I tried the Torquedo 1003 on my Venture 23. Iv'e been using the Honda 2 hp for years and get about 5 mph at full power, the Torqeedo gets same speed!
Your M or X will get 4.5 mph. The only problem is short run time at full power, only 20- 30 min. This with the supplied Lith battery. I tried this for possible use as alternative elec power for the M. OK for some folks and I now sell the Torq on some M's. But, seriously recommend the E-Tec 60. Cost of the pricey little 1003 watt motor with the needed options is over $2,000.
The original post regards adding a bunch of solar panels and two batteries to go about 2knots on solar only.. which is interesting but this would further degrade the sailing performance. Some wont care about that - but I would and unless the sceneraio in the movie "Water World" happens - then I will want this for sure
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However.. I cant help think about another reason for the electric motor. I have a 30 pound thrust electric trolling motor on my modified C15 sailboat and the main reason for this is that the trolling motor is only 13 pounds so is very light on the transom. I have the battery just under the mast and as low as possible where it acts as ballast.
The setup that is interesting would be to get hold of an old 26D that you didnt mind REALLY experimenting on. You (Mike I.) would know a lot better than I but I am of the impression that the D and S models also benifit from a light weight transom and overall light weight - assuming it is sailing performance.
http://www.torqeedo.com/us/electric-out ... dimensions
Torquedo makes a couple tiller outboards and the higher power one runs off 48 volts. What is interesting to me about this outboard is that it only weighs a little over 40 pounds - and is supposed to be about the same as an 8 hp gas outboard (which Ive heard is true even though its little hard to beleive). 40 pounds on the transom on a D model - good thing.
I would power this from 8 six volt golf cart batteries. This is where I would really start to cut up the D but I would cut up the water ballast area just under and slighty behind the mast. This might be 500 pounds of battery - but its also in a very good spot as ballast and these would work better than water. You would still want the remainder of the water ballast area to be useful as water ballast - but also maybe a way to pump out the water ballast and use just the 500 pound battery weight. For 12 volt typical accessories, just put in a 48 to 12 volt DC to DC converter. Since the goal here is a fast boat, you want to keep it light (ie, no fridge).
The complication comes in for charging the batteries. Solar.. OK for trickle charge (or 2 knots if you dont mind 240 watts of panel but the point of this boat is sailing peformance - dont want that panel area). The six volt batteres have a capacity of around 200 amp hours so you can charge them in bulk at 20%C which is 40 amps. So your maxiumum charging POWER would be 48V*40amps = 1920 watts. A 2000 watt genset like the Honda would be just about right for this.
But.. a 2000 watt genset is about 60 pounds and the most convenient place to put it is at the back of the boat - which kills the whole idea since you are now back to being heavier than say a 6 hp gas outboard..
Put that rotating carbon fiber mast on the D with the light transom.. might be interesting. Finding a good way to charge the batteries that preserves the light weight on the transom is what hurst the idea
(plus this would be very expensive.. you would spend way more on powering the boat than you spent on the boat itself).
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made 4 knots on a glassy smooth Buzzaeds Bay at full throttle with a Nissan 4HP.....that's 3000 watts.
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. Might even be able to sell electricity at different anchorages 
, and in our landspeed racing I know it takes 8 times the HP to go twice as fast and according to this source...
