ELECTRIC CRUISING
A viable option?
L‘I AM AN ELECTRIC CONVERT’
et’s be clear, electric propulsion is nowhere near a 300-mile range at 6 knots on a 38ft yacht, but I think it is viable for a typical 30 footer in the Solent and crossing the Channel occasionally, as long as you don’t motor long distances against full-bore spring tides, and use the sails most of the time. For example, a 60-mile range under power in a flat calm at 4.5 knots looks achievable.
That’s why I have decided to convert my Sadler 29 to electric propulsion. You may need a more traditional approach to cruising, but for me having no noise, no vibration, no smell and no maintenance is worth the compromise.
After a season of real-world testing in our Sadler 29 here’s what we found. We fitted a prototype 10kw pod in August, with 18kwh of lithium batteries where the Bukh DV20 used to be. This gave us the following results: ■ 3.3 knots at 1kw output, 54-mile range ■ 4.5 knots at 2kw, 40-mile range ■ 5-5.5 knots at 3kw, 30-mile range Additionally, the power generated under sail often puts nearly as much charge in on passage as we’ve used coming in or out of harbour. On a sail of more than a couple of hours, we might even make a net gain in battery charge.
Cost aside, it would be possible to add another 50% in battery capacity and still come in just under the weight of the Bukh and diesel tank removed, and double that again if you took out all the 12V batteries.
This would make
80-100 miles on battery alone achievable, although I didn’t feel the need for that much capacity.
If you accept 4 knots as a useful speed then a 2kw petrol suitcase generator small enough to keep in a locker would charge the batteries at about the same rate that you’re using electricity, getting you home if the wind died mid-channel.
Electric motors are incredibly efficient, but you also don’t seem to need as much power as a direct conversion of horsepower to kilowatts would suggest. 3kw is about 4.5hp, and we can achieve 5 knots with 3kw. We’re actually going to change the 10kw pod for a 6kw pod, as there are no circumstances in which 10kw does any more than 6kw, just as you very rarely use all 20hp of a diesel engine. And the 6kw pod is smaller (less drag) and lighter, so there are incremental gains there too. This
disparity between rating and power delivered could be due to a couple of different reasons:
■ The torque is instantaneous so you can turn a propeller of a larger more efficient size for cruising that would stall an equivalent power diesel at idle.
■ The propeller itself, in a pod installation, is vertical rather than at an angle as on a shaft drive, converting all the power into forwards rather than upwards thrust.
Another advantage when manoeuvring is the complete controllability. You don’t have to knock it in and out of gear at idle, you can run it at 50rpm if you wish. The lack of noise and vibration is fantastic. Similarly, motoring downwind in light airs with a Sunday morning hangover, there are no diesel fumes in the cockpit, and there’s no oil in the bilge. What’s not to like?