Many years ago I wrote to the British Waterways Board asking for plans for the new Eco-hull and they sent me some free. You get bow & stern, and the length of the middle is up to you. That's fine if you want an Eco-hull - but it should give you less wash and therefore drag, or vice versa, and the bow should be dead easy to do in ply. Incidentally, I think that propellor sizes for HPV boats are quite large - some year ago I saw a Dutch pedal-powered inflatable catamaran on the Basingstoke Canal with an outboard type submerged drive and the prop had large paddle blades and was about 10" at least in diaa. Think WW1 aircraft propellors - low revs, low power, plenty of torque - big wide blades. A smaller prop would probably need gearing up and you'd lose any extra propellor efficiency in the gears. I think. To keep weight down you could reduce freeboard - it might be worth your while looking at canal tug styles, or the BWB workboats which are more flat-iron style. But if your heart is set on roses and castles, go for it.
