Page 16 - WestlawnMasthead23_Sept12.pub

The Masthead
Know It All Contest Solution
continued
expensive wire. In fact 4/0 boat cable is running about $9.50 per foot at the moment. Assuming about 40 feet ordered for
the job, that’s about $380 for the cable alone.
The superior option for
Pretty Penny
s new thruster would be to use the 24-volt version of the thruster available from the
same manufacturer. This is essentially the identical unit and it delivers the same thrust with the same power, but at half
the current draw—140 amps.
You could use the existing 1 AWG power cables and have even less voltage drop than with the original thruster:
Voltage drop = 10.75 x 140 amps x 2 x 16.84 ft. ÷ 83,690 Cm = 0.6 volts
0.6
volts
÷
24
volts = 0.025 = 2.5%
This is really ideal. Though under-10% voltage drop may be tolerated for DC motors, the lower the drop the better and un-
der-3% drop is strongly recommended. Using the 24-volt thruster, you’d also save the labor of pulling the old cable and
replacing it with the new, plus you’d save the cost of the new cable itself. This could largely pay for the 12-to-24-volt trans-
former that would be required. Some thruster manufacturers offer series/parallel switches that put a battery in series, in-
stead of parallel with the others when the 24-volt thruster is used.
Yet another option would be to stay with the new 12-volt thruster, but add a largish (say, group 31) battery up near the
thruster. The thruster runs directly off this dedicated thruster battery. Since the battery-charging amps are considerably
less than the thruster’s current draw, the original 1 AWG cables can be used to charge the new bow-thruster battery, and
the cables from the bow battery to the thruster itself will be short, and so can be of modest gauge and cost.
This 12-volt battery option, however, adds the extra weight of the battery up in the bow, where it is also usually difficult to
access and maintain. There is also the cost of the battery, battery box and proper mounting. It requires a charging control-
ler for the battery, and proper ventilation as well. This is an acceptable approach, but—in my opinion—the 24-volt thruster
will give superior results at a very competitive cost, possibly at less cost.
Flash Flooder
is a new sloop being built at Baggy Wrinkle Boatyard under your supervision. She is:
48
ft. LOA
13.3
ft. Beam
53
in. Freeboard at midships
Flash Flooder
s Cockpit is:
8.25
ft. long
6.5
ft. wide
29
in. high
The bottom of the cockpit sole is 13 inches above the waterline.
This is a well-type cockpit, with cockpit side walls the same height all around. The crew has to step up on deck to go to the
companionway door to the cabin, so there is no sill or opening into the boat in the cockpit itself.
The drawings detail two cockpit scupper drains. Each has a 90-degree elbow and a screen to keep things from falling into
them through the cockpit and causing clogs. Each is 1-1/2-inch in diameter.
Are these scuppers adequate under current ABYC standards?
Who Will Be The Sept. 2012 Know It All Winner?
Email your answer to:
Want to see how much you know? Want to show everyone else how much you know?
The first three people to submit the correct answer to the following question will win a
Westlawn tee shirt and cap, and will also receive a Know It All certificate. The answer
and winners to be published in the next issue of
The Masthead.
Sept. 2012 Page 16