PTO Unit - Need to Call in The Experts!

PD: Thanks. You obviously know what you are talking about here.

The problem with the 4 pole is they seem to weigh in excess of 200lbs (90kg). I have weight requirements, which is why I'm doing this in the first place. A separate dedicated genset is 300lbs. The 2 pole is about 120lbs (as PAR mentioned).

I kind of need to stick to lighter weight things.

Also, a lot of people have missed it, but above, please see the graph and link I put in. It shows the engine's max load on the front PTO. There are "A" hookups and "D" hookups. "A" hookups are when you mount something the way a normal alternator or water pump is mounted. "D" hookups are when you use a flange to mount directly to the front PTO shaft.

At 1800RPM, you can only get about 7HP, or a 3.5KW generator head running from the front PTO. This is the manufacturer's graph. It's in all the manuals I have. I can't run a larger generator end off the front PTO. It's prohibited by Yanmar and will void the warranty (and break the shaft).

So, I'm going to have to be on the aft shaft only.

Are Universal joints out because they don't provide a constant speed over the whole rotation? I was planning on possibly using stainless universal joints on the retracting prop way at the end of this monster, but they would be in the sea water.

 

Maybe look at the Beta hybrids and see how they are hooked up . Rick

 

You're nailing these posts, Rick!

I have looked at that. They look like this:

Somehow, they seem to have the pulley system AFTER the transmission. That's what I'm not following about their setup. Maybe they are geared to take a prop shaft speed and spin up the generator from that? I guess that would make sense since they are selling it as something to make some power from the prop while sailing.

 

OK, the weight budget - needs a bit more filled in here.

2 pole generator head - 120 lbs.

Toothed belt sprocket on engine PTO stub shaft - ?lbs

2:1 toothed belt sprocket on layshaft - ?lbs

1.5" or 1.75" layshaft - how long TBA - ?lbs

2 pillow block bearings & fabricated mounts - ?lbs

Fair bit of extra weight to get that 2 pole head to spin faster, plus more power losses. You might find it's marginal gain.

I take the point re limitations on fwd end PTO. No point breaking stuff. Probably only a tapered flange with a key up there.

How are you going to run the shaft(s) and support the generator head and still be able to get access to everything? Not an objection, just something to consider. You're going to need a few brackets to support it all regardless of 2 pole or 4 pole head, just more with the 2 pole unit most likely.

If you could post a reference or picture of the gen head you have in mind that'd help. Some are designed to mount to an engine and use its bearings for partial support, others totally standalone WRT bearings and rotor support.

Uni joints, IIRC you need them to be at about a minimum 15 deg angle so they move properly (bearings in them tend to go ****-up otherwise), always need to be fitted as pairs, equal angle. CV joints aren't quite as picky which is why they're used for front drive systems etc. About $115 each on Ebay for the Toyota ones IIRC. You could use the s/steel uni-joints as long as you work within their limitations and if you're going to be carrying some as spares anyway, probably a better way to go. It's engineering, lots of things can work, you pick the tradeoffs you can live with.

Only advantage of hydraulics is you can run the pipes to wherever you want but it's noisy and has considerable power loss plus expensive and if a pipe or hose fractures, what a mess. I've been toying with the idea of a small hydraulic system operated via an electric clutch but probably won't as it's too much hassle I think. Only really want it for an anchor winch I can operate from the wheel - I hate low voltage high current electrics.

PDW

 

Maybe you should take a look at other brands if their "D" loads are more generous..

 

How will you compensate for the weight of a 3.5 kw generator, subframe and coupling... 75 kgs hanging 500mm off the front end of the engine ? The volvo engine mounting system will have to be changed.

 

Not sure what Catbuilder intends to use, but here is a belt-driven head - rated at 10 kW max, 7.2 kW continuous, 90 pounds... and only $290!

http://www.harborfreight.com/10000-watts-max-7200-watts-rated-belt-driven-generator-head-45416.html

 

Exactly. That's pretty much the kind of thing. Weighs nothing, costs little and produces tons of power. Probably not the prettiest power and it'll probably need replacing after 500 hours, but still... a good way to go.

That's what the idea is centered around. That type of generator head.

PD: Will respond to your questions soon...