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Several people I've sailed with tell me I should be putting my engine in reverse gear when sailing to stop the fixed prop from rotating (while in neutral) and creating unnecessary wear. Others say it makes no difference. I'm wondering of this is just over caution or if there is something to it. Any thoughts?

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There are a few variables to consider.

Firstly, moving parts are going to create wear so a rotating prop will presumably have some impact on the life of the gearbox and drive train.

On the other hand there is a lot of energy bound up in the gearbox when it is in reverse gear to prevent a prop from rotating. I don't know what the long term effects of this would have, especially on a cone type box.

If you do choose to allow the prop to rotate when sailing then you need to ensure from the manufacturer that the gearbox will be adequately lubricated - some require the engine to be running to achieve this.

On my last boat I locked the prop whilst sailing because it was noisy. On my present boat I let it rotate because it is very quiet.

Sorry, not very helpful.

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What is the gearbox ( make and model).

Dragging a locked prop is like towing a bucket. On some fast boats, esp multis (where prop can come out of water) it has been known to start the engine - in reverse!

Personally I'd ditch the fixed prop, but I know that's not the question!

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It's a Yanmar 2GM20. I see the manual says the gearbox is constant mesh gear with servo cone clutch if that helps. Gaining another knot in speed sounds quite appealing.... That's got me thinking! But in the meantime, fixed prop remains a bit longer.

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I was told that too. I ended up getting a kiwi feathering prop fitted and added nearly a knot of boat speed

Do you have trouble getting in reverse?off topic sorry, but mine stalls unless I go in quick for max revs.then can ease off

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harrytom. Yes when the kiwiprop was first fitted I had that problem. The guys who fitted it changed something which got rid of that problem. Sorry I can't remember what they changed but kiwiprop can help you

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Let the prop spin and connect it via a belt and manual clutch to a small generator to keep your batteries topped off.

 

It's gonna spin.  Use the energy instead of wasting it.

 

 

I had thought about a system whereby a battery bank could be charged up with the prop and then turn the energy back around and spin the prop slowly when the bank was charged, allowing the prop to return some of the previously stored energy.

 

Hell, such a setup on the right boat would be all that was needed to charge a battery bank to run the prop off an electric motor.  Cruise for a few weeks, then motor with the charged batteries to anchor or the dock at the end of the cruise.

 

 

It's your boat, and your world.  Don't wait for some manufacturer to come up with a product.  Make this yourself.  Find a way to attach a belt to the shaft.  Mount a generator.  Install an easy clutch.  Wire up some batteries.  Done.

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Thats already been done on some boats.

 

WARNING It is not possible with some gearboxes and stuffing box arrangements. Some require the engine to be running to provide lubrication and or cooling to the stuffing box. You need to be certain that your setup is suitable before making what could be an expensive mistake.

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Thats already been done on some boats.

 

WARNING It is not possible with some gearboxes and stuffing box arrangements. Some require the engine to be running to provide lubrication and or cooling to the stuffing box. You need to be certain that your setup is suitable before making what could be an expensive mistake.

Funny I was  just about to say the same thing, With the Yanmar gearbox, they are ok to rotate but some of the hydraulic assisted boxes are not. Re the drag issue, Frank Kinney a past senior designer for Sparkman and Stephens (book Skenes Elements of yacht design) wrote of the research involving extensive testing in Hoboken regarding free wheeling or locking the shaft. Their research indicated there was less drag with the shaft locked than with it rotating.

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WARNING It is not possible with some gearboxes and stuffing box arrangements.

 

As IT has mentioned above. Thus It is not the Engine model, but the Gear box model we need to know.

Some boxes must be locked and not allowed to run in free wheel. Some can be free wheeled for set intervals before running the engine to get oil around them and then they can be free wheeled for a time again. And then there are some that can be free wheeled 100% continuously with no issues. It is all down to how the Box gets lubricated. Some have the final drive gear in Oil and this gear picks up the oil and takes it around the gears and bearing that are being spun. Others have gears/bearings that are being spun that do not get oil unless the engine is run and the front section of the box is spreading around the oil. There are a few that need to be fully locked. But not common to come across. The Manual should tell you what is best practice.

       To lock or not for less resistance to Sailing, this is also a factor of Prop design and speed of Sailing and so on. A fixed prop can as IT said, be like towing a bucket. But some props, especially Sail boat props, are not always the most efficient. So it can kind of depend. Remember that a Prop is a Rotary Wing. Like any wing, in certain circumstances, they will stall. A stalled Wing will not keep a Plane in the air. A Stalled prop will not create a great deal of drag. When a prop free wheels, it is acting efficiently as a Wing and the ability of it to create drag, is proportional to the effort that goes into turning it. KM and I have a friend that has a Generator driven by the prop. But the Boat is 60ft or more. So big sail area and the Prop/Gen does not make a great deal of difference. But on a smaller boat, it can. If there is little effort required to spin the Pop/shaft/box, then you won't get held back too much. But for others, the resistance to spinning all that gear can be high and thus it will be like that bucket.

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There is one other thing to consider - if you have a shaft seal that is fed cooling and lubricating water from the engine and you are just freewheeling -this will not be happening . Not too much of a problem in most heavy yachts but on some of the faster lighter ones ...

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Funny I was  just about to say the same thing, With the Yanmar gearbox, they are ok to rotate but some of the hydraulic assisted boxes are not. Re the drag issue, Frank Kinney a past senior designer for Sparkman and Stephens (book Skenes Elements of yacht design) wrote of the research involving extensive testing in Hoboken regarding free wheeling or locking the shaft. Their research indicated there was less drag with the shaft locked than with it rotating.

 

 

Really, I'd like to see a study that defies the laws of physics.  Drag is what causes the prop to rotate.  So if the prop is locked and not allowed to rotate, then the drag component of the prop itself goes UP, not DOWN.

 

Surely you are misquoting the study.  I mean, I know yacht designers aren't exactly interested in physics over profit, but they can't violate the laws of physics, and they certainly can't expect us to believe they can.

 

 

Please quote the study so we can rest our minds that there aren't idiots designing yachts who don't even have a grasp of basic physics.

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Really, I'd like to see a study that defies the laws of physics.  Drag is what causes the prop to rotate.  So if the prop is locked and not allowed to rotate, then the drag component of the prop itself goes UP, not DOWN.

 

Surely you are misquoting the study.  I mean, I know yacht designers aren't exactly interested in physics over profit, but they can't violate the laws of physics, and they certainly can't expect us to believe they can.

 

 

Please quote the study so we can rest our minds that there aren't idiots designing yachts who don't even have a grasp of basic physics.

The tests were done in either the late 1o960's or early 1970's Frank's book a reprint of Skene's elements of Yacht design  did not give the exact date but designers involved included Dave Pedrick and Mario Taraboccia and Bill Langan, all of these so called idiots were involved in 12 metre yacht design in the Americas Cup. Skene's Elements of Yacht design was the main text book for trainee yacht designer's. The trials inlolved the test tank at Hoboken as well as full size Tests on Franks own boat the 43 ft yawl Santa Maria. The conclusion was due to friction with shaft bearings the prop could not rotate fast enough to allow a lamina flow through the blades so the rotating prop basically created turbulence for the entire circle swept by the blade tips but the fixed prop would allow flow between the blades. Remember sailing vessel fixed propellers at that time had a blade area less than 35%.  

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