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Old 16-06-2021, 20:46   #1
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Propeller making the engine turn (in reverse?)

Hi, Any advice on diagnosing the situation would be great.

The boat / propulsion:
Catamaran 44" with two Yanmar 3JH4E engines and SD50 saildrive
Maxprop whisper propellers

What happens and when:
When I start sailing and after stopping the engine (gear in neutral) I can hear the sound of the saildrive turning. So I reverse... the turning noise stops... and I replace the gear in neutral.
When sailing above 7.5 to 8 knots, it sometimes happen that the engine and the saildrive jump up and down a few times with very loud clanking noise.

Analyze:
The noise make me think that it might be the engine being forced to turn (in reverse?). But the saildrive gear is in neutral, so even if the propeller unfolds and turns, it should only turn freely!!!

It does not happen often, but I need to do something as this cannot be good for the engine, the saildrive and the silent blocks.

Anyone has experienced such problem? Any idea to diagnose further and / or fix the problem?

Thank you for any suggestion.
Philippe
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Old 16-06-2021, 22:28   #2
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Re: Propeller making the engine turn (in reverse?)

Wow, those whispers are a lot of blade area. Ive never seen or worked on em yet but a quick read of the PYI brochure revealed that they are best suited to Heavy displacement cruisers over 50 feet which is pretty darned far from your boat spec. Id contact PYI for advice but would suggest that those SD 50s ( historically a problematic cone type saildrive) might suffer coupled to such a powerful propeller and you are right to be concerned.
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Old 16-06-2021, 22:49   #3
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Re: Propeller making the engine turn (in reverse?)

i'm no mechanic, and we have a pair of 4JH - not the 3JH you have, but i cannot believe that a prop would turn over the diesel engine

my guess is some problem with the saildrive/s.

does it happen on both sides or just one ?
if just one, always the same side ?
how many hours on the saildrives and when were these last serviced ?

maybe the s/d is slipping into gear somehow ?

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Old 16-06-2021, 23:03   #4
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Re: Propeller making the engine turn (in reverse?)

Just a quick question, do you really have a five bladed prop on each saildrive or have you confused the prop model?
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Old 16-06-2021, 23:50   #5
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Re: Propeller making the engine turn (in reverse?)

Quote:
Originally Posted by skipperpete View Post
Wow, those whispers are a lot of blade area.
Quote:
Rob aka Uncle Bob : Just a quick question, do you really have a five bladed prop on each saildrive or have you confused the prop model?
Actually the manual says "Easy / Whisper"... and the actual model is "Easy 3 blades / diameter: 457"

Thanks for pointing that out. I change the model in the original message
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Old 16-06-2021, 23:55   #6
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Re: Propeller making the engine turn (in reverse?)

Quote:
Originally Posted by skipperpete View Post
those SD 50s ( historically a problematic cone type saildrive) might suffer coupled to such a powerful propeller and you are right to be concerned.
Pete.
I lapped the cones a few months ago and installed the upgrade kit sold by saildrives (at) yahoo.com

Problem existed before and I thought it was now cured... until this morning!
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Old 17-06-2021, 00:00   #7
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Re: Propeller making the engine turn (in reverse?)

Quote:
Originally Posted by chrisr View Post
does it happen on both sides or just one ?
if just one, always the same side ?
how many hours on the saildrives and when were these last serviced ?

maybe the s/d is slipping into gear somehow ?
In the past it has happened on both sides (although only one side this morning)

Last saildrive service in February 2021 + upgrade kit + replacement of diaphragms

I would agree with you when you say it "slips into gear"... but could that make the engine turn?
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Old 17-06-2021, 00:30   #8
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Re: Propeller making the engine turn (in reverse?)

max props should self feather unless they are fouled,fishing line and polypropalene rope fibers will jam up the blades and form a thin fiber washer between the hub and blade that can make them slow to feather.

i have had a fixed blade prop turning a stopped 3 cylinder yanmar that was locked in reverse before when reaching hull speed on a 39ft bene i delivered a few years ago.
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Old 17-06-2021, 00:35   #9
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Re: Propeller making the engine turn (in reverse?)

..the Swales supposedly bump-started the diesel(s) in reverse(!!) on their way to Cape Horn...
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Old 17-06-2021, 02:06   #10
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Re: Propeller making the engine turn (in reverse?)

On my Yanmar saildrives, the feathering props would play up when they were dirty. Similar to what you experienced. When switching from motoring to sailing, if going over 6 knots, the prop was not feathering so lots of judder etc. Putting in reverse normally fixed it, but sometimes had to do a few times.
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Old 17-06-2021, 13:41   #11
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Re: Propeller making the engine turn (in reverse?)

Leave it in forward - as I used to had to do. It stopped the rotation, but did nothing for drag.
When I cought the boat it came with a 2-blade folder - to go with the recon 2GM.
When I re-engined with a 3YM (only marginally more than a full rebuild) I fitted the biggest Autoprop, I could fit, which allowed a nearly 9 knot maximum, abot x2 the under-power speed of the original set-up.
That also needs to be left in forward gear to ensure it feathers.
Whilst all the pundits recommend locking the boat in reverse, my experience has proved them wrong.
I suapect you'll have to try all the alternatives - forward, reverse and neutral, at all sailing speeds, and check the increase/decrease in VMG.
Nice little exercise - you could even plot it graphically.
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Old 17-06-2021, 14:14   #12
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Re: Propeller making the engine turn (in reverse?)

Thank you all for sharing your experience and suggestions.

1) I now have confirmation that it is possible for the propeller to drive the engine. Would the loud noise I hear be a sign the engine is driven in reverse (opposite from normal rotation)? my assumption being that if it is driven in its normal rotation way it would do the same thing as when the engine is driven with the starter motor (but no diesel)... so no reason for loud noise and engine jumping on its silent blocks.
How much internal damage can be done to the engine if it is driven in reverse?

2) Water starts to be quite cold here in NZ, but I will go and check the propeller for fouling and anything that could prevent blade rotation.

3) I will try to leave in forward next week when we will have good SW winds and we sail from Auckland to Bay of Islands.

Thanks again and I will report here on any new experiments / findings...
Cheers
Philippe
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Old 17-06-2021, 14:15   #13
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Re: Propeller making the engine turn (in reverse?)

The best way to gall a cone clutch is to leave it in gear while sailing, matters not if forward or reverse gear is used. Yanmar/Kanzaki has a technical bulletin on this.
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Old 17-06-2021, 14:20   #14
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Re: Propeller making the engine turn (in reverse?)

My old Crowther had a pair of 3GMD and a 4 blade fixed props.

Engine off , at high boat speed the props did turn the engine on a couple of occasions.
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Old 17-06-2021, 14:20   #15
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Re: Propeller making the engine turn (in reverse?)

Quote:
Originally Posted by chasfgr View Post
Whilst all the pundits recommend locking the boat in reverse, my experience has proved them wrong.
Yes this is what I read and was doing with older Maxprop... but the same problem happened. For these new propellers installed in February, the user manual says clearly the gear must be in neutral after the blades are feathered... Obviously this is not right either (in all conditions)
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