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Old 22-01-2016, 15:37   #31
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Re: transmission nuetral or locked while sailing

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Originally Posted by jmschmidt View Post
Wotname: I read all the BS the last time this subject came up. A free-wheeling prop extracts energy for the forward motion of the boat by induced drag. That's what makes the prop turn. It also creates parasite drag from the exposed blade area. The combination of the two is greater that just the drag of the stopped blade. Why do you think larger propellor driven airplaines are equipped with full-feathering, including auto-feathering propeller systems?
Leaving aside the BS reference, thank you for providing some theroy to support your point of view. What you suggest is true up to the point that the combination of the induced drag plus parasitisic drag is greater than drag of a stopped prop. That simply isn't true and can be shown both in practice and therory. If what you suggest was true, it would take no effort (energy) to stop and hold stopped a freewheeling prop. If you remain unconvinced after thinking more about, let us know and I will attempt to explain again the vectors involved.

I only talking about a fixed pitched boat prop. The analogy to various types of airplane props and heli rotors doesn't hold true due to the quite difference in design and concepts. I know why and how airplane props feather etc but as that isn't the issue here, I won't go down that rabbit hole.
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Old 22-01-2016, 15:42   #32
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Re: transmission nuetral or locked while sailing

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Originally Posted by Liam Wald View Post
Been doing more searching (as suggested by Stu, thank you) on this and other sites and still REALLY confused and pretty uncertain on this issue!!!
Is this just a CYA on the part of Yanmar because of damage caused by people trying to shift from reverse to neutral while still moving and forcing against the load?
I would rather come to a stop before shifting to neutral than have the prop spinning for hours and days on end.
Is there evidence that this method will cause damage?
Thanks, Liam.

CYA? Evidence?

Look, a service bulletin, from ANY vendor, is usually there to prevent issues. Think of it as a mini-recall or a modification to the installation & maintenance manual for any particular piece of equipment.

I sure don't think they do it just for fun.

There are a number of service bulletins from the maker of my engine. In our C34 Critical Upgrades topic, we posted this:

ENGINE SERVICE BULLETINS

YOU'D BE REALLY DUMB TO NOT CHECK THESE

AND THEN ACTUALLY DO THEM


And here's a good reason WHY: Raw water pump failure and SERVICE BULLETINS (M35B) Sorry to hear about Dave's misfortune.

I'm not sure at all why you'd want to even question service bulletins. Aren't they there to help?

The consensus for the K transmissions on all the same boating forums you just searched on is the one mentioned right here in these replies: neutral and if ya dunna like da noise, fit a shaft brake.

If that was the transmission I had on my boat, that's what I'd do.

And many of the skippers on our boats, with Universals & Hurth transmissions, NOT K transmissions, decided they want to feather their props in a certain position, so they leave them in neutral and fit shaft brakes. OUR Hurth transmissions allow reverse OR neutral, but never forward.

I read the bulletins & the blinkin' manuals that come with the transmissions and have posted them on our website.
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Old 22-01-2016, 15:49   #33
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Re: transmission nuetral or locked while sailing

Simple to visualize. If the water flow onto the prop is allowed to rotate the prop, then the resulting forces act laterally more so than longitudinal, slowing the boat less. Spilling the forces, if you will.

If flow is onto a locked prop, then the forces act longitudinally more so than laterally, slowing the boat more. Stacking up the forces, if you will.
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Old 22-01-2016, 15:49   #34
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Re: transmission nuetral or locked while sailing

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Originally Posted by Liam Wald View Post
I believe that is also why helicopters drop more slowly if the engine stops and the blades are still turning (controlled crash or hard landing) than if the engine stops and the blades also stop turning, in which case the helicopter drops like a rock.
Gawd.... I'm going to regret doing this.. but you have auto-rotation all wrong.
The reason that rotor-craft spin their rotor on a unpowered decent is to use the momentum of the spinning rotor to maintain the rotation after the collective has been pulled up just before touch down.

Very common practice that all helo pilots practice in-case of power failure.
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Old 22-01-2016, 15:49   #35
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Re: transmission nuetral or locked while sailing

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Originally Posted by Stu Jackson View Post
Thanks, Liam.

CYA? Evidence?

Look, a service bulletin, from ANY vendor, is usually there to prevent issues. Think of it as a mini-recall or a modification to the installation & maintenance manual for any particular piece of equipment.

I sure don't think they do it just for fun.

There are a number of service bulletins from the maker of my engine. In our C34 Critical Upgrades topic, we posted this:

ENGINE SERVICE BULLETINS

YOU'D BE REALLY DUMB TO NOT CHECK THESE

AND THEN ACTUALLY DO THEM


And here's a good reason WHY: Raw water pump failure and SERVICE BULLETINS (M35B) Sorry to hear about Dave's misfortune.

I'm not sure at all why you'd want to even question service bulletins. Aren't they there to help?

The consensus for the K transmissions on all the same boating forums you just searched on is the one mentioned right here in these replies: neutral and if ya dunna like da noise, fit a shaft brake.

If that was the transmission I had on my boat, that's what I'd do.

And many of the skippers on our boats, with Universals & Hurth transmissions, NOT K transmissions, decided they want to feather their props in a certain position, so they leave them in neutral and fit shaft brakes. OUR Hurth transmissions allow reverse OR neutral, but never forward.

I read the bulletins & the blinkin' manuals that come with the transmissions and have posted them on our website.
All good points. Thanks.
Glad that I read all this and did some research.
No more reverse for me with my K tranny.
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Old 22-01-2016, 15:54   #36
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Re: Transmission nuetral or locked while sailing

Only armchair sailors would argue about this. Anybody who has been sailing with fixed blade prop has tried both locking and freewheeling and knows the difference.. It is very very obvious.

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Old 22-01-2016, 15:54   #37
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Re: transmission nuetral or locked while sailing

Quote:
Originally Posted by Liam Wald View Post
All good points. Thanks.
Glad that I read all this and did some research.
No more reverse for me with my K tranny.
Liam, on one of the thousands of these topics, there was a very creative skipper who fitted a remote shaft brake. I forget the details, but it was something as simple as a bicycle inner tube so that if he ever forgot it wouldn't damage the transmission. I'd do a search on "remote shaft brake" if you're interested in finding out more about it. I thought it was quite clever.
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Old 22-01-2016, 16:00   #38
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Re: Transmission nuetral or locked while sailing

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Originally Posted by Littlechay View Post
Only armchair sailors would argue about this. Anybody who has been sailing with fixed blade prop has tried both locking and freewheeling and knows the difference.. It is very very obvious.

Now that's what I call definitive.
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Old 22-01-2016, 16:58   #39
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Re: Transmission nuetral or locked while sailing

I'm just a simple country sailor, not a physicist. I don't know from cosines and quadratic equations.

As an expaireemint, while guzzling grain belt beer, I locked my transmission in reverse (Atomic 4 engine on a Pearson Triton - 2 bladed 12X9 prop) while under sail in smooth water. I noted my GPS speed. I disengaged the transmission and let the prop spin. I again noted my GPS speed. After that I took a bucket with an opening the same diameter as the propellor (I noted the "expert" equating a spinning prop to a disk of the same diameter in terms of the amount of drag exerted on the boat) - tied it to a rope and dropped it overboard after tying it off to a stern cleat. This was done with the prop free wheeling while under sail. I noted that speed on my GPS.

I noted very little difference in speed between the stopped prop and the free wheeling prop - 0.1 to 0.2 mph loss when I locked the prop even after I confirmed that the prop was not hiding behind the deadwood. When I tossed the bucket overboard the boat lost 1.5 mph immediately.

Then I tossed L'il Abner overboard and the boat smelled like roses again.

But, I am just a simple country sailor.
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Old 22-01-2016, 19:14   #40
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Re: transmission nuetral or locked while sailing

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Originally Posted by missourisailor View Post
Gawd.... I'm going to regret doing this.. but you have auto-rotation all wrong.
The reason that rotor-craft spin their rotor on a unpowered decent is to use the momentum of the spinning rotor to maintain the rotation after the collective has been pulled up just before touch down.

Very common practice that all helo pilots practice in-case of power failure.
Yep, you probably will regret it.

In essence you have pretty well nailed it so I will just make a minor correction if I might.

Try this "The reason that rotor-craft spin their rotor on a unpowered decent is to use the momentum (energy contained in) of the spinning rotor to create lift after the collective has been pulled up just before touch down."

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Old 22-01-2016, 19:18   #41
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Re: Transmission nuetral or locked while sailing

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Originally Posted by crazyoldboatguy View Post
I'm just a simple country sailor, not a physicist. I don't know from cosines and quadratic equations.

As an expaireemint, while guzzling grain belt beer, I locked my transmission in reverse (Atomic 4 engine on a Pearson Triton - 2 bladed 12X9 prop) while under sail in smooth water. I noted my GPS speed. I disengaged the transmission and let the prop spin. I again noted my GPS speed. After that I took a bucket with an opening the same diameter as the propellor (I noted the "expert" equating a spinning prop to a disk of the same diameter in terms of the amount of drag exerted on the boat) - tied it to a rope and dropped it overboard after tying it off to a stern cleat. This was done with the prop free wheeling while under sail. I noted that speed on my GPS.

I noted very little difference in speed between the stopped prop and the free wheeling prop - 0.1 to 0.2 mph loss when I locked the prop even after I confirmed that the prop was not hiding behind the deadwood. When I tossed the bucket overboard the boat lost 1.5 mph immediately.

Then I tossed L'il Abner overboard and the boat smelled like roses again.

But, I am just a simple country sailor.
But smart enough to work it out and to empirically prove your point
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Old 22-01-2016, 19:24   #42
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Re: transmission nuetral or locked while sailing

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Originally Posted by four winds View Post
Simple to visualize. If the water flow onto the prop is allowed to rotate the prop, then the resulting forces act laterally more so than longitudinal, slowing the boat less. Spilling the forces, if you will.

If flow is onto a locked prop, then the forces act longitudinally more so than laterally, slowing the boat more. Stacking up the forces, if you will.
Correct conclusion and reasonable assumption for why however I would explain slightly differently!

The flow of water on the locked prop creates torque which must be overcome by the locking mechanism (if it didn't, prop would continue to rotate ).
The torque is absorbed by trying to rotate the hull in opposite direction etc.
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Old 22-01-2016, 19:30   #43
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Re: transmission nuetral or locked while sailing

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Yep, you probably will regret it.

In essence you have pretty well nailed it so I will just make a minor correction if I might.

Try this "The reason that rotor-craft spin their rotor on a unpowered decent is to use the momentum (energy contained in) of the spinning rotor to create lift after the collective has been pulled up just before touch down."

Yeah... I don't know if I like your wording any better.
But hey, at least we are reading from the same page.
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Old 22-01-2016, 19:44   #44
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Re: transmission nuetral or locked while sailing

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The torque is absorbed by trying to rotate the hull in opposite direction etc.
Although this is 100% true, I don't think that it is why the boat is slowing down.

It's kinda like saying that by sticking your hand in the water, you are slowing your boat down because it is trying to TURN in that direction.

The main reason the boat is slowing is because you have two or three big flat surfaces at about 90 degrees to the flow causing drag and thus lots of turbulence.

Where as with a spinning prop, the apparent angle of attack is less thus less apparent surface area, thus less turbulence.

Of course we are only talking about a prop in water not air.
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Old 23-01-2016, 01:42   #45
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Re: transmission nuetral or locked while sailing

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Originally Posted by missourisailor View Post
Although this is 100% true, I don't think that it is why the boat is slowing down.

It's kinda like saying that by sticking your hand in the water, you are slowing your boat down because it is trying to TURN in that direction.

The main reason the boat is slowing is because you have two or three big flat surfaces at about 90 degrees to the flow causing drag and thus lots of turbulence.

Where as with a spinning prop, the apparent angle of attack is less thus less apparent surface area, thus less turbulence.

Of course we are only talking about a prop in water not air.
We are still on the same page .

And yes, the locked prop is creating much turbulence and drag. I was using the torque aspects as this is where we notice the force required to keep the prop stopped.
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