Some times a Diesel/Electric combo is used for the instant torque that could only be achieved from Electric drive (or Steam). ie; Ice breakers use Electric coupled directly to the props so that should the prop become frozen in they can apply full torque from 0rpm. this is not possible if a diesel engine is connected to the prop (unless there is a clutch
mechanism but even then its a bit dodgy, think dropping the clutch
on your 5,000hp Diesel).
This may be a little off the topic in relation to small boat hybrids, but should you take your small yacht through the Northwest passage
with a diesel electric system you will be able to spin your prop regardless as you watch the ice crush your boat when frozen over in a northern winter.
Personally I like the Diesel Electric setups for many of the same reasons Capt. Mike has already pointed out. in theory they are not as efficient but in practice they are more efficient (depending on your specific usage).
Regarding reducing the fraction in electric systems there are ways to improve this.
These two are 87-91% efficient. When combined with the increased efficiency of a smaller generator running at a more optimal power setting, these set-ups cant be two far off a stock direct drive diesel.
And as for cost we priced it as cheaper to go with an electric pod, 3.5kw diesel generator and 12 deep cycle batteries than buying
a new diesel/g/box combo.
Plus with the pods outside the boat (tucked in tightly against the hull
and well protected by the full keel) we now have a shower
box where the diesel used to be. In our 28ft boat any additional space found feels like the council just added another 1/2 acre to your back yard.
Electrics can have more efficient props as well (ie large dia with more aggressive pitch
turning at a much lower rpm
, as the ability to apply 100% torque from 0rpm lends itself to spinning a big prop from startup. A diesel (or petrol) needs to start a prop from a speed where the engine is not every efficient. This means either a gearbox
(which adds friction, wear, maintenance
and heat) or a smaller prop (or both a small prop and gearbox). This is why they use diesel electric in locomotives the diesel just wouldn't be able to get the load moving as it needs to start at 800rpm, versus the electrics 0rpm.
I am certainly not saying electric are better than diesel, but nor am I saying diesel is better than electric. its comes back to the way you use your boat.
MANY weekend boaters could actually be better off by being electric, if they have zero intention of doing anything with there boats than motor off their slip to race
round the cans then reverse back in, electric and batteries make a huge amount of sense here. it would be lighter and could be recharged over the week from shore power
. Cheaper and almost zero maintenance compared to the norm.
Im assuming I will get flamed for being another idiot electric fan, but thats cool. if it isnt for the crew that take things up early nobody gets to experience the refined versions in later generations.
(diesel or electric)