John,
You have made my point exactly. Would I operate a sailboat with an ICE and a 1 gallon tank? Yes. Would I operate a 40' ICE houseboat with a 3 gallon gas tank? Absolutely not. Would I build a ski boat with a 2 gallon gas tank? Nope.
For power boats, the power requirements are typically too high and the electric "tanks" are too heavy for driving range that goes past tens of minutes. While sailboaters are used to slow speeds, very few people buy a power boat to motor along at 4 kts. For most power boaters, 8 to 10kts is consdiered a slow boat.
You don't have to convince me about how sailboats are appropriate candidates for electric power. But not all sailboats. My F-27 Trimaran has a new 9.8 HP outboard. I could have converted to electric. But the whole outboard driveline with enough fuel to motor over 40nm weighs less than 2 group 31 batteries. Since weight is very critical on this boat, I could not "afford" the extra weight. That type of motoring range is a safety requirement for offshore racing, I wouldn't be allowed to race without it. So no electric drive for my trimaran
On the other hand, I am already converting my 1964 Cheoy Lee Bermuda 30 ketch to electric using a system from Propulsion Marine in Santa Barbara. Their product, like many other 5-6kW systems available from other vendors, is a direct drop-in replacement for an Atomic 4 for sailboat installations. However, they are not good replacements for boats like the old A4 powered speed launch in my marina. Completely different use cases and duty cycles.
As for hybrids in pleasure boats, for me the positives don't outweigh the negatives. If I had a perfectly functional deisel drive, then I wouldn't add the weight and complexity of an additional electric drive for occasional use. But that is for how I use my boat. For other people, it may make more sense.
And for all of the people expounding the efficiencies of deisel-electric drives, it is a matter of scale. Container ships, Cruise lines and railroads can all take advantage of turbo diesel 2 stroke engines that are bigger than an RV and operate at close to 60% thermal efficiency. But have you seen any deisel-electric semi trucks? If it could be made to work more effeciently than a regular deisel driveline, you would see them everywhere. Now try to make them even smaller and lighter, to something that would fit in a pleasure boat. Some ideas don't scale down so well.
So the bottom line is that I use the gas tank analogy to do the 15 second feasability analysis when someone talks about converting to electric. If it seems like the idea is not even close to working, no amount of calculations or creative engineering is going to change that.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "John Green" <v_2jgree@...> wrote:
>
> Eric, Good points.
> Now, do the same musing regarding a sailboat, and the whole thing changes....
> The way to make electric power take off, is for a company with foresight to produce the "New Atomic 4" of electric systems. A unit that could be sold to boat builders. Then for a houseboat application, just double up on the units....
> The point is good though Eric, electric is like ICE except that the gas tank costs more than the engine...
>
> John
>
> Posted by: "Eric" ewdysar@... ewdysar
> Date: Fri Nov 5, 2010 5:42 pm ((PDT))
>
> Capt. Bill,
>
> You might want to look at this from another direction. 500 pounds of
> Lead/Acid batteries (10kWh) is equivalent to less than 1 gallon of
> gasoline, already adjusted for the increased efficiency of electric
> drive. (1 gallon of gasoline = 33kWh) These batteries will cost about
> $1200.
>
> So if you add 1000 pounds of batteries to your boat ($2500) you've
> got an electric gas tank that holds the equivalent of about 1 3/4
> gallons. How far will your houseboat run on that size tank? A full
> ton of batteries ($5000) will last almost as long as 3 1/2 gallons
> through the ICE that drives the boat today....
>
> Even for a hybrid, the math stays the same for "silent running" mode.
> The battery bank with an electric motor is just like a little gas
> tank with an ICE drive.
>
> Fair winds,
> Eric
> Marina del Rey, CA
>
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