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Old 28-07-2015, 14:09   #121
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Re: Do you sail with your transmission in gear?

TC: The info I posted from the Volvo manual is on page 22 of the D2-40 manual not page 21 and clearly states that either neutral or reverse can be engaged, the difference being in reverse you will go slower but be quieter.

Yachting Monthly showed in a repeatable test that allowing a fixed blade prop to free spin produced less drag than locking it in reverse. They also showed that a feathered prop produced virtually no drag in it's feathered state which would be the ideal scenario.

Funny isn't it that despite reputable organisations coming up with the same result we still end up arguing which is best. If MIT and YM have shown beyond doubt that allowing a fixed blade prop to free rotate reduces your drag why do some people keep insisting that you lock it?

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Old 28-07-2015, 14:37   #122
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Re: Do you sail with your transmission in gear?

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Originally Posted by kas_1611 View Post
TC: The info I posted from the Volvo manual is on page 22 of the D2-40 manual not page 21 and clearly states that either neutral or reverse can be engaged, the difference being in reverse you will go slower but be quieter.

Yachting Monthly showed in a repeatable test that allowing a fixed blade prop to free spin produced less drag than locking it in reverse. They also showed that a feathered prop produced virtually no drag in it's feathered state which would be the ideal scenario.

Funny isn't it that despite reputable organisations coming up with the same result we still end up arguing which is best. If MIT and YM have shown beyond doubt that allowing a fixed blade prop to free rotate reduces your drag why do some people keep insisting that you lock it?

Keiron

It's because all these damn aviators can't accept that all props are not created equal. The difference between a stalled prop and a spinning one is so dramatic in a plane, that it must be true for a boat too.
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Old 28-07-2015, 16:55   #123
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Re: Do you sail with your transmission in gear?

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Originally Posted by Guy View Post
It's because all these damn aviators can't accept that all props are not created equal. The difference between a stalled prop and a spinning one is so dramatic in a plane, that it must be true for a boat too.

I believe the difference is due to the blade design, an airplane prop has a very thin cord, but is relatively long, a stopped prop on an airplane, the blade area is maybe 10% of the prop disk?
Now look at a three blade sailboat prop, almost the entire disk is covered by prop blade, and even a two blade covers a significant portion.
Pure apples and oranges comparison, like trying to compare a displacement sailboat hull to say a high speed bass boat

But your right, to a pilot a spinning prop is a very high drag device, I believe almost all pilots are shown to stop the prop and experience the dramatic increase in glide distance a stopped prop gives, and this on a piston single, that you cannot feather.
So it's natural for us to assume a spinning boat prop acts the same.

But, even on my IP, a heavy displacement cruising boat not known for speed, the difference in a feathering prop is dramatic, I can't see other than $$, why anyone would want a fixed prop on a sailboat, I would assume the difference on lighter, faster boats is even more dramatic?

Now I noticed not much difference in light wind sailing, which makes sense as the drag of a fixed prop at three kts isn't much, but at the higher wind speeds, I believe I picked up a kt, where I was sailing six kts, now I'm sailing seven


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Old 28-07-2015, 17:16   #124
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Re: Do you sail with your transmission in gear?

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Now I noticed not much difference in light wind sailing, which makes sense as the drag of a fixed prop at three kts isn't much, but at the higher wind speeds, I believe I picked up a kt, where I was sailing six kts, now I'm sailing seven
If you look at the total drag components you will likely find:

At low boat speeds the main component is skin friction, coming from the entire wetted area of the hull and appendages. The prop contributes a small fraction of the total.

At high boat speeds, as one approaches or reaches hull speed, wave making is the largest contributor to drag. Again the prop is a small fraction of the total.

At intermediate speeds the prop develops a considerably larger portion of the total drag, and it is in this regime where the folding or feathering prop will make the greatest improvement in performance. And that speed range is where one spends the greatest portion of one's sailing hours! IMO, if sailing performance is important to you, a low drag prop is a great investment.

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Old 28-07-2015, 17:26   #125
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Re: Do you sail with your transmission in gear?

Ok poeple the prop on an airplane is NOT freewheeling. It is spinning the whole motor making it way more draggy than a boat prop with the trans in neutral. Apples and oranges no comparison.

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Old 28-07-2015, 17:49   #126
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Re: Do you sail with your transmission in gear?

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Originally Posted by wellin View Post
Ok poeple the prop on an airplane is NOT freewheeling. It is spinning the whole motor making it way more draggy than a boat prop with the trans in neutral. Apples and oranges no comparison.

Andy

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Another airplane expert That is not true. It is only true for a single engine piston job. Multi engine piston planes all have feathering props that when feathered do not turn. Turbine engine planes can change the pitch from forward to backwards. When the engine quits they automatically go into feather.
You can even back up! Ask A-64 pilot. He probably bombs around the ramp backwards.
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Old 28-07-2015, 18:15   #127
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Re: Do you sail with your transmission in gear?

If you have a two bladed prop with deadwood in front of it like in a skeg or keel attached rudder (full keel), the prop fixed in vertical alignment with the deadwood will have less drag. On our old boat locked the prop in the vertical position with my secret locking device (ViceGrips). To do that had to grab hold of the spinning propellor shaft and rotate till I felt almost all the pressure go off the prop when it was vertical. In the opposite situation, had to hand crank the Volvo MD2. It was way easier to crank with the engine in forward especially if we were sailing at 4K or above. Two bladed prop aligned vertically behind the deadwood had near zero turning force which meant near zero drag.
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Old 28-07-2015, 18:43   #128
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Re: Do you sail with your transmission in gear?

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Another airplane expert That is not true. It is only true for a single engine piston job. Multi engine piston planes all have feathering props that when feathered do not turn. Turbine engine planes can change the pitch from forward to backwards. When the engine quits they automatically go into feather.
You can even back up! Ask A-64 pilot. He probably bombs around the ramp backwards.
Only partly true...

Here are some facts, readers can make what conclusions they want but please remember, the core facts remain true, only the conclusions drawn may change!

The overwhelming majority of piston power aircraft engines have the propeller hub bolted to the crankshaft of the engine, thus if the propeller is turning, the engine is turning - normally at a one to one ratio. There are a few gear driven props but the principle remains the same. A very very few very light aircraft with Rotax style engines do have a centrifugal clutch but I repeat, they are rare.

If the pitch is fixed, then the blades and hub are one integral unit just like a fixed pitch prop on a boat. A side note, fixed pitch plane props are invariably two bladed, not three.

If the pitch is variable, then the blades are attached to the hub via a Constant Speed Unit which allows the pitch of the blades to be varied but it does not allow the hub to rotate independently of the hub. Full fine pitch presents the flat area to the airstream and full coarse (ie fleathered) presents the edge of the blade to the airstream. Thus feathered props offer the least drag but not only due the blade dynamics but mainly because they do not produce enough torque to turn the engine over.

The fundamental point is that if the prop is turning on almost any piston engine aircraft, the engine is also turning. This why is is vitally important for a pilot to stop the prop turning in order to reduce drag if an engine fails. With a fixed prop he has very few choices but with a variable prop, he can feather it to reduce the torque applied to the engine crank thus leaving the both the prop and engine stationary.

Turbine engined props are a whole different ball game except to to say, fleathered offers least drag.

If nothing else, please note that aircraft and boat props are attached to the drive source in quite diverse ways. It is a case of apples and oranges!
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Old 28-07-2015, 19:43   #129
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Re: Do you sail with your transmission in gear?

Wotname; You say some strange stuff. You obviously know something about aircraft but not that much. Don't say "invariably" when talking about fixed pitched propellers only having 2 blades, 3 and 4 are common ( think wood.). Don't explain an aircraft prop as connected to the engine through a drive unit or something., they are bolted directly to the engine. The controls for blade angle are either electric or hydraulic. In the case of hydraulic, it is internal in the propeller and drive shaft and the control unit, ie., governor, is mounted somewhere else on the engine.
You may focus on piston engines for your argument but the most popular turbine engine on the planet, the PT-6 is a free turbine. The propeller is essentially independent from the engine and will spin quite freely. It also needs to be in the feathered position if you are about to crash.
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Old 28-07-2015, 20:07   #130
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Re: Do you sail with your transmission in gear?

There was no mention of the KM3P Transmission. Mentioned the KM2P and the KM35P and above but not the KM3P. Is that transmission okay in reverse or does it need to be in neutral?? Of course that's my new transmission.

Quote:
Originally Posted by MarcHall View Post
Attached is a more recent and more detailed notice from Yanmar

TECHNICAL BULLETIN
Ref No.: YMTQTBll-017
Date: October 18, 2011
To : Yanmar Marine Regional Head Quarters and All Yanmar marine distributors
Subjects Yanmar Sailboat engine control lever position during sailing under sail with engine stopped

1. Introduction
Yanmar wishes to inform you about the instruction of the control lever position during sailing under sail with engine operation stopped. This instruction is subjected to mechanical type gearboxes and sail drives only.

2. Ooeration instruction
2~1 Mechanical Cone Clutch':
Applicable models: Sail Drive: Models SD 40, SDSO and SD50-4T
Marine gear: Models KM2P, KM35P, KM35A and KM4A

When mechanical cone clutch type gearbox or sail drive is equipped with the following propeller:

a. Fixed propeller:
When sailing under sail with engine operation stopped put control lever into Neutral. The output shaft keeps rotating.

Notice:
When control lever is put in Reverse position, cone slippage will be introduced and void your warranty and there is possibility that the clutch doesn't disengage. This can be a problem for engine re-starting.

There are options to stop free rotation of propeller-shaft if customer doesn't want occur noise from rotating propeller:

1) For sail drive: install folding propeller or Feathering propeller instead of fixed propeller.

2) For marine gear: install the Shaft-Lock device, Yanmar does not supply, on the propeller shaft.

b. Folding propeller: (including GORI Over-drive propeller)
When sailing under sail with engine operation stopped put control lever into Reverse position, this to operate the folding propeller to fold close blade and output-shaft stops from rotating. After this operation put the control lever back into Neutral.

c. Feathering propeller:
When sailing under sail with engine operation stopped put control lever into Reverse position, this to operate the feathering propeller into feathering position and output-shaft stops from rotating. After this operation put the control lever back into Neutral.

2~2 Other Mechanical clutch:
Applicable model: Sail Drive: Model SD20, SD31 (Dog clutch type)
Marine gear: Model KBW10, KBW20, KBW21
(Mechanical single or multi disc clutch)

When mechanical dog clutch or mechanical disc clutch is equipped with the following propeller:

a. Fixed propeller:
When sailing under sail with motor stopped put control lever into Neutral. The output shaft keeps rotating.
Notice:
When control lever is put in Reverse position there is a possibility the clutch does not disengage. This can be a problem for engine re-starting. There are Options to stop free rotation on propeller shaft if customer doesn't want occur noise by rotating:

1) For sail drive: install folding propeller or Feathering propeller instead of fixed propeller.

2) For marine gear: install the Shaft-Lock device, Yanmar does not supply, on the propeller shaft

b. Folding propeller: When sailing under sail with engine stopped put control lever into reverse position, this enables the folding propeller to fold close blade and output-shaft stops from rotating. After this operation put the control lever back into neutral or remain reverse position as you like.

c. Feathering propeller: When sailing under sail with engine stopped put control lever into reverse position, this enables the feathering propeller into feathering position and output-shaft stops from rotating. After this operation put the control lever back into neutral or remain reverse position as you like.
Notice:
Do above mentioned operations with a boat speed <3knts when sailing under sail with engine operation stopped.

Shuji Ando
Manager, Overseas Group
Quality Assurance Department
Marine Operations Division
Yanmar Co. ltd
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Old 28-07-2015, 20:25   #131
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Re: Do you sail with your transmission in gear?

My KM3V is neutral only as well.

Roverhi, is your new transmission a cone clutch type?. That is the determining factor I believe. The reverse cone will slip if in reverse when sailing engine off.
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Old 28-07-2015, 20:51   #132
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Re: Do you sail with your transmission in gear?

Listed as a Servo Cone clutch so guess it's listen to the damned prop turn. Way too tight in the engine room to get to shaft to clamp vice grips on the shaft.
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Old 29-07-2015, 07:49   #133
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Re: Do you sail with your transmission in gear?

Thread drift alert , most of you might prefer to skip this post but some may be slightly interested

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Originally Posted by Guy View Post
Wotname; You say some strange stuff.

Well they do say truth is stranger than fiction


You obviously know something about aircraft but not that much.

It is all relative, I certainly don't know as much as say Mr Boeing or his colleagues and there are shipload of folk who do know more than me but on the other hand, being an aircraft engineer and pilot, I do know a little.

Don't say "invariably" when talking about fixed pitched propellers only having 2 blades, 3 and 4 are common ( think wood.).

I'm using the word "invariably" as it "almost always but not absolutely". I have never seen a modern 4 bladed fixed pitch aircraft prop or for that matter a three bladed one. I accept there may be a couple of 3 bladed ones somewhere and perhaps 4 bladed one on some antique machines. But in everyday general aviation - none. Perhaps you might post some pictures or other references to support your claim that they are common.

As for wood, they would even be rarer and probably impossible. A wooden aircraft prop has only 2 blades. The grain of the timber has to go from one blade tip to the other. When was the last time you saw a piece of timber with the grain going in three directions each exactly 120 degrees apart. Technically you might be able to laminate a 4 bladed wooden prop but why would you.

Again, please post a link to a working modern wooden fixed pitch prop with more than 2 blades


Don't explain an aircraft prop as connected to the engine through a drive unit or something., they are bolted directly to the engine.

Oh please… I have stated several times that the aircraft prop is bolted directly to the crankshaft. However in the case of the variable and / or constant speed prop, the blades are not directly connected to the engine, rather they are connected to the hub which is then bolted to the engine.

But don't take my word for it, read what Mr McCauley says. They have being making aircraft props since 1938 and have a few runs on the board.

http://www.mccauley.textron.com/tech_guide.pdf

and a rather nice link about wooden propellers from a manufacturer.

http://www.gt-propellers.com



………….
You may focus on piston engines for your argument but the most popular turbine engine on the planet, the PT-6 is a free turbine. The propeller is essentially independent from the engine and will spin quite freely. It also needs to be in the feathered position if you are about to crash.

Let's not get into the why and wherefores of turbine engines and their prop performance and characteristics. It is a much bigger field and and even more off topic than the piston engine questions. I am willing to but it will have to be off-line via PM if you really must.

I have focussed on piston engines as that is what the posters have dealt with; I do not wish to broaden and more confuse the discussion. It also more approximates how our boats are powered. Not many of us as using turbines in our recreational boats . It is also pertinent to the argument that some make about why they believe (incorrectly) a non turning fixed pitch prop on a boat has less drag than a free to rotate one.

To reiterate and put simply:
Piston Engined Aircraft and engine not powered up:

Prop not turning = least drag
Prop turning = most drag

All because (in the main) if the prop is turning, the engine is turning

Boat sailing, fixed pitch prop and engine not powered up:
Prop not turning (locked) = most drag
Prop turning (gearbox in neutral) = least drag

All because 1. it is possible to freewheel the prop and 2. a freewheeling prop develops less torque than a locked prop.
Really nothing more to say!
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Old 29-07-2015, 09:36   #134
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Re: Do you sail with your transmission in gear?

Wotname: It's good that you are giving up. For general information, wooden Props are laminated. You can make them in just about any configuration you want. Wood props and blades are still quite popular to this day.
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Old 30-07-2015, 00:56   #135
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Re: Do you sail with your transmission in gear?

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Wotname: It's good that you are giving up. For general information, wooden Props are laminated. You can make them in just about any configuration you want. Wood props and blades are still quite popular to this day.
Ah, yes, wooden props are laminated... what then is this one?

Jim
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