Hi Steve,
You might be missing the point of most of the responses. People with electric drives rarely spend much time at full throttle. The 8.5kW drive in the Valiant 40 is not "minimal", it meets the typical conversion guidelines of 1hp per ton of displacement and should drive the boat at very close to hull speed. On this boat, that means between 6.5 and 7kts.
I'm getting the impression that you haven't spent much time operating an electric sailing auxiliary. One learns that the traditional ICE hp guidelines don't really apply. For example, the top speed on my 30' ketch was about 5.5 kts with the previous 12hp Yanmar SVE12. The engine was propped correctly; full throttle matched with top speed and hit max rated RPM. When I switched to a 7.3hp electric with the appropriate prop, my top speed jumped to 6kts+.
Looking at the Valiant 40 that is being discussed, there is no question that the 11hp electric will provide more operational performance than the 20hp diesel that is coming out. So the "minimal" electric drive is considerably more capable and safer than the diesel that someone installed some years ago.
If you wanted to focus on the hp numbers alone, then you would fall back to the other conversion rule of thumb where 1hp of electric can replace 2.5-3hp of ICE. Since the Valiant 40 typically came with various 40hp diesels, the conversion would suggest a 13 to 16hp electric drive. The reason that we steer away from basing one's conversion on hp alone, is that it requires that you believe that the installed engine was appropriately sized for the hull. Looking at the Catalina 30, the factory installed a variety of engines from the ubiquitous Atomic 30, to an 11hp diesel twin in the 80', and all the way up to a 28hp 3cyl diesel today. Based on that info, how much power does a Catalina 30 need? We know that the answer is that many successful electric conversions using 5kW electric drives which fit perfectly with the 10,200 lb displacement. Base on hp alone, a Catalina 30 owner might think that they need an 11kW drive to replace their 28hp diesel, and that is obviously overkill.
And again, the electric drive as spec'ed should drive the Valiant 40 at 4.5kts using just the output of a 48V 50A charger that can be run from a 3.5kW generator. Getting to that point is a fallback to the fallback. The batteries are there in case the sails won't work. The generator is there in case you exceed the capacity of the battery bank. Once you shift to electric power at reasonable speeds on this proposed conversion, if you still have issues 15 miles later, then you can run at 4.5kts on the "little" generator for as long as you've got fuel. Installing a 15kW generator misses the point of the whole conversion. The batteries will run at full throttle for more than an hour with no external support, if you're still in panic mode after an hour at full speed, then you're not practicing safe seamanship.
I believe that the power model that you describe is more suited for a cabin cruiser where the electric drive is the primary or only source of propulsion. That is also why I'm not a proponent of converting cruising powerboats to electric, hybrid or otherwise.
Fair winds,
Eric
Marina del Rey, CA
PS. Please don't feel that I'm picking on your posts, it gives me the opportunity to cover some of the basic conversion considerations that some of the newer members may not have heard yet.
--- In electricboats@yahoogroups.com, "Steve" <sstuller@...> wrote:
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> 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.
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