Saildrive propellor

[GRP]

Hi,
I was out sailing on my brother's boat today for the first time - a Bavaria 46. It has a saildrive whereas I am more accustomed to having a normal propshaft. When the boat was under sail with the engine off there was a noise coming from below which sounded initially like a pump running but which turned out to be the prop windmilling. Is this normal? It's very noisy!

Graham

 

[Boomshanka]

If it's a folding prop, then stick it in reverse when under sail

 

[GRP]

It doesn't fold apparently. Having said that I will ask my brother to check again whether it may be!!

 

[Ken_Irby]

Saildrives wear far less (in their selector forks primarily) if they are allowed to freewheel when sailing. I know that this doesn't do much for the hydrodynamics and hence the drag but that's how it is and Volvo won't have any other arguement.
Chas (on Kentrina's id)

 

[GRP]

I didn't go down to look at this (I really do hate going below when it is choppy!) but I am told that the windmilling prop was causing some sort of vibration in the engine - described as the engine being driven by the prop when switched off and moving under sail. Does this make any sense? It sort of takes away the peaceful element of being under sail!

 

[Tranona]

No, the noise is the prop turning. Volvo recommend you leave it in Neutral when sailing if you have a standard fixed blade prop. There are, however conflicting views about this advice. The "official" reason is that locking it puts strain on the gears. Others claim the real reason is that it results in the gearbox locking in reverse and you can't get it in neutral before starting the engine. Therefore you have to start the engine in reverse gear which can cause the locking bolt that holds the prop on to start to undo. Running in reverse then results in the bolt coming loose, the cone coming undone and the prop falling off! With a folding or feathering prop there is no load when the engine is not running so the gearbox does not lock up in the same way.

My Bavaria has a different locking system which uses both the normal bolt and a grub screw at 90 degrees into the shaft, which is claimed to prevent the cone coming undone. This system is fitted to many charter boats in Greece and seems effective.

 

[GRP]

Fair enough! I've never really noticed anything like it on the boats I have owned, none of which have had saildrives. It was a surprisingly insistent and constant noise!

Graham

 

[WindermereColvic]

Im not too familiar with sail drives, but how is starting in reverse any different from running in reverse, which surly cant make the prop fall off? Not a criticism, just curious, Matt

 

[charles_reed]

Most propellers will windmill under way, the usual method of prevention is to leave the gearbox in gear. Usually reverse, but sometimes forward gear.

Dependent on boat speed and underwater configuration this can reduce or increase drag.

Invariably this continuity, anathema to the majority with discontinuous minds, leads to long and contentious threads on the subject of locking propellers, usually descending into opprobrium.

 

[charles_reed]

<<The "official" reason is that locking it puts strain on the gears. Others claim the real reason is that it results in the gearbox locking in reverse and you can't get it in neutral before starting the engine. Therefore you have to start the engine in reverse gear which can cause the locking bolt that holds the prop on to start to undo. Running in reverse then results in the bolt coming loose, the cone coming undone and the prop falling off! With a folding or feathering prop there is no load when the engine is not running so the gearbox does not lock up in the same way.>>

Spot who's trying to cover their "deliberate" design mistake. Other gearbox manufacturers don't need this caveat. It is arguable that allowing the windmilling increases wear on the moving parts.

Incidentally, whilst folding props usually don't windmill, in my experience many of the feathering ones will unless there is some form of shaft brake.

 

[charles_reed]

[ QUOTE ]
It doesn't fold apparently. Having said that I will ask my brother to check again whether it may be!!

[/ QUOTE ]

Very unlikely, the original comment was apocryphal.

The reason you've never experienced windmilling before is probably:-
1. The prop is sufficiently hidden behind a deadwood to park ie it's not in an unobstructed water flow and or
2. You've never gone fast enough and or
3. Your conventional stuffing box acts sufficiently as a brake on the shaft to prevent windmilling starting.

Saildrives are easily the most efficient means of fitting auxiliary power to a sailboat, not only optimising drive but dramatically improving handling manners under power.

 

[Tranona]

The prop is on a straight spline rather than a taper as on a "conventional" shaft. It has a rubber bush inside to take shock loadings. The prop is held on by a cone nut which is locked in place by a bolt which goes through the centre of the cone nut into a thread in the end of the shaft. The end of the bolt has loctite on it.

Provided the bolt holds all is OK. However, both the cone and the bolt have the same handed threads and if the bolt comes loose the whole lot can come undone in reverse and as there is no taper the prop slides of. Those who have experienced this suggest that it is starting the engine in gear that puts a shock load on the threads and can start the unwinding.

I must stress that this is not from personal experience, but the explanation was given by the engineer who serviced my Saildrive this winter, I queried why the cone nut was different from a standard one because it had a separate locking grub screw going into the nut sideways and locking onto the main thread on the shaft. Explanation (which seems logical to me as others such as Kiwi use the same method) as above.

If you do put the gear into reverse when sailing to get rid of the noise, you will find that it is almost impossible to get it back into neutral using the lever, and the only way is to turn the engine over with the starter. You can imagine the loads this puts on the transmission.

 

[Sailfree]

[ QUOTE ]

Incidentally, whilst folding props usually don't windmill, in my experience many of the feathering ones will unless there is some form of shaft brake.

[/ QUOTE ]

Not quite right. On my Yanmar instructions were do not put in astern to lock prop and when we did it jammed in astern so had to start that way and quickly select neutral.

I could not stand the constant whinning from the gearbox when sailing so fitted feathering prop. Blades feather immediatly when sailing and engine off as no longer any gearbox whine but instructions for feathering prop state engage astern to ensure blade feather and we do that with no problem in engaging neutral when restarting engine.

If blades dont feather suggest lack of servicing /grease which should be done annually.

 

[GRP]

[ QUOTE ]
Saildrives are easily the most efficient means of fitting auxiliary power to a sailboat, not only optimising drive but dramatically improving handling manners under power.

[/ QUOTE ]

Actually, that was quite noticeable. The boat handles very well under power. It seemed that there was no prop walk to speak of at all and that you could reliably spin the boat almost in its own length with full rudder and a solid blast of forward power. I think if it were mine though I would be looking for a way to stop that interminable whine!

Thanks all!

 

[Tranona]

You will find that many Saildrive owners fit folding or feathering props, which although a lot of money are not that expensive as a proportion of new boat cost. As others have said these eliminate the whine when sailing as well as reducing drag. However, a new form of whining may be heard (from the owner) when the effect on life of anodes is seen - particularly on boats moored in marinas and connected to shorepower. There is no such thing as a free lunch!

 

[DaveS]

Unless you fit a featherer with plastic blades. The Kiwi is also a fair bit cheaper than the others, too. So getting closer to a free lunch! /forums/images/graemlins/smile.gif

 

[joss_stick]

Have been putting our saildrive into reverse for the past 6 years. Never have a problem putting into neutral before starting engine. Never lost a prop. Nothing appears to have worn out. Never had any problems whatsoever. The spinning when it is left in neutral is a pain inthe @rse.