When sailing do you put.......

[Largslout]

your engine in gear, if so forward or reverse or leave in neutral? I ask as if I select forward or reverse then come to select neutral for engine start the box won't budge and I have to start in gear then all is normal. Anyone else had this problem? Yanmar 3YM20 shaft drive.

 

[Searush]

I leave it in neutral & disengage the clutch as well. I would rather the prop rotated slowly than was fixed.

 

[copterdoctor]

Over the years I've heard good arguments for every option so I just do what comes to mind, unless the sound of the shaft turning gets on my nerves.

 

[Danny Jo]

[ QUOTE ]
if I select forward or reverse then come to select neutral for engine start the box won't budge and I have to start in gear

[/ QUOTE ] I never had the problem before, but since changing to a Yanmar YM 30 and a Brunton autoprop, I've had the same problem. With one difference - putting the engine into gear doesn't always stop the prop. Whether it will continue to rotate in forward or reverse gear is unpredicatable, but I can always stop the prop by selecting the other gear. Like you, I cannot then get it out of gear without starting the engine.

I checked with the fitter at Dickies, and he says, "Not a problem, just start it in gear."

 

[Largslout]

Thanks, just start in gear was the same response I got!

 

[bobgoode]

Volvo state that the shaft should be locked by putting then engine into reverse when sailing in order to minise wear on gearbox and shaft seals. FWIW This has the effect of reducing speed through the water by about 0.2 kts.

 

[Danny Jo]

When I had a folding prop, there was an appreciable increase in speed (not measured, but my impression is just under half a knot) when I stopped it spinning (allowing it to fold).

With the Brunton, I cannot detect a difference in speed - presumably it feathers itself according to how fast the shaft rotates. But I stop it anyway, because I don't like things spinning unnecessarily.

 

[ChrisE]

If you have an Autoprop, as I do, then Bruntons say stop the engine in forward gear and leave it there. With our Beta and (?) gearbox have no probs engaging neutral to start although usually start in gear.

 

[Habebty]

I put the gear into reverse and the prop folds thus gaining about 0.6-0.7 knot.
/forums/images/graemlins/cool.gif I know this is a perrenial favourite, but if i had a fixed prop I would let it spin as the flow of water past the prop would be less turbulent as the blades would be following the path of least resistance and creating less turbulence and less drag.

The bearing surfaces I imagine would be well lubricated - cutless bearing by water, hull bearing by stern gland grease and gearbox by gear oil? /forums/images/graemlins/cool.gif

 

[Danny Jo]

[ QUOTE ]
if i had a fixed prop I would let it spin as the flow of water past the prop would be less turbulent as the blades would be following the path of least resistance and creating less turbulence and less drag.

[/ QUOTE ] Hmm. Definitely an area where empirical tests would be more convincing than this kind of conjecture.

But if we're into conjecture, think of a prop blade like a keel, or an aeroplane wing. I postulate that a non-rotating prop is effectively stalled, whereas a rotating one is not - it reduces the resistance it would otherwise cause by corkscrewing through the water, but to do this requires it to work at overcoming the friction of the cutlass bearings and gear box. This work requires energy. I guess that it might be possible to calculate whether that energy is more or less than the energy required to drag a stalled prop through the water, but it is much simpler to test it.

 

[mpopeye]

IN Gear always,
1, most gear boxes lubrication system is pumped from the input shaft, so aside from the general wear issue you could find excessive un lubricated wear.
2, Normally in the gear opposite to direction of travel as some gear boxes have a ratched mechanism, try it with an outboard(plug removed) in forward you can turn the prop with clicks from the ratchet.

 

[Robin2]

There is no conjecture involved. Why would the prop rotate if there was less resistance by remaining stationary? /forums/images/graemlins/smile.gif

 

[Lakesailor]

I suggested a test ages ago on a couple of these locked/unlocked threads.
The suggestion was either poo-pooed or ignored.
Why? A tow boat with a simple spring balance in the towing warp. keep a steady speed and observe the strain with prop unlocked, then pop it in gear and observe any change.
It's too easy, so perhaps those with strong opinions are unwilling to put them to the test.

On the point of gearbox lubrication. Motorcycles, cars and commercials use splash lubrication as the sole method. I haven't had a marine gearbox to bits, are they different?

 

[Danny Jo]

[ QUOTE ]
There is no conjecture involved. Why would the prop rotate if there was less resistance by remaining stationary?

[/ QUOTE ] For much the same reason that a model glider flies forwards, and thereby stays aloft.

I think there may be some confusion based on turbulent vs lamina flow. Yes, laminar flow provides less resistance in the direction of travel (which in the case of a prop is a corkscrew motion). But it also produces lift, as in a close hauled sail. The lift that a prop produces if forwards if it is under power (where its forward corkscrewing through the water is faster than the flow of water) and reverse if it is being turned by the flow of water (where its forward motion corkscrewing through the water is slower than the flow of water).

As for conjecture, watch an apple fall from a tree. "The apple fell from the tree" is observation. "That apple still on the tree will fall before the month is out" is conjecture.

 

[srp]

I was discussing this with my brother only yesterday, and we came up with the same solution, ie a simple test exactly as you describe.
My personal feeling is that if you let the prop rotate freely the drag will be lower. As for wear on the shaft, if I wanted to machine a groove in a stainless bar I wouldn't choose to use a piece of lubricated string to do it. The radial loads exerted by the stuffing gland and the cutless bearing on a freewheeling shaft, and therefore the wear, must surely be very low.
However, if someone has already done the simple test Lakey has proposed, then my personal feelings will obviously change /forums/images/graemlins/smile.gif

 

[Danny Jo]

Answers.com's view is that the reason this argument rolls on and on is that the difference, one way or the other, is so small - link . But they do quote Eric Hiscock, who wrote [ QUOTE ]
Experiments made by P. Newall Petticrow Ltd. have shown that a two- or three-bladed propeller offers less drag when it is locked than when it is free to spin, and that the drag of a spinning propeller is greatest at about 100 rpm.

[/ QUOTE ] In the case of folding or feathering props, you must stop the rotation if you want to take advantage of those features.

 

[Lakesailor]

"P. Newall Petticrow Ltd". Never heard of them!!

Nothing like proving it for yourself. /forums/images/graemlins/grin.gif

 

[Danny Jo]

[ QUOTE ]
Nothing like proving it for yourself.

[/ QUOTE ] Agreed. Stopping my previous folding prop made up to 0.4 knot difference. I cannot detect any difference with the Brunton Autoprop. The skippers of most of the other boats I've sailed in have generally fallen into one of two camps: go quicker with a stopped prop, or no appreciable difference.

 

[Danny Jo]

[ QUOTE ]
I think there may be some confusion based on turbulent vs lamina flow. Yes, laminar flow provides less resistance in the direction of travel (which in the case of a prop is a corkscrew motion). But it also produces lift, as in a close hauled sail. The lift that a prop produces if forwards if it is under power (where its forward corkscrewing through the water is faster than the flow of water) and reverse if it is being turned by the flow of water (where its forward motion corkscrewing through the water is slower than the flow of water).

[/ QUOTE ] Erm, perhaps I should have added that this is not so much conjecture as idle speculation. It is based on complete ignorance of the subject.

A glance at this extract from Cruising World, 1979, suggests that the argument has not been settled for a very simple reason: there is no single answer that is right for every combination of boat and prop. Shaft/gear box friction and boat speed are critical factors. If friction is low enough, you may be better off letting the prop spin.

 

[Nick_Pam]

Yanmar recommend "In Astern Gear" because of potential damage to the gearbox through rotation without sufficient oil circulation - at least the manual for my 4JH-4E says so.
They also say starting in gear is not an issue.

Nick