free spinning shaft makes whirring noise

[Uncle Bob]

Originally Posted by jmschmidt

Maybe you read the wrong test. A locked prop does not create more drag than a spinning one, not in a boat or in an airplane. A free-wheeling or wind-milling propeller will create drag equal to a solid disc the diameter of the prop. A locked fixed-blade prop will create drag slightly less that the surface area of the exposed blades. A folding or feathering prop on a boat will create the least drag.

If you really want to create drag, rig some kind of shaft driven generator, every KW of energy it produces is extracted directly from the power produced by your sails. There ain't no free lunch in physics.

Multi-engine propeller driven airplanes all have full feather propellers and many have auto-feathering systems which activate when an engine fails.

I assume that you are able to link to at least one test performed by a reputable source that supports your positions, both that a locked prop on a boat does not create more drag than a spinning one and that props in water perform in an identical manner to props in air??

Here is an example of an earlier thread on the subject.

"Maine Sail did his own tests and also links test results from Michigan Wheel and MIT. All point in the same direction. I'm convinced even if others aren't."

These results quite clearly indicate that a freewheeling prop creates less drag in water.

[transmitterdan]

Originally Posted by jmschmidt

Maybe you read the wrong test. A locked prop does not create more drag than a spinning one, not in a boat or in an airplane. A free-wheeling or wind-milling propeller will create drag equal to a solid disc the diameter of the prop. A locked fixed-blade prop will create drag slightly less that the surface area of the exposed blades. A folding or feathering prop on a boat will create the least drag.

Water is not air. A propeller in water free spinning does not act like a solid disk.

One cannot extrapolate behavior of an air foil propeller to a three bladed water propeller. The only thing they have in common is the name “propeller”. The way they work is completely different. An airplane propeller is shaped like an aircraft wing but a boat propeller is not. There are several other differences. Many studies prove that a locked boat propeller slows the boat more than free spinning.

[FPNC]

QUOTE=Capn Jimbo;2783781] Unfortunately like the BMW cyclist in Zen and the Art of Motorcycle maintenance, fixing a problem with an aluminum shim from a beer can just was simply untihinkable by a certain number of owners.


I own an old BMW motorcycle. Reason being... I can fix it with shims from a beer can.

[jmschmidt]

Sure can Uncle Bob but that subject has been beat to death on this forum so I'm not going to look it up again so why don't you find evidence that supports the opposite.

[piloto]

Originally Posted by Capn Jimbo

This is without question, the most sensible and useful solution for the time being. Seriously. Unfortunately like the BMW cyclist in Zen and the Art of Motorcycle maintenance, fixing a problem with an aluminum shim from a beer can just was simply untihinkable by a certain number of owners.

I await the OP's solution...

one caveat, don't forget to take it off before engine start....if you do, call it a flying vise grip breaking stuff projectile.

[Uncle Bob]

Originally Posted by jmschmidt

Sure can Uncle Bob but that subject has been beat to death on this forum so I'm not going to look it up again so why don't you find evidence that supports the opposite.

Could have guessed that would be the response!

[Wotname]

Originally Posted by jmschmidt

Sure can Uncle Bob but that subject has been beat to death on this forum so I'm not going to look it up again so why don't you find evidence that supports the opposite.

The principle reason you won't provide any link to Uncle Bob's request is that you can't - because it doesn't exist.

Yes, you can find stuff on the internet that supports your view but it is not scientifically valid. Put another way - in your responses in past threads concerning prop drag, you have provided "alternative facts" and when presented with actual (real / proper) facts you have just ignored them rather to present a factual counter argument to support your viewpoint.

It is a binary question and as such there can be only one correct answer; A valid analysis of the physics leads to a conclusive answer and this is confirmed by empirical testing. You seem unwilling to accept the answer and that is OK as you are free to believe whatever you want regardless of the truth of the matter.

However please don't state your view on the matter as a fact and don't try to convert others to accept the invalid answer unless you are willing to argue for it's validity.

For other readers of this post, the facts are simple - a free spinning fixed pitch boat prop produces less drag than when the same prop is locked (i.e. prevented physically from rotating freely). If any of you wish to provide a valid argument that counters my claim, I will be happy to hear them and respond. If any what further confirmation of my claim, please ask.

[Pete7]

Originally Posted by jmschmidt

Sure can Uncle Bob but that subject has been beat to death on this forum so I'm not going to look it up again so why don't you find evidence that supports the opposite.

Here you go:


https://strathprints.strath.ac.uk/56...ints005670.pdf

[Uncle Bob]

Originally Posted by Pete7

Here you go:


https://strathprints.strath.ac.uk/56...ints005670.pdf

Thanks for that. Once past all the hypothesizing, projecting and assuming, table 4 towards the end of the doc indicates quite clearly that the drag of a locked prop is projected to be approximately double that of a freewheeling one, although that lovely term predicted is used.
I much prefer the testing done by Mainsail and Yachting monthly, actual video of the equipment, process and results presented in an unbiased logical manner.

[OldMan]

I lock the props, more chance of a crab pot line slipping off a stationary prop, where as a spinning prop more likely to hold onto the line.

[jmschmidt]

And I could have guessed that would be yours. When I dig it out I will post it.

[Jim Cate]

I think I could dig out some docs that support the Flat Earth Society's doctrines, too.

Conclusive, eh?

Jim

[Wotname]

Originally Posted by Jim Cate

I think I could dig out some docs that support the Flat Earth Society's doctrines, too.

Conclusive, eh?

Jim

At least the early believers had some empirical evidence to support the proposition and none for the alternative propositions. Their position was understandable. The current believers - not so much!

But yeah with the ultra modern movement of alternative facts, truth ain't truth etc, I guess we are in for a resurgence of ignorance (conclusive ignorance perhaps) - sad

[GILow]

Back on how to lock the prop...

I use a piece of cord. About 3mm thick. A loop in the end, I snag one of the flange bolts with it and the other end is tied to a strong point (needs to be quite strong, the forces are surprising).

Advantage over the vice grips:

1. Fails “safely”. If you forget to remove it, it just snaps with the engine in gear.

2. CRITICAL for PSS style seals, it does not damage the shaft face which would chew out the O ring when you fit the seal.

3. Cheaper than leaving a metal tool down in the bilge.

When I have the loop on the flange I tie a small piece of the same cord through the ignition key to remind me to remove the cord before I start the engine. Advantage of this system is that it introduces no delay if you have to start and engage the engine in a hurry. Since the cord will snap instantly and I am not forced to change anything to start the engine. I’ve read lots of systems, like the vice grip, that introduce potentially dangerous delays to being able to use the engine.

[Jim Cate]

Back on how to lock the prop...

So, Matt, how do you stop the shaft in the first place? If sailing fast when you shut down the engine, the torque developed by the fixed props we've had in the past was surprisingly large.

Jim