Prop shaft running without engine on

[scevrog]

Very strange thing happened this weekend.

The engine was off and in neutral. We were sailing in rough conditions.
I heard what sounded like "part" the motor running. "Part" in the sense that some part of the motor was running. No exhaust though.
I went down below and saw the prop shaft running very quickly. The only way I was able to get it to stop was to put the engine in reverse and leave it there.

Closer to the marina I needed to fire up the engine. Again in neutral the shaft was running. I started it anyways and it ran no problem.

Back at the slip, when I put it in neutral again the shaft was no longer spinning.

This has never happened before. I've been having some starter problems lately, but I doubt thaty is causing this.

What in the world could this be?

Thanks.

 

[kappykaplan]

From your description, I'm guessing you don't have a feathering or folding prop. If that's the case, it's normal for the prop shaft to be spinning without the engine running.

 

[Snotter]

If you do have a fixed-bladed prop, you need to consult your owners manual to see if you need to lock your prop shaft when sailing. Most marine transmissions aren't designed to provide lubrication when the shaft is free-wheeling. Many of these transmissions need to be put in reverse when the engine is off when sailing to lock the shaft. However, some need to be put in forward; still other transmissions should be allowed to free-wheel. Not following the recommendations of the transmission manufacturer could cause premature wear of the transmission. Transmissions are very expensive to repair.

 

[Rob2435]

spinning most probably caused by weather/current, it happens on my boat when I hit about 3.5knots while sailing, the shaft will start spinning. I've heard suggestions on both sides, leave it spin and put it in gear to stop the spin. My transmission is immersed in fluid so I don't think it matters either way. But I am sure someone will have a different opinion...

 

[Benny17441]

Prop spin induced by boat motion is hardly a mystery. If it is a Yanmar the manufacturer recommends to let ii spin.

 

[Stu Jackson]

It's a Catalina, most likely not a Yanmanr.

What engine?

M25 series?

http://www.c34.org/wiki/index.php?title=The_Right_Transmission_Gear_for_Sailing

 

[kloudie1]

IT should be noted that in these little "forward/reverse clutches" like the Kanzaki (Yanmar) and small Hurth (Universal) gearboxes, the gears do not turn when the engine is not running. When sailing in neutral, the output shaft spins inside a stationary gear. It typically spins on needle bearings inside the output gears which are stationary. The bearings are lubricated by the lowest rollers dipping into the oil level in the transmission case as the bearings roll around the shaft. There is essentially no load on those needle bearings. The big output shaft bearings are typically angular contact rollers and are lubricated the same way; by the lower rollers dipping into the oil level as the bearing rolls around. This carries the oil up and through the whole bearing. Again, very light load from the dragging spinning prop compared to the load those bearings see when the prop is pushing the boat through those bearings while powering .. There are no pumps in those little gearboxes. It is critical that the oil level be correct. The transmission will be more tolerant of a low oil level when the engine is running in gear because then the gears are also dipping into the oil and throwing the oil everywhere inside the case. The gears are larger diameter than the bearings so they will fling oil from a much lower level in the box and lubricate everything. That may be why folks used to recommend not sailing in neutral.. with a low level of oil, you could potentially damage the needles much more than if running the engine with a low oil level in the box..

 

[scevrog]

Thanks for all the replies. It's an m25 universal. So, it seems like neutral or reverse is the way to go.
I think I will stick with reverse and accept a little bit of drag. When I checked the fluid a couple of weeks back it was totally dry. Who knows what damage has been done through the years. The PO had zero coolant, trans fluid and old fuel filters. It surprisingly works pretty well.

 

[WayneH]

Check your owners manual. And then check your transmission. My boat is a 1980 model with a Westerbeke engine and a two bladed fixed prop. The owners manual has instructions for FOUR different transmissions. Two will not turn under sail. One will but should be put in reverse to stop it. And one transmission is ok to free wheel. Which is the one on my boat.

I liked to have wore out a sailing glove trying to stop the shaft from spinning so we could put the transmission in gear. Couldn't get the prop to stop spinning in forward or reverse so I read the manual. "Instructions? We don't need any sticking instructions!"