Anyone with a water powered generator with a towed prop?

[Allan]

I have a small generator left over from a non-boat related project. I fancy trying to use it with a towed prop. I also have a couple of plastic props of different pitches. If anyone has one of the old type of generator could they answer a few questions?

1. Approximately what does the towed unit weigh?
2. How long is the shaft?
3. How long is the rope?
4. What's the best type of rope?

As, at this stage, I don't know what I don't know, any other information or suggestions would gratefully received.
Allan

 

[duncan99210]

The photos are of the propeller for my Aquair towed system. It weighs about 3kg and is made of stainless steel. I use an old reefing line, 14mm polyester braid on braid that’s 27m long. Works well for me up to about 8 knots.

If these pics are too small, pm me with an email address and I’ll send the full size pics to you.

 

[kalanka]

I have successfully used an Aquair towed/wind generator on two Atlantic crossings in a 34 foot sloop. Not sure that the company still operates but a search will reveal a fair bit of information. The kit is on the boat and I am not but, from memory, the prop unit is quite heavy - about 3 kg, with a shaft about a metre in length. I recall the connecting rope being 20=30 metres in length and about 14mm in diameter - non-stretch rope. I imagine that any reasonably hefty rope would successfully transfer the torque to the generator. It is important to attach the generator to the transom with lashings so that the angle of pull can adjust with the pitching of the boat.

It is a highly efficient bit of kit but retrieving the prop unit when the boat is doing more than 2 or 3 knots is difficult and potentially hazardous - it is very easy to get a hand trapped in the twisting rope. Good luck!

 

[hrchivers]

1. Approximately what does the towed unit weigh?
2. How long is the shaft?
3. How long is the rope?
4. What's the best type of rope?

I'm away from the boat so can't give a exact details, roughly:
I would guess that the shaft is about 750mm long of 25mm dia solid stainless to which I've added a lead anode for additional weight at the prop end. Rope is at least twice the length of my boat (so over 60 ft) the rope is a plait, perhaps 14mm (do not use laid rope - it would unravel). I use a funnel over the rope to slide down to shield the prop if I need to recover at speed, but generally better to slow down and do it quickly hand-over-hand. Use gloves. The generator is worth deploying above say 3kt of boat speed, much slower than that then putting a fishing line out is probably more useful. Also be careful launching - too slow and the rope twist will grab anything within reach (don't ask!). I put the output through a charge controller with a resitive dump, which I also use for a few small solar panels.

 

[Neeves]

We have an LVM or aqua gen towed generator. Best thing since sliced bread - but a bit of a faff for short trips. If you are making passages of some real distance ours produces enough power to run the whole yacht, at 8-10 knots of boat speed, fridge, autopilot etc etc.

The blades of the prop are fibre glass and we broke one (anecdotally people say this is due to shark attack - I think they have very fertile imaginations), we also found that at speeds over 10 knots the generator prop leapt out of the water like a demented dog. I made some smaller stainless blades. Dimensions as above. Ours came with 2 sets of blades, larger for lower boat speed and smaller for faster - our home made ones are even smaller.

Don't ignore the advise - wear good leather gloves for retrieval. We sit, securely, on the transom and retrieve hand over hand.

I'd send pics, but don't have any - and its all on the boat

One of the best buys we made, simple and does what is says on the box.

Jonathan

 

[duncan99210]

Another thought on the topic. If the generator/alternator is a standard one it will be designed to spin quickly; upwards of 1000 rpm. You won’t achieve that with the prop on a rope set up. The alternators are designed to produce current at much lower speeds. So you might have to look at a gearbox to increase the rpm to match the speed needed for generator/alternator.

 

[Allan]

Another thought on the topic. If the generator/alternator is a standard one it will be designed to spin quickly; upwards of 1000 rpm. You won’t achieve that with the prop on a rope set up. The alternators are designed to produce current at much lower speeds. So you might have to look at a gearbox to increase the rpm to match the speed needed for generator/alternator.

I'm not sure what revs this unit needs but as I have the generator, two different props and 1.2m of stainless shaft, I thought, why not? On passage, I think we use 4-5 amp/hour, our 150w of solar panels is nearly enough. We only need less than 100w if it runs all the time.
Allan