Prop shaft

[Sunset]

I have a 2gm 13 hp Yanmar in my Islander 28, when under sail the shaft is turning. This makes since to me in neutral but when I put it in gear it keeps on turning, that doesn't make since. Why does the transmission not stop the shaft? I don't know what kind of transmission it is. Is this normal?
Drag is not important to me I just don't understand this and will it hurt anything?

[CharlieJ]

I had a 2 gm 20 in my trimaran. Yanmar told me to put it in reverse when sailing. That stopped the spin

[Sunset]

Thanks Charlie, I'll give it a try this weekend.

[Norman]

I have had modest experience with inboard engines and transmissions, all on other peoples boats, so the following is generic.

There are 3 types of transmission, and you do not have the positive engagement, clutch less type.

Manual shifted transmissions  engage forward or reverse with leverage and arm strength, and if the prop continues to turn in gear, the related clutch is slipping, and drive in that gear is not available.  Sailing with that clutch engaged will continue to wear the clutch, and should be avoided.  The clutch needs to be adjusted to get firm engagement.  Hopefully this is not your type of transmission.

Hydraulic shifted transmissions use hydraulic pressure from a pump on the input shaft to engage the selected gear, and shifting the selector without the engine running does not move anything.  In this case, putting the selector in either gear leaves the actual transmission in neutral.  With this type of transmission, a disc with a notch must be installed on the output shaft, with a plunger to lock the shaft, if rotation is not acceptable.  This is found on high dollar race boats, and must be interlocked with the shift selector to prevent damage from attempting to engage a gear with the shaft locked.

I hope this generic information helps solve the problem, or at least makes the symptoms more logical.

Norman

[CharlieJ]

one other point, on that boat if you hit about 10--12 knots boat speed, with the trans in forward, it would bump start the engine!!! Surprised us big time at first :)