Hmmm...I did the conversion based on those same assumptions - that I'd be able to catch the ebb out, slack back, and wouldn't get slammed in the nose - but real life intervenes (at least at my skill level).
I've found more often than I'd care to admit that on my boat, < 1/2 yours in displacement, that the rig you describe is inadequate when, for example, the tide is 2' higher than the book estimated and turns an hour earlier, or it gets hotter in Stockton than planned and the big Bay wind-machine turns on. Then you're cooked (unless you can anchor out without repercussions from the Admiral)
I believe you'll need at least twice as much motor and 4x the batteries you describe below. 4 hours at 3 kts (~50amps is my guess) is 200AH - you need 3X that at minimum to keep your batteries healthy. And yes these are sailboats, but you know how fickle wind on the Bay can be.
It isn't just speed...it's sufficient power to punch through a headwind, chop, or a contrary current. That's a combination of the horsepower AND the prop - and then how long the batteries will last.
I'll go back to my previous post - imagine all the trips you've taken in the bay - now imagine you started with 2g of fuel (and actually, ~50% of the horsepower) - that's what it's like on electric. Generator can help - but not as much as you think unless you turn it on way sooner than you need it. And most people only get a 1KW charger - 20amps won't push you very fast.
That is a very cool but stoutly built, heavy and I think full-keel boat. It's going to want some horsepower I think. You can start small and do some tests in the estuary to see what the real-world performance is like, but design nd budget it so you can easily add more battery and motor for best results.
-Keith
--- In electricboats@
>
> I've been reading this board for a few years now and have since gotten my own boat over 30' and have been waiting for the right time to jump in. I know nothing of the technical electrical stuff but from what I've read here and see what's available for sale. I am mechanically able to create my own set up, but I guess the question always comes back to power, and juice, which for me is still hard to determine will be enough. Below is my info, but I still need confirmation that this is suitable and/or reasonable. Thanks for the great posts. I'm still learning much.
>
> Union Polaris sailboat
> displacement type hull
> 36' on deck
> 32' waterline
> 22,000 lbs
> perkins 4-108 (taken out)
> 100 gal diesel tank (taken out)
>
> The challenge for me is to be able to mosey motor (3 knots?) out of the Alameda Estuary to the Gate and back on battery power in mild wind and at slack water. By then the batteries should be down to 80 - 70%? I will have a honda 2000 generator for anything further and to stop depleting the batteries. Speed is not so important. But I figure this is the range I'd like to make me feel comfortable on batteries only at a reasonable pace.
>
> I'm looking at one 48 volt Etek-RT
> 8 - 6 volt trojans for 48 volts
> mounted a la thoosa style with the pulleys and such at 2.3:1.
> My prop is 15", but I don't know pitch. It is in an aperture behind the rudder.
>
> Is this a reasonable starting point for a setup? I've seen a similar setup in the photos section in Vallejo.
>
> Thanks for sharing.
>
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