Vibration starts at 5.5Knts . . saildrive

[collinsp]

Hi All,

This weekend we were out on a boat relatively new to me and started to get a vibration whenever we went over 5.5Knts and also a whining/whirring noise that appears to be coming from the saildrive which leads me to believe that the issue is the prop spinning when we get over 5.5Knts? We did not get it when we were using the engine over 5.5Knts, just when under sail.

So couple of questions . . . I have read different opinions about putting the engine into either forward or reverse when you switch it off and are solely under sail, what are the pros and cons of forward or reverse? Wouldn't this cause significant drag and put a lot of strain on the bearings in the saildrive ? Would a folding prop be an option, though they are eye wateringly expensive for the S130 saildrive and does this effect the performance of the engine, especially in reverse ??

I'm sure other people have experienced this issue so any insights would be greatly received as we have a few long crossings planned over the next few months and don't want to be spending significant hours feeling the vibration and the noise at night :-(

Thanks in advance . . . .

 

[Tranona]

Quite normal. Just put it in reverse gear and accept the small amount of extra drag, but no noise. Otherwise invest in a Flexofold or a Featherstream depending on the boat. I had a Flexofold 2 blade on a Bavaria 37 with a 2030 and a later 33 with a D1 30. With a larger, heavier model and bigger engine a 3 blade Featherstream may be a better choice. . Folder is no different in reverse from a fixed and Featherstream arguably better.

 

[Porthandbuoy]

I get a rumbling noise sailing, it's the prop spinning. Great, put the gearbox in reverse and it stops.
Get to 5kts and above and the propeller 'sings', or howls, like a banshee. Noticeable on deck but loud and very intrusive down below.
Think I'll have to save up my pennies for a folding or feathering prop if I want peace and serenity.
Mind you, a set of earplugs would be cheaper.

 

[johnalison]

Locking the prop is quite normal for most set-ups though I vaguely remember that instructions with my engine said something about letting it run when installed with a shaft. I understood that there is less drag with a fixed prop when locked, though this may differ between 2 or 3-bladed props. I have a 2-bladed folder which should be the worst option with regard to going in reverse but my experience has been that although it needs a bit more throttle that with fixed prop it is quite manageable and I have never lacked confidence in it.

 

[johnalison]

I get a rumbling noise sailing, it's the prop spinning. Great, put the gearbox in reverse and it stops.
Get to 5kts and above and the propeller 'sings', or howls, like a banshee. Noticeable on deck but loud and very intrusive down below.
Think I'll have to save up my pennies for a folding or feathering prop if I want peace and serenity.
Mind you, a set of earplugs would be cheaper.

Go for it. I let my engine idle when changing to sail until it has cooled a bit, so the prop spins. The change when I stop the engine and lock the prop is very rewarding, losing the turbulence on the rudder and gaining a fraction of a knot in speed.

 

[wonkywinch]

Check your sail drive manual and type of prop. I have a Yanmar SD25 and the manual states to keep it in astern under 10kts sailing and for a folding prop, leave it in neutral, however, Flexofold recommend locking the gearbox (in forward or astern) to ensure the prop folds fully and there is no centrifugal force to open it.

Your sail drive may have different advice depending on the type of clutch it has.

It is a mistake to assume a stationary prop exerts more drag than a freewheeling one. As in aviation, a windmilling prop exerts the similar drag as a full disc of the same diameter, so it is better to feather the propeller to reduce drag.

My Flexofold 3 blade with Hydroaxe rope cutter just fitted.

 

[vyv_cox]

The YM tests showed that a locked, fixed propeller generates far more drag than a spinning one.
My Bruntons feathering prop continues to rotate under sail. I put the gear in astern (Yanmar) but it becomes a problem to put it into neutral when the engine is next needed. Just start it in astern, when the lever is easily moved to neutral and forward.

 

[wonkywinch]

The YM tests showed that a locked, fixed propeller generates far more drag than a spinning one.
My Bruntons feathering prop continues to rotate under sail. I put the gear in astern (Yanmar) but it becomes a problem to put it into neutral when the engine is next needed. Just start it in astern, when the lever is easily moved to neutral and forward.

Interesting. I guess aeroplane propellors are thinner but even Darglow told me there was more drag with rotating prop which gave me confirmation bias it was true.

 

[capnsensible]

Careful with yanmar gearboxes if you got a shaft. There is a technical warning issued by them ....can't find it at first look.....regarding putting the engine into astern to lock the prop when sailing. It knackers the cone drive. They aren't cheap to replace. Guess how I know....

 

[Ammonite]

Interesting. I have a Bruntons Autoprop and a VP 120SD and have been advised to switch off the engine while in ahead as the gearbox still rotates if you select astern after switching off the engine. This is because the Autoprop tends to the reverse position and the cone clutch doesn't engage properly without the engine running so it knackers it prematurely. Guess how I know....
You can test this by removing the cap on the top of the gearbox and will see it turning despite being in reverse. I'm not sure if this applies to other saildrive models but it definitely applies in my case...and the expired 120SE I had before.

 

[Porthandbuoy]

Careful with yanmar gearboxes if you got a shaft. There is a technical warning issued by them ....can't find it at first look.....regarding putting the engine into astern to lock the prop when sailing. It knackers the cone drive. They aren't cheap to replace. Guess how I know....

Your correct. Not all Yanmar gearboxes can be put into astern when sailing. I've checked, mine can, but with the minor inconvenience that it might not disengage the clutch when going back to neutral. As mentioned, just start the engine in astern then select neutral.

 

[capnsensible]

That's the one. Mind you I could change the gearbox in less than half an hour.....