Sail driving damaging clutch?

[Annabel]

Hello All, We are waiting patiently in NZ to get a way to return to our Hanse 455 in Greece. In the meantime, keeping positive, I need some advice on motor sailing. A yachting friend made a comment one day about motor sailing being bad for the clutch, as the propellor goes around and around at a fixed pace, but the sails might propel the boat at a faster speed putting pressure on the fixed rotation of the prop, i.e. clutch. Is there any truth in this?
Thank you

[Montanan]

Originally Posted by Annabel

Hello All, We are waiting patiently in NZ to get a way to return to our Hanse 455 in Greece. In the meantime, keeping positive, I need some advice on motor sailing. A yachting friend made a comment one day about motor sailing being bad for the clutch, as the propellor goes around and around at a fixed pace, but the sails might propel the boat at a faster speed putting pressure on the fixed rotation of the prop, i.e. clutch. Is there any truth in this?
Thank you

Seemingly that could be a potential if the boat was sailing at very high speeds and the propeller was being spun at low speed. The torque of the water pushing on the propeller would need to be pretty dramatic to cause the clutch to slip and seemingly would instead be inclined to cause the engine to reeve to higher rpms because instead of the engine pushing against a load imposed by a propeller that was thrusting the boat, the engine itself would be being added in accelerating in rpm by the combination of the external force of the water flow trying to accelerate the propeller to a faster speed and the engines dynamic torque due to combustion / compression.

Under ordinary conditions, motor sailing is common practice and the engine is only used to aid in accelerating the boat to a desired modestly higher speed or to push against a strong current. In both such instances the engine is underload and the propeller is pushing the boat. For the clutch to slip it would require the propeller to be rotating slowly or stopped and placed in gear and then driven harshly by oncoming flow of water and you would feel the propeller braking the boat, with turbulence as the water was backing against the propeller; sort of like having the vessel put into reverse while moving forward.

I suppose this might happen if you were to surf down a steep, tall wave and gain speed rapidly but that would be intermittent and one can see from a tachometer and hear engines change in their speed and loading when one is in rough water due to cyclic loading. And one would be desiring to slow the boat in such steep and likely trailing seas, not accelerate by motoring and likely the wind would also be up so again the sails would be reefed so as to not cause the boat to travel excessively fast.

Clutches engage with a lot of friction, I just can't see wherein in conditions where one is going to motor sail that there would be slippage.

I just don't see how motor sailing would derive clutch damage.

They are called Sail Drives, if they were just used when not sailing their name would seemingly be called Non-Sail Drives.

Does anyone else see where or whence there could be adverse loading occur during motor sailing?

[Haddock1]

I would guess even at tick over the prop will be pushing positive against boat speed under sail. Don't think there is any truth in this but I am no expert.

[Annabel]

Thank you Montanan for your detailed response to my motor sailing query and also Haddock1. I think this is good logic, just what I needed. Annabel