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[Electric Boats] Re: feasible regen
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Eric,
I would suggest that the regen may not be practical on a 2 or 3 hour 5 knot sail but what if you sail for a distance and use power for the stereo or a few gauges? What if the total usage of power during an overnight run equaled your regeneration rate? "Anything that is free is for me" so any power I can get is good thing. It may not be able to fully charge your batteries but it's better than nothing unless the drag exceeds the benefit. What if you're on the back of a 20 foot wave heading down and can get 6 amps (or more) all the way down and half the way up the next wave? You could run your motors at 2 knots and gain 50 miles in a 24 hour period at no cost. I didn't do the math but should be close. Anyway even a little regen is better than no regen. But then again the majority of boats here are smaller and don't travel as far. I think if I had a smaller boat and it was free or included in the package I would think of it as a plus. Now if I had a tri (I do have a MR2 spyder) for nothing but speed the weight would definitely be a consideration. I'm surprised you don't just have a couple of paddles! You could probably still get up to 5 knots :o) Steve in Solomons I know that my 30' ketch has only touched 6kts a couple of times in over 10 years. 5kts takes a solid breeze for my old boat. So I don't expect much from regen from my electric drive, even when headed offshore to our local islands. Alternatively, my 27' trimaran has hit 6kts boat speed in only 5kts true wind. If I converted that boat to electric, that kind of performance would no longer be possible. I'm not willing to sacrifice my good runs at 15kts+ boat speed to go electric. The 9.8hp outboard is auxilliary power that works for me. |
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Steve,
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For me at least -- and this may be because I don't fully understand the technology -- the issue is that regen isn't just a switch you flip or an option you order with the controller...it's also about selecting a prop that can regen efficiently. Such a prop will incur worse drag whether it is re-gen'ing or not, correct? My boat has a two-blade prop which hides in the aperture when vertical (or pretends to, at least). I feel like this makes a difference when sailing, though I don't have a knotmeter so I can't back that up with data. If I keep this prop (or one similar), my understanding is that regen performance will be even worse than otherwise. In other words, you commit to the drag when you affix the prop, and you can't take it off in light air when you can't stand the drag. Is this understanding correct? Paul --- In electricboats@..., Steve Dolan <sdolan@...> wrote:
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Paul,
I forgot about the prop design and you are correct. The pitch is more and 3 blades is a normal design. It's not a switch, you're in neutral or in my case a slight bump on. It's more again dependent on the size of the boat as to how much drag you incur. Heck I have 2 of them down there! Anything is going to incur drag but how much depends on a number of factors. A fast, light boat is going to be much more susceptible to anything hanging down below on a fixed installation. There are several manufactures with retractable props for smaller boats out there and I would probably be looking at that for light air. But us big nasty CondoCats are not so susceptible to anything hanging down. We might loose a 1/2 knot or 1 knot but we don't care sitting in the back drinking coolaid and burning the dogs! :o) Steve in Solomons MD Steve, For me at least -- and this may be because I don't fully understand the technology -- the issue is that regen isn't just a switch you flip or an option you order with the controller...it's also about selecting a prop that can regen efficiently. Such a prop will incur worse drag whether it is re-gen'ing or not, correct? My boat has a two-blade prop which hides in the aperture when vertical (or pretends to, at least). I feel like this makes a difference when sailing, though I don't have a knotmeter so I can't back that up with data. If I keep this prop (or one similar), my understanding is that regen performance will be even worse than otherwise. In other words, you commit to the drag when you affix the prop, and you can't take it off in light air when you can't stand the drag. Is this understanding correct? Paul --- In electricboats@..., Steve Dolan <sdolan@...> wrote:
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Steve,
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I completely agree with you. My drive system is regen capable and I certainly won't disable that feature, any "free" power is welcome on my boat. But I will not count on any significant contribution to my charge from regen, it will be a present from Poseidon. Unfortunately, with my boat (a Herrschoff H-28 knockoff), 5kts is just about all I can count on, a 120 mile day would be stretching the boundaries. But like you have stated, 100W x 24 hours will deliver 2.4kWh a day and that will easily cover all but the most wasteful house loads. Now I just hope I can get 100W out of my drive.... On the trimaran, the outboard comes out of the water less than a minute after being shut down, so the only thing that I'm suffering is the weight. My offshore racing org's safety requirements is "Sufficient power and fuel for the boat to achieve a speed equal to the square root of her waterline (5kts for me), for a distance of 30 nautical miles in flat water without a headwind." 3 gallons of gas is technically enough, although I generally carry between 4 and 6 gallons for long races (that extra 20 pounds is worth my peace of mind). Electric is not yet feasible to meet this requirement. BTW, in the last 3 years, I've spent more on new sails for the trimaran than my entire drive conversion with LiFePO4 batteries in the ketch. Don't let my wife find out.... :) Fair winds, Eric --- In electricboats@..., Steve Dolan <sdolan@...> wrote:
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--- On Wed, 11/24/10, Eric wrote:
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Bill,
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So you were getting about 60 watts at 4 or 5 knots? That's right back where this conversation started.... I find it much more effective to talk about watts instead of amps in this kind of discussion due to the varied voltages that are used by different boats. But I think that you're on the right track. By using a dedicated water powered generator, that entire component can be optimized for extracting power from the water flowing by at the speeds that you expect to achieve regularly. An additional benefit is, like you said, you don't have to take the performance hit unless you choose to harvest power. The typical problem with using an electric drive for regen is that a prop that is optimized for providing thrust will not be as efficient for collecting energy and vice versa. I noticed that Robbie stated that he uses 2 dedicated Aquair units rather than the drive unit regen typically discussed here, the Aquairs obviously don't function as drives too. And the same performance data keeps coming up. From the Aquair website "The reason for the choice is that when sailing downwind at 6 knots, the Aquair 100 Water Drive generates approx. 5 amps continuous charge." So they quote 60 watts (5A x 12V) from 6 knots of boat speed. Their chart also shows less than 25 watts from 4 knots of boat speed. That works out to less than 0.5A charging for my 48V boat, or 1 solid week of continuous sailing to charge my 8kWh battery bank from 50% discharged. That assumes no other electrical loads along the way. So I'm back to my original premise. Regen will not provide any significant charging to a traction battery bank for most conversions being discussed here. Regen or water generators can provide enough to cover most house loads but not much more. I would personally love to be proven wrong on this premise, but I'm still waiting.... Fair winds, Eric --- In electricboats@..., Steamboat Willie <stmbtwle@...> wrote:
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