Re: [Amel Yacht Owners] Fixed prop
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I notice a ½ knot difference when the engine is running in neutral and the autoprop is freewheeling.
When the engine is stopped the brake locks the shaft and I gain ½ a knot.
When I used to build race cars we always disconnected the drive shaft as many transmissions are lubricated
by the fluid / lubricant being splashed on the mechanism by the engine driving the gears. Many times people who did not do this blew the rear seals on their transmissions. I do not know if the same holds true for my tranny. But I am happy to have the shaft brake.
Kimberlite Amel Super Maramu #376
From: amelyachtowners@... [mailto:amelyachtowners@...]
Sent: Wednesday, June 03, 2015 3:11 PM
Subject: Re: [Amel Yacht Owners] Fixed prop
Seems to me that a freewheeling prop could wear out the drive, while a prop that is not turning wouldn't cause any damage at all unless you hit something with it (highly unlikely on our boats).
It's hard to evaluate the difference between a fixed prop, freewheeling fixed pitch prop, and folding or feathering prop, as wind and wave conditions are always changing. I used a fixed pitch prop for a year and always put the engine in gear while sailing. When I put my feathering MaxProp on I think I gained an average of about a half knot while sailing in varied conditions. I always put the transmission in gear long enough to feather the prop, then put it back in neutral while sailing.
If it's OK to let it freewheel, there must not be a significant difference in boat speed...so maybe I wasted a bundle on my MaxProp, eh?
I just read another study that also determined that a fixed prop created more than twice as much drag as a freewheeling prop. But what I want to relate is that this article claimed that Yanmar and Volvo both believe that the transmissions should be in neutral to prevent damage and could cause warranty issues .I do not know if that is true ,if concerned you may want to speak to a rep. Pat
Just as I sent my question about fixed vs. unfixed props to the group , my wife sent me the results of her google search . Yachting monthly said that this subject had been debated for decades so they conducted tests that determined that a spinning prop produced less than half the drag of a fixed prop. That at seven knots you would lose approx. one knot while fixed. That seems to jive with what I experienced. Pat
We have a fixed prop due to the original owner opting for the prop driven alternator , which I have dismantled since my solar panels and wind generator supplies all the electric I need. I have been told, that it is more efficient from the standpoint of drag for a prop to be fixed opposed to be freewheeling, from a pilot who's opinion I respect. While sailing I do not like to switch in and out of gear due to the loud clunk that sounds as though it could damage the transmission, so its hard to experiment to draw conclusions. However we just sailed back from the BVIs via Bermuda and we were in gear fixed and then I put it in neutral and it seemed that we picked up a knot. I never put it back in gear as we were sailing too fast and for the next three days we averaged 173 nms. with true wind avg. 12 - 16 . Could someone that is knowledgeable about props and drag tell me which is more efficient ? I am also concerned about wear on the transmis sion while freewheeling .
Thanks, Pat SM Shenanigans