I've been eyeballing that design too, thinking it could make a good "fast electric" runabout, but was thinking it might work better as an inboard. You could probably swing a bigger (more efficient) prop, and you could skin over the outboard "slot" in the back which would add some buoyancy which would help carry more battery weight.
As a design exercise, my suggestion would be to start out by forgetting the motor/reduction/prop details for a bit and start with the batteries, since they will likely be be the limiting factor. First how much weight can you carry, and then how much can you afford. If you can settle for about 3.25 HP at cruise, you can get a couple hours, with some reserve, out of a set of 8 golf car batteries. They'll weigh about 500 lb, and cost about $600 to $800 last I checked. If you need much more than that, you may need to start looking at some of the "high tech" batteries out there, assuming your budget will allow.
Do you have any info on HP vs. speed for the Sneakeasy?
--- In electricboats@yahoogroups.com, "b504now" <b504now@...> wrote:
>
> Last year, we converted a small outboard to electric power. We ended up with a Etek clone (MARS), a AXE controller, 48V car battery system but it was on top of a B&S electric outboard base (the previous owner had stripped the motor out). The boat was a 18ft homebuilt garvey flats and to say it was inefficient is being kind. We can run about 1 hr all out and even that gets about 6mph. (105ah batteries). Deep cycle (thats what I had). My guess is that since the outboard was built for 5hp, pushing with 10 was ineffective (prop size)
>
> We are about to build a Bolger Sneakeasy. James M Rudholm built one with electric power, but sadly, his web site seems to have gone away, which is terrible for me since I was hoping to lift his experience.
>
> Looks like the Sneakeasy was getting 12mph on 8hp gas. If I look at the charts, I should get about 10 on my 48V ETEK. But I'd like to get a longer running time. About 2 hours is where I need to be. But... there are lots of other factors that I can balance so I need some guidance.
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> We are using a 25hp outboard as a base (10in prop) but we have rigged a pulley drive to the motor. Since cruising speed is more important to me that pure speed, any feel for the optimum prop speed ?
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> Since I can gear up or down the motor. My inclination was to get speed up the prop but should I allow the motor to turn faster and the prop slower ? Whats the current best thinking ?
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> Mr Rudholm used 8- 6v batteries, given my setup, any recommendations on battery ? My westmarine deep cycle were "free" but now that I have authority to buy new ones, any thoughts ? Go Carts batteries ? Car ? What ? I've read a lot of the posts and nominally more confused than illuminated.
>
> Thanks
>
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