prop' shaft turning-under sail

[Guest]

prop\' shaft turning-under sail

Is there a simple way to prevent a propellor shaft from turning when under way under sail? [Without putting the engine in gear !]

 

[Guest]

No*

*

 

[Guest]

Re: prop\' shaft turning-under sail

A few years back, we asked Borg Warner about this and they said "Just let it turn. It will not harm our gear box which was engineered with this in mind." Tis company had a booklet which tells about this.

 

[Guest]

Re: prop\' shaft turning-under sail

A few years back, we asked Borg Warner about this and they said "Just let it turn. It will not harm our gear box which was engineered with this in mind." This company had a booklet which tells about this.

 

[Guest]

Re: prop\' shaft turning-under sail

For once, I am inclined to disagree with you,Colin.Not for the reason of wear,or damage,but for the retarding effect of a rotating prop. The unpowered Autogiro/Gyrocopter analogy seems to provide the best explanation.An Autogiro with a fixed blade will plummet to earth: one with a freely rotating blade will glide to earth.Clearly,the rotating blade produces an upwards pressure. I would go for preventing the prop turning every time and I see no problem in placing the engine in gear.(Also easier on the ears!)

 

[Guest]

Re: prop\' shaft turning-under sail

Nothing there that I would disagree with. I used to have a shaft brake on the system. It was a real pain. We are not aware of noise - but our bluff hull is not exactly silent. If I wanted to sail faster I would possibly put the beast in gear, but have no experience of comparisons.

 

[Guest]

Re: prop\' shaft turning-under sail

In fact Stewart your argument is in favour of letting the prop rotate! A rotor produces lift by a drop in pressure on the top of the blade, thus lift, ergo, a spinning prop should produce lift (forward thrust) as well!

But I put mine in gear 'cos I cant stand the whining !

 

[Guest]

Re: prop\' shaft turning-under sail

John, grateful to you for taking time to respond. However,I disagree with your reasoning. Consider the Autogiro(no power) with a fixed blade - it will plummet to ground, i.e. no resistance from air.On the other hand,an unpowered Autogiro with rotating blade will float to ground, i.e.an upwards resistance is created by the rotation.Translate this phenomenon to the situation in water and the fixed prop will create no resistance while the rotating prop will slow the vehicle down.

 

[Guest]

Re: prop\' shaft turning-under sail

your argument is fundamentally flawed.

The autogiro flies for the same reason an aircraft does, LIFT, and it has 4 rotating wings providing that lift! stop the wings and you loose the lift and CRASH ! however, there is a slight parachute effect from air resistance (DRAG) on the blades as it falls when you stop them, I would guess that you hit the ground all of 1mph slower.

A marine prop will cause drag whether locked or rotating, but theoretically, the rotating prop should have less drag. However, the differance is not worth bothering about. So you just pays yer money and takes yer pick,

oh btw an auto giro cannot descend vertically without crashing, it needs the forward componant to rotate the blades...which in turn provides lift, and it doesnt "float" anywhere! Without main engine thrust it still has to maintain forward velocity.