Electric Power

[Lazy Jack]

Remember that 'doomed' gunning dory built of AC plywood? Well after two seasons and much use/abuse, it is holding up great. The novelty of rowing it however is wearing off especially since I've built an adirondack guideboat in the meantime. I'm contemplating the use of an electric trolling motor as a viable alternative to oars, but I have absolutely no experience with trolling motors. Would a 50 or 75 lb thrust trolling motor provide adequate thrust to get me to windward at a respectible speed when I'm too lazy to row? Could I carry enough batteries in a dory to make this practicable?

[whb]

Jack,

Take a look at Minn Kota's site for battery usage.

A 28 lb. motor I was looking at went from 14 hours on a charge at speed 1 to slightly over 2 hours (I think) on speed 6. What these equate to I don't know but it does show that the relationship of speed to fuel use is much more linear in the electric world.

Howard

[Steve Paskey]

Hi Jack: If you haven't been there, you might try posting your question in the electric boats group at Yahoo: http://groups.yahoo.com/group/electricboats/
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The specifics of LILY, a 15-foot electric launch designed by Suzanne Altenberger (Phil Bolger's partner), may help you get handle on what will work. Lily is a flat-bottomed skiff that uses a trolling motor as the sole means of propulsion. The motor is a 24-volt, 65-lb thrust Minnkota; power is provided by six 12v, 117 amp-hour batteries totalling 330 lbs. (Batteries are connected as three pairs in series, with the three 24-volt pairs then connected parallel.) Total displacement, including two people, looks to be around 1200-1300 pounds.
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Bolger reports that this configuration will push the boat for 8 hours at 3.8 knots, or 14 hours at 3 knots. Those numbers are based on four seasons of using Lily as a dayboat for inland and protected coastal cruising. Among other things, she's taken Phil and Suzanne around Cape Ann, a 22 mile trip along the exposed Atlantic coast, with battery capacity to spare. And I believe that her home cruising area -- in the vicinity of Gloucester, Mass. -- has fairly strong tides.
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Given that your gunning dory is probably lighter and offers less resistance, you could do with less power. And if you're not planning to run all day, you won't need as many amp hours available. I'd bet that you'd do just fine with a 12-volt, 55 lb thrust motor (MinnKota's most powerful 12-volt), connected to a pair of 12-volt deep-cycle batteries weighing about 120-130 pounds. (Or, alternatively, two 6-volt golf-cart type batteries in series would give slightly more amp hours for about the same weight.)
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That's just my guess, based on reading rather than experience, but I'll be trying a similar configuration with a 16-foot swampscott dory as soon as the weather warms up a bit.

[ 03-08-2003, 09:06 PM: Message edited by: Steve Paskey ]

[Buddy Sharpton]

Jack, my 15 foot 1300 pound (with two people aboard) uses a 47 pound thrust MotorGuide, and two Group 24, 85 hours batteries, hooked up on at a time, one in reverse. Flat water and can get about 3 1/2 mph wide open, and supposedly 2/12 hours out of each battery at that rate. On speed four out of five, 3 mph and maybe four hours. So I guess maybe 25 miles out of the whole shooting match. I have a foiur stroke, two horse Honda for the long distance stuff, and it will push the boat to about 5 mph, which is the huol speed for this boat.

[Buddy Sharpton]

Oh yeah this is a 15 foot, 7 foot beam catboat

[Rocky]

I had a 34-foot-pounder that moved my 16-foot saiboat quite nicely, but was too small for my present boat. I was gonna offer to send it to you for testing til I remembered I gave it away last fall - sorry. Since you're rowing anyway you probably want a minimal configuration. One deep-cycle battery would do if you still have your oars.

[ 03-09-2003, 10:14 PM: Message edited by: Rocky ]