Transmission nuetral or locked while sailing

[Liam Wald]

Having read this I am now confused...again.
I tried searching with no real luck.
I have a Yanmar 3gm30f with a 3-blade fixed prop.
I seem to remember somewhere along the way reading that tranny should be in reverse when sailing to stop the prop.
I have been doing this with no problem except that I need to slow the boat to almost stopped to shift back into neutral for starting the engine. (not a huge problem)
Now I am wondering if I should be letting it freewheel for the health of the transmission but can't find the answer by searching.
I would really appreciate some advice on this.

[a64pilot]

Best answer is find out which transmission you have and get that manual and look at it.
I have I believe an old KB-20 and I believe it's OK to lock it in reverse, but not fwd.
I now have an Autoprop so it's a mute point for me, but I would look in the manual as there is just so much misinformation and apparently different answers.
My boat manual I am sure says lock it in reverse when sailing, but IP didn't build the tranny?

[Stu Jackson]

Originally Posted by Liam Wald

I have a Yanmar 3gm30f with a 3-blade fixed prop.
I seem to remember somewhere along the way reading that tranny should be in reverse when sailing to stop the prop.

Yanmars most but not always have K transmissions. A search on "transmission position" will find numerous posts that say Yanmar recently (past one or two years) have issued a service bulletin on this question.

I don't have a Yanmar, but IIRC, they say neutral.

Others with this transmission (NOT the OP's) can chime in.

[jmschmidt]

Locked or in reverse gear. A free-wheeling prop creates drag equal to a solid disk the diameter of the prop. Same in airplanes.

[Wotname]

@ jmschmidt - I give you the benefit of the doubt that you aren't trolling .

Try reading this (and the complete thread) and if you still think the same, come back here and put up a serious argument to defend your viewpoint.

http://www.cruisersforum.com/forums/...ml#post1866273

[Wotname]

Originally Posted by Stu Jackson

Yanmars most but not always have K transmissions. A search on "transmission position" will find numerous posts that say Yanmar recently (past one or two years) have issued a service bulletin on this question.

I don't have a Yanmar, but IIRC, they say neutral.

Others with this transmission (NOT the OP's) can chime in.

I have a K transmission

And you are 100% correct!
Yanmar's service bulletin insists these transmissions should be neutral to avoid damage to the transmission.

[jmschmidt]

Wotname: I read all the BS the last time this subject came up. A free-wheeling prop extracts energy for the forward motion of the boat by induced drag. That's what makes the prop turn. It also creates parasite drag from the exposed blade area. The combination of the two is greater that just the drag of the stopped blade. Why do you think larger propellor driven airplaines are equipped with full-feathering, including auto-feathering propeller systems?

[Liam Wald]

Originally Posted by jmschmidt

Wotname: I read all the BS the last time this subject came up. A free-wheeling prop extracts energy for the forward motion of the boat by induced drag. That's what makes the prop turn. It also creates parasite drag from the exposed blade area. The combination of the two is greater that just the drag of the stopped blade. Why do you think larger propellor driven airplaines are equipped with full-feathering, including auto-feathering propeller systems?

I believe that is also why helicopters drop more slowly if the engine stops and the blades are still turning (controlled crash or hard landing) than if the engine stops and the blades also stop turning, in which case the helicopter drops like a rock.

[Liam Wald]

Been doing more searching (as suggested by Stu, thank you) on this and other sites and still REALLY confused and pretty uncertain on this issue!!!
Is this just a CYA on the part of Yanmar because of damage caused by people trying to shift from reverse to neutral while still moving and forcing against the load?
I would rather come to a stop before shifting to neutral than have the prop spinning for hours and days on end.
Is there evidence that this method will cause damage?

[StuM]

Originally Posted by Stu Jackson

Thanks for helping.

Yours, soup nazi

No soup for you! Next!

[StuM]

Originally Posted by jmschmidt

Locked or in reverse gear. A free-wheeling prop creates drag equal to a solid disk the diameter of the prop. Same in airplanes.

Not that one again. Go and read a few of the previous threads. There's plenty of evidence de-bunking this old canard.

A boat prop in water is nothing like an aircraft prop in air. Locking increases drag both theoretically and in practical tests.

[Pete7]

Originally Posted by jmschmidt

Locked or in reverse gear. A free-wheeling prop creates drag equal to a solid disk the diameter of the prop. Same in airplanes.

I beg to differ, a yacht will sail faster with the gearbox in neutral. Reference for view point:

http://www.plaisance-pratique.com/IM...rag-Thesis.pdf

[reed1v]

Ablin diesel(Swedish), manual transmission mfg unknown. We broke gear shear pins once in a while when we shifted the moving prop into gear, and/or out of gear when we were moving along in windy conditions with the motor shut down.
Most transmissions really do not like changing gears without a real clutch.
Normally you bring the engine and transmission to idle before shifting, but obviously that is not possible if the shaft is already turning or you want to shift to allow it to turn and you are doing 7 knots. Another reason to get a folding prop like a Maxi.

[reed1v]

Practical Sailor also found a spinning prop allows the boat to move faster than a locked prop from their empirical research. Same with Office of Naval Research tank tests. So for small and big boats, let it turn.

[Emmalina]

I have a borg werner velvet drive and a shaft lock ! Don't know if it actually makes a difference but its bloody noisy with a spinning shaft ! So I lock it....