Several people on this thread have discussed making a diesel hybrid system which certainly solves the issues of range provided that the diesel has sufficient output but in the big picture, it may not be any better for some applications. We are talking about series hybrids, not parallel hybrids like you would find in a prius. Series hybrids do not have many of the benefits mileage wise that a parallel does but a parallel doesn't make sense for boats due to the constant output nature of the application.
The biggest advantage to going to a series hybrid is that you can operate the engine
at a constant rpm
where it very efficient. However, in a sailboat application, this rpm
is very close to what a normal cruising rpm would be anyways so if you have a good setup to start with, there isn't that much advantage. In certain applications, the ability to have the diesel somewhere other than right next to the prop is certainly helpful. In the case of a catamaran
, it can make a lot of sense.
There are a few big disadvantages to hybrids. For one, every time you convert forms of energy, you loose some of it to heat. An example of a well designed electric drive system would be:
controller efficiency 95%
Motor efficiency 90% (this really depends on the type)
Gearing efficiency (almost all electric drive systems will need gearing) 95%
Total efficiency 77%
Comparing 77% to something like 30% for diesel shows that you need to store a lot less energy. If you wanted to do a fair comparison from an environmental perspective, you would need to go all the way back to extracting the fuel but that isn't the point of this. So you need to store a lot less energy but that doesn't do you any good since energy density is poor in batteries. If you go to that hybrid drive system, even if you could magically raise your engine efficiency to 40% and generate power at 95% efficiency and have no charging losses (you wouldn't be charging), your total efficiency would still be 31% which is negligibly different.
To do this, you would be adding significant complexity and weight to your vessel while probably decreasing overall reliability
. If your reason for going electric were noise
, it wouldn't help you at all on long trips although the short motors would certainly be more pleasant.
I have ignored the operating costs of these systems since most people just don't burn enough fuel to make it matter. On my own boat, I haven't burned $100 worth of fuel yet this season even though I have been out a lot. Installation
cost is very important in all of this but it is very system specific.
There have been a few responses of people on this thread who have gone electric and are very happy with it. However, none of them have claimed to motor at 6 knots for 40 hours which is something that some of us do on a somewhat regular basis when trying to make ground. It really comes back to how you use the boat and if you need range and decent power output, electric only isn't an option and hybrid is a complicated option that doesn't necessarily offer any improvement. For people who don't feel that having the ability to motor hard for long periods of time is a safety
or otherwise necessary feature, electric is great, that is why I have 3 electric cars. In my mind, anyone considering it should carefully work out the worst case scenarios for their use and figure out what size battery
bank/generator they would need and make their decision from there. The equations are really easy and they don't lie, the only thing that gets messed up are the inputs.