If you want to maintain a fifty percent state of charge for your batteries then the generator has to meet the demands of the 8.5 KW motor so there is no more battery depletion. An 8.5 KW motor at full throttle for a Valient 40 is a minimal HP solution. Thanks. Steve S.
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> Apparently, you lost all of your ground tackle too. I'm not sure why anyone would motor into the darkness near dangerous waters with the primary drive near empty, but this scenario is filled with a series of bad decisions. Even a Honda portable generator would get you away from the rocks unless you're in a current that exceeds 3kts.
>
> If you had a diesel as your primary drive, would your first response be to take off at full throttle? As long as we're creating a worst case scenario, we might as well include that you used all of your fuel making microwave popcorn and fresh water for the converted cockpit jacuzzi party, so the geneset won't run anyway.
>
> Seriously, dropping an anchor stops all of this right now. If you're in blue water, in conditions that you would rather not sail in, the traditional responses like lying ahull or deploying a sea anchor are still efffective.
>
> Back to sizing the generator, the capacity of the generator only needs to be enough to power your battery charger, in the case of a 48V charger than can deliver 50A, everything in excess of 4kW is surplus. You could probably get away with the 3.5kW Kubota generator (70 lbs lighter than the 5.5kW, though the 2 cylinder 5.5 is probably smoother) if you pick the right charger and can refrain from excessive house loads during a self-induced emergency. I'm not sure that sizing the generator to drive the motor on the verge of overheating while supplying an additional 18A of 120VAC is a realistic requirement. I can't imagine that anyone would wire the genset starter motor to their traction or house banks instead of a dedicated starting battery, so starting the genset should be unaffected by ignorant use of the traction or house batteries.
>
> On the proposed Valiant 40, I would bet that the genset would rarely be run underway and very rarely for traction energy. Steve, when was the last time you depleted your traction bank completely and then wanted to resort to generator power only to drive the boat? Did you find that you desired to operate the boat at full throttle for a long period right then? On my boat, the only time I've pushed the throttle to the stops is to measure the power consumption and potential speed. I've never done it while sailing. Everyone that has reported using their gensets to supplement their traction bank starts the process long before the primary bank gets below 50% depth of discharge.
>
> If I was going to install a 15kW (20hp) diesel on this boat, I would skip the extra weight, cost and complexity of adding a parallel or serial electric drive and go straight to the prop with diesel power. I would use the weight and money that I saved to upgrade to 35 hp and a 100+A alternator and finish lighter and cheaper. There's a reason that 99% of the blue water cruisers go this route, it works and works well.
>
> OK, I'll step down off my soapbox now. I hope that I haven't offended anyone.
>
> Fair winds,
> Eric
> Marina del Rey, CA
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