Hi Warren,
Not sure what you consider a small boat, but I have a 31' foot O'day on a mooring. When doing the math (as I did) before building my system over two years ago, it seems like you couldn't possibly fit enough solar on the boat to effectively supply enough power. I was pleasantly surprised to learn I use way less power than anticipated. I have yet to draw by battery bank down to less than about 50%. I use the boat most weekends, sometimes during the week and spend 2-3 nights on board every week. A typical day sail I use maybe 10% which is often fully recharged the next day. Every year I do a at least 2 trips around 45 NM miles and a few around 25 NM. I have only charged via shore power 4 times for piece of mind and every time I could have continued on without charging. I own a Honda 2200, which I have never used and no longer keep it on board.
I have 460 watts of solar, on my Bimini and dodger. Totally out of the way, in what is otherwise unused space. While you can never have too much solar, this is really all I need. My boat is usually fully charged whenever I head out.
As for cost I spent about 13.5k all in. This includes new prop, shaft, drip-less shaft seal and a few other items not every conversion will need. While I saved money doing the work, I didn't spare many expenses when it came to equipment. Yes, you could spend north of 20K paying someone to install. Conversely, i have seen people install perfectly functional systems for a few grand using inexpensive/salvaged components.
I agree, the average life span of lead acid batteries in any application is probably 5 years if you are lucky. They are automotive batteries which simply are not designed to last long and most people don't care for them as they should. Honestly, automotive batteries are what has left early electric boat adopters with a bad taste in their mouth.
The largest cost in my system is the 10kw lifepo4 battery bank. It was about 6 grand including the BMS. The cost of lithium batteries is dropping every day while their energy density and cycle life is improving. Today If I swapped out my batteries with salvaged EV batteries, I could have twice the capacity at half the cost and a third of the weight. There is no reason my batteries can't last 10, 20, 30 years.
Yes, I would be limited to 3-4 hours at 5 knots on a windless day. Keep in mind for every knot you slow down, you will double your range.. This isn't anything unique to an electric propulsion, it's a function of a displacement hull. Given the way I use my boat it's not impossible, but very unlikely I would encounter a day where I needed to motor that long without wind. I do end up using my motor 90% of the time while sailing to add an extra knot or two as its not usually as windy as one would hope. With a little bit of wind it doesn't take much power from the prop to add speed. It also helps point higher and help maintain course on a choppy day. It's true that in many situations, if i had a diesel, I would have arrived at my destination sooner if I had dropped sail and motored in. Now, I find myself sailing much more with the aid of my electric motor. Without getting too metaphysical and sappy, my boat has gone form two of the most disjointed power sources I can think of, to one of unity.
Matt Foley
Sunlight Conversions
Perpetual Energy, LLC
201-914-0466
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