Electric inboard auxillery / generator for 33foot boat

[blampied]

Hi Formites

We have a 10 meter (33 foot) single engine semi-displacement Aquastar motor boat, (about 8 tons)
We are currently living on the boat in the Med (France and Spain) we travel on the sea and also along the canals
A recent (non serious) breakdown with the boats singe 370hp Volvo has got me thinking that an auxillery of some sort would be desirable as an emergency get me back.
At the same time the heat of the Med has got me thinking that a generator to run the air conditioning would also be desirable.

Would an electric inboard motor powered from a generator be a feasible option?
I'm thinking an electric motor in the lazarette driving the boats propsharft via a toothed belt?
If it works well, there would be the possibility of using the electric when on the slow speed canals
The boat is all 12v (with 400w of solar panels and a shore power charger of 40amp)

An electric motor that would be able to push the boat up to about 5 knots should be sufficient?
(I'm thinking possibly the electric equivalent of a 15hp motor would achieve that)
Would such an arrangement be workable? Assuming I select neutral from the throttle control:-
Would it be a problem for the Volvo engine or A.ZF2201M gearbox having the drive shaft turned by an electric motor?
And the other way around, cause problems for the electric motor being forcibly turned when the main engine is running?
Would the size of the main drive propellor and pitch (370hp motor) be a problem for a small electric motor?

Assuming the above is workable?
What is the minimum size electric motor required, (I'm assuming it would need to be more than 12v)
What the minimum size generator needed, could I power the electric motor directly from the generator without a battery bank?

Thank you for looking

 

[rogerthebodger]

Have a look at Vetus, they used to do an auxiliary electric motor that would drive the main prop through some belt drive setup.

http://www.vetus.com/engines-and-around-the-engine/electric-propulsion.html

 

[Iodine]

You could look here for ideas:

http://www.hybrid-marine.co.uk/12.html

Probably not going to be easy, most 15hp (~10 kW) DC electric motors need at least a 48V supply.

You can see that they use a hydraulic gearbox (PRM150), that can safely "free-wheel", otherwise you'd need a clutch on your mechanical gearbox

 

[blampied]

Thank you for the replies,
Vetus have electric direct drives, but can't see anything with a belt drive.
Hybrid marine looks more promising, I will investigate further.

 

[Tranona]

For an auxilliary engine a 25hp wing engine would be fine for canal work. You could use a folding or feathering prop to reduce drag when using main engine and have a powerful alternator to keep your batteries topped up, but unlikely to have enough to run serious AC.