I spent about 3 years looking at diesel/electric for a 65' trawler
. I even went up to the point of having Bill Crealock
design the boat abot 2 years before he passed away. I spent many hours with Siemens folks on the disign of the system. the technology is not new, Siemens powered a diesel electric
boat in like 1905. I have looked at porbably 12-15 installations both in pleasure raft up to 100' and in very large commercial
ships. Based on everything I could find, I came to several conclusions. First, the technology is not hard to find and to make work. It is out there and has been for a long time. The major advances lately have been in controllers. Second, there is no real fuel
savings on propulsion
engines, maybe 5% at best. If you need a total of 350 hp with direct drive, you will need a very similar sized power plant to run the DE system. While the generator
does run at a constant speed, the fuel
savings are negligible.
In these respects, direct or DE was really about a wash.
I did find two advanntages, at least regarding trawler
design. First, a 65' ttrawler would normally have 4 diesel
plants, 2 propulsion
, 1 large generator
and 1 smaller generator. In a DE system, you can design a good system that would only have two diesels, 1 large, 1 medium. Second, is the size of the mechanical space and the placement of the engines. In the 65' design we did, we could make the engine
room about 25% smaller, thus increasing usable space on the boat. This is because the engines do not need to be in line with the shafts. You can place the engines anywhere and you can totally enclose them in sound shields as you would a generator. The DE can be a very quiet system.
We did figure out that we could carry enough batteries to run the ship's power, with all them amenities of a 65' yacht, for about 48-60 hour without running the generator. That is a decent benefit for a powerboat.
But, in the end, we just did not feel that the potential benefit,chiefly space, outweighed the up-front cost. To us. all other factors were about equal. I wouldn't think that the space issue would apply in a sailing cat and engine
palcment is pretty much set whichever system you go with.