Required propulsive power increases in proportion to the cube of the speed.
A general rule of thumb, you double the amount of power to get 1 knot in speed. So if 8 knots requires 20kW, 9 knots = 40kW ; 10 knots = 80 kW(not actual data), just to get an idea. This is only for non planing hulls.
So setting your top speed needed down a couple knots, could lower your costs greatly.
The other big factor on power requirements will be adverse weather. If you have to head into a 20+ knot wind, you will need significantly more power. Wind resistance is exponential.
If money is not a big factor, you could look at Torqueedo's Deep Blue motors.
2 of them should get you to the speed you want, with some safety room for adverse winds.
Getting the right propeller is very important, which I think they could help you figure out. You will want the biggest one you can fit. You will be constrained by the proximity to the hull. You need a minimum of 2 inches of clearance.
Another option, that might be more cost effective, is a hybrid system. Have 2 electric motors, batteries for 2-3 hours at modest speed, and a generator for when you need more power or longer distance.
Good luck!
On Mon, Jan 31, 2022 at 3:34 PM angelo merico via groups.io <angelomerico=yahoo.it@groups.io> wrote:
Hi Dennis, I think about stern unfoldable floating solar panels, but is only an idea.best regards, Angelo MericoIl lunedì 31 gennaio 2022, 20:51:47 CET, Dennis Cohen <dac@theconcordance.com> ha scritto:I am, hopefully, in the process of removing my two 8v71 Detroit Diesels (which each weigh about 4,000 pounds) and replacing them with electric motors, batteries, and a generator.
She weighs in at 32 tons. I keep her in or close to the marina, so my desired range is probably 10-15 miles max, at a speed of 8-10 knots.
I have shore power and the capability of using either one or two 100 sq.ft spaces for solar arrays.
I have looked at several systems, and I realize it's a big project. I'm looking for whatever suggestions I can get on engine size, voltage, genset requirements, prop size and pitch, etc.
Also am aware of having to add ballast to account for the large amount of weight I will be removing from the hull line.
Any thoughts are appreciated.
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