Bob,
I made a speed power table for your boat with a conservative assumption for a 48v system.
| Speed & Power | |
| Kts | Amps | Watts |
| 2.5 | 10 | 480 |
| 3.2 | 20 | 960 |
| 4.0 | 40 | 1920 |
| 5.1 | 80 | 3840 |
| 5.8 | 120 | 5760 |
| 6.4 | 160 | 7680 |
| 6.9 | 190 | 9120 |
| Hull speed | 6.14 |
|
Both a 5kW and a 10kW would push your boat well with proper gearing and propeller as Eric suggests. The 5kW will likely get you to about 90% of hull speed in calm conditions while the 10.0 will drive the boat more like an 18hp diesel. There is really not a great deal of concern for the heat issue as long as you understand that maximum power is for short bursts as it is limited by the size of the battery pack. Continuous power for these motors is likely 85% of the "advertised number" ie 5kW is 4.25kW and the 10kW is 8.5kW and it is not the motor that is most impacted by heat but the controller. With both of these systems you would be able to reach cruising speed (70% of hull speed or 4.3kts) with ease and enjoy the system. The 10.0 properly engineered will give you better emergency power just like a larger diesel would. What we have learned is that electric propulsion is much better at slow speeds and sailing assist than a diesel and the diesel is better at high speed and extended range.
You should be well served with any of the systems from the marine vendors who frequent this group.
Mike
Electric Yacht of Southern California
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