Or you could do nothing and in a few years your hearing will decline to the point that you will not hear the engine over-temperature alarm, let alone the singing prop.
Singing Prop
- Thread starter DannyS
- Start date
(1) Singing propeller? - YouTube
I had the same issue with a B-323 and a fixed two bladed prop. I tried filing it and polishing it to no effect and mostly just did not travel very far in the affected rev range. Fortunately it was not a speed I needed so it was easy. Traded the boat so I never did fix it.
Keep us posted.
Dan
edit: forgot to mention that the singing did not occur if the boat was tied to the dock and run through the same rev ranges in gear.
I had the same issue with a B-323 and a fixed two bladed prop. I tried filing it and polishing it to no effect and mostly just did not travel very far in the affected rev range. Fortunately it was not a speed I needed so it was easy. Traded the boat so I never did fix it.
Keep us posted.
Dan
edit: forgot to mention that the singing did not occur if the boat was tied to the dock and run through the same rev ranges in gear.
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Our friends had a C22 that sang. They said it was the keel cable. They liked the "tune". I found it really annoying.
If it were my money: After you isolate it to the prop so you're positive it's the problem, go with a feathering or folding replacement. You'll pick up some speed on your cruises.
If it were my money: After you isolate it to the prop so you're positive it's the problem, go with a feathering or folding replacement. You'll pick up some speed on your cruises.
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Most boats don't have a shaft brush. If you have one it would be obvious - a 12" copper strap between the transmission and the stuffing box. You usually find them on boats with a flexible coupling that electrically insulates the shaft from the engine.
If it does turn out to be a strap. You could probably bridge an isolating flex coupling with a jumper wire from one side of the coupling to the other.
Firstly, I sailed my 39 for 15 years with the transmission in reverse with no ill effects. Secondly, the singing prop is caused by the water passing the leading edge and setting up a harmonic. The simple solution is to take the prop off, bring it to a prop shop and have the leading edge knurled. Singing gone, peace and quiet restored.
My experience was that with the two blade fixed prop, there was a harmonic that showed up with the freewheeling prop and the boat sailing just about at hull speed. It was annoying enough that I changed to a two blade Gori folding prop. Not the cheapest way to eliminate a problem, but I never liked the Yanmar direction to leave the gearbox in neutral anyway.
Not that I’ve gone looking for one, I’m almost certain our boat doesn’t have a shaft brush.
I had a Beneteau 50 that had a singing prop. I always sailed in reverse, but when I motored , it was tuning to harmonic at low rpm. I changed it for a max-prop and voila, forgot about it. A few years later I put it back on to have the max-prop rebuilt, and the singing that I had forgotten just came back. I put the Max back on and all quiet again. So you have a choice, spend time to try to fix it or spend money and buy a Flex-o-fold prop.( my choice). You can have it delivered from the factiry. Rumors say Yanmar bought them out!!!
I spoke with a prop shop this morning and they were well aware of this phenomenon. For less than $40 they said they could take care of it. I figure that’s well worth the trouble. If it persists after that, I’ll revisit the new prop conundrum. Thanks all for your input.
Wow...
Post #8 "...would suggest your altering the prop shape might change the harmonic sounds from such cavitation. I would be more inclined to discuss this with a competent prop shop."
You found a great solution Danny. Hope it resolves the issue.
Post #8 "...would suggest your altering the prop shape might change the harmonic sounds from such cavitation. I would be more inclined to discuss this with a competent prop shop."
You found a great solution Danny. Hope it resolves the issue.
I'm not sure my experience is completely relevant.
My old Hunter 34 is over propped with a 15"x15" 2-blade (6.25 knots @ 2,300 rpm!) using less than 1/2 gal/hour. Once when on a strong broad reach (should have furled but the old girl lifted her skirts and flew), trying to exceed maximum hull speed, the prop roared loudly under the transom from the drag.
Like an airplane propellor, with an engine 'out' a locked prop has much less drag than a spinning one with no power which acts like a drag disc. I agree with the previous writer and have since locked the Yanmar in reverse when sailing and have picked up probably 1/4 knot under sail. Hard to see what 'damage' one could expect in the engine/transmission - after all, the 'locked in gear' is simply the prop being held by the diesel compression, and with much less torque than when it is running.
Just sayin'.
My old Hunter 34 is over propped with a 15"x15" 2-blade (6.25 knots @ 2,300 rpm!) using less than 1/2 gal/hour. Once when on a strong broad reach (should have furled but the old girl lifted her skirts and flew), trying to exceed maximum hull speed, the prop roared loudly under the transom from the drag.
Like an airplane propellor, with an engine 'out' a locked prop has much less drag than a spinning one with no power which acts like a drag disc. I agree with the previous writer and have since locked the Yanmar in reverse when sailing and have picked up probably 1/4 knot under sail. Hard to see what 'damage' one could expect in the engine/transmission - after all, the 'locked in gear' is simply the prop being held by the diesel compression, and with much less torque than when it is running.
Just sayin'.
Yanmar recommends against sailing in reverse because they say the way the transmission works could make it hard to shift back out of reverse before starting the engine. Something about the continuous torque from the prop that could jam the shifting mechanism, and if that happens it’s best just to start in reverse rather than trying to force it.
I think Maine Sail posted some test results dragging a fixed and freewheeling prop a while back. Freewheeling was less drag in his case. I think that was with a Michigan Wheel style prop, so your mileage may vary.
Here is the result of Maine Sail's drag test: freewheeeling vs. locked: Propeller Drag Under Sail Test – CatamaranSite
The singing prop is caused in simple terms by cavitation off the trailing edge of the prop. My prop shop said they normally come across it mostly when the antifouling sags toward the trailing edge during application thus making the trailing edge more bulbous than it should be. The noise will also reduce as the prop fouls and the flow across the foil becomes more turbulent.
Further note: the Yanmar SD20 can be locked in gear as it has a "dog clutch". The bigger Yanmars have a cone clutch and should not be locked when the engine is not running.
Further note: the Yanmar SD20 can be locked in gear as it has a "dog clutch". The bigger Yanmars have a cone clutch and should not be locked when the engine is not running.
Hello!
Thank you for the interesting article and references! I note the MIT report says:
"(They do not directly identify the source of these CD values, and one assumes that the coefficient given for the locked shaft condition may simply be that of a flat disc, bluff body.) Part of the present work would be directed at assessing the veracity of this convenient approach".
The research seems to show markedly higher drag with a locked prop. Notwithstanding the 'experts' views and results, empirical evidence on my boat (Hunter 34) shows about 1/4 knot increase at 5.5 knots under sail - with a locked prop vs. free wheeling. Perhaps my 15x15 overprop is part of the reason? At hull speed (8kn?) under strong winds, the freewheeling prop was extremely noisy (actually roaring) with all the turbulence created. Locking it of course ended all that.
I never have had any problem in shifting out of reverse to neutral but if i ever did, the other writer's comment applies: start the engine in reverse: all's well. Note also that some transmissions are not properly lubed when freewheeling if the engine is not turning. Not sure which brand/models they would be.
My airplane analogy (I have flown a lot) is what is taught in aviation. For a fixed pitch prop, if your engine quits it is best to slow down until the engine compression stops the spinning prop then increase speed to best glide speed. Less drag equals greater gliding distance equals more landing site options. Yes, air is a compressible fluid unlike water(!) but I personally feel the same logic applies.
Happy sailing!
I normally sail with the tranny in neutral, but a few years ago, on an after-work solo sail, I decided to try locking it in reverse.
I had a great sail, and returned back to the Marina. I tried to shift into Neutral but it was very hard to move the lever. Then it suddenly moved. When I tried to fire up the engine, something didn’t seem right, and the engine would not start.
As it turned out, the tranny was locked up in reverse, and when I tried to force it into neutral, it pulled thr cable out of the cable holder at the transmission...so the cable would move, but it was still in neutral.
I haven’t sailed in reverse since.
Greg