Hi Jace,
You make some interesting points, though I have to say that I never converted a car to electric that started out weighing more than 1000kg in ICE form, even 20 years ago when we didn't have sophisticated drives available.
The main reason that most electric boat conversions are done with displacement type hulls is their superior weight tolerance. Even with Lithium batteries, electric drives are noticably heavy.
You state that getting a boat into the 8 to 12 knot range is easy. When was the last time that you sailed a boat at 10 knots?
I have an F-27 8.5m trimaran that uses "modern design and engineering" (it's actually 22 years old) that I have sailed at 17kts, but until the true wind gets past 12-14kts, my average speed is close to 7kts. I had the opportunity to convert to electric, but even the weight of a small electric drive (8kWh battery pack with a Torqeedo Cruise 4.0) would have been a performance penalty that I wasn't willing to accept. If you have sailed a fast boat, imagine adding a 110kg passenger that never leaves the boat. For any performance boat under 10m, that's a considerable penalty.
You'll find that for multihulls, you need to go big (expensive) to get enough weight capacity to carry an electric drive while maintaining reasonable performance. Of course, these larger boats need more powerful drives, which weigh more, which affects performance, and you're into the vicious cycle of weight and power. The lower threashold that seems to work occurs somewhere around a 12.5m cruising catamaran (not a light racing catamaran).
And as you've already alluded to, a ballasted keel boat needs LWL to get to 8 kts. You'll need at least 11m at the waterline for an 8kt hull speed. But it's been my experience that a performance ULDB keelboat needs about 14m of waterline before it can average 8kts for more than a few minutes at a time. With a light 16m boat weighing in at 10 tons, it needs a more powerful drive and bigger batteries, which weigh more, etc. etc.
So what you're saying is easy to write, but much more difficult to execute in the real world. Since few of the members here have $100,000 - $200,000 or more to spend on their boats, the 8.5-10m auxilary sailboats deliver very successful conversions at a reasonable price. They may not develop much in the way of regeneration, but if you talk to the people that have actually converted their boats, little regen is not really a problem.
If you've got some more specific details about your concept, please share them, there's enough practical experience in this group to vet the concept without having to build one from scratch.
Fair winds,
Eric
Marina del Rey, CA
PS. I have been working with a group of people, including Pete Melvin (lead designer of the new AC45 and AC72), that are slowly trying to develop an electric offshore power cat with a range of 100nm at 12-15kts. It's a lot harder than it sounds.
--- In electricboats@yahoogroups.com, "Jace Hobbs" <jacehobbs@...> wrote:
>
> It strikes me that almost all of the conversion projects that people are
> involved with are on boats with slow hull speeds that make the mild
> horsepower less attractive and make the regen argument a non-starter. This
> reminds me of electric car conversions that started with a heavy antiquated
> chassis because it was available cheaply. Poor performance in the cars and
> boats is the result.
>
> To get efficiency, we must look at the whole system approach, and that
> starts with the boat we will convert. Weight and hull form (inextricably
> connected) must be prime considerations. The cheap hulks that we cram our
> lovely electronics into perhaps don't deserve the upgrade as they will
> disappoint with short range and low average speeds.
>
> The regen situation puts this in high relief, because getting a boat in
> the 8-12 knot range is easy today if you use modern designs and engineering.
> Often this means going to an unballasted boat (usually a multihull) but it
> surely means advanced building techniques to keep the structure with little
> wave inducing drag. With the higher sailing speeds easily produced, the
> regen suddenly makes sense. Cheers
>
>
>
> ________________
>
> Jace Hobbs
>
> P: +64 3 5451122
>
> M: +64 21 051 1666
>
> www.electricbikehub.co.nz
>
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