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

Sizing the Anchor

Now that we’ve reviewed the basic anchor
components, we can start selecting and siz-
ing the anchor and rode. One of the common
methods is using ABYC recommendations
per ABYC standard H-40, Anchoring, Moor-
ing, and Strong Points. This approach gives
the assumed design loads based on boat type
(sail or power) and on LOA or beam
(whichever is greater). The results have
proven themselves, but there are two draw-
backs. One is that the table only goes up to
60 feet (18.3 m) LOA. The other is that there
is no way to know what the holding power of
a given anchor is. Sure, many manufacturers
provide tables of holding strengths for their
anchors, but the results of independent tests
of these same anchors vary widely, both from
the manufacturers’ data and among inde-
pendent tests. Also, anchor test results will
naturally vary with different bottoms, with
boats that have different motions, in different
sea conditions, and with different anchor
gear. Finally, some manufacturers don’t pro-
vide anchor holding strengths at all.
Accordingly, I’ve developed a system to
give recommended working anchor weights
for standard modern anchors: the CQR plow,
Delta, Bruce or Claw, Danforth Hi-Tensile, or

spade type. The procedure is as described by

Formula 24-1.

As noted earlier, I’m not enthusiastic about

lightweight anchors—I like heft. It makes the

anchor drop quickly and positively, and it gives

you a nice warm feeling of security when it

breezes up overnight.

Formula 24-1. Recommended Anchor

Weight

Working or bower anchor weight, lb. = 6. 8 ×

(disp. tons)^0.^75

or

Working or bower anchor weight, kg = 3. 03 ×

(disp. tonnes)^0.^75

Storm or street anchor weight, lb. or kg =

1. 35 × working anchor

Lunch hook/stream/kedge, lb. or kg = 0. 6 ×

working anchor weight

Where

tons =boat displacement in long tons

(2,240 lbs.)

tonnes =boat displacement in metric tons

(2,200 lbs.)

For yachtsman anchors (Herreshoff or

Luke) intended as storm anchors, use 2. 2

times the bower anchor weight above. If you

CHAPTER 24

Sizing the Anchor and

Rode and Selecting

Anchor-Handling Gear

Formula 24-1.