Kevin,
That catboat is a good candidate for E power. Hull speed is 6.5 mph, which takes 2.9 hp or 2200 watts or 45 amps at 48 volts. A efficient cruise speed might be 5 mph which requires 20a at 48v. (based on 18' WL and 2000# weight). I'd go with a motor and controller each rated for more than 60 amps continuous operation. This wquld be the maximum practical power. You could go lower if you were OK with the lower top speed.
(4) group 31 105ah 12v batteries would give you about 3 hours cruise at 5 mph. These weigh about 260#. I wouldn't go with any smaller bank than this.
(8) 220 ah 6v batteries would give nearly 8 hours cruise and weigh 520#.
A 36v system with (6) 6v batteries would be a good bank size too - 6 hrs at 5 mph.
You removed (13) 35# lead pigs so that's 455# out. The hull will easily float the (8) 6v bank as long as the bilge and your wallet have room for them.
Figure out where the center of the lead pig assortment was and center the batteries on that same point and the boat will have the correct fore - aft trim. The weight of the motor, shaft, etc is too small to worry about.
Be sure you really have room for that big prop. You want a minimum of 10% of diameter clearance top and bottom and 15% back to the leading edge of the rudder. On e of the best things about electric power is the quiet and if the prop is too close to the hull it will make a noticible vibration.
A starting point of 50% slip with a 17" pitch prop at 6.5 mph gives a prop rpm of 800 so pick a gear ratio that reduces the motor rpm to 800 at the shaft. This can be fine tuned by changing the gear ratio or prop pitch to get the amp draw where you want it once you have the boat in the water.
Denny
www.wolfEboats.
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