auxiliary power, outboard

[LCR]

Hi Everyone,

I would like to have an extra 2.5+ kw of electrical power available on a boat
powered by an outboard engine. My idea was to connect a large (bus
alternator) through a coupling to the flywheel end of the motor. Has anyone
attempted this? Can anyone recommend a brand/model (200Hp+) that might
be suited to this? Ie clear access and connection to the fly wheel end of the
motor. I have not picked my engine yet, and I am very willing to drill extra
holes in the cowling as needed. Any other ideas?

Thanks LCR

[PAR]

You will need a full 5 HP to drive 2.5 KW. You may want to look into an electric clutch, much like used in automotive A/C compressor applications, which could be belted to the flywheel. This would take the load off the starter.

On the other hand, I'm not sure about how an outboard will like having more rotating mass attached to it's crank. Maybe new balancing. Secondly would be thrust loading from the heavily torqued up belt on the wrong side of the bearing.

[LCR]

Thanks for the reply PAR,

There are a lot of issues to worry about. I would hope that a 200hp+ motor
could handle the nice smooth 5hp load from an alternator. I would like to use an inline rubber coupler, to avoid and resonances, and bearing loads. An
inline electric clutch (if it exists) would really help out with the starter.

However there is nothing like having done it. Short of someone having done
this, are there any recommendations (maybe some pictures) of the top end
of some big outboards. My big concern is easy access to the top end.

[PAR]

I've seen some attempts at PTO's on outboards. You'll need to modify or make a new cover.

Personally, with the low cost of a small generator, which could run off house gas and be contained in a reasonably sound proof box, why wouldn't you just use this. It would eliminate engine coupling, balance and other outboard related issues, plus you could use it separately, without having to fire up a 200 HP engine just to warm up you coffee.

I'd do a "load" list and see what you really need this generator for (amp hours per day). You might find you only need a house battery bank, an invertors and charge/monitoring systems upgrades.

[LCR]

My backup idea is a Honda Generator. It is not perfect, as I will have to mount it somewhere, and put the exaust somewhere, etc... I need to run
an air conditioning unit. I know... why? Well lets say I have to.

[PAR]

You might consider an evaporation based cooling unit, rather then a traditional compressor based A/C unit. In your climate, it would be more then enough to keep you cool.

A simple system I saw in the Caribbean, used by the clever locals, who couldn't afford the amperage of a real A/C unit was a "swamp cooler". Basically a hose was lead over the side, weighted with a screened inlet. A small electric pump brought the water up into a hot water, base board heat radiator. A small fan forced air through the fins and cooled the cabin air considerably.

No, it doesn't blow out 35 degree air, like a compressor based system, but it does take the cool water 10' (or so) below the boat and use it's energy to extract the heat from the hotter cabin air. The best thing is it's energy consumption, which is a fraction of what a compressor based unit requires.

[LCR]

Hello Again PAR,

This will be used down south. (Belize) I had also considered this option. If
it works "good enough" then clearly it is the best solution. I will only have
access to water 2-3 ft below the surface. Have you experienced these
systems? I guess I need to research surface water temps etc.

[PAR]

Tropical water, 2 - 3 feet down is still fairly warm, so the swamp cooler wouldn't be as effective. In Belize, during the summer, the water will be high 80's to low 90's if shallow enough. I've played with the concept in my semi tropical waters, but with more depth, usually about 7 to 10'. The deeper the cooler of course, but once you're about 4' down, it's generally cool enough to consider.

[CDK]

LCR, the alternator idea doesn't work.
To obtain a significant amount of power from a bus alternator, it should spin at 10.000 rpm or more. Look at the pulleys on your car engine, they are 1:3 for high revving engines, 1:4 or higher for slower diesels.
Direct coupling to the crankshaft limits the output to 1/4 of the nominal value.

[LCR]

Hi CDK,

Take a look at
http://eco-techalternators.com/pdf/S...nsheet-28V.pdf

They claim
28v,
127 Amperes at 1800 rpm
165 Amperes at 6000 rpm

That should be ideal. (I would like to run 24V DC)

[CDK]

What can I say? I am stunned!
My knowledge about electro-technics is somewhat dusty, but that things have changed so dramatically in the 45 years since I graduated, I would never have believed.
The old formulas to calculate the core size needed for generating 7 KW and the wire diameter to handle 165 Amps really seem to be obsolete now. These guys MUST have secret technologies.

An ordinary automotive alternator at 1800 rpm barely generates enough to maintain its field current, yet these eco-guys promise an output current the average welding transformer would be proud of.

There are ways to get more out of a certain size electric motor or generator. You can make the air gap smaller, but if you make it too small the life expectancy is impaired because the least bit of bearing play or vibration will cause damage. Or you can use quite exotic core materials that have a higher saturation point than iron and use precious metals instead of copper for the stator windings. With all these together I'd say that such an alternator performs twice as good as an ordinary one, but it still wouldn't reach the figures this manufacturer claims. And it would cost a fortune!

I am very curious indeed.....

[LCR]

Hi CDK,

You are right they are expensive. I think it just boils down to the size of the
thing.
Any ideas on the most suitable "brand" of outboard for something like this?
I don't have any pics or diagrams of the top ends.
Any other potential problems with this idea?