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

Chapter 23: Anchor Rode

200 to 300 feet (60 to 90 m) of rope simply fed
into a locker, it is much better to store longer
lengths wound up on a spool. A serious voy-
ager might want to carry, say, 600 feet (180 m)
of^1 / 2 - inch (12 mm) warp to join to the end of
a standard 300-foot (90 m) chain for deep-
water emergency anchoring.
You can determine the size of the
required spool from the following formula.

Formula 23-2. Rope Spool Size

or

Where

Feet of line= spool capacity in feet

Meters of line= spool capacity in meters

W= width of drum, in. or cm

F= outside diameter of flange, in. or cm

D= diameter of central drum, in. or cm

D must be 12× rope diameter or greater;

larger diameters are easier on the line

Example: For 600 feet of^1 / 2 - inch line, try
a 22-inch width, a 16-m. flange, and a 12-inch
diameter as follows:

Or

For 90 meters of 12 mm line, try a 40 cm
width, a 40 cm flange, and a 34 cm diameter
as follows:

which gives a bit of reserve capacity.

Wire Anchor Rode

Wire anchor rode is rare and found in use al-
most exclusively on some commercial fishing

boats in the Pacific Northwest. The advan-

tage of wire-rope anchor rode is that it can be

wound up automatically and reliably on a hy-

draulically operated reel-cable drum winch.

This also allows neat and clean stowage of a

great length of wire rode. If you need to an-

chor at a 5:1 scope in 250 feet (75 m) of water,

you need 1,250 feet (375 m) of rode. This is

prohibitive for routine anchoring, except for

wire rope on such a hydraulic drum.

The big disadvantage is that wire rope

has virtually no give or shock-absorbing abil-

ity. Everything must be sized extra strong and

heavy to accept the shock loads, and such

repeated large shocks can pull out the anchor

as well. Some installations split the wire into

100-foot (30 m) lengths joined with inter-

locked thimbles. You can use a shackle or

claw to fasten a snubber or snatch line to one

of these thimbles. Otherwise, you cannot

even attach a nylon rope snubbing line to the

wire rode. I suppose—using the right gear—it

would be possible to run a kellet, or sentinel,

down a wire anchor rode, but I’ve never

heard of it being done. You could also attach

such a kellet to one of the thimbles. In spite

of this drawback, the fishermen who employ

wire-rope anchor rode appear to be very sat-

isfied with them.

The only wire rope suitable for use as

anchor rode is 7× 19 flexible wire rope of 316

stainless steel. Kolstrand Marine Supply of

Seattle, Washington, makes complete wire-

rode reel windlass units of galvanized steel

and of aluminum. The larger of these units

can handle up to 4,850 feet (1,478 m) of

(^1) / 2 - inch (12.7 mm) cable or 2,200 feet (670 m)
of^1 / 2 - inch (12.7 mm) cable with 85 feet (26 m)
of^5 /8-inch (15.87 mm) chain! Now thisis
40 cm ((40 cm) 34 cm
mm rope

×−^2

×

())

. (

2

1 275 12 dia.

m,

)^2

= 96

22 in. ((16in.)12in.

in.

×−^2

×

())

. (.

2

15 3 0 5 rrope dia.,

644 ft.,

which gives a bitof

)^2

=

reserve capacity

Me te rs of line

W, cm ((F, cm D, cm

=

×−)( ))

,

22

12275 ×()rope da.,mm^2 i

Feet of line

W,in. ((F,in.)D,^2 in.

=

×−())^2

1553. ×()rope dia.,in.^2

Figure 23-16.

Wire-rope

windlass

(Courtesy

Kolstrand)

Formula 23-2.