How sailboats sail

[darmoose]

[quote="John Vigor"]Well, there. What did I tell you? I was right after all about locking your prop and the helicopter theory.

I am very gratified to have my theory confirmed by no less a personage than Byron Anderson, a sailor and nuclear physicist who is chairman of the physics department at Kent State University.

Buried in his wonderful dissertation on the physics of sailing is this equation:

R = (LÏ…)/(µ/Ï

[Neil Gordon]

Darrell,

The motorcycle braking post wasn't mine. Mine was where I suggested that props and their dynamics spinning or fixed are complicated creatures.

It's curious that the science seems to be on both sides of this. Why is that?

[tartansailor]

Darrell,

It's curious that the science seems to be on both sides of this. Why is that?

No Neil,
Science (laminar vs turbulent flow) is on your side, while intuition is on the other side.

Dick

[darmoose]

Darrell,

The motorcycle braking post wasn't mine. Mine was where I suggested that props and their dynamics spinning or fixed are complicated creatures.

It's curious that the science seems to be on both sides of this. Why is that?

Neil,

I am sorry if I besmurched you for something you didn't say, it is hard to keep track of all that flys around, and i'm too lazy to go back and check every detail, please excuse me. As for props being complicated creatures, let me give you one thing to think about. There is no force, or combination of forces of any kind acting on a freewheeling propeller (affecting its rate of rotation) that is not transferred to the shaft. Do you disagree with that statement?

Also,just want to let you know that it is 78 degrees and clear and sunny here today. Very sorry we didn't get to meet but I do understand.

On the subject at hand, it just seems to me that no amount of evidence or proof or logic seems to get through to you dedicated proplockers. To Dick, I say that there is far more in support of freewheeling than just simple intuition. I would challenge him or anyone to disagree in detail with, and explain why, my earlier posted examples of the boat being towed, or the example using the shaft and braking the speed of rotation and what that specifically shows and proves.

If I give you clear demonstrations and examples like those, and if they stand up, you simply cant deny what they mean.

Love to all

Darrell

[Neil Gordon]

>>There is no force, or combination of forces of any kind acting on a freewheeling propeller (affecting its rate of rotation) that is not transferred to the shaft.<<

I think I agree with that. But it's the forces that in the aggregate that act on the prop that makes this more complicated than it seems to the casual observer.

>>Also,just want to let you know that it is 78 degrees and clear and sunny here today.<<

It's snowing here. Perfect in preparation for two or three days of cross country skiing.

[darmoose]

>>There is no force, or combination of forces of any kind acting on a freewheeling propeller (affecting its rate of rotation) that is not transferred to the shaft.<<

I think I agree with that. But it's the forces that in the aggregate that act on the prop that makes this more complicated than it seems to the casual observer

Neil (ole buddy)

You're two sentences above are direct contradictions of each other. If you agree with my earlier statement regarding ALL of the forces affecting the propeller (in aggregate) being transferred to the shaft, then you must admit there are NO other forces to take into account, don't you see? The propellers rate of spin is a resultant of ALL the forces in play. It is just that simple.

Do any of you "proplockers" disagree with that

Darrell

[Neil Gordon]

If you agree with my earlier statement regarding ALL of the forces affecting the propeller (in aggregate) being transferred to the shaft, then you must admit there are NO other forces to take into account, don't you see? The propellers rate of spin is a resultant of ALL the forces in play. It is just that simple.

I think we can all agree that the prop and shaft are locked to each other. So forces on the prop transfer to the shaft (when sailing) and vice versa when motoring. We've disregarded the friction of the cutlass bearing, etc., of course... those forces are transferred to the hull.

My point is that while the force on the prop/shaft is measurable whether the prop is locked or free to spin, there's more at play here. What about the forces on the water that's flowing past the boat? Do you suggest that the water flow isn't diverted by either the spinning or locked prop? I suggest that the flow changes direction in either case and that's a force that acts on the water (vs. the prop) and so doesn't transfer to the shaft.

Has anyone considered prop walk and the like and a force? (Did I already mention that?) Spinning props don't act equally on both sides of the boat, as the "Steering in Reverse" threads point out. What's the cost of that inefficiency?

[darmoose]

If you agree with my earlier statement regarding ALL of the forces affecting the propeller (in aggregate) being transferred to the shaft, then you must admit there are NO other forces to take into account, don't you see? The propellers rate of spin is a resultant of ALL the forces in play. It is just that simple.

I think we can all agree that the prop and shaft are locked to each other. So forces on the prop transfer to the shaft (when sailing) and vice versa when motoring. We've disregarded the friction of the cutlass bearing, etc., of course... those forces are transferred to the hull.

My point is that while the force on the prop/shaft is measurable whether the prop is locked or free to spin, there's more at play here. What about the forces on the water that's flowing past the boat? Do you suggest that the water flow isn't diverted by either the spinning or locked prop? I suggest that the flow changes direction in either case and that's a force that acts on the water (vs. the prop) and so doesn't transfer to the shaft.

Has anyone considered prop walk and the like and a force? (Did I already mention that?) Spinning props don't act equally on both sides of the boat, as the "Steering in Reverse" threads point out. What's the cost of that inefficiency?

Neil,

Whatever the cost of efficiency is of any the factors you just mentioned (could be zilch), we can still use the prop shaft to prove the point.

If i say that that I am going to apply friction to the shaft while freewheeling and under sail...YOU WILL SAY THE BOAT SPEEDS UP (to which I disagree), so lets let that go for a moment.

Now, if I say that I am going to release some or all of the friction that I am applying to the shaft...YOU WILL SAY THAT THE BOAT SLOWS DOWN, which couldn't be more wrong because we just went through the excercise of me slowing the shaft by applying friction, which means that if I release the friction the propeller and shaft must speed up, and the only way the shaft CAN speed up is if the boat is moving through the water faster causing the water to flow past the propeller faster. There is no other possible conclusion.

How canyou see this differently?

Darrell

[Neil Gordon]

Now, if I say that I am going to release some or all of the friction that I am applying to the shaft...YOU WILL SAY THAT THE BOAT SLOWS DOWN, which couldn't be more wrong because we just went through the excercise of me slowing the shaft by applying friction, which means that if I release the friction the propeller and shaft must speed up, and the only way the shaft CAN speed up is if the boat is moving through the water faster causing the water to flow past the propeller faster. There is no other possible conclusion.

Take a pin wheel. Hold it so that it can't spin. Now release the pinwheel. It starts spinning, yes? Other than spinning, did the pin wheel overall speed up? Did the wind speed up?

Stand at the bottom of an escalator. Step on. You are now going faster. (And the escalator is going slower.) Why doesn't the escalator need to speed up in order for you to speed up?

[darmoose]

Now, if I say that I am going to release some or all of the friction that I am applying to the shaft...YOU WILL SAY THAT THE BOAT SLOWS DOWN, which couldn't be more wrong because we just went through the excercise of me slowing the shaft by applying friction, which means that if I release the friction the propeller and shaft must speed up, and the only way the shaft CAN speed up is if the boat is moving through the water faster causing the water to flow past the propeller faster. There is no other possible conclusion.

Take a pin wheel. Hold it so that it can't spin. Now release the pinwheel. It starts spinning, yes? Other than spinning, did the pin wheel overall speed up? Did the wind speed up?

Stand at the bottom of an escalator. Step on. You are now going faster. (And the escalator is going slower.) Why doesn't the escalator need to speed up in order for you to speed up?

Neil,

Are you trying to deny that when I release the friction on the shaft that the propeller will speed up? Are you trying to deny that when it does speed up it is because the water is flowing past the propeller faster as a result of the boat speeding up?

You simply connot support that view!

Darrell

[Neil Gordon]

>>Are you trying to deny that when I release the friction on the shaft that the propeller will speed up?<<

No. My pin wheel analogy confirms that.

>>Are you trying to deny that when it does speed up it is because the water is flowing past the propeller faster as a result of the boat speeding up?<<

Yes.

The prop spins because the water is already flowing past it. The prop will spin if (i) the boat speeds up, (ii) slows down or (iii) remains the same.

[darmoose]

>>Are you trying to deny that when I release the friction on the shaft that the propeller will speed up?<<

No. My pin wheel analogy confirms that.

>>Are you trying to deny that when it does speed up it is because the water is flowing past the propeller faster as a result of the boat speeding up?<<

Yes.

The prop spins because the water is already flowing past it. The prop will spin if (i) the boat speeds up, (ii) slows down or (iii) remains the same.

Neil,

My question was not that the prop spins, but rather that it SPINS FASTER when I release the friction. And of course it spins FASTER because we previously slowed it by applying the friction (we did not change the sails while doing all of this). So, while you incorrectly say the boat sped up when I applied the friction, the fact is that the boat slowed down, and then when I released the friction, the propeller sped back up which can ONLY be explained by the fact that the boat sped up causing the propeller to speed back up. Thus proving my position.

Rather than change the subject by imagining other analogies that may or may not be applicable, why don't we, in our quest for the truth, concentrate on what I have stated, and address where you think I am wrong and why, hummm?

Darrell

[Neil Gordon]

Darrell,

There's no dispute that the prop spins faster or slower depending on whether it's restricted from turning (so long as the boat's moving). To be extreme in my example...

If the prop is locked and the boat is going 6 knots and you release the prop... and releasing the prop slows the boat to 4 knots, the prop will be spinning.

If the prop is locked and the boat is going 6 knots and you release the prop... and releasing the prop propells the boat to 8 knots, the prop will be spinning.

Proving that the prop spins does not prove or even suggest either an increase of decrease in the speed of the boat.

[darmoose]

Darrell,

There's no dispute that the prop spins faster or slower depending on whether it's restricted from turning (so long as the boat's moving). To be extreme in my example...

If the prop is locked and the boat is going 6 knots and you release the prop... and releasing the prop slows the boat to 4 knots, the prop will be spinning.

If the prop is locked and the boat is going 6 knots and you release the prop... and releasing the prop propells the boat to 8 knots, the prop will be spinning.

Proving that the prop spins does not prove or even suggest either an increase of decrease in the speed of the boat.

Neil,

You are missing the whole point my friend. I dont know if you are deliberately being evasive, or you just dont see it, but let me try to explain.

WE are sailing along at say five knots, and we are FREEWHEELING. I slow the prop using friction to the shaft. You say the boat SPEEDS UP (wrong), but lets go on.

Now, with the shaft artificially SLOWED, (and presumably the boat has changed speeds, either slower or faster), I now release the friction to the shaft.

Do you think now that the shaft will return to its previously higher speed or not? Of course it will. Which means that the prop is turning FASTER now.

So, how would you explain that the prop is NOW turning FASTER? There is ONLY one explanation. The boat has sped up.

The point being, WHEN THE PROP IS RELEASED AND ALLOWED TO FREEWHEEL WITHOUT FRICTION THE BOAT SPEEDS UP.

You simply cannot believe that the boat speeds up when I slow the prop, and AGAIN when I release the prop. So you are wrong to think that slowing the prop speeds up the boat.

For you not to believe this, you have to believe that when I release the shaft from any friction, it either remains at the same speed or slows down (both of which are IMPOSSIBLE)

Now you tell me where you disagree with what I have said above.

Darrell

[Neil Gordon]

Darrell,

The boat goes from here to there. It's forward motion is measured in knots. The prop and shaft spin around. That speed is measured in RPM. Note that the boat's speed doesn't require the boat to have RPM and the prop's speed doesn't require forward motion. Having noted that, I conclude that the boat can go faster/slower and the prop can go faster/slower, each independently of the other.

I've often noted while tied in my spip that no matter how fast the prop turns, the boat's speed remains zero.