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Old 29-09-2007, 02:24   #76
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The3 blade propellers we have designed for the 9,6 Kw Green Motion underwater motors are only 1.6 kilo in weight each, the blade size is .53 contrary to the more frequently used . 34 , more of a tugboat type prop , they are 18 x 18 so in fact 35 % larger than would be the case for a high rpm diesel saildrive with a max prop rpm of 1800 while we rotate this prop at max 900 rpm since they are out of the water while sailing they offer no resistance at all.
These propellers are shrouded to increase the efficiency both for propulsion and for generation with an extra 15 % coming to a efficiency of close to 60 %. to take the example of Alan 1 hour of motoring around and into the harbor or going out with the same time motoring we use around 8 KW of battery power. when sailing along and using the underwaer motorgens for regeneration at 9 knots of speed we generate 4 Kw per side or a total of 8 Kw so it takes us 1 hour to get the batteries to the same level as when we entered or left the harbor without using any fossil fuels.
Besides generating with the underwater motogens we also install 860 watt of solar panels on the bimini top ( 4 x sanyyo 2 d 215 )and one new Air Breeze mast top mounted wind generator that gives us an average of 200 watt per hour
on average we get 10 Kw per day from solar and wind power , sufficient to run all systems including electric induction cooking when moored for longer periods.
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Old 29-09-2007, 02:32   #77
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retractable shrouded underwater motogen and prop

I have attached a picture of the retractable shrouded underwater motor and propeller and the masthead mounted wind generator.
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Old 29-09-2007, 12:19   #78
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The smaller prop normally has more energy lost to swirl and jet, the larger prop has more energy lost to friction with the water.

The optimum prop for a given hull will have the best balance of these loses (at other loses e.g. vortex generation,cavitation, etc) and have the highest highest efficiency.

It may be entirely possible to put on a larger prop and have lower efficiency, this is typical of small outboards.

Normally a larger prop on a sailboat will result in less shaft horespower to drive it.

I would suggest by 20%.

Yes, the horespower to drive a specific boat at a specific speed would be constant (cater parabis).

That is the numerator of the efficeicny, the shaft horsepower would be the denominator.
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Old 12-09-2008, 20:34   #79
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Lithium polymer batteries, etc

I have just noticed some posts by Simon Slater, and others, referring to my boat, PDQ 4422 - Cat Ion. Cat Ion is hybrid and uses lithium polymer batteries. I would like to dispel some myths from previous posts. These batteries are safe, lightweight and have incredible power density (24KWH from 2 80Kg banks). They have a failsafe embedded battery management unit (BMU) which will turn the batteries off if an individual cell voltage is too high or too low, or if a cell temperature is too high. The BMU itself does a series of self checks and if a problem with the BMU is detected it would turn itself off. In addition there is a boat monitoring and control system that would sound an alarm if the battery voltage was too high or too low. The batteries can be charged at a far greater rate than is possible with the generator (the generator in reality can only charges batteries at C/2 and the cell can be charged at 2C), so they cannot be charged too quickly. These are the ideal batteries in all respects except their cost. Cat Ion has been cruising now for almost one year now and we have had absolutely no problem with the batteries, they are the ideal battery.

Ian Underdown
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