While I have never done the install on a boat
(I have been on a few though), I have built 3 electric cars and 1 hybrid racecar. Electric motors are really cool but they have limited application on boats. The reason that diesel is so good is that it is incredibly energy dense and can be transferred quickly. We don't yet have a cost effective way to store electricity as densely yet and it cannot be transferred nearly as quickly.
I am glad that you have a somewhat realistic idea of the number of batteries you will need. I did a few calculations for a boat using a 10kw output (should push a 35'er along nicely in smooth conditions) and 2 hours of run time and recommended 18 Trojan T-105's. There are many voltages that you can run and these are determined by your components so the exact number of batteries is determined by this. Regarding voltage, the higher it is, the better because your wires are smaller and everything is more efficient. The biggest considerations with batteries are cost (lead acid is the best bang for you buck), weight, and where you will put them.
The correct way to approach this is to look at your needs and then engineer
a system around it. Having not seen your boat, I would suspect that you would want 5-7kw continuous output and 10kw(~15hp) peak. Then you will need to decide on a dc or ac system. DC systems have great low end torque but the torque is lower at high rpms when the back EMF is great. AC systems have a more constant torque curve and are more likely to offer the ability to regenerate power while sailing or moored in current
. From this you can select a motor
controller. One popular motor is an etek. There are a lot of motors out there that would fit the bill and I would recommend looking at what is used in electric vehicles. Once a motor is selected, a controller will need to be selected although most AC motors specify certain controllers.
Then a battery bank will need to be selected. To do this, you should figure out the worst case scenario of how you plan to use the system. If you plan to push into a headwind for 2 hours, then you would need 2 hours* 10kw=20kwhrs of useable energy storage
. However, if you never plan to motor for more than 1.5 hours and don't plan to motor when it is rough, something like 1.5hrs*6kw=9kwhrs might be reasonable.
is a big issue for a boat. You will need to plug
into shore power
to do this, it would take a very very large solar
array or many wind
generators if you are on a mooring
. The battery pack that I quoted above using 18 batteries could be charged off of a 30A plug
in about 3hrs with the right charger
. The real trick is that you cannot recharge when you don't have shore power. There are a lot of chargers out there, my personal favorite is the manzanita.
Once you have the basics of the system figured out, you will need to figure out how to install it. Gearing is very important and you should match the motor's max rpm
with the max rpm
of your shaft. Since many of these motors spin 4-5000rpm, you are likely to need a gear
reduction of somewhere around 2.5-1. The easiest way to get a gear
reduction like this is to belt drive the shaft but that requires at least 1 extra bearing and ideally 2 on the shaft.
I hope that this helps.