Prop spin under sail

[djousset]

I've noticed what I think is new behavior with my prop. When under sail the shaft is rotating...pretty fast. I first noticed it because the engine was bouncing around. I never sail with the gear in reverse but that is the only thing that stops it, forward and neutral it spins. Is this an engine shut down sequence thing or might I have an issue?

[mlydon]

Standard procedure to lock it by putting it in reverse, if you have a manual (non-hydraulic) transmission.

Do so - spinning with engine off is bad for trannies - no lube oil to the bearings

Matt

[chris95040]

The expected behavior, and the proper thing to do while under sail (whether put it in fwd, rev, neutral) is a function of your transmission. Read your transmission's user manual.

(Someone already beat me to it and offered a suggestion on what to do, despite not knowing what transmission you have! Trust your user manual, not them. )

[djousset]

Yanmar 2gm20f, Kanzaki tran. Recommendation is neutral under sail. Prop didn't used to spin, now it does, and fast. That's the mystery. Is there a preferred engine shut down sequence?

[Rumrace]

It’s why sailboats have those special lame two bladed props. Truth is folding props are pretty bulky folded and the real saving over a sucks for sure two blade isn’t much. Over a 3 blade it’s huge and worth the investment. They tend to be high maintenance, no surprise.

[Rumrace]

Same as mine except the 40. Says neutral in my manual also. I think they spinning is an early sign of clutch going south.

[pcmm]

Originally Posted by djousset

Yanmar 2gm20f, Kanzaki tran. Recommendation is neutral under sail. Prop didn't used to spin, now it does, and fast. That's the mystery. Is there a preferred engine shut down sequence?

Is your prop a fixed blade? Folding? Feathering?

If Feathering (or folding) the procedure is to stop the engine and then put the transmission in reverse for a few seconds to force the blades to feather, then return to neutral on a Kanzaki.

IF you've done that and its still spinning, the prop isn't feathering and needs some maintenance. Likely just growth preventing the blades from feathering easily.

If you have a Fixed prop, this is completely normal behaviour, you just didn't notice it before.

Your "engine bouncing around" implies that your engine mounts may be worn out. There shouldn't be enough torque coming through the prop and shaft to really throw the engine around.

[Rumrace]

“Return to neutral to shut down engine” hell yes. A dozen reasons to be in neutral. We do have lawn mower engines hooked up to really weak transmissions as compared to power boat drives. The clutch and cooling seem the weak spot.
My boat is young but the previous owner put an aggressive 3 blade on which is hard on the clutch sail drive or shaft. I swapped out to a folding prop before it hit the water.
There is a neutral safety switch which kills ignition to a gas marine engine during shifts. Makes life easy on the cone or dog clutches. No such luxury in diesel. Those cute old Atomic Gas motors in the C&C have these switches.
The other way we abuse transmissions is running the motor as a generator. A sail drive doesn’t get proper cooling I’m not sure about shaft drives as they differ. Sounds like you are doing everything correctly.
Certainly in neutral it should take a good deal of power to spin it. In reverse impossible but effects shaft joints linkages. Neither a motor or a transmission should be used as a brake. .

[pcmm]

Originally Posted by Rumrace

Same as mine except the 40. Says neutral in my manual also. I think they spinning is an early sign of clutch going south.

Spinning just means the trans is out of gear.

[pcmm]

Originally Posted by Rumrace

Those cute old Atomic Gas motors in the C&C have these switches.
.

Actually those cute little Atomics did not have nuetral switches on them at all. The planetary gearbox built into the engine was pretty bulletproof, well except the reverse brake band. Those were a pain in the back side!

[Calif.Ted]

I've found that with fresh packing it doesn't spin as much and starts at a higher STW, as the packing wears in it starts spinning sooner. Last boat had a Perkins and it was locked in reverse so took me a while to adjust to the sound of the spinning prop. It should not cause the engine to bounce as you describe it in neutral.

[DEAN2140]

I have a two-blade folding prop on a Yanmar saildrive. The manual says if you keep the transmission in gear while sailing you will void the warranty. I shut the engine while in forward gear and then shift to neutral. This seems to work.

[chris mac]

Originally Posted by djousset

Yanmar 2gm20f, Kanzaki tran. Recommendation is neutral under sail. Prop didn't used to spin, now it does, and fast. That's the mystery. Is there a preferred engine shut down sequence?

We have the 3gm30f with kanzaki tranny. Manual says neutral when sailing.
Ours start to spin around 3 knots of boat speed and always have. We even just had our engines and trannies rebuilt, today was the first test sail. They still spin at around 3 knots of boat speed.
My guess is yours are supposed to as well. If it's faster or more noticable now, I would question why. Packing gland easing up? Is there noticable water intake in the bilge?
Or maybe engine mounts failing, causing the vibration to be more noticeable?
Good luck with the mystery

[qwert]

You could always put a brake on the propshaft.

No stress on the gearbox, bearings, etc and if you mark the shaft you can apply the brake so the 2 blade prop is vertical. Saves the complexity and cost of a folder for much the same resistance

[Knotical]

We have a Westerbeke and the manual suggests to lock it in reverse gear while sailing.