Tom,
I don't think your requirements are too 'out there'. Seems to me there are just a few constraints on your project. 1) You must be willing to accept slow speed and maybe even no speed (i.e. don't go) when adverse wind or current conditions occur. 2) Recharging from shore power must be convenient because that's the energy source that's cheap and quiet. All the other options, when sized to be practical for every-day use are either very expensive or bring with them the downsides of ICE power. Plus most of them would work better driving the prop directly instead of the daisy chain of prime mover to generator to battery to motor to prop.
I could see a long narrow light hull ( a catamaran would be even better) optimized for a speed/length ratio of perhaps 0.6. A boat with a 30' waterline length, weighing 3000# with (16) 220ah 6v batteries could go 140 miles at 4 mph.(11 amps at 48v) 100 amps would give 8 mph for 22 miles. Total battery weight would be about 1000# and cost maybe $3500 for top of the line AGMs. Maybe 1/3 that for wet batteries. You could cut the bank size in half in you were happy with less E range or more reliance on a gen set.
A 2kw quiet generator like Honda EU2000 ($900, 50#) hooked to a 1.5 kw battery charger would drive the boat about 5 mph with no battery drain. You'd want the generator out in the open for cooling and gasoline safety. They are not marine rated and not safe in an enclosed area. They are very quiet though, I'd say as quiet as a little four stroke outboard. It could recharge your 80% depleted bank in about 15 hours.
You stated you don't want a 'regular' sailboat with aux E power. Just about anything will sail down wind, though, and that's what I'd set up, making the rig easy to strike when not sailing. A 150 sq ft balance lug rig would have spars short and light enough to be taken down and stowed without any mechanical advantage (build them hollow) and would perform well off the wind. You don't want any foils sailing down wind and a simple lee board would give you a modest reaching ability.
Denny Wolfe
PS: I envy you the time spent with Robb White. I was a great fan of his and had hoped to make it to one of his speaking engagements one day.
----- Original Message -----
Sent: Thursday, November 12, 2009 12:08 AM
Subject: Re: [Electric Boats] electric prop and re-charging
Thanks, I'm no authority on the White family, just happened to visit 'the T'ville boat shop' just before the time everyone was hooked up to the internet or before I knew Robb White wrote for Wooden Boat and other. But he seemed quite happy that I liked pokin' around on the water, and knew many of the same watery places in which one can poke. I hope some of the water oriented Whites will continue to 'slap'em together', their collective good workshop, boating & plain ole pokin' around example has enabled lots of people to begin playing with materials and designs - and combine old methods with new materials.
So, . . . back to electric boating and extended travel with electric.
An extended travel electric boat with the ELECTRIC wagging the dog's tail, not a sail-boat with small/minor electric power is what I'd like to construct, and have the workshop space and time in which to do so.
Lee-board(s) could be added to the tunnel-stern designs sail to increase the range. Sails would be in proportion to the size of the craft as with canoe or kayak sails to those boats.
Each 'easy off the shelf' change of state seems to be expensive :
solar to electricity,
internal combustion to electricity,
water/prop re-charge to electricity,
wind to electricity (docked),
or stationary bike to electicity,
and so on.
And electric storage is quite expensive for the amount of total mileage/life of the battery bank/storage, though as one of the links pointed out above that the slower one can travel, the more mileage comes from a battery charge, and I suppose that also means a bank of batteries could ultimately pack in double or triple the miles or more than storage banks that were quickly dis-charged.
I'll continue to read the links and posts, thanks for continuing to consider and respond to this thread.
Tom Johnson
Pine Mountain, Georgia
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