Originally Posted by boat_alexandra
high efficiency 20hp electric motors are about $400 brand new, and require no maintenance
True, but a 37' boat ought to have about a 10kw motor. I am thinking ME0913, and they run about $700. Then you want a good gen4 controller and that's another $500 to $800. The battery
bank ought to be at least 48v and a minimum of 100ah, with twice as much preferred, so $1000 in batts for a modest setup, twice as much if you want to get medieval about it. 72v would be better for a boat over 35'. Without a marine transmission
, a thrust bearing is needed... a bit over $100 for bearing alone and you make the housing, or about $300 for a ready to rock unit. Then while you don't need a mechanical reverse because the motor can run in reverse (some can't do that for long because the fan only blows one way) you still usually need between 1.5/1 to 3/1 reduction via gearbox
, chain and sprocket, or belt. Add a 48v smart charger
, DC/DC converter, 400w of solar
and a windcharger, and maybe a small portable generator
, and you have a bit more invested in electric propulsion than your $400 figure. Around 3k, typically, for a DIY type person. Still cheaper than a new Beta and indeed, less maintenance
, but not $400, even for just the motor. And the diesel
can run until your tanks
are dry. The electric drive can run until your batts are nearly dead, but for longer battery
life, you only draw them down to about 50%. Typically this will be about an hour as you approach hull speed
, depending on about a dozen parameters such as hull
size and weight, bottom condition, motor, reduction, and prop combo, and of course the size of the battery bank. Solar
won't keep up with the draw on the batts unless you are just idling along. Same with portable genset. You would want about a 15kw generator
if you wanted to just run indefinitely. Electric is great for short runs, and fantastic for maneuvering in a harbor, and if you don't cruise
under motor, it can work out well. But a diesel
gives you the option to motor for days if you have the fuel
capacity. Just sayin. I am a fan of electric and I will be going electric on my boat in a few months, but I will be the first to admit that while it can be pretty cheap
, it isn't THAT cheap
Pulling the old diesel and fuel tank
sheds a lot of weight, but the batteries pretty much double the weight of the old plant. (the motor is only gonna be 30 to 100 lbs and the controller, charger
, converter, etc are negligible) So thought has to be given to trim and stability issues.
Usually the old prop and shaft can be used, but a folding prop should probably be replaced, because a solid prop can (very very slowly) under ideal conditions, recharge the batts while under sail.
Me, I might go electric for that boat, depending on how it was to be used. Electric isn't for everyone. If you only use the prop to get in and out of the slip, I would rate electric much better than diesel or gas. But a new Beta isn't such a bad option, either. They seem to be good little engines, and most parts
can be bought through the Kubota tractor dealerships, for way less than the same part for a pure marine
engine. If the engine were to be seldom used, I might go with a used or rebuilt diesel just to have an engine, but there are dependability issues. A used engine is a time bomb. A new one, too, yeah, but the timer has already run down on the used one. A used engine of known low hours and well maintained might be okay. Rebuilt? Crap shoot. Too many members here have had them disintegrate after a few hundred hours. As with a used one, if you go with a rebuild
you better know something about that particular engine and the man who did the work.
So my final recommendation is a new Beta. I has spoken.