I have had conflicting stories on letting the prop freewheel or keep the transmission in gear while sailing. I have read the some crusiers have attached an alternator and pulleys to the shaft and use the spinning prop to create electricity while sailing. Then others have told me not to let the shaft spin because of damage to the transmission. (wear on packing gland and cutlass bearing) I have watched the knotmeter and there is less drag by letting the prop (freewheel). Is it doing damage? Tell me your thoughts on the matter. I have a 2 blade prop and a Hurth transmission. Comments please!
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Bob
Check your owner's manual...
Hi Ron, Most owner's manuals I've seen will tell you to either leave it in neutral or reverse, but never in forward. Neutral is the preferred position. As far as using the shaft to generate power while underway, never heard of anyone doing it. It doesn't seem like the shaft would be able to sustain suitable RPM's to generate an appreciable amount of juice. Aside from that, I don't think I'd be comfortable applying lateral force to my propshaft just to maintain tension on a belt to drive an alternator that probably wouldn't produce enough juice to operate a single instrument, let alone top up a battery. I think you're just begging for stuffing box and cutless bearing problems. Howaboutit? Any experts out there willing to go out on a limb for this one? Just my two-cents (US) Cheers, Bob
Hi Ron, Most owner's manuals I've seen will tell you to either leave it in neutral or reverse, but never in forward. Neutral is the preferred position. As far as using the shaft to generate power while underway, never heard of anyone doing it. It doesn't seem like the shaft would be able to sustain suitable RPM's to generate an appreciable amount of juice. Aside from that, I don't think I'd be comfortable applying lateral force to my propshaft just to maintain tension on a belt to drive an alternator that probably wouldn't produce enough juice to operate a single instrument, let alone top up a battery. I think you're just begging for stuffing box and cutless bearing problems. Howaboutit? Any experts out there willing to go out on a limb for this one? Just my two-cents (US) Cheers, Bob
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Ron Dague
Freewheel vs. Reverse
This topic comes up about ever 3-6 months. A search of the archives looking for "freewheel", will give you the entire discussion. In short, some transmission such as Borg Werner, use pressure lubrication. They should never be allowed to freewheel. Other transmission use "splash" lubricaton. Those can be allowed to freewheel. To lock, put in reverse, not forward. If I recall correctly, with a fixed prop, you get slightly less drag by letting the prop freewheel. I know there's been a lot of discussion about "autorotation of helicopter blades", etc., but the tests say freewheel. However, it is noisier. Here's a caution: I had a packing gland loosen up and start to leak at high volume when doing this. I'm sure it is unusual, but water over the floorboard is rather exciting! I always locked mine. A better solution to reduce the drag of the fixed prop is get a folding or feathering prop. (I have a Martec folding prop, which when put in reverse, will fold minimizing drag.) I also agree that it would not be worth the work and problems to try and generate electric power this way. A final comment. I've heard that sometimes it can be hard to shift from reverse to neutral prior to starting the engine while underway. Yanmar reps have said that it is okay to start in reverse, and then shift, if this happens. Ron Dague S/V Finesse, h34 www.ExploreScuba.com
This topic comes up about ever 3-6 months. A search of the archives looking for "freewheel", will give you the entire discussion. In short, some transmission such as Borg Werner, use pressure lubrication. They should never be allowed to freewheel. Other transmission use "splash" lubricaton. Those can be allowed to freewheel. To lock, put in reverse, not forward. If I recall correctly, with a fixed prop, you get slightly less drag by letting the prop freewheel. I know there's been a lot of discussion about "autorotation of helicopter blades", etc., but the tests say freewheel. However, it is noisier. Here's a caution: I had a packing gland loosen up and start to leak at high volume when doing this. I'm sure it is unusual, but water over the floorboard is rather exciting! I always locked mine. A better solution to reduce the drag of the fixed prop is get a folding or feathering prop. (I have a Martec folding prop, which when put in reverse, will fold minimizing drag.) I also agree that it would not be worth the work and problems to try and generate electric power this way. A final comment. I've heard that sometimes it can be hard to shift from reverse to neutral prior to starting the engine while underway. Yanmar reps have said that it is okay to start in reverse, and then shift, if this happens. Ron Dague S/V Finesse, h34 www.ExploreScuba.com
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Brian Pickton of BeneteauOwners.net
Agree with Bob and Ron
Feb19,2001 Dear Ron, Bob and Ron have the right advice. Check your owners manual or call the transmission manufacturer and ask. Also simply because you can allow the prop to freewheel does not necessarily make doing so a good idea because of the wear issues on the stuffing box, cutlass beariing, etc. Even if your transmisssion is the splash type freewheeling adds wear. I would add that if that extra half knot is important to you go with the feathering prop option. Why lock the transmission in reverse? I know of one sailor who started his engine unintentionally by shifting it into forward while undersail at 6 1/2 knots with the key on. It came as quite a surprise. Finally, I have met hundreds of sailors over the years and none of them has an electrical set up designed to run off of the freewheeling shaft, although I can recall a number of discussions about trying it. I'm sure somebody must have tried it somewhere and you would think if someone had tried this set up and it worked well we would have heard about it by now. Frankly I can't imagine the free wheeling shaft giving enough RPM to spin up an alternator effectively, and going through a bunch of gearing rigamarole to make it work at various boat speeds doesn't seem worth the effort. If you need the power why not just turn on the engine and use the alternator supplied rather than add all of that complexity to your boat? Fair winds, Brian Pickton of BeneteauOwners.net aboard The Legend, Rodney Bay, St. Lucia
Feb19,2001 Dear Ron, Bob and Ron have the right advice. Check your owners manual or call the transmission manufacturer and ask. Also simply because you can allow the prop to freewheel does not necessarily make doing so a good idea because of the wear issues on the stuffing box, cutlass beariing, etc. Even if your transmisssion is the splash type freewheeling adds wear. I would add that if that extra half knot is important to you go with the feathering prop option. Why lock the transmission in reverse? I know of one sailor who started his engine unintentionally by shifting it into forward while undersail at 6 1/2 knots with the key on. It came as quite a surprise. Finally, I have met hundreds of sailors over the years and none of them has an electrical set up designed to run off of the freewheeling shaft, although I can recall a number of discussions about trying it. I'm sure somebody must have tried it somewhere and you would think if someone had tried this set up and it worked well we would have heard about it by now. Frankly I can't imagine the free wheeling shaft giving enough RPM to spin up an alternator effectively, and going through a bunch of gearing rigamarole to make it work at various boat speeds doesn't seem worth the effort. If you need the power why not just turn on the engine and use the alternator supplied rather than add all of that complexity to your boat? Fair winds, Brian Pickton of BeneteauOwners.net aboard The Legend, Rodney Bay, St. Lucia
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Bob
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Tom Soko
Freewheel
Ron, I think I remember a number of years ago reading an article written by Steve Dashew describing a new boat he had just designed and built. If I remember correctly, he had installed an extra shaft, with a large 3 bladed prop, just for the purpose of generating electricity. It was not connected to any transmission, just a thrust bearing and a few belts and pulleys and an alternator. The boat was also in the 60-70 ft range. I don't think it makes any sense to do so in most normal boats. My Hurth owners manual says specifically to put the tranny in reverse when sailing. You might loose a small fraction of a knot, but the wear and tear will be a lot less.
Ron, I think I remember a number of years ago reading an article written by Steve Dashew describing a new boat he had just designed and built. If I remember correctly, he had installed an extra shaft, with a large 3 bladed prop, just for the purpose of generating electricity. It was not connected to any transmission, just a thrust bearing and a few belts and pulleys and an alternator. The boat was also in the 60-70 ft range. I don't think it makes any sense to do so in most normal boats. My Hurth owners manual says specifically to put the tranny in reverse when sailing. You might loose a small fraction of a knot, but the wear and tear will be a lot less.
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