This has been covered in the past in the engine
forum. To sum it up, electric is only an option if you plan on daysailing and never straying far from your electric hookup. It is the same problem as with electric cars, range. I have built 3 electric cars and they make great commuter vehicles but none of them would work for a multi state drive.
The reason this is a problem is energy density of your power storage
. Diesel fuel
is incredibly energy dense and it can be moved quite quickly through a hose. Batteries have poor energy density and cannot be charged very quickly. To figure out how much battery
capacity you would need is actually quite easy. For most boats, a reasonable approximation of the power draw would be to divide the horsepower of the diesel engine
by 2. Then convert that to kilowatts and multiply it by the maximum number of hours you would ever want to be able to motor
for. Remember that this is the maximum number of hours between shore power
hook ups not just the maximum amount at any one time. This gives you the number of Kw Hrs that you need to store in your battery bank. If the number of batteries this requires hasn't scared you yet, you need to start taking into account things like reduced capacity due to age/temp, reserve capacity etc. I ran a rough calculation for a 35' boat a year or so ago and came up with 18 Trojan T105s. I can't remember how long it could power the boat for off the top of my head
but it wasn't exceptional.
There is a common misconception that you can greatly increase your range by adding a solar
panel, wind generator
, or gas generator
. It comes back to simple energy conservation, if you don't put as much energy into the system as you take out, you will be depleting your batteries. These things will increase your range but not by much. Considering that a 30' boat motoring at a conservative speed is consuming 5kw of power, that would be a large generator
to keep up and doing it with solar panels
or a wind generator
is out of the question even in ideal weather
This brings you back to needing to store all of the energy that you will need. Since it is hard to change the power consumption
, the only way to change the number of batteries you need is to use it for less time. For this reason, it only really makes sense for daysailors that are kept at docks with shore power
or cruising boats without a schedule to keep that avoid bad weather
There are many other design considerations if you actually want to go ahead with an electric drive system like voltage, gearing, ac vs dc, etc that I would be happy to talk about. At this point in time, it makes much more sense for the vast majority of people to use an inboard diesel.