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  #21  
Old 11-05-2011
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One additional note... with the lock fixed prop under sail, once we were up close to hull speed there was a detectable 'shimmy' in the wheel as the rudder sensed the 'swirl' coming off the prop.

This, of course, has disappeared with the Max.
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  #22  
Old 11-05-2011
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Quote:
Originally Posted by blt2ski View Post
This was probably a "10th of a knot" The previous owner of my boat mentions something similar for speed gains under sail as Faster did, about 1/2 knot. A few folks that have "OTHER" props that have been on my boat comment about how smooth, lack of prop walk etc, the max prop is in reverse. Marty
Actually, no - it was seconds per mile. I agree that at world championship Quarter Ton racing, "back in the day", 1/10th of a knot would have been significant - about a 2% improvement. He was talking about performance against rating though where seconds per mile was what mattered. Things got pretty looney at that level back then - the boat had hydraulics on the backstay & headstay, the turnbuckles were below deck "to minimize windage", there were 17, count'em 17, different adjustments that could be made to the sails and so forth - all this on a 26 footer.
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  #23  
Old 11-05-2011
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On my last boat (brother owns it now) we switched from a three blade fixed to an Autoprop (this was in the mid 90's) and gained at least half a knot in lighter winds. We also were able to motor at the same boat speed as before but at about 400 rpm less on the Yanmar 3GM. The Autoprop has performed flawlessly since new. I just took the boat from the San Juan Islands to Seattle and encountered some steep 10' waves due to a strong ebb flowing against 16-20 knots of wind and was able to power right thru it. Great prop, no prop walk and tremendous thrust under power and only slightly more drag than a straight blade prop. I currently have a fixed three blade Campbell sailor and like the simplicity, but miss the added thrust and lower rpm cruise I would get from an Autoprop, especially in rough conditions.
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  #24  
Old 11-05-2011
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Thanks everyone. I gather from the responses that a "streaming" type of prop can make anything up to about a 8 - 10% difference in light winds over a fixed prop but the benefit fades away as windspeed increases.

That is certainly significant, especially around here, with our notoriously light summer air.
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Old 11-06-2011
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I like the Autoprop because of the automatic adjustment of propeller pitch to engine RPM. When diesel burns in the combustion chamber, it takes place over a time dependent on how fast the injection takes place and how long it takes for the burning process to become established. On an engine with an injection pump (not the more modern electronically controlled fuel injection), the optimum RPM for economy is in a narrow range. Diesel engine - Wikipedia, the free encyclopedia has a lot of information about diesels. If you search down to the heading of ‘Power and Torque’ note that the speed range is usually 1600 to 2000 RPM for smaller engines and this applies to sailboat engines as they all have fuel injection pumps mounted on them as far as I can tell. Naturally aspired engines (not turbo) loose torque at higher RPM (bad for fuel economy) so an Autoprop will help with fuel economy, but allow for maximum power when needed and can be fully feathered when engine is off
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Old 11-06-2011
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Quote:
Originally Posted by LakeSuperiorGeezer View Post
the optimum RPM for economy is in a narrow range.
I think you will find that operating a diesel engine at its torque peak RPM will give you the most efficiency. The specific RPM of the torque peak of your particular engine can be obtained from the manufacturer if it isn't in your owners documentation.

That is the essential principle that a TRUE hybrid vehicle operates on. A true hybrid, unlike the current dual propulsion systems that are called hybrids, has a small generator on board that runs at a steady state at the engines torque peak. This is used to recharge the batteries of the electric system that actually propels the car. It is incredibly efficient.

Look up the latest Jaguar concept car - it is set up that way, with motors in each hub and an onboard generator. It has something like 500+ horsepower to the wheels, obviously supercar performance and is propelled ONLY by electricity - it doesn't swap back & forth like the dual propulsion cars such as the Prius.
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Last edited by SloopJonB; 11-06-2011 at 02:01 PM.
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Old 11-06-2011
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Quote:
Originally Posted by SloopJonB View Post
...has a small generator on board that runs at a steady state at the engines torque peak. This is used to recharge the batteries of the electric system that actually propels the car. It is incredibly efficient...
Someone should do this for an electric drive on a sailboat. Lack of range is what I think is the real downside for the electric drive. I am thinking it could be setup to function like a variable pitch propeller where the propeller is really fixed. The engine speed would be independent of the propeller RPM.
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Old 11-06-2011
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Quote:
Originally Posted by LakeSuperiorGeezer View Post
Someone should do this for an electric drive on a sailboat. Lack of range is what I think is the real downside for the electric drive. I am thinking it could be setup to function like a variable pitch propeller where the propeller is really fixed. The engine speed would be independent of the propeller RPM.
I think the reason no-one has is because the majority of sailboats main engines are not much bigger than the gen sets in a true hybrid. Fuel costs are also not an issue since so little is used over the long haul.

It could be worthwhile for larger boats that carry a gen set already, particularly since usually they already have big battery banks as well.
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Old 11-06-2011
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On my Jeanneau 45.2 went from the OEM 3 blade fixed prop to a Maxprop. Always towed a dinghy (10 foot RIB with 15 HP outboard). Maxprop was better under sail, much better in reverse and gave us 7 Knots cruise speed with 200 fewer RPM. Once a gear greasing at haul-out and no issues at all. A good upgrade in my book.
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Charge Batteries

Quote:
Originally Posted by SloopJonB View Post
It could be worthwhile for larger boats that carry a gen set already, particularly since usually they already have big battery banks as well.
Yes, and the electric motor can also be used as a generator and charge the batteries when under sail.
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