I have played around with the components required for electric propulsion on easily driven hulls.
I believe if you have a bit of nouse about the electrics they are a really good choice. The components required for a good system on something that is easily driven like a proa are reasonably economic.
I have a couple of Mars PMSM motors. I got a deal on two motors and controllers a couple of years ago from this place:
These are quite robust motors although not waterproof. They give a combined motor/controller efficiency just over 90%. The 3001s I have are good for 4.5kW continuous and 9kW peak. The Kelly switching controllers are trapeziodal so quite noisy due to magnetic resonance.
I have a motor running up to speed on 24V here:
I made a crude outboard that was limited by the batteries to 230W but it worked reasonably with a 2:1 reduction and relatively large prop:
The light guage aluminium cover amplifies the noise. It does not sound as bad in reality because the camera microphone was quite close to the motor. Noise is considerably less than a small outboard but they are certainly not silent. There is no apparent gear noise on this one because the reduction is underwater.
I have played around with the model airplane stuff. The motor on the boat in the linked clip weighs 159g and the battery 750g. It will get over 6kts even limiting limiting power to 230W:
The reduction is 12:1 and I am driving a high aspect prop on a curved shaft. Overall system efficiency from battery to boat moving through the water is around 70%.
The range of motors available are increasing all the time. There are now some large induction motors available:
The lithium batteries are also becoming more affordable. I found this supplier in Australia but have not purchased any of the large format cells:
For auxiliary power something like a dozen or so of the 100Ah batteries would do a good job on a proa like Visionarry. Battery weight would be less than 50kg. A sedate cruise around 6kts could be achieved with less than 1kW giving range around 20nm without any charging. Pushing up to rated power (4.5kW) on a Mars motor could get over 12kts.
The price of solar panels are also coming down:
In good sunlight on a balmy day these 600W combined would get close to 6kts on Visionarry without any drain on batteries.
If you are after something smaller and cheaper to get in and out of a berth then there are some good model aircraft parts. This is the low cost stuff:
Take the ratings with a grain of salt because they are short duration with good cooling from a strong air stream - neither applicable to most boat applications. The most efficient model aircraft motors that I have found are made by Hyperion (up to 92%) but they are expensive compared with the ones coming out of China.
I have found toothed belt reductions to be quite good to enable swinging a large diameter prop. There is a little trick to setting these up so they do not waste power. It still pays to get motors with lowest Kv in the power range you are considering.
Some have been adding variable speed controllers and high aspect props to Minn Kota thrusters to lift performance in dinghy size boats. Done well these have a range of 50nm using a couple of lead acid deep cycle batteries.
To me the big advantage with decent solar collection and electric drive is the avoidance of liquid hydrocarbons and associated fire risk particularly with the more volatile fuels. It is feasible to do away with internal combustion engines but you still need electrics on all but the smallest dinghy. Many of them now carry instruments of various types. So why not go all electric.
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