T-Pain Is On A Boat: [Electric Boats] Re: 17' sailboat

Friday, June 5, 2009

[Electric Boats] Re: 17' sailboat

James Hitchman,

Why only two batteries, and what battery size limitation do you have? Other's know more, but a Mars or an Etek or an Agni motor would make you a happy/safe boat if you absolutely must have an inboard system.

ThunderStruck's Mars basic system @ 36 or 48 volts is around $1200 parts plus batteries. They are expensive, but 24volt aircraft batteries are available... two of those brings you to an efficient 48volts!

ElectricMotorSport's Etek basic system @ 24 - 48 volts is around $1100 parts plus batteries. Even a 24 volt system would give you the magic 4knots at 20amps for 4hours, or 10hours with big deep cycle 8D (160pound) batteries, if you had the right propeller.

I'm not sure who sells Agni motors yet in the US. Arby Bernt (on this list) is on the west coast working on some new motors, though they may be much more power than your boat needs.

The blessing/cursing about electric propulsion is the batteries and their amp-hour rating. Better batteries are rated at both 20hour and 5 or 6 hour depletion rates: "in 20 hours, drawing "X" amps per hour, the battery is exhausted." X in amps would be that battery's 20ah rating. For a longer battery life, plan to cut that in half, or just a third (a 100ah battery should only normally supply 30 to 50 amp-hours.) So if you had a good motor/controller/prop/battery combination, the magic 4hr 4kts 20a uses 80ah, so you need at least 200ah of lead acid battery. That is about 250 pounds @ 24volts.

LiFePO4 (lithium) batteries are roughly 4 times the expense, but 1/4 the size, 1/4 the weight, and 4 times the longevity. Ballpark estimates.

With that size boat, and even for much larger ones, a rudder mounted motor instead of an inboard, makes owners very happy. Just find some place to put 3 or 4 batteries. Re-E-Power has more thrust than you can use, and a new rudder looking outboard. Some people glue a simple electric trolling motor onto their rudder.

Ask this group some more (specific) questions, and we all will be appreciative of the honest real-world answers.

Mark Stafford

--- In electricboats@yahoogroups.com, "jameshitchman" <jimcar@...> wrote:
>
> Hi: I am looking for an inboard electric system to power a 17 ft, 4000 lb sailboat built of wood that originally had a 3.7 gas Kermath or Lauson engine. I contacted Elco, Asmo, solomon, Thunderstruck and only Oz Marine made a bid at $6500. The question seems to be how to obtain a 3-4 hr range with only two batteries. Do you know of a different company? Thanks, jim hitchman
>