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Old 21-06-2013, 13:22   #61
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Boat: Pearson Ariel, 26 feet
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Re: Water Generator Concept Thread

Here are my measurements of the actual output from a Hamilton Ferris WP-200 generator. My hull speed is 5.8 knots, so the measurements cut off near that speed.

The numbers below were derived with a Fluke laboratory averaging ammeter and with speeds computed with GPS by taking two sets of readings while sailing on reciprocal headings to compensate for any current (no differences were observed).

Here are my results:

<3.0 kts: zero output
3.5 kts: 0.2 amp
4.0 kts: 1.0
4.5 kts: 2.0
4.7 kts: 2.2
5.0 kts 2.5
5.2 kts: 2.8
5.3 kts: 4.0
5.5 kts: 4.5
5.6 kts: 4.8

The results above were obtained while charging a 400 amp/hour lead/acid battery bank with a terminal voltage of 12.5 volts.

The graph shown on the product's brochure displays an output beginning at 1 knot, which is impossible, and leads me to believe that either short-circuit current was measured instead of practical charging current, or that the person producing the graph attempted to extrapolate the current at 1 knot while neglecting the non-linear electrical characteristics involved. The generator cannot produce charging current until its loaded output voltage exceeds the sum of the battery terminal voltage, plus the forward voltage drop of the series steering diode (1.1 volt when using the diode provided by Hamilton Ferris) and whatever voltage drop occurs in the series resistance loses in the generator-to-battery wiring.

At a speed of 5.6 knots, one can expect 115 amp/hours per day (24 X 4.8). While that's a little more than half the 200 amp/hours/day claimed on the product's web site (no speed is stated for that output number), it's still not too bad for the claims made by wind and water power products -- which in my experience tend to be wildly exaggerated industry-wide.

I built my own diversion load to alleviate hockels in the tow line when switching away from the batteries at a state of full charge. I used Schottky steering diodes to improve efficiency and 14 volt zener diodes to balance the diversion load to the generator output at the switching threshold. I also used a large value electrolytic capacitor to damp fluctuations in rotation speed to maintain a more stable torque on the tow line, and installed a ferrite toroid RF interference suppressor near the generator. If you'd like a schematic with a parts list, send me a private email.

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Old 15-12-2016, 05:02   #62
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Re: Prop-pitch calculations / Motor Calculations + My $00.02 (Long Post)

did you ever get this running? what were results?

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Old 16-12-2016, 02:29   #63
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Location: Cape Town
Boat: An Aluminium cruiser about 50 ft or less long
Posts: 21
Re: Water Generator Concept Thread

I'm planning to make my own towed generator, having bought several permanent magnet motors a while ago when the prices were low.
I wonder if the axial position of the prop on the towed shaft determines whether the prop jumps or not?
Presumably if the prop is at the outer end of the shaft there will be more tendency to jump, whereas closer to the boat would cause it to fish-tail?
Is there an optimum position?
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Old 03-05-2017, 13:00   #64
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Re: Water Generator Concept Thread

The biggest weaknesses of towed motors are that the boat is sitting still 90% of the time, and it's power output isn't all that much higher than wind (although I think it's much better than wind because the spinning death blade are AWAY FROM WHERE I'M GETTING DRUNK)... I have 2 theories and possible ideas;

1. Dual Towed/Tidal instead of Dual Towed/Wind.

2. Thinking of Hydro as an active power source instead of a passive one.

First, Tidal. What if instead of making something like the duogen you made a leg or rope towed gen that had a way of harnessing hydro power while anchored?

1. One end of the spinnaker pole affixed to the crank and the other end to the dinghy, wave motion would pump the electric generator like a water well.
2. Drop the Aft anchor, only instead of affixing it to the boat you'd run it through a pulley, with a counter-weight dropped into the water underneath. Up swells would generate power, down swells would reset the chain.

These system couldn't be made commercially, since the sizes of pulleys, chains, weights, etc. all depend on the boats size. In order to get the pumping to a reasonable rpm you'd need a high gear ratio and a flywheel to stabilize, which would all have to be done your self, and you'd have to have be adjustable so you could keep the rpm in the right range depending on wave height. (maybe a 10:1 sealed gearbox+Flywheel, and then external 1:1, 2:1, 4:1 attachments on the PMA's shaft?)

The interesting thing about this is that the power is being generated like a Point Absorber Buoy, by holding the boat partially underwater. This means that your power is limited by the PPI of your boat and the height of your freeboard (along with making sure the equipment/mount is strong enough to handle that much strain), but if your PPI is 600 you could build a system with 300 lbs of pull and waves would only raise 0.5" higher... Granted the actual pull length is like 1 foot, lol, which is why you use gears; and 300 lbs of strain would mean having to reinforce your transom pretty intensely (which is why I think this would work great as a custom job, but never as a commercial product).


Second, Active vs Passive. I always thought the main reason hydro did so poorly was because it's more hassle than solar, and has fewer usable days than wind; It just can't compete in the "Passively top off your batteries" market. So why not make one with an output so high that it shifts out of competition with Solar and into competition with the Honda EU2000?

Make it with a high wind or motor driven PMA, the kind with 30A+, and a prop large enough to handle it. It couldn't be rope based with stresses that high, but why not use an outboard leg (40HP?), and a PMA like this:

Permanent Magnet Alternator Wind Blue Motor Wind

Sure it would slow the boat down loads, the damn thing is basically a sea anchor with power output (BOOM, second use for it ), but cruisers aren't in a rush. Assuming it's efficiency is similar to the current smaller tow motors it will end up costing you the same total speed, it will just take all the speed at once, instead of over a longer time.

The primary benefit of a system like this would be the fact that you could drop it when sailing from island to island and stay topped off, and if you anchor for a week and start to get low you can just pull up anchor and sail for a few hours. A system that lets a cruiser replace the sound and smell of a gas generator with "an excuse to daysail" could actually be really popular.

I'm sure there are a thousand reasons these wouldn't work, anyone know a few?

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concept, generator, water

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