Eric,
Ran the information through my model also. I used 80% maximum DOD which is the only difference. I concur that a 10kW is all that is needed. If you are actually looking at using the vessel as a tug, than a bigger propeller would be more important and then the more powerful 20kW would also be appropriate.
To your point about evaluating the way we run our boats, 70% of hull speed is right where electric boat should live. If you run at 95% of hull speed you should not have an electric boat or a displacement boat. If you want to go faster with a displacement boat, get one with a longer waterline. The rule of thumb that you double the power used for every knot you increase the speed is fairly accurate.
This is what I came up with which matching the weight of the three battery banks. Very close to your data:
| Range | 80% | DOD | ||||||
| Flooded | AGM | LiFePo4 | ||||||
| 250 | ah | 200 | ah | 400 | ah | |||
| Kts | Hrs | Nm | Hrs | Nm | Hrs | Nm | ||
| 2.8 | 21.9 | 60.8 | 16.5 | 45.9 | 34.2 | 94.9 | ||
| 3.5 | 9.3 | 32.4 | 7.6 | 26.6 | 16.5 | 57.7 | ||
| 4.4 | 3.9 | 17.3 | 3.5 | 15.4 | 8.0 | 35.1 | ||
| 5.0 | 2.4 | 12.0 | 2.2 | 11.2 | 5.2 | 26.3 | ||
| 5.6 | 1.7 | 9.2 | 1.6 | 8.9 | 3.8 | 21.4 | ||
| 6.0 | 1.3 | 7.5 | 1.3 | 7.5 | 3.0 | 18.2 | ||
| *DOD = Depth of Discharge | ||||||||
Mike
Electric Yachts of Southern California
Posted by: mike@electricyachtssocal.com
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