John7
New member
I have had a 1GM10 fitted and are unsure if I should sail it with the engine in neutral or reverse?
Sailing with a 1GM10
- Thread starter John7
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vyv_cox
Well-known member
If I stop my 3GM30 in forward, the prop continues to rotate. I put it in reverse to stop it. However, if I stop the engine in reverse it continues to rotate. In this case putting it in forward stops it. There have been many threads on these forums on this subject over the years. Consensus of opinion seems to be that the prop should not rotate.
Robin2
New member
I'm not sure what is the right answer. Clearly the resistance to the boat is lower if the prop turns - otherwise it would not turn!
ccscott49
Active member
Apparently thats not quite true, don't ask me why, but they say a turning prop offers more resistance, I can't see it either!!
claymore
Well-known member
There was a fairly long debate back in the winter on this. I used to put mine in reverse to lock the prop as I was told that the spinning effect would add wear to the bearings and and stern tube lubrication system. A friend who races a lot even marks his propshaft so that the folded prop can be aligned vertically as this reduces drag.
John S
The fairytale ends here
John S
The fairytale ends here
seaesta
New member
To understand why there is less drag with the prop rotating you have to have in mind the concepts of WORK and ENERGY rather than RESISTANCE.
If you (very briefly) put your hand over the outlet of a hair dryer then you will find that the fan suddenly goes faster rather than slower. This is because the fan is doing less work (even though you may think there would be more "resistance" )
A prop is a very "hydrodynamic" object designed to drive energy into water to get "thrust" it is not really surprising that when energy is going into the prop from the water (to rotate it) then it is efficient at creating reverse thrust or drag.
This same situation occurs on aeroplane propellors which is why on multi engined planes are always "feathered" when they are not in use.
Here endeth the first lesson !!
Martin of Seaesta of Whitby
If you (very briefly) put your hand over the outlet of a hair dryer then you will find that the fan suddenly goes faster rather than slower. This is because the fan is doing less work (even though you may think there would be more "resistance" )
A prop is a very "hydrodynamic" object designed to drive energy into water to get "thrust" it is not really surprising that when energy is going into the prop from the water (to rotate it) then it is efficient at creating reverse thrust or drag.
This same situation occurs on aeroplane propellors which is why on multi engined planes are always "feathered" when they are not in use.
Here endeth the first lesson !!
Martin of Seaesta of Whitby
ccscott49
Active member
Dont you mean less drag with the prop not rotating???
seaesta
New member
Ooops - you are right I did mean LESS drag with the prop not rotating.
Robin2
New member
Well, I don't agree. There is a difference between a feathered propellor and a non-feathered one. Feathered propellors obviously have less drag.
But if you have a non-feathering prop then it seems sensible to me that the drag will be lower if it is turning rather than stationary - and the more freely it can turn the better.
Whether turning is good for the gearbox is a different question to which I do not have an opinion - yet!
But if you have a non-feathering prop then it seems sensible to me that the drag will be lower if it is turning rather than stationary - and the more freely it can turn the better.
Whether turning is good for the gearbox is a different question to which I do not have an opinion - yet!
chippie
New member
Try yanmarhelp.com
jfkal
Active member
I tend to agree. Why don't we all run some tests and see whether it really matters anyway. I am sure that there is a difference but it might be too small. And yes the gear box will suffer same wear and tear.
vyv_cox
Well-known member
I have been reading and posting on these boards virtually since day 1 and this topic has probably been aired more frequently than any other, except possibly flag ettiquette. In the past we have been given very strong scientific arguments that a fixed prop offers less drag than a spinning one. Racing boats that have fixed props always lock them to reduce drag. I don't think the drag we are talking about is very significant: in the days when I had a non-feathering prop I used to try to measure the difference but was never successful. But I see no sense in letting something rotate that might wear bearings or gearbox, might entangle floating ropes, nets and plastic bags and makes an annoying noise.
claymore
Well-known member
The quiet voice of reason - thats succinctly put, my friend the racer reckons that it makes some percentage of a knot difference - I talked to someone about titanium fittings on a racing dinghy once and whilst he was in favour of spending a bit of money to reduce weight - he was fully aware that it only takes a duff tack to counter all the weight saving strategies you've employed.
I always pop into reverse once we've switched off the engine and apart frm the feeling that I'm reducing wear - the locked prop and shaft add to that blissful silence from the mechanical department!
regards
John S
Sans Signature
I always pop into reverse once we've switched off the engine and apart frm the feeling that I'm reducing wear - the locked prop and shaft add to that blissful silence from the mechanical department!
regards
John S
Sans Signature