T-Pain Is On A Boat: Re: [Electric Boats] Electric trimaran conversion

Friday, October 31, 2014

Re: [Electric Boats] Electric trimaran conversion

Hi Phil,

You forgot to mention the displacement of the boat.

Also, when reaching under sail in say 15kts of wind,what kind of speeds do you see with your existing setup?

I suspect that you may want to consider a higher voltage system, if only to keep currents down to manageable levels. A light displacement trimaran is still going to displace in the neighbourhood of 10 tonnes.

You should be looking at a 10-12kw system running at 72V which would keep amps down around 160A max.

Look for posts in the archives about "Current Sunshine", a 37' trimaran who's owner (used to?) post here.

Sounds like a fun project of you go ahead with it.

Cheers,

/Jason

On Oct 20, 2014, at 11:42, Phil Aylsworth paylsworth@yahoo.com [electricboats] <electricboats@yahoogroups.com> wrote:

Hi all,
I'm looking for what some of you have already sent; real world results and accounts of the conversion process.
First I've got to see if converting to electric drive is a good idea of a bad one. Considering that the motor part is just a way to transfer fuel/energy into propeller force, it's the energy or fuel I need to focus on. And the cost to use diesel or electric. The Perkins engine is getting old in years but still has only 600hrs on it. There's resale value here if I convert and can sell the engine. But if not there's still life in it.

The boat is a 49' trimaran, driven by a Perkins 4.108. Perkins rated power curve shows about 47hp at 3,000 rpms but I never get up that high. At 2200-2500 rpm, good sea (1-3' wind waves, 1-4' swells) and up to 10knots wind I can make 8knots easy. For a displacement hull my hull speed should be 8.9knots, for a semi-displacement it's 16knots. I believe a trimaran falls in between, and the drawn (from designer) hull speed is 16. These are all theoretical and I'm happy motoring at 8. I've got lots of room for batteries or diesel so space isn't an issue, weight is.

Cruising is on the Pacific coast, mostly shoreline but in the coming years there will be several crossings to HI and South Pacific islands. I'm a sailor so most of this will be under sail. There are 500W of solar and a large wind generator available for replenishing battery banks. And the power regen may be more effective on an electric drive if I'm sailing at higher speeds than a full displacement monohull. This again is theoretical. The prop is a big 18" three-blade at a pitch of about 12, fixed.

The Perkins power curves list a propeller law power loss of 2.8. Figuring this; the 2600rpm hp available to the prop falls to 15hp. The torque at 2600rpm is 75 ft/lb. This is information from the Perkins mfr for this exact engine and roughly the same year. My gearbox has about a 2.1:1 conversion so I am figuring that a 2:1 belt reduction will serve well as both a way to safely couple engine to shaft and to increase hp and torque with higher electric motor revs. (not sure this is accurate and if not I want to eliminate the reduction).

Now the energy. The plan is to have a 300A/hr bank at 48V, with a portable gas generator (gas will be onboard for the dinghy outboard anyway). The generator will be used off the boat too, for construction work or whatever else. It will be sized to wire directly into the motor controller, giving enough motor power for a 60 or 70% throttle in case of prolonged motoring. There are 48V generators so this is the chosen voltage. Again, just theoretical but it sounds correct.
I don't expect solar and wind to provide all the electricity I'll need for motoring, though they do provide more than enough for living off the grid for the rest of the boat.

Any suggestions or comments on this would be greatly appreciated.