Gaer box when sailing

[Harriett]

I hope someone can help me out please.

I have a part share in a Sadler 32, one of our partners is a know all Motor Mechanic. Now I have read in various articles just lately that it is wise to "lock" the propshaft in the astern position whilst sailing as the gearbox will not be sufficiently lubricated when the shaft is turning and the engine is not running.

Can someone answer me a couple of questions please so that I can shut him up.
1 What effect does a locked prop have on drag (standard 2 blade) compared to a prop that is freewheeling (so to speak)
2 Why locked in reverse - can't I lock the prop in forward ?

Thanks in advance
Ken Pugh

 

[romany123]

Ive always locked my prop in reverse to stop the noise when sleeping in the navigators berth (its in the ally next to the engine) thats the only reason I do it.Bet you get loads of replies.


Dave

 

[billskip]

you should get lots of replies..but please tell us "what your know all partner has said...

Bill
www.aegeansailing.co.uk

www.macsyachting.com

 

[Guest]

I'm looking forward to the replies on this one!
The manufacturers destruction book for my boat says put it in reverse(lack of cooling water circulation) and the engine handbook says leave to free wheel !
I put it in reverse to stop noise.
There was an article in one of the recent mags giving details of drag in various situations,sorry i cant remember which mag or when.
Good luck with your partner.

 

[Trevor_swfyc]

Re: Gear box when sailing

I don't think it makes any difference if its in forward or reverse as long as it stops the prop.
As for drag the difference between the energy required to turn the prop and a stationary prop drag would be very small and hardly a factor.
The only reason I stop mine by putting it in reverse (custom & practice) is the drone/whirling noise and wear, but there again if you leave it turning its not the end of the world or is it?.
Take it your partner in the boat, does not frequent this site!
More harm is done motoring with the sails flogging how often do we see this.
All the best.
Trevor

 

[Harriett]

Re: Gear box when sailing

Trevor

No - he'll be reading GearBox and Propshaft Monthly !!

 

[deejames]

My two-pennorth

There are two issues :
1. Possible damage. I think this depends on the make and type of gearbox - for example, is it mechanical or hydraulic ?? Probably mechanical in a Sadler 32, but wise to check.
2. Speed of boat and whether she goes quicker or slower with the prop turning or locked ? I seem to remember a very long thread on this one some time ago, but with a 2-blade prop, much seemed to depend on whether you could lock the propshaft so the prop was vertical with respect to the rudder and skeg (and therefore not creating much additional drag).


deejames

 

[Guest]

Gearboxes

Discovered this when fitting a new prop to a boat, when it is in gear (forward or reverse) the shaft will turn in one direction and not the other. I think you need to put it in reverse to stop the prop and shaft rotating, as it will still be free to rotate in forwards.

 

[colin_jones]

I have a Borg-Warner Velvet Drive 1.2:1, which used to have a shaft brake, which was a real pain.

Then I read the handbook and talked to the comapny engineers. Both said "Just let it freewheel and self lubricate".

Since then it has done about 5000+ hours and was tested perfect in December.

Other gearboxes might well have other reccommendations.

 

[Chris_Stannard]

The prop should be locked to save wear particularly on the cutlass bearing, but also it saves wear on the stern gland and the gearbox bearings. I understand that there is little difference between leaving ithe prop free to rotate and locking it from a drag point of view, in both cases you are effectively towing a small bucket.

Chris Stannard

 

[Trevor_swfyc]

Re: Gear box when sailing

Harriett,

Now thats what I call sad ! when does it come out ?

See Ya

Trevor

 

[ParaHandy]

Re: Gear box when sailing

Not 100% agree with you there. If a Yanmar box, the spline of the mainshaft will be pushing the male cone against the female reverse cone (I think Vile-vos work the same?) which will lock it quite hard, particularly if cones in good nick. If you wanted to start the engine in a hurry, you have to start her in gear (v. difficult to pull her into neutral) which I have serious objections to as, apart from wear and tear on battery, you are likely to be going forwards and mad panic wrenching throttle/gear lever. True, get more wear on cutlass etc but this should be minimal as forces are zilch and should not be a serious consideration.

If cones a bit shot, then easier gear disengagement and no problems except for cones.

 

[claymore]

Hmm
I always lock it in reverse because it stops the whole drive train rotating therefore reduces wear. I'm sure my engine man said that the rotation carried on into the engine wia the gearbox and got all the pistons, crank etc turning as well - I might be wrong there but anyway its definately about reducing wear on stern tube/drive train bearings and gearbox.
A folding prop will obviously cut down on drag, particularly on the Sadler which is capable of good performance. Fat-bottomed Claymores don't get involved in stuff like that - although I'm sure they should!
Finally you cannot lock it in forward because the motion of the boat going forward through the water would try to spin the prop which would have the effect of constantly trying to bump start the engine. (I think!)
regards
JohnS

<P ID="edit"><FONT SIZE=-1>Edited by claymore on Wed Mar 13 17:19:20 2002 (server time).</FONT></P>

 

[ccscott49]

On gearboxes with an oil pump, whether it's to lubricate the bearings or hold the clutches/brake bands in contact, the oil pump is normally on the input shft from the engine, for obviuos reasoins. When the box is freewheeling, as when sailing, the box is not being lubricated by the pump. Putting it in gear, with a mechanical box, stops the gears/bearings turning, thus no wear. with a hydraulic box, (borg warner velvet) this is not the case, as the oil pressure engages the clutches and lubricates the box. I have velvet drives and would need shaft brakes I don't have them, so my boxes rotate, I've had no problems with them and neither have previous owners, in 30 years. The shaft lubrication problem isn;'t there, the cutlass bearings in the p bracket will lubricate themselves, if you have engine water fed inner cutlasses, you may get excessive wear in these, but the speed at which the shaft turns when sailing isn't too high. A temporary shaft brake, when deep sea, ie. when you wont need your engine in a hurry, is to wrap aroound several turns of rope, against the shaft rotation and make the end fast, this will stop or at least sloww the shaft down. I hope this explanation helps.
Colin.

 

[Avocet]

I've often wondered about this. I only have a baby 12 horse inboard driving through the smallest Hurth box on the market and I'm pretty certain it doesn't have an oil pump in it. That said, I could understand the need for forced lubrication in a bigger box but would be extremely surprised if, when freewheeling and transmitting no significant torque, there would be any need for the forced lubrication. The splash lubrication from all the geartrain turning inside the box should be plenty. When you tow a broken-down manual car, nobody worries about lubricating the gearbox and final drive do they?

Automatics are, of course, different but not (I believe) because of what happens to the gearbox. I think it's because of what happens to the torque converter and I'm pretty certain most boats won't have one of these. Certainly, I always leave my prop turning It keeps everything lubricated and I think (very subjectively) that it makes the boat go a tiny bit faster.

If you want to stio the prop turning, a loat of gearboxes let the prop "freewheel" in "Ahead" - that's why it ought to be locked in "astern".

 

[ccscott49]

If a bearing needs pressure lubrication, it needs pressure lubrication or they would not fit an oil pump. Some of the gearboxes we are talking about use oil pressure to keep the clutches in engagement, the levers sometimes just move the cones into place, then the oil pressure holds then there. Manual boxes, such as your little hurth, do not have an oil pump (I think), because they don't need them. Also some bigger trucks, had to have there propshafts taken off before towing, so as to not turn the gearbox, when being towed over long distances. I don't thinbk it will matter to most boxes, if they are left to turn for a short time, a day or three at a time, but over an ocean ppassage with a pump lubricated gearbox, significant wear could be induced, especially to the thrust bearings. The gears in most even small boxes are also epicyclic, they do not splash lubricate very well. Car/truck gearboxesw are different, most have normal gear trains, which spalsh lubricate quite well.