Alternator attached to propshaft, any views?

[pvb]

I have a 32ft AWB, with fixed prop.... and a permanent magnet alternator fixed directly inline on the propshaft.

Interesting. What make, and how's it fitted?

 

[davidej]

what a totally pointless exercise when you can buy an SMDO generator that makes toast for £229!....surely you have better thing to do before you die?

(that attitude ring any bells?)

Revenge must taste sweet!

 

[Heckler]

Revenge must taste sweet!

Yeah, but my posts were logical reasons for why I preferred to go down my route.
My alternator thread is just asking for advice and thoughts plus it is an apples and pears scenario, I dont use my gennie when Im sailing but I would appreciate "3 or 4 amps" for "nothing"!
Stu

 

[Ric]

Interesting. What make, and how's it fitted?

I made it out of a permanent magnet electric motor used to lift metal rollerblinds. There wasn't room to fit it in parallel to propshaft on a layshaft, so I fitted it in "series" in the propshaft. I had to shorten the propshaft and fit an extra support bearing.

I had some conversations a few years ago with a German company about making a commercial version. It would have to be much simpler to install than my solution, so we looked at making something that could be fitted around the propshaft.

 

[pvb]

I made it out of a permanent magnet electric motor used to lift metal rollerblinds. There wasn't room to fit it in parallel to propshaft on a layshaft, so I fitted it in "series" in the propshaft. I had to shorten the propshaft and fit an extra support bearing.

Thanks, sounds intriguing! Does the motor take the prop thrust, or do you have a thrust bearing before it?

 

[Ric]

Thanks, sounds intriguing! Does the motor take the prop thrust, or do you have a thrust bearing before it?

Thrust bearing takes the load.

To work out what power of 12v motor to fit, I first fitted a bucycle computer to the propshaft. This allowed me to calculate rpm of shaft while sailing. I then fitted temporarily a pulley inline in the propshaft, used a half turn of cord around the pulley as a "brake", and pulled on the end using a spring-balance.

I could then take measures of rpm against torque, giving me a range of power output that I could expect from my freewheeling prop. I then took a conservative guesstimate of the efficiency of a 12v motor as a generator, and used that as a guide to selecting an appropriate motor.

 

[DorsetPete]

prop shaft alternators...

My Nauticat had a prop shaft alternator...
We also had a generator and of course the usual engine alternator.

Your problem will be geting the electrics sorted out so they all charge your batteries...

The previous owner of my boat who had all this kit fitted had a very expensive automatic system designed and built to handle it all.

I imagine it dwarfed the cost of having a pulley put on the shaft and buying an alternator.

Not am amateur job I suspect...
Good luck

 

[pvb]

Thrust bearing takes the load.

To work out what power of 12v motor to fit, I first fitted a bucycle computer to the propshaft. This allowed me to calculate rpm of shaft while sailing. I then fitted temporarily a pulley inline in the propshaft, used a half turn of cord around the pulley as a "brake", and pulled on the end using a spring-balance.

I could then take measures of rpm against torque, giving me a range of power output that I could expect from my freewheeling prop. I then took a conservative guesstimate of the efficiency of a 12v motor as a generator, and used that as a guide to selecting an appropriate motor.

Excellent - truly a Practical Boat Owner!