRESSOR INLET

V LVE

TR IN ; ; :o

EXHAUST V LVE

EXHAUST MANIFOLD

PISTON WITH

CHAMBER IN TOP

CONNECTING

RO

aterpillar

Four

ycle

HIGH PRESSURE FUEL

INJECTtON PUMP

FILTERS

INJECTOR

i •HEAT

EXCHANGER

LUBRIC TING OIL PUMP

Diesel Design

3



CATERPILLAR 3208 TA FOUR-CYCLE DIESELS

Caterpillar has

followed a similar development program with

the 636 cubic Inch V-8 line of

engines.

Originally introduced in

the mid-1970s at 210 HP, the

power output

had grown through

turbocharging

and

design refinement to 25 HP by 1980. This

grew

to 300 HP,

and

the addition

of aftercooling

the induction

air and the

use

of larger oil coolers allowed the power output to

rise

to 375 at 2800 RPM. This represents a growth from 210 HP

•

33

H P

/cubic inch)

to

375 HP

in the same

636 cubic inches. The

path

is

not

always

smooth.

The

maximum

pressures

developed by

turbocharging

could not

be

handled

by the

original

636

cubic

inch

block,

and

a very time

consuming and expensive

redesign was

required to

strengthen

all of the key elements sufficiently to allow

a 7 percent growth in power output to .575

HP/cubic inch.

MTU 396 SERIES ENGINES

The

highest

powered

diesels engines

currently in

general

use on

American yachts are the

MTU

line

of six

to

sixteen cylinder four cycle

diesels.

MTU represents a combine

of

old line German diesel

manufacturers

including

M.A.N.,

Maybach,

and

Mercedes Benz. M.A.N. has traditiona lly

been

strong In the

huge

three

story direct connected marine diesels.

The largest, a 12 cylinder, develops 56,160 horsepower, or 4680 HP

per cylinder turning

at less than

100 RPM.

The MTU six-cylinder engine is

shown

in FIGURE TWENTY

FOUR.

The

V-12 is

basically

two

six cylinder blocks bolted end

to

end, so the construction details are similar. Two

intake

and

two

exhaust

valves

per cylinder

are

fitted

with a fuel

injector

mounted

in the

center,·oHhe cylinder head

between the

four valves.

The design

is so compact

that recesses must be

machined

into

the

top

of

each

piston to

allow

the

valves to

open

with the

piston

at

top

dead

center. A Bosch in-line fuel

injection pump

is mounted in the center

between the

banks

of cylinders,

and

is gear driven from the camshaft.

High strength steel distribution lines carry the 2500 PSI

injection

fuel

from the pump to the individual

injectors.



EXHAUST OUTLET

HIGH PRESSURE FUEL

AIR INTAKE

MANIFOLD

COOLANT TANK WITH

HEAT EXCHANGER

GEAR TRAIN TO DRIVE

FUEL INJECTION PUMP

FRONT ENG

MOUNT

CAMSHAFT DRIVING VALVE

TRAIN

THROUGH ROLLER

FOLLOWERS ON PUSHRODS

GEAR DRIVEN

OIL PUMP

Four Cycle

MTU

OIL

P N

WITH

BAFFLES

Model

4

CRANKSHAFT WITH

COUNTERWEIGHTS

396

EXHAUST OUTLET

INTAKE

AND

EXHAUST VALVES

CYLINDER

INJECTION VALVE IN

CENTER

OF

CYLINDER

EXHAUST VALVE

WATER COOLED

EXHAUST M N I FOLD

REAR ENGINE

MOUNT

11T UIDF8

s

Engine



MTU

396

SERIES ENGINES CONTINUED)

At

the

end of each

cylinder

bank a turbocharger is installed

in a water cooled housing. The gas exhausts from the turbocharger

upward and

the compressed incoming air flows in toward the

engine

centerline through a cooler

and

then forward into a

pair of

intake

distribution

manifolds.

The MTU twelve cylinder

engine can provide

1930

horsepower

at 2100 RPM,

for

a

specific

power

output of

•

67

horsepower per

cubic inch. These engines

or the Detroit Diesel

12V-92-TA models

are

becoming poular in

yachts

in

the

55

to 9

foot

size. Higher

power

levels are available but the

cost

escalates rapidly.

The MTY 16V-396-TB63 can provide 2610 horsepower at 2100 RPM, and

this is accomplished in

an

engine just

over

five

tons

in weight. High

powered American diesels such

as

the Detroit Diesel 16V-149-TI have

primarily

been

designed

for commercial

service and turn

out 1600 BHP

at

1900 RPM in commercial trim

and

up to 2000 BHP modified for

yachting

use. Weight without marine gear

for

these

engines

is

just

under

six

tons.

The

difference is the

MTU focus

on military

appli-

cations

with a

high value

on

minimum

size and weight compared to

the American commercial objectives

of

moderate cost with extended

service life and minimum maintenance expense.



MARINE DRIVE SYSTEMS

Most

early

marine gasoline

engines were

built

using

a common

base for the

engine and

transmission. This type of

design is shown

in the Easthope

engine

in FIGURE ONE. A short drive shaft bridges

the space between the

two

units.

A manual

lever

was used to engage

the

forward

or reverse gear set, and generally these small

slow-turning

engines

required

no

reduction. The

huge flywheel,

required

to

allow

idling

at

100 RPM dominates the front of the engine

and

weighs more

than the entire transmission

assembly.

As engines became more

powerful

and

manufacturing

more

specialized,

the

use

of a separate transmission assembly bolted to

the engine flywheel housing became the accepted method of construction.

A modern in-line transmission manufactured by Borg-Warner is shown

in FIGURE TWENTY FIVE. Since engine flywheels differ in diameter,

an adapter

plate

is

bolted to

the flywheel housing and

the

transmission

input shaft is splined to

the crankshaft.

At

the

front of

the assembly

a gear-type oil

pump

is

mounted.

Since

this

is

always

rotating with

the

.engine,

it

provides

a

constant

supply

of

high

pressure

lubricating

oil

to

operate,

lubricate

and cool

the transmission.

CLUTCHES

There

is a large diameter clutch assembly

located

behind

the

oil pump.

There

are

only

a few elements in the ·clutch pack since

the

large diameter

give

excellent torque transmission

characteristics.

The clutch pack

is

engaged by

bringing

high-pressure oil into a

large diameter piston

area. The

piston is just forward of

the

clutch

pack

in the illustration, and

when

150 to 200 PSI oil operates

on

the

ring-shaped piston

surface, the

forward

gear

clutch locks up

very

tightly.



OIL

PRESSURE PUMP

INPUT SHAFT

FROM ENGINE

Marine

OUTER CLUTCH PLATE

MULTIPLE

DISK

CLUTCHES

PLANETARY

GE R SET

REDUCTION GE RS

T PERED ROLLER

BEARINGS

TR NSMISSION COUPLING

{CONNECTS TO PROPELLER SHAFT

Transmission Gas Engines

25

___



0

MARINE DRIVE SYSTEMS CONTINUED)

CLUTCHES CONTINUED)

A

multiple

disk clutch

pack is shown

behind the

large

clutch assembly. While smaller in diameter, it has more elements

to provide the torque transmission required. This

pack is

built

into

a planetary

gear set.

FORWARD AND REVERSE

Examination

of FIGURE TWENTY FIVE will show

that

there

are actually three distinct shafts between input and

output.

The

input

shaft is

locked to the engine

and the forward planetary gear

set

spins

at engine

speed.

It is a characteristic of planetary sets

to spin freely, with the small gears

walking

around the internal

gear and the external gear with

no

power output. To go into

FORWARD, the large diameter clutch is used to lock all the elements

of the planetary together. The middle shaft then turns at engine

speed,

and

the

yacht

is in

forward

gear.

When

reverse

is

desired,

the

outer clutch is released, and the small clutch pack engaged.

Under these circumstances,

the

small planetary gears reverse the

motion of

their carrier so that the center

of

the

shaft rotates in

the

reverse

direction.

REDUCTION GEARS

Bolted on

to the aft end of the transmission is a set of

reduction gears. In

small,

light yachts this

can

be eliminated,

but

normally

1. 5 to 1

or

2 to 1 reduction gears

are

fitted to yachts above

24

feet

in length.

As

yachts get

to 4 feet,

a reduction of 2. 5

to

1

needs to

be

considered in the propeller calculations to give the best



UPPER B LL BE RINGS

CONE CLUTCHES FOR

FORW RD ND REVERSE

EXH UST P TH

C VIT TION

TRIM T B

PROPELLER ON

SPLINED SH FT

TILLER RM WHICH

TURNS ENTIRE

LOWER

STERN DRIVE SSEMBLY

TR NSOM

OF

Y CHT

BEVEL GE RS ND BE RINGS

SUBMERGED IN LIGHT OIL

VO VO

UNIVERS L

JOINTS TO

LLOW STERN DRIVE

TO TURN ND

LIFT

HORIZONT L

SH F

FROM ENGINE

EXH UST P TH THROUGH

FLEXIBLE

BELLOWS

VERTIC L SH FT

COOLING W TER

INT KE

STERNDRIVE ONSTRU TION



MARINE DRIVE

SYSTEMS

CONTINUED)

STERN

DRIVE

SYSTEM

CONTINUED)

transmission of

power

as

the

unit is

turned

from side to side for

steering and also allows a limited vertical angular motion. By this

means, the

unit

is

trimmed out

to give the

maximum thrust

efficiency.

In the

hands

of a skilled operator on high-speed

boats

running in

the 60

mile per hour range, careful trimming out

can

add

three

or four miles per hour

to the

top speed.

BEVEL

GE RS

AND CLUTCHES

After

the universal joints the shaft passes through a

pair

of

high-capacity ball bearings and

terminates

in a

bevel

gear. The

gear drives both an upper and lower

bevel

gear mounted

on

the

vertical

shaft. There are

cone clutches mounted

between the hor

izontal

gears,

and if

one

clutch is engaged,

the

transmission is in

forward and the other clutch

is

used

to

provide reverse.

Power

passes down

the

vertical shaft which terminates in

another bevel gear driving the propeller shaft. Large bearings to

absorb

propeller side

loads are installed,

as

in an oil pump. The

entire gear

train

is

submerged in low viscosity

oil, so

the transmission

losses are low,

and

heat is easily i:lissipated through direct heat

trans

fer from the oil

to

the surrounding water.

ADVANTAGES

OF

STERNDRIVES

The

sterndrive has proven to be the most efficient method

of

marine

propulsion in wide

use

today. In racing applications, the

combination

of a high power output

four-cycle

gasoline

engine

with




ADVANTAGES OF STERNDRIVES CONTINUED)

a specially constructed sterndrive, such as that shown in FIGURE

SEVEN, leads to tremendous speeds. In deep-vee hulls,

such

as

the Cigarette 38, speeds over 8 miles

per

hour are possible, and

some of the new 30-foot catermeran

designs

have

operated at

over

100 miles

per

hour in

relatively

calm waters. The

cats

partially

ride

on an air cushion between the two

hulls,

leading to

higher

speeds, but

when

waters get rough,

nothing

will

perform

or

stand

up

as well as a racing deep-vee hull.

For

highest efficiency the sterndrive

should:

1. Have a fuel

efficient

four-cycle engine.

2. Run

with

a stainless

steel

propeller of optimum design.

At high

speed,

a Cleaver

design

as shown in

FIG.

7

has

proven

to most efficient.

3. Have a clean, smooth lower unit

on the

sterndrive.

4. Operate

on

a clean, smooth hull.

The

high

efficiency of the sterndrives is due to a reduction

of appendage resistance . In a

standard

inboard engine configuration,

the

propeller

shaft

and

main

strut

cause considerable turbulance in

the

water

before it gets

to

the

propeller. In addition, the rudder

has

surface

area resistance and

adds considerably more drag when it is

at

an angle

to

the

water

flow. In

the

sterndrive,

steering

is

by

turning

the thrust line and

the

lower unit

is

carefully

streamlined to

reduce

drag to minimize levels.




DIESEL TRANSMISSIONS

Diesel engines for marine use are all

designed

for commercial

applications and the transmissions match the heavy-duty design

philosophy. A typical

marine

transmission

is

shown in FIGURE TWENTY

·sEVEN. The

torque is

generally much higher

on

diesels and almost all

have a reduction built In

so

the general approach is to have offset

shafts

with

the forward and

reverse gears

both splined

to the

input

shaft. Normally there is a small clearance between the input and

output

gear

in

reverse

and the change in direction

is accomplished

through

an

idler gear

mounted

to one

side of

the

shaft

line.

In the Caterpillar Model 7241, transmission

shown there

are

concentric shafts on the

input and the sintered

bronze

clutch packs

are locked

up

by hydraulic pressure to drive through either the

forward or

the reverse

gear. The oil

pump is

mounted at

the

extreme

aft end of the upper shaft so It is always rotating and draws oil

from

the

huge

sump

in

the

transmission

housing.

Some

reduction

is

accomplished in the

gearing

between the

input and

output shafts but

the

overall

reduction

ratio

is determined by the planetary gear set

located on

the

output shaft. A

pair

of heavy tapered roller bearings

are Installed just forward of the output flange to absorb the forward

and

aft thrust of the

propeller

and

also

any

side

loads

due to

propeller

shaft misalignment.

Marine diesel transmissions are made in many variations and

by differing techniques. Z has a process where

the gears are driven

onto tapered seats and have no splines. Many accomplish the reduction

through

spur gears

instead of planetary

but

all of the

basic

elements

will be

present.



724

OUTPUT

PLANET GEAR

3 USED)

MAIN THRUST BEARING

STATIONARY RING

SUN

SINTERED BRONZE

CLUTCH PACKS

FORWARD

EVERSE

FORWARD GEAR

REVERSE GEAR

ELEMENTS OF A M RINE

DIESEL

TR NSMISSION

FIGURE 7




ARNESON DRIVE

A

relative newcomer to

the

marine

propulsion

scene

is

the

Arneson

Drive which combines

a steerable surface

propeller

with a

small rudder

for

low speed operation.

The

configuration of a drive

with

offset

shafts

is

shown in FIGURE TWENTY EIGHT. The

penetration

through the transom is very similar to the sterndrive,

and

the

housing

includes a pair of gears with a strong drive belt,

which

provides a

lower

shaft

speed on the output,

and

also lowers

the

output

shaft

line. A pair of universal joints held within the transom

housing

allow

the shaft assembly to move

up

and down for

trim

and

from

side

to

side for

steering.

The

steering

is

controlled

by a

powerful

hydraulic

cylinder

mounted to the port side, and the elevation is controlled

by

a cylinder mounted above and bolted through the reinforced transom.

Steering is

accomplished

by both the

skeg and

the thrust line

of the propeller. The skeg

provides

a

measure

of

protection

for

the

prop

and

the

upper

blade includes a

spray

shield to cut down

on

the

vertical

spray

thrown off

the prop.

A

highly polished

stainless steel

or

N1-bral prop is used,

and

the best

operation

is normally found with

only the lower half of

the

prop in

the

water. This

is

a surface prop,

and until the Arneson system was

invented,

the

exact

trim to achieve

optimum propulsion was

very

difficult to

achieve.

The propeller

diameter on sterndrives is limited to about

6 inches,

but the

design

of the larger Arneson or KAAMA units permit much larger shaft

diameters, and

the application

of

the system to

large diesels in

the

1000 HP range.



HYDR ULIC CYLINDER TO

R ISE ND

SPR Y DEFLECTOR

PROPELLER

SKEG FOR PROPELLER PROTECTION

ND

OW

SPEED STEERING

RNESON DRIVE

8



HYDR ULIC CYLINDER TO

R ISE ND

STEERING CYLINDER

SPR Y DEFLECTOR

SKEG

FOR

PROPELLER PROTECTION

ND

LOW

SPEE STEERING

marine propulsion for small crafts

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