Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

Selecting a Windlass

Once you know what size anchor and rode

you’re going to use, you are ready to select

the proper windlass. I chose to make Hold

Fastthe size of boat I did because it is on the

border of needing a windlass: There could be

no windlass if you used, say, the 18-pound

(8.1 kg) Guardian with a high-test-chain

leader and a rope warp. Alternatively, with

high-test chain and anchors around 35

pounds (16 kg), you could use a manual

windlass. Most cruisers today would choose

a powered windlass on a 32-foot (9.7 m)

powerboat. Obviously, as boats get larger and

the anchor gear heavier, a powered windlass

becomes mandatory, but many smaller ves-

sels—even with anchors as light as the 18-

pound (8.1 kg) Guardian—are installing pow-

ered windlasses.

We settled on Hold Fast’s full anchor and

rode specifications as a 35-pound (16 kg)

Delta,^5 / 16 - inch (8.73 mm wire dia.) BBB chain,

and^1 / 2 - inch (12 mm) three-strand nylon.

We’re ready to size the windlass. The rule

is that the windlass’s rated pull should be

3times or more the total weight of the chain,

rope, and anchor combined. Let’s say that we

plan to use 100 feet (30 m) of BBB chain and

200 feet (60 m) of nylon.

Chain weight can be found from Table

23-2. A useful formula I developed, which you

can put in a spreadsheet to approximate BBB

chain weight, follows.

Formula 24-4. BBB Chain Weight

BBB chain weight, lb./ft. ≈ 10. 505 ×

(chain dia., in.)^1.^858

Or

BBB chain weight, kg/m ≈(chain wire

dia., mm)^2.^12 ÷ 61. 1

NOTE: For BBB chain, refer to the BBB

chain table (Table 23-2) for the metric wire

diameter to find the nominal English-unit

chain size.

Or referring to Table 23-2, we find that Hold

Fast’s^5 / 16 - inch BBB chain weighs 110 pounds

per 100 feet, or 1.1 pounds per foot (the

PART SEVEN: ANCHORING SYSTEMS

TABLE 24-2. ABYC H40 TABLE AP-1—WORKING LOAD LIMIT FOR ANCHOR RODES

Nylon Galvanized Chain

Nominal Shackles—Welded

Diameter 3- and 8-Strand Double Braided BBB Proof Coil High Test Drop Forged

in. mm lb. kN lb. kN lb. kN lb. kN lb. kN lb. kN

(^1) / 4 6 186 0.82 208 0.93 1,300 5.8 1,300 5.8 2,600 11.6 1,000 4.4
(^5) / 16 8 287 1.3 326 1.5 1,900 8.5 1,900 8.5 3,900 17.3 1,500 6.7
(^3) / 8 10 405 1.8 463 2.1 2,650 11.8 2,650 11.8 5,400 24 2,000 8.9
(^7) /
16 11 557 2.5^624 2.8 – – – – – – 3,000 13.3
(^1) / 2 12 709 3.2 816 3.6 4,500 20.0 4,500 20.0 9,200 41 4,000 17.8
(^9) / 16 14 888 4.0 1,020 4.5 5,875 26.1 – – 11,500 51.2 – –
(^5) / 8 16 1,114 5.0 1,275 5.7 6,900 30.7 6,900 30.7 16,200 72 6,500 29
(^3) / 4 18 1,598 7.1 1,813 8.1 10,600 47.2 10,600 47.2 – – 9,500 42.3
(^7) / 8 22 2,160 9.6 2,063 9.2 – – 12,800 57 – – 12,000 53.4
1 24 2,795 12.4 3,153 14.0 – – 13,950 62 – – 15,000 66.7
11 / 4 30 4,345 19.3 4,838 21.5 – – – – – – 23,000 102.3
11 / 2 36 6,075 27.0 6,875 30.6 – – – – – – – –
2 48 10,575 47.0 12,363 55.0 – – – – – – – –
Only nylon is shown because ofits elasticity. Working loads are based on factors of safety, strength loss due to knots
and splices, and abrasion and aging. Thimbles shall be designated for the rope size. Check manufacturers’
recommendations for all materials. (Courtesy American Boat & Yacht Council, http://www.abycinc.org))
Formula 24-4.