As the owner of a 25 foot boat, I can say that there are a problem with diesel engine for such small boats as my. The smallest marine diesel have a weight about 100+ kg in the stern area and it size creates problems for
maintenance in a tight engine compartment.
Other option -
outboard gasoline at transom is not a good option for seas (I think it's not necessary to explain why).
I tried to install electric drive to my boat last year and happy with it, for now. But I need to point that electric drive without a gen - solution is only suitable for daysailers (for example my batteries provide a 32 nm range at speed 4 knots). I have a 3 kW 7 kg motor, 50 kg batteries 7 kWh and plan to install a 3 kW gen (30 kg) stationary under the
cockpit.
Pros:
- daysailing using motor only (less than 32 nm) cost nothing for me, as electricity included in the
price of parking
- daysailing using motor only (less than 32 nm) is silent
- drive weight is distributed next way: 50 kg batteries located near
keel and do not give a trim; 30 kg gen + 7 kg motor located in the stern area and cause less trim than possible diesel engine.
- instant torque and no
winter maintenance (as I can easily take a gen to warm room).
- reliable
work (at least engine-batteries pair, it is possible issues with gen)
- I will install a 320W solar
panels, at summer time batteries will recharge (from empty state) in 5 days in my region.
Cons:
- motoring more than 32 nm involve a gen to work, resulting a
noise.
- little time tested such a system - I can not say anything about
reliability yet
Generally, for 25 ft boat it is not bad option comparing to other options suitable for small boats, but it is important to test it over long time (few years) to make sure it is reliable.
Important note: to make it real option you need to understand how to plan such system by yourself, because prices for ready solutions (elco, oceanvolt, etc.) is very high.
Make such system by your own is cheaper in 3-4 times (this way I go electric).
One more note: 0.7 l of gasoline at gen is sufficient to move my boat at 4 knots for 1 hour in calm
water. This is slightly less than
outboard consumption for same speed. I beleive that losses caused by energy transformations "fuel -> electricity -> prop power" is overlaped by bigger prop located deeper (so more effective) and gen gasoline engine work in optimal mode (rotation speed) all time.