ship form nomenclature & principal views lines & offsets coefficients of form

Ship FormShip Form

Nomenclature & Principal Views

Lines & Offsets

Coefficients of Form

Ship DimensionsShip DimensionsLength Overall (LOA)

After Perpendicular

Forward Perpendicular

Designed Waterline Length (DWL)

Length Between Perpendiculars (LBP)

Afterbody (STERN)

Forebody (BOW)

Designed Waterline Plane

Beam

Parallel Midbody

DepthMidship Section

Lines Drawings: Lines Drawings: waterlineswaterlines

Length Between Perpendiculars (LBP)

DWLWL2

WL1Baseline

Half-Breadth Plan

Lines Drawings: Lines Drawings: sectionssections

Sta 10 9 8 7 6 4 3 2 1 0

FPAP

Sta 0 (FP)

Sta 2

Sta 4Sta 6

Sta 8

Sta 10 (AP)

Body Plan

Forward SectionsAfter Sections

MIDSHIP SECTION

Section NomenclatureSection Nomenclature

Baseline

DWL

Freeboard

Draft

Depth

Deadrise

BeamHalf-breadth

Camber

Flair Tumblehome

Lines Drawings: Lines Drawings: buttocksbuttocks

DWL

Sheer Plan

Centerline Plane

BP1

BP3BP2

BP1

DWL PLANE

Butt 1

Butt 2Butt 3

DWL

Sheer & CamberSheer & Camber

Sheer Plan

Centerline Plane

BP1

DWL PLANE

Camber

Sheer

Lines DrawingsLines Drawings

Three sets of drawings define the hull shapeHalf-Breadth Plan

Body Plan

Sheer Plan

BP1

OffsetsOffsets

Ships lines may be represented numerically in a table For example

Sta No. Half-breadth @ 30’ (DWL)

Half-breadth @ 25 ‘

Half-breadth @ 20’

… etc. Half-breadth @ Baseline

0 (FP) 16 12 10 4

2 35 33 30 6

4 50 48 45 40

5 () 50 50 48 45

6 50 48 45 40

8 45 42 35 10

10(AP) 40 32 15 0

OffsetsOffsets

Half-breadths for different WL’s at a given station may be used to determine the A of that station

Sta No. Half-breadth @ 30’ (DWL)

Half-breadth @ 25 ‘

Half-breadth @ 20’

… etc. Half-breadth @ Baseline

0 (FP) 16 12 10 4

2 35 33 30 6

4 50 48 45 40

(DWL)30’

25’

20’

15’

10’

5’

(BL) 0’

h= 5B1 = 35

B2 = 33A1= ½ (35+33) x 5 = 170

A2

A3

A4

A5

A6

Hull VolumeHull Volume Section Areas define hull shape Volumes between sections summed to determine displacement

volume,

Midship Section (Station 5)

Area below DWL

Section Volume V5 = ½ (A5+A4) x d

OffsetsOffsets

Likewise, waterplane areas may be calculated from Offset tables

Sta No.

½ -brth @ 30’

½ -brth @ 25’

0 (FP) 16 12

2 35 33

4 50 48

5 () 50 50

6 50 48

8 45 42

10(AP) 40 32

Sta. 10 9 8 7 6 5 4 3 2 1 0

NOTE: The above is distorted because the frame spacing (probably 60’ is not at the same scale as the half-breadths. (Plot to scale below.)

Other Hull Form Dimensions

Besides areas & volumes, hull form determines the location of other critical dimensions.

The centroid (geometric center) of the underwater portion of the hull is the Center of Buoyancy

KBLCBB

The vertical location of B is measured from the keel (KB). The Longitudinal Center of Buoyancy (LCB) is measured

from the Forward Perpendicular The location of B changes with draft (displacement).

Other Hull Form Dimensions

Besides areas & volumes, hull form determines the location of other critical dimensions.

The centroid of the waterplane area is the Center of Floatation (F)

Its location (distance from the fwd perpendicular – LCF) is also a function of displacement

LCF

F

Other Hull Form Dimensions

Besides areas & volumes, hull form determines the location of other critical dimensions.

The distribution of waterplane area determines the Metacentric Radius (BM)

The Center of Buoyancy moves along this arc as the ship rolls

With KB known, the Metacentric Height (KM) becomes an important parameter in stability calculations.

M

B

K

Waterplane Area

Hydrostatic CurvesHydrostatic Curves

27

26

25

24

23

27

26

25

24

23

681800268279

31.1

31.05

31.1

31.2

278

277

276

275

274

267

266

1700

1600

67

66

19000

18000

17000

16000

15000

65

MEAN DRAFT

(FT).

KM

(FT)

LCF (AFT FP)

(FT)

LCB (AFT FP)

(FT)

MT1

(FT-TON)TPI

DISPL in S.W.

(L.TONS)

MEAN DRAFT

(FT)

Block Coefficient: CB = / (L x B x T)

Hull Volume, (under DWL)

Coefficients of FormCoefficients of Form

AP

FP

L (along DWL}Beam, B

Draft, T

Block Volume, L x B x T

Coefficients of FormCoefficients of Form

Prismatic Coefficient: CP = / (A x L)

Hull Volume, (under DWL)

Midship Section Area, A

Prism Volume, (A x L)

Coefficients of FormCoefficients of Form

Midship Section Coefficient: CM = A / (B x T)Beam, B

Draft T A

Rectangle, B x T

Same B & T smaller CM

Note that CM = CB / CP

COF’s are used in the early stages of design to compare characteristics of new design with existing types for estimating performance