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

length, ft. or m =length from power

source (usually battery) to equipment

andback again

allowable voltage drop =allowable drop

in volts

NOTE: A circular mil is the equivalent area
of a circle whose diameter is 0.001 (10–3)
inch, or approximately 0.7854 millionths of a
square inch.
In the United States, wire is sized using
American Wire Gauge (AWG), which is also
the Brown & Sharpe gauge, see Table 24-3.
Note that in AWG, the smaller the AWG wire
number, the largerthe wire. The largest wires
commonly available are AWG size 0, 00, 000,
and 0000. These are also written as 1/0, 2/0,
3/0, and 4/0.
In metric wire size, the wire is called out
directly by its total conductor cross-section
area. Referring to Table 24-3, you can see that
a U.S. no. 6 AWG wire has 26,240 circular mils,
and the nearest metric wire size is 16mm^2 ,
which has 31,580 equivalent circular mils.
Allowable voltage drop is as follows:

3 percent of 12 volts = 0 .36 volt

10 percent of 12 volts = 1 .2 volts

3 percent of 24 volts = 0 .72 volt

10 percent of 24 volts = 2 .4 volts

Example: In our case, the required cir-
cular mils for 3 percent voltage drop work
out as

Referring to Table 24-3, we see that we
would need 1 gauge wire (AWG). This is a
pretty hefty wire at approximately 0. 332 in.
OD.
Or
In our case, the required circular mils for
3 percent voltage drop work out as

Referring to the Table 24-3, we see that
50 mm^2 wire is the smallest standard metric
size with more than this cross-section area.
This is a pretty hefty wire at approximately
9 .27 mm OD.

This check on wire size has to be done

for every electric installation, and break-

ers must notexceed the ampacity of the

wire and must meet the manufacturer’s

spec for the windlass (or other equipment)

as well. Equally important is that electric

windlasses cannot be run for too long un-

der load. The crew has to be sure to sail up

to the anchor and reel the rode in on the

windlass under minimum load until the an-

chor is apeak (straight up and down). At

this point, sailing the anchor out is easier

on the windlass, but the windlass will be

used as well.

This sort of limitation in operation can

reduce the windlass’s utility. On one occa-

sion, I was cruising on a 60-foot (18.3 m)

motor cruiser my office designed. We were

anchored off a lee shore in over 50 knots of

wind. We motored up to the anchor, reeling in

the all-chain rode as we did so. We pulled the

hook and sailed out of the harbor with no

problem. In such a strong wind and sea, how-

ever, the process took a good 15 minutes of

nearly continuous windlass operation under

varying loads. This would not have been

practical with an electric windlass. So what

did we use? Hydraulic.

For larger and serious cruising boats,

particularly powerboats and motorsailers, I

recommend hydraulic windlasses. Hydraulics

will allow you to run the windlass virtually

as long as you wish under load, making for

great flexibility. The catch—there’s always a

catch—is that the hydraulics are powered off

the main engine (occasionally off a gen set).

This means that the engine must be running

to use the windlass. For powerboats, this will

always be the case. For motorsailers, too,

this will virtually always be the case. How-

ever, smaller sailboats in particular (even

larger auxiliaries) will not want to have to

turn on their engine (or gen set) every time

they set or retrieve the anchor, so electric

windlasses are usually the best choice for

them.

Power Up and Power Down,

and Wildcat Versus Gypsy

Another feature to look for in a windlass is that

it has a power-down feature. Small anchors can

be allowed to free fall, but over about 20

pounds (9 kg) of anchor and chain, you want

50 amps 16 m

55 .97 0.36 volts

39 .7mm^2

×

×

=

10 .75 50 amps 52 ft.

0 .36 volt

77,639 cm

××

=

Chapter 24: Sizing the Anchor and Rode and Selecting Anchor-Handling Gear