anchoring seminar - pbps.org

USPS University – Seminar Series

Seminar Series

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AnchoringUnited States Power Squadrons®

Seminar Series

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Objective

Increase recreational boater’s knowledge of and use of anchoring equipment, concepts, and capabilities.

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Seminar Elements Anchor Types What size anchor Anchor Rode Anchor Scope Anchoring Tips and Tricks

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Types of Anchors Burying anchors

• Plough• Claw• Spade• Large Area Pivoting Fluke (LAPF)

Hooking anchors• Fisherman• Northill

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Plow Anchor - CQRProven old design

• Best in firm sand, thick mud, rock, coral, weeds• Hinged shank• Trip line eye• Awkward to stow

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Plow Anchor - Delta Fixed shank Large area flanks Trip line eye Modern metals

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Claw Anchor – Bruce, Lewmar One piece construction Best in sand, rock, weed, coral Good resetting characteristics Holding power

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Burying Anchor - Spade Sharp plough with concave blade and weighted tip Proven performance Can be dismantled for stowing

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LAPF Anchors Commonly found Sand or soft mud Holding power

• Excellent when dug in• More susceptible to tripping under changing conditions• Excellent when pull direction doesn’t change

Easy to stow>>


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LAPF Anchors – Danforth Three types

• Standard• Hi-Tensile• Deepset® II

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LAPF Anchor - Fortress High tensile aluminum Dismantles for stowing Adjustable shank angle High holding power to weight ratio >>


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Hooking Anchor - Fisherman a.k.a. Traditional Good in weeds and rocks Heavier Can be dismantled for stowage Not common today

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Hooking Anchor - Northill Stainless steel Arms and stock hinged – folds Sold as KB Ultralight Danforth Utility version made of galvanized cast steel Good working anchor on light displacement boats >>


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Hooking Anchor - Grapnel Good on coral or rock Use as dinghy anchor

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Where Common Anchors Work Best

AnchorType

Bottom ConditionsSand/Clay Mud Gravel Coral/Rock Weed

Plow X X X LAPF X XClaw X X X

Fisherman X X X XGrapnel X

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What Size Anchor? Use charts/tables found in many different books Match an anchor to your boat Remember to consider current load

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Typical Anchor Size TableBoat Length

(feet)CQR

Delta

Bruce

Danforth HT

Fortress

10 20 30 40 50 60

25 lb 35 lb 45 lb 15 lb

9 lb 14 lb 22 lb 35 lb 44 lb

11 lb 16 lb 22 lb 33 lb 44 lb

5 lb 12 lb 20 lb 35 lb 60 lb

4 lb 7 lb 5 lb 21 lb 32 lb 47 lb10 lb

66 lb

60 lb

For medium displacement boats, and 30 kts of wind >>


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Calculate Anchor SizeUse formulae for rode tension and anchor holding power

In addition to calculating anchor size by using a table, there are formulas that allow more accuracy. These will be taught at the end of the seminar for those who want to use them.

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Summary of Anchor Matching Assume worse case conditions likely to be encountered Estimate maximum horizontal pull Select optimum anchor type(s) Calculate anchor weights Select anchor within range

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Anchor Rode ComponentsTypical rode

100 ft nylon line

Height 5 ft above surface

Depth 15ftScope = (100+20)/(5+15) = 6 or 6:1 Sentinel

Line to sentinel

20 ft chain

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Anchor Rode Design Goals

• Maintain zero lead angle• Provide elasticity to absorb shock loads in swells• Keep weight to a minimum• Keep chafe to a minimum

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Rode Types

All chainAll lineCombination line-chain

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All Chain Rode Attributes Positive

• 0° lead angle can be achieved• Scope is minimized• No chafe

Negative• No elasticity• Heavy• Windlass highly desirable

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Anchor Chain Chain

• Proof Coil• BBB• High Test

5/16 in Chain TypeWorking Load Test Load Breaking Load

Proof 1,300 lbs 2,600 lbs 5,800 lbs

BBB 2,400 lbs 4,800 lbs 7,000 lbs

High Test 3,900 lbs 6,800 lbs 12,000 lbsRepresentative Values

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All Nylon Rode Attributes Positive

• Elasticity absorbs shock load• Minimal weight• Easy to stow

Negative• 0° lead angle never achieved• Greater scope• Chafing

3-strand nylon

Braided nylon

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Breaking Strengths

Size (in) 3-strand Braid BBB Chain5/16 7,0001/2 6,100 8,300 10,0005/8 9,350 17,0003/4 n/a 21,000

Working strengths are approximately 30% of the breaking strength. >>


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Chain-Nylon Combination Rode Compromise Minimum

• 6 feet of chain at anchor Recommended

• 30 to 60 feet chain>>


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ScopeRatio of rode length to depth of water + height of bow roller above waterNeeds to be just sufficient to maintain 0° lead angle under worst conditions forecast0° lead angle not achieved with all lineNon-zero lead angle reduces holding power

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Rode Lead AngleCritical Angles of a Set Anchor

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Reduction of Holding Power with Rode Lead Angle

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0° Lead Angle with all Chain Rode

Chain forms a catenary Chain length can be calculated for 0° lead angle Need to estimate horizontal pull

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Catenary - Line

Natural catenary – provides cushion Straightens under wind and wave conditions>>Adapted from: Powerboat Handling Illustrated


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Catenary - Chain

Chain contours bottom Peels from bottom under wind and wave conditions >>Adapted from: Powerboat Handling Illustrated


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Holding Power with Chain

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0° Lead Angle for a Chain – Nylon Rode

Chain forms a catenary Nylon line (light in weight) is nearly a straight line Assume fixed length of chain (e.g.60 ft) Line length can be calculated for 0° lead angle if horizontal pull is known

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Chain–Line Combination Rode

01020304050

0 20 40 60 80 100 120 140 160Distance from Anchor (ft)

Heigh

t abo

ve Bo

ttom

(ft) Water Surface

60 feet BBB chain

Horizontal Pull = 50 lbs

Horizontal Pull = 200 lbs

14 ft Line102 ft Line

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Effectiveness of Line-Chain Rode

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Snubbers

Nylon line between chain and samson post or mast Attach line to chain by chain hook, devil’s claw, or rolling hitch

Snubber

Devil’s Claw

>>Adapted from: Powerboat Handling Illustrated

Line


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Summary of Rode Design All chain rode can be used in sheltered anchorages (no swell) Chain has no elasticity when “Bar Taut” All line rode not recommended Use combination rode especially when surge is present Deploy lengths of chain and line to maintain 0° lead angle

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Rode Connectors – Chain to Anchor

Chain Hook

Swivel

Shackle with Swivel

Shackle

Thimble

>>© Quick Guide - Anchoring


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Combination Rode Connections Thimbled eye splice and shackle

Splice line to chain – necessary for certain windlasses



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Anchor Windlass

SwitchLock



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Choosing an Anchorage Choose a sheltered location Check weather and sea conditions Other boats Emergency departure

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Make sure you have room to swing around


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Anchoring

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Scope

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Anchor Recovery

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Tips and Tricks Sentinel Riding Sails Trip Line Multihulls Kedging

Chafe Protection Marking the Rode Line Ashore Setting two Anchors Hand Signaling

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Anchor Sentinal or Kellet

Sentinal – weight deployed on anchor rode• Alters catenary to flatter position• Reduced swinging circle• Sentinal suspended and held in place by line: “Preventer” (red)• Must be 40 pounds or more to be effective



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Riding Sails

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Trip Line Line attached to anchor Attach a float to the line Helps to free snagged anchor Float indicates anchor position to other boaters



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Multihulls Sailing around anchors can be minimized by using a bridle attached to outer hulls



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Kedging

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Row out anchor and rode Drop anchor Move boat by hauling in anchor Useful when aground

© Powerboat Handling Illustrated


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Chafe Protection

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• Fire hose best• Can also use plastic water pipe of simply rags


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Marking the Rode Chain

• Paint 3 - 4 links with different colors• Use cable ties or plastic markers

Line• Use plastic marked tapes threaded through strands• Use waterproof black marker

Mark predetermined points>>


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Setting Two Anchors Fore and Aft

• Use in restricted waters where wind and current are steady• To keep boat pointing into swell • Use in crowded anchorages if other boats follow

Bahamian Moor• Use when mooring in reversing current

Mediterranean Moor• Use in crowded marinas

Tandem• Use when holding is poor or high winds are forecast

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Fore and Aft

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Tandem Mooring

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Mediterranean Moor Commonly used in• Europe• Caribbean Islands Works well • confined anchorages• along bulkheads

Commonly used in• Europe• Caribbean Islands Works well • confined anchorages• along bulkheads


© Quick Guide - Anchoring


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Hand Signaling

Used to communicate between foredeck and helm during anchoring

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Anchoring References Greé, Alain, “Anchoring and Mooring Techniques Illustrated” (1984) Hinz, Earl, “The Complete Book of Anchoring and Mooring,” (1986) Smith, Robert A. “Anchors, Selection and Use” (1996) Van Dorn, William G., “Oceanography and Seamanship,” 2nd Edition, (1992) United States Power Squadrons, “The Ensign,” Jan/Feb 2007 Samson Rope Web Site: www.samsonrope.com USPS “Seamanship” course Sweet, Robert, “Powerboat Handling Illustrated,” McGraw-Hill (2007) >>


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General References Good Cruising, 1997, Aiken Zora and David, McGraw-Hill Good Boatkeeping, 1995, Aiken, Zora and David, McGraw-Hill Boatman’s Guide to Light Salvage, 1979, Reid, G., Cornell Maritime Press Bluewater Handbook: A Guide to Cruising Seamanship, 1992, Dashew, Steve and Linda, Beowulf Publishing Sailor’s Secrets, 1997, Badham, M and Robinson, R., ed, McGraw-Hill

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This concludes our seminar

Do you have questions? Following will be the discussion on calculating by formulas.

To learn more about boating and have fun too - join your local USPS squadron.

Check out USPS University! >>


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Calculate Anchor Size

Use formulae for rode tension and anchor holding power

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Matching an Anchor to your Boat Assumptions

• Yaw angle up to 30 degrees• Wind gusts 50% greater than average speed

Use simple approximate equations

Wind Velocity Wind Pressure10 kts 13 lbs30 kts 1200 lbs60 kts 10,800 lbs

100 kts 32,000 lbsBoat area 45 square feet

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Anchor Rode TensionHorizontal force on anchor rode

Fh = 0.18 x V2 x W2/3 Sail boat Fh = 0.21 x V2 x W2/3 Power boat

WhereFh = horizontal force on anchor rodeV = wind speed in knotsW = displacement of boat in long tons**Definition: One long ton = 2240 pounds

Hint – use logarithm or yx function on calculator>>


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Rode Tension Examples 35 ft Sailboat

Displacement W = 16,000lbs or 7.1 long tons

W2/3 = 7.12/3 = 3.7Maximum wind speed V = 40 knotsFh = 0.18 x V2 x W2/3 Sail boat Fh = 0.18 x 40 x 40 x 3.7 = 1065 lbs

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Rode Tension Examples 38 ft Trawler

Displacement W = 36,000 lbs or 16.1 long tons

W2/3 = 16.12/3 = 6.4Maximum wind speed V = 40 knotsFh = 0.21 x V2 x W2/3 Power boatFh = 0.21 x 40 x 40 x 6.4 = 2150 lbs

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Catenaries for 5/16” BBB Chain

0

50

100

150

200

250

0 100 200 300 400 500Horizontal Pull (lbs)

Chain

Leng

th (ft)

Depth = 20 ftDepth = 30 ftDepth = 40 ftDepth = 50 ft

5/16" BBB Chain

Chain Length for 0o Lead Angle

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Catenaries for 3/8” BBB Chain

050

100150200250300

0 200 400 600 800 1000Horizontal Pull (lbs)

Chain

Leng

th (ft)

Depth = 20 ftDepth = 30 ftDepth = 40 ftDepth = 50 ft

3/8" BBB Chain

Chain Length for 0o Lead Angle

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5/16” Chain-Line Combination Rode

0

100

200

300

400

0 100 200 300 400 500 600Horizontal Pull (lbs)

Line L

ength

(ft) Depth = 20 ft

Depth = 30 ftDepth = 40 ftDepth = 50 ft

Chain = 5/16" BBB

Line Length for 0o Lead Angle

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3/8” Chain-Line Combination Rode

0

100

200

300

400

500

0 100 200 300 400 500 600 700 800 900 1000Horizontal Pull (lbs)

Line L

ength

(ft) Depth = 20 ft

Depth = 30 ftDepth = 40 ftDepth = 50 ft

Chain = 3/8" BBBLength = 60 feet

Line Length for 0o Lead Angle

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Anchor Holding PowerAnchor holding power:

Fh = 2.3 x Cs x Ka x w2/3 lbsWhere: Cs = bottom coefficient

Ka = Anchor coefficientw = weight of anchor



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Anchor Holding PowerSelecting Anchor to match need:

w2/3 = (Fh ÷ 2.3 ÷ Ks ÷ Cs)or w = (Fh ÷ 2.3 ÷ Ks ÷ Cs) 3/2

Where: Cs = bottom coefficientKa = Anchor coefficientw = weight of anchor



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Anchor and Bottom CoefficientsType of Sediment CsSilty clay 1Silt with shells 2Coral sand 4Sand with clay 6Sticky clay 8Stiff clay & sand 10

Type of anchor Ks

Fortress 19Danforth HT 10Plow 7Claw 6Fisherman 2

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Calculate Anchor Weight

35 ft Sailboat – Plow in coral sand Fh = 1065 lbs, Ks = 7, Cs = 4w = (Fh ÷ 2.3 ÷ Ks ÷ Cs)3/2w = (1065 ÷ 2.3 ÷ 7 ÷ 4)3/2 = 67 lbs



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Calculate Anchor Weight

38 ft Trawler – Bruce in sticky clayFh = 2150 lbs, Ks = 6, Cs = 8w = (Fh ÷ 2.3 ÷ Ks ÷ Cs)3/2w = (2150 ÷ 2.3 ÷6 ÷ 8)3/2 = 85 lbs

Hint – use logarithm or yx function on calculator

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Summary of Anchor Matching Assume worse case conditions likely to be encountered Estimate maximum horizontal pull Select optimum anchor type(s) Calculate anchor weights Select anchor within range

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anchoring seminar - pbps.org

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