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-   -   In gear or out when sailing? (https://www.cruisersforum.com/forums/f114/in-gear-or-out-when-sailing-9923.html)

viking69 31-08-2007 14:54

In gear or out when sailing?
 
ok we were having a chat the other day around the pub if you leave your engine in gear when sailing so as to stop the prop turning. the argument was that if left out of gear and the prop is turning it makes the gears in the box run on the back faces of the gears causing damage. of course some said this was true and some said it was rubbish. Which way do you all sail? In gear or out of gear?

mike d. 31-08-2007 15:26

sailing in gear or out
 
it depends on the transmision you have, some are designed for it others aren't.
also if it is hydaulic as a rule unless you have a brake set up you cannot stop the shaft from turning

JusDreaming 31-08-2007 16:01

we have a hurth transmission and it recomends putting it in reverse to lock it from spinning

Pblais 31-08-2007 17:08

It's all about the transmission cooling. Read the transmission docs. based om the advanced studies done by the Navy they say lock the prop. The difference if there is no transmission issues is pointless to argue. You can't go that fast one way or another so long as your transmission is properly cooled. All my boats say lock in reverse with the Mickey Ears up (like you could really check).

charlies 31-08-2007 18:30

Having owned one boat and chartering boats for the past three years, I have made it a practice to always sail with the transmission in reverse. I figure if it doesn't need to be in reverse, it certainly want hurt (that,s an engineer's viewpoint anyway ;) ) We owned an Oday 28 at one time and if I forgot to put the transmission in reverse, I would always know because I could actually hear and feel the transmission turning.

Sandero 31-08-2007 18:33

MD17D with a direct drive - In reverse for sailing.

jef
sv shiva

Terra Nova 31-08-2007 20:48

Quote:

Originally Posted by viking69 (Post 98747)
ok we were having a chat the other day around the pub if you leave your engine in gear when sailing so as to stop the prop turning. the argument was that if left out of gear and the prop is turning it makes the gears in the box run on the back faces of the gears causing damage. of course some said this was true and some said it was rubbish. Which way do you all sail? In gear or out of gear?

Yo Viking,

in reverse is most common, as it is possible to damage some transmissions. A spinning propeller is presumed to create significantly more drag.

best, andy

seafox 31-08-2007 21:44

Our Volvo manual says in reverse. Saildrive.

Tropic Cat 01-09-2007 02:54

I think if you do a search on here for this issue, you'll find this has been dicussed time and time again. It's a question for which there is no correct answer.

Transmissions which have an independent oil supply may be sailed in neutral. Those which are lubricated from the engine sump, must be locked, usually in reverse. The difference in speed is seldom more than 1/2 knot with one 2 bladed prop in the water.

On my boat it's a a 1 knot difference with two, 2 bladed props.

viking69 01-09-2007 13:03

ok thanks all. it would appear that most run with it locked in gear.

billangiep 01-09-2007 16:13

This is from Yanmarhelp.com......



The gear lever should never be put into ahead to stop the shaft turning. Yanmar recommend that the gear lever is left in neutral as this will not damage the gearbox. If left in astern the clutch cone may jam and will only release once the engine is started. This means you have to start the engine in astern gear. Unfortunately some boats (particually American boats - U.S. Coastguard reg) are fitted with "start in gear protection" this prevents the engine from starting if it is in gear, this would leave you unable to start the engine.
Ideally a shaft brake should be used to prevent the shaft from turning

Tropic Cat 01-09-2007 17:35

Right... I have twin Yanmars and my manuals say the same thing.

Shaft breaks would save a little wear and tear on the cutlass bearing, but I enjoy sailing fast so my transmissions are both in neutral while sailing. By the way, if you do have Yanmars, it's also the safest per the manual.

bruadair 01-09-2007 18:39

Rick,

you said you enjoy sailing fast so you leave your transmissions in neutral. If you do an internet search you'll actually find many sources to state that a fixed prop has less drag than a rotating prop. Surprising, but through all my internet research this seems to be the concensus.

Our Yanmar 3QM30F has a Kanzaki KH18 gear box which has a bath type cooling system. Yanmar says it's okay to let it free spin but we use a shaft lock made by Shaftloc, works pretty good.

senormechanico 01-09-2007 21:29

I'm a big fan of folding or feathering props. Had a 3 blade maxprop on my last boat and my current boat has a Gori 2 blade. It's ok but I'm looking...

Steve B.

Alan Wheeler 02-09-2007 01:48

Quote:

If you do an internet search you'll actually find many sources to state that a fixed prop has less drag than a rotating prop. Surprising, but through all my internet research this seems to be the concensus
This is because a Propellor is a form of a "Rotary Wing". Each blade is a wing and once water flows over it's surface correctly, it creates "lift" just like any wing. If a prop is allowed to free wheel in the water, then it will act in the same way a Helicopter uses Auto rotate to stop it from going into the ground when the engine fails. The drag on the boat is created as the speed of propellor rotation increases. As it increases, more resistance to the rotation is applied by friction from the gearbox. So the propellor becomes drag to the boat, just like the helicopter blade. It is less noticable at slow speeds and greatly increases as speed increases.
If the propellor is locked, then water flows over the blade in the wrong way and the blade "stalls". This has a reverse affect. At low speed, the drag of the stalled propellor is large. At a higher speed, the drag is less noticable to the increased force from the wind.

I won't go into the issue of in/out of gear. As Rick505 said, there has been a lot discussed int he past and a search will reveal much information.

Tropic Cat 02-09-2007 03:46

Freewheeling the prop is best
 
bruadair I find that simply to not be the case. My experience tallys almost exactly with the MIT research paper on this subject, which was written because of all the false information out there on this subject. I guess it's easier for me to see this since I have twice the prop resisitance of mono guys. I'd like to be clear that I'm not trying to convince anyone, and just letting you know what I've discovered. Like Alan said, we've all been there and done that already but it might be best if you read about this for yourself. I would recommend that you do a search for an online copy of:

"Comparison of Ten Sailboat Propellers" by Beth Lurie and Todd Taylor of the MIT Marine Hydrodynamics Laboratory. The charts and graphs are all there.

Freewheeling the prop produces the least amount of drag and results in higher boat speeds, of this there is no argument. The real issue is whether your engine/ tranny setup can do this without damage. In the end we have to comply with our engine manuals.

Stranded Mariner 15-09-2007 23:05

Quote:

Originally Posted by Alan Wheeler (Post 98871)
This is because a Propellor is a form of a "Rotary Wing". Each blade is a wing and once water flows over it's surface correctly, it creates "lift" just like any wing. If a prop is allowed to free wheel in the water, then it will act in the same way a Helicopter uses Auto rotate to stop it from going into the ground when the engine fails. The drag on the boat is created as the speed of propellor rotation increases. As it increases, more resistance to the rotation is applied by friction from the gearbox. So the propellor becomes drag to the boat, just like the helicopter blade. It is less noticable at slow speeds and greatly increases as speed increases.
If the propellor is locked, then water flows over the blade in the wrong way and the blade "stalls". This has a reverse affect. At low speed, the drag of the stalled propellor is large. At a higher speed, the drag is less noticable to the increased force from the wind.

I won't go into the issue of in/out of gear. As Rick505 said, there has been a lot discussed int he past and a search will reveal much information.

Hmm, thanks for that. This is the first time I have seen a plausible explanation of this phenomenon. I first read about it in one of the books of Nigel Calder, but he did not give any explanation.

Connemara 16-09-2007 08:06

Hmmm.

I have an OMC saildrive and I've been putting in neutral. In fact we usually put it in neutral and then pull out the wee black button that lets it start, whatever that's called.

Haven't tried it with the transmission engaged.

Anybody have any opinions on the OMC saildrive? Can't remember what the manual says, if it even mentions the issue.

Connemara

jscott 18-09-2007 07:34

All of the charterers recommend that the tranny be put in reverse, to lock the prop when sailing. Including Yanmars.

And yes the Yanmars are a bitch to get out of reverse to start the engine, more often you have to start the engine in reverse and then put it in neutral, then forward to pull in the sails.

The question of which has more drag a stopped prop or a turning prop, can not be answered in general, depending on the speed, the prop, and the setting, some may have more drag stopped then rotating or vice versa. It also depends on the amount of tranny drag there may be since this removes power from the prop system.

Indeed properly set-up a prop should be able to develop about some 60% of it forward power if rotated at the proper speed, into a generator arrangement. (freewheeling is of sourse different than this).

When using axial pumps has turbines the power curves for various set-ups often cross each other.

Ex-Calif 18-09-2007 18:19

This is like religion...

It is transmission and prop specific. Do what works for you and your equipment.

Tropic Cat 18-09-2007 18:49

the definitive research
 
Another expert opinion!!

Here's the definitive research on the subject.

The MIT paper

Please, only refute with your own research documentation

Ex-Calif 18-09-2007 19:09

Quote:

Originally Posted by rickm505 (Post 101396)
Another expert opinion!!

Here's the definitive research on the subject.

The MIT paper

Please, only refute with your own research documentation

Rick - This paper gets cited as the difinitive work everytime this subject comes up. It should be noted that they did not test under freewheeling conditions due to the limitations of their test rig. They extrapolated and calculated the data. I am not sying they are wrong. I am just saying it is not conclusive.

It's the first paragraph on page 19.

Tropic Cat 18-09-2007 22:28

Dan

It's the only non biased research which has been published on the subject. Fortunately the research was done by a lab with impecable credentials, and in 13 years this report hasn't been refuted. I would think that ought to be conclusive enough in anyone's book. If MIT wrote it, I have no reason to question their methods, or conclusions and am a little surprised that anyone would.

I mean, come on, it's MIT..... not some fly by night outfit or rumors spread by marina rats.

As I said earlier, this is the definitive work on the subject. If you'd like to tell us that their scientists, methods, and conclusions are all wrong, all I can say is that I'll stick with MIT's report.

Ex-Calif 19-09-2007 00:31

I have no problem with any credible results. The problem lies in extrapolating those results beyond the assumptions and facts of the test environment.

The MIT study is conclusive for the props and conditions they tested. It is not conclusive for a windmilling prop of any kind.

They specifically state that they did not test windmilling props.

Once you attach a transmission and the associated drag the numbers in the study go out the window. The study was one of prop efficiencies not installation effects.

In regards to it being unrefuted for 13 years. How long was the world flat? how long did man believe the sound "barrier" was impenetrable?

Tropic Cat 19-09-2007 03:39

Point taken but this isn't rocket science. Besides, I own the perfect test platform as I have two of everything. So results are amplified so to speak.

Freewheeling is much better.

Pblais 19-09-2007 06:00

Quote:

Freewheeling is much better.
It's more about the issues with the transmission. If the transmission vendor prefers the shaft to be locked then it should be. The two boats I've owned both require the transmission shaft not to freewheel. The more common situation is there is a problem with the transmission being able to freewheel without damage and more or less drag is moot.

drh1965 19-09-2007 06:39

This topic is very interesting and ironic (at least to me). One of my other hobbies is 4-wheeling (Jeeps). A problem 4-wheelers often have is getting their heavily modified trucks to the trails. Often, these trucks are unpleasant to drive on-road (huge/load tires, axle lockers, under-powered brakes, etc) to say the least. So, often we flat-tow our Jeeps to the trails. That is, a tow bar is attached to the front bumper that is then attached to a tow-vehicles hitch. For the most part, this sounds like an obvious solution. But noooo.. few transmissions/transfer cases can handle being free-wheeled. The problem is that the drive shafts continue to spin the gears in the front and back of the transfer case that attach to the axles. But, because the transfer case is left in neutral (to prevent spinning the manual tranny gears which wear rapidly when left in neutral), the bulk of the transfer case does not get lubricated. This causes wear and failure over time. Well, clever 4-wheeler guys have come up with a solution. They weld little paddles on the shaft inside the transfer case so that when the front and rear of the transfer case is free-wheeling, the little paddles toss the lubricant all over the inside of the case. No more problems :)

Does this not seem like the exact same problem that sailboat transmissions have when free-wheeling? I wonder if some manufacturers have installed paddles inside the transmissions while others have not. I know that Hurth claims that the tranny in my boat can be left in neutral or in reverse. Hmmmm??? I wish I had a parts diagram for my transmission. I'm very curious how Hurth allows for free-wheeling the tranny...

rtbates 19-09-2007 07:13

Quote:

Originally Posted by rickm505 (Post 101421)
Dan

It's the only non biased research which has been published on the subject. Fortunately the research was done by a lab with impecable credentials, and in 13 years this report hasn't been refuted. I would think that ought to be conclusive enough in anyone's book. If MIT wrote it, I have no reason to question their methods, or conclusions and am a little surprised that anyone would.

I mean, come on, it's MIT..... not some fly by night outfit or rumors spread by marina rats.

As I said earlier, this is the definitive work on the subject. If you'd like to tell us that their scientists, methods, and conclusions are all wrong, all I can say is that I'll stick with MIT's report.

Didn't I read somewhere that MIT's research was funded by the 'Organization of Cutlass and Transmission Bearing Replacers Local 110'??

Wannafish 19-09-2007 07:39

Quote:

Originally Posted by Connemara (Post 101010)
Hmmm.

I have an OMC saildrive and I've been putting in neutral. In fact we usually put it in neutral and then pull out the wee black button that lets it start, whatever that's called.

Haven't tried it with the transmission engaged.

Anybody have any opinions on the OMC saildrive? Can't remember what the manual says, if it even mentions the issue.

Connemara

OMC Saildrive - the "transmission" is basically identical to the bottom end of a regular outboard motor, hence the gears are in an oil bath. Freewheeling should cause no ill effects to the gear train.

drh1965 19-09-2007 08:05

Quote:

Originally Posted by Wannafish (Post 101480)
OMC Saildrive - the "transmission" is basically identical to the bottom end of a regular outboard motor, hence the gears are in an oil bath. Freewheeling should cause no ill effects to the gear train.

Do you mean that the "case" is actually nearly filled with oil? Another solution I've heard of in the 4-wheeler world is to fill the entire transfer case with fluid prior to flat-towing. The problem with that solution was that there was localized super-heating of the oil because of the lack of circulation.

Does fluid ever come out of the breather on the OMC Saildrive?

Wannafish 19-09-2007 08:12

Quote:

Originally Posted by drh1965 (Post 101485)
Do you mean that the "case" is actually nearly filled with oil?

Does fluid ever come out of the breather on the OMC Saildrive?

The "case" is filled only to the approx. center of the gears - in other words only about 3" up in the bottom of the gear case.

The OMC sail drive is not like a 4X$ transfer case (where you can change the oil after going thru a river). There is no "breather" per se on the sail drive. If there were, moisture could enter which is what you don't want since you can't change the gear oil without pulling the boat out of the water.

drh1965 19-09-2007 08:26

Quote:

Originally Posted by Wannafish (Post 101487)
The "case" is filled only to the approx. center of the gears - in other words only about 3" up in the bottom of the gear case.

The OMC sail drive is not like a 4X$ transfer case (where you can change the oil after going thru a river). There is no "breather" per se on the sail drive. If there were, moisture could enter which is what you don't want since you can't change the gear oil without pulling the boat out of the water.

Interesting... I noticed on my Hurth that there isn't a breather either. I figured that was why the case had what seemed like a tiny amount of fluid. If it had much, the pressure would build up radically in the case without a breather... I bet if you look closely, the OMC saildrive has a mechanism to disperse the fluid when the transmission is free-wheeled.

PS. We had snorkels on the breathers that went up to the roll-bars on the transfer case, transmission and axles to avoid having to change the darn fluids all the time. The cost adds up replacing that stuff...

Tropic Cat 19-09-2007 10:02

I agree and already mentioned this.

Quote:

Originally Posted by Pblais (Post 101467)
It's more about the issues with the transmission. If the transmission vendor prefers the shaft to be locked then it should be. The two boats I've owned both require the transmission shaft not to freewheel. The more common situation is there is a problem with the transmission being able to freewheel without damage and more or less drag is moot.


jscott 19-09-2007 10:37

The report also mentions the impact of prop settings and transmissions etc on the conclusions.

There are certainly cases where "freewheeling" will induce more drag, I would think that these would be less likely to occur.

The worst "drag" will occur when the prop is turning and producing power into the drive system, perhaps intentionally.

I would like install a electric motor drive that can produce power as well as consume it. Then drive this motor with a diesel generator, through a VFD (Variable Frequency Drive models are available to produce pwoer back as well). This would allow the boat to produce power when underway, lock-up or drive the boat off batteries, and solar power or just motor as normal. The driven efficiency will almost certainly be higher since the prop and motor can be operated a different optimal RPM, much like a feathing prop (The electrical transmission efficiency can be as high as 70%)

Alan Wheeler 19-09-2007 12:18

Quote:

It's more about the issues with the transmission. If the transmission vendor prefers the shaft to be locked then it should be.
The above statement by Paul has already been echoed, but it is important enough to state it once again. No one make of box will determin the rule for all others. Each box is different and the advice of the manufacturer needs to heeded for each.

Ex-Calif 19-09-2007 21:24

Although I am loathe to extrapolate aviation data to the nautical world the physics involved are very similar. The main difference is the incompressibility of the fluid that a boat propeller works in.

In powered operation the propeller meets the water just on the concave side of the leading edge. The concave side of the prop "paddles" water aft and some water rushes around the leading edge. In air this creates lift thanks to bernoulli. In water it must create some small drag. A big difference is that most boat propellers are not airfoil cross sections because the medium is incompressible. But ultimately there is a thrust vector, most nearly at right angles to the blade.

Lot's of interesting things must be happening on a props that are not mounted along the longitudinal axis of the boat - i.e. the shaft angles down. In this case the blades going up and the blades going down see a different angle of attack to the oncoming water and therefore must produce different thrust - mathematical ice cream headache...

When the prop freewheels water strikes the blade on the convex side. The blade rotates and the unbelievable thing is the thrust vector goes negative. Negative thrust is drag. Added to this is the hp required to turn any machinery such as a gearbox and engine.

Another difference in boats is that in most cases you can disconnect the machinery, at least the engine and only turn the relatively easy to turn gearbox.

So bottom line is that you have to follow your manufacturers recommendations or do your own testing and weigh the factors.

One final thought regarding the autogyro. It works right? But the forward thrust engine is used to overcome the drag of the rotor. If the engine fails energy stored in the rotating rotor is converted by angle of attack to create a flair for a safe landing.

How well do you think that would work if the gyroplane's rotor was locked in place?

For an interesting cartoon about windmilling and the forces have a look at this.

Drag From Windmilling Propeller

Tropic Cat 20-09-2007 04:46

This topic is like discussing religion

GordMay 20-09-2007 04:59

It is very difficult to debate a (religious) point of view that is concerned with the very core of one’s existence. A person of faith in God has that faith planted firmly in their emotional and physical core.
I hope that none of us on the CF adhere’s that emphatically to their technical opinions on free-wheeling prop’s.
Most religions (and secular cultures) follow some version of the Golden Rule, "do unto others as you would have them do unto you". Why then is it so hard to be kind, patient, understanding, etc, with people who cherish beliefs different from our own?

Ex-Calif 20-09-2007 05:32

The good news that this is not religion. It's physics.

The better news is I have a feathering prop so I'm just stirring the crap from the bottom of the pot - LOL!

Alan Wheeler 20-09-2007 12:09

Quote:

The better news is I have a feathering prop
Arrrr, feathering props. Don't get me started on those ;-) :-)


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