B323 Prop Rotation Under Sail

[Astrid]

Might have been a poor translation from the original Swedish.

[Astrid]

Managed it once with a Nicolson 55 surfing down some fair sized waves, sailing along the English South Coast. Frightened the living daylights out of us as we shot down the wave at 11 knots only for the engine to fire up in forward with a wide open throttle setting and suddenly we really did accelerate.

That must have been exciting alright.

[FSMike]

[QUOTE=Pete7;78546--- we shot down the wave at 11 knots only for the engine to fire up in forward with a wide open throttle setting and suddenly we really did accelerate.

Pete[/QUOTE]

I guess that's why it's recommended that the engine be left in reverse, not forward.

[Victory49]

What about putting an alternator on that shaft and generating some power? Id think that would be better drag wise than locking it in place?
I'm thinking of doing this as a winter project. I've known people who've done it. Maybe someone on here has.

[roverhi]

First, what catastrophic damage??? The engine can be turned in reverse just as in forward without damage. Kind of unnerving as the engine will make strange noises but that's just air. Suppose you might be able to cause problems with valve timing with a chain driven cam If the chain tensioner didn't work but you'd have to get the engine turning over pretty fast to do it. Back in the good old days of handcranking petrol engines with spark retard mechanisms, sometimes they would actually start and run in reverse, though poorly.

Second, doubt very highly that you could ever get a diesel to turn over from water force on the prop with the transmission in reverse. Used to hand crank my MD2b by popping the compression releases. Even at 4 knots or more with the transmission in forward, the engine wouldn't turn over by itself with the compression released. Did make it easier to crank, however.

[Maine Sail]

Originally Posted by DJBrookster

Engine is a Yanmar 3ym20. Not sure about the gearbox, is this better left in neutral or put in reverse?

Here's what Yanmar says:

Yanmar MSA Advisory / Gear In Neutral While Sailing (LINK)

[svlamorocha]

Originally Posted by roverhi

First, what catastrophic damage??? The engine can be turned in reverse just as in forward without damage. Kind of unnerving as the engine will make strange noises but that's just air.

It will be just air unless the engine sucks water through the wet exhaust. I am unaware of a mechanism to prevent the cylinders from flooding if the engine in my 323 turns backwards while the muffler system has the usual water in it or the exhaust outlet is submerged as when surfing waves, but I would appreciate enlightening if I missed something.

Originally Posted by roverhi

Second, doubt very highly that you could ever get a diesel to turn over from water force on the prop with the transmission in reverse.

I think the concern from Sweden and others is about boats surfing waves at over 10 knots. If my fluid mechanics still works (not sure about that!),the forces at 12 knots (say in Pete7's experience posted above) would be 9 times bigger than at 4 knots as in your experience.

[roverhi]

I called the Yanmar number listed in the link and got a voicemail that was absolutely worthless. It will only allow you to forward your call to a specific extension number, not an operator. Didn't have the time to mess with it to see if a real body could be found by gaming an extension number.

I'm one of those people who want to know the why/why not of a directive not just the command. The message sates for saildrives as well as shaft drives but wonder if it effects both the same way. I seem to remember there are some transmissions that can be damaged by being allowed to rotate but think those were hydraulic and had something to do with reversing the flow of fluid in the transmission. Logical reasoning would seem that locking the prop via the transmission in reverse would stop the wear and tear on the bearings in the transmission.

Still find it hard to believe that a prop in the slipstream of a boat would generate the force to overcome the 20-1 or higher compression ratio of a diesel, especially in reverse. It's probably a mute point in my full keel boat as one of the blades is shielded in the dead wood won't provide much, if any, rotating force.

[Ziggy]

Originally Posted by roverhi

I called the Yanmar number listed in the link and got a voicemail that was absolutely worthless. It will only allow you to forward your call to a specific extension number, not an operator. Didn't have the time to mess with it to see if a real body could be found by gaming an extension number.

Why don't you contact them by email (cs_support@yanmar.com) and let us know what you find out?

[charliehows]

i've been wondering about this myself - my issue is i notice maybe some small increase in water incursion through sterngland and wonder if locking in reverse (no possible chance of turning the engine -yanmar 2qm20, cant even turn the handcrank) would reduce water incursion...???