So what is the consensus around engaging the transmission to prevent the prop from rotating under sail OR leaving it in neutral so the shaft turns? I tend to leave mine in neutral to allow the prop to sping under sail... but I have heard that doing this can damage the transmission. Any true to this? What so you all? Merry Christmas to you all, Kevin S/V Weekend Pass 1982 Morgan 321
Props Under Sail... to turn or not to turn
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In gear..
In reverse. There should be a lot of discussion about this in the archives. I think it also depends on the transmission. If it's a Hurth, reverse while under sail is my recommendation.
In reverse. There should be a lot of discussion about this in the archives. I think it also depends on the transmission. If it's a Hurth, reverse while under sail is my recommendation.
Check with the manufacturer
Westerbeke recommends sailing in neutral. Since this conflicted with what I usually read on the net, I sent an email to them and asked. Their reply confirmed that the transmission should be in neutral when sailing. The reverse recommendation is for other brands. (Mine lives in my Catalina 270.)
Westerbeke recommends sailing in neutral. Since this conflicted with what I usually read on the net, I sent an email to them and asked. Their reply confirmed that the transmission should be in neutral when sailing. The reverse recommendation is for other brands. (Mine lives in my Catalina 270.)
It depends on your gear box
Per MER here in Seattle, when under sail: If you have a mechnical gear trani, it can be in reverse or neutral. If it is in neutral the lower shaft is physically disconnected from the engine, the shaft just rotates in the gear box. Also since it is sitting in oil, so no problem. Our Yanmar 3HM35F on our h37.5 is setup this way. If you have hydraulic gear, then that is a no-no, put it in reverse.
Per MER here in Seattle, when under sail: If you have a mechnical gear trani, it can be in reverse or neutral. If it is in neutral the lower shaft is physically disconnected from the engine, the shaft just rotates in the gear box. Also since it is sitting in oil, so no problem. Our Yanmar 3HM35F on our h37.5 is setup this way. If you have hydraulic gear, then that is a no-no, put it in reverse.
I think that the archive opinion that wins out is,
for faster SAILING leave the tranny in gear to stop the prop.
for faster SAILING leave the tranny in gear to stop the prop.
Under Sail
It is entirely "Engine/Transmission combination" dependent. Check with the manufacturer for the proper setting. You could possibly burn up the gears in the transmission by letting the shaft turn.
It is entirely "Engine/Transmission combination" dependent. Check with the manufacturer for the proper setting. You could possibly burn up the gears in the transmission by letting the shaft turn.
jBearings
It seems to me that a freewheeling prop is causing wear on the trans bearing and the cutlass bearing. Friction is involved and friction means wear. A freewheeling prop can foul a line that goes overboard - another reason to put it is gear. I cannot see how putting the boat in gear could possibly harm a transmission. Nothing moving nothing wearing.
It seems to me that a freewheeling prop is causing wear on the trans bearing and the cutlass bearing. Friction is involved and friction means wear. A freewheeling prop can foul a line that goes overboard - another reason to put it is gear. I cannot see how putting the boat in gear could possibly harm a transmission. Nothing moving nothing wearing.
transmission wear
some of the transmissions use clutches instead of gears to engage, and use some type of mechanical assist for application force, so if the engine's not running, the clutches are only slightly touching and will wear out. other trannies need the engine running to provide lubricant, generally if there's no seperate fill for the trans they have this type most of the older types, and the 'better' ones will have gears and seperate pans for engine and trans, transmissions are notorious for shavings and flecks in the oil, and it's best to keep it out of the engine. As for the freewheel or locked prop, in regards to drag, I haven't made up my mind yet, but I have the junk together to make a definitive test this spring and I intend to find out. ken.
some of the transmissions use clutches instead of gears to engage, and use some type of mechanical assist for application force, so if the engine's not running, the clutches are only slightly touching and will wear out. other trannies need the engine running to provide lubricant, generally if there's no seperate fill for the trans they have this type most of the older types, and the 'better' ones will have gears and seperate pans for engine and trans, transmissions are notorious for shavings and flecks in the oil, and it's best to keep it out of the engine. As for the freewheel or locked prop, in regards to drag, I haven't made up my mind yet, but I have the junk together to make a definitive test this spring and I intend to find out. ken.
Nothing to do with the engine
just the transmission. See the link for an example. Westerbeke should not be advising on transmissions. They make engines. Many Westerbekes and Universals have Hurth transmissions.
just the transmission. See the link for an example. Westerbeke should not be advising on transmissions. They make engines. Many Westerbekes and Universals have Hurth transmissions.
Constant Mesh
Yanmar is a constant mesh transmission which means all the gears are engaged at all times. When spinning they create the splash which lubricates the gears. You may leave them in neutral with the shaft spinning with no ill effect other than wear. To shift it into reverse is also acceptable. The gear configuration in reverse mode better handles the force created by water pressure. Also the justification for it is that the reverse gear is used for a lot less time than forward so the wear created by water pressure just may balance things out. Be warned that sailing with reverse gear engaged will cause the transmission to lock in gear above 2 knots on the average. To be able to shift into neutral you will be best served to slow the boat down. To force the shifter or to start the motor in reverse will defeat the strain and wear factor we are trying to minimize. To use neutral additionally places wear in the packing gland and the cutlass bearing. I believe either way the wear will be minimal unless you have a bad vibration that is best stopped. I have seen some mechanical axle locks in the market but I have not had any experience with them but they could be an alternative. I have heard of pressure plyers being used by long distance cruisers but you better attach the ignition key to it lest you forget.
Yanmar is a constant mesh transmission which means all the gears are engaged at all times. When spinning they create the splash which lubricates the gears. You may leave them in neutral with the shaft spinning with no ill effect other than wear. To shift it into reverse is also acceptable. The gear configuration in reverse mode better handles the force created by water pressure. Also the justification for it is that the reverse gear is used for a lot less time than forward so the wear created by water pressure just may balance things out. Be warned that sailing with reverse gear engaged will cause the transmission to lock in gear above 2 knots on the average. To be able to shift into neutral you will be best served to slow the boat down. To force the shifter or to start the motor in reverse will defeat the strain and wear factor we are trying to minimize. To use neutral additionally places wear in the packing gland and the cutlass bearing. I believe either way the wear will be minimal unless you have a bad vibration that is best stopped. I have seen some mechanical axle locks in the market but I have not had any experience with them but they could be an alternative. I have heard of pressure plyers being used by long distance cruisers but you better attach the ignition key to it lest you forget.
Gear
I have a Yanmar and a Kanzaki xmsn...my Yanmar guru agrees with Stu. Reverse is preferred, neutral is okay, never in forward. I use neutral.
I have a Yanmar and a Kanzaki xmsn...my Yanmar guru agrees with Stu. Reverse is preferred, neutral is okay, never in forward. I use neutral.
Slow
This question comes up frequently on many forums. The answer seems to be that leaving the prop in gear or letting it spin depends upon the transmission (as has been said here, again) and what the manufacturer says about it possibly damaging the transmission, or not. Another question related to this has been broached here: which creates more drag; a freewheeling prop or one that's not moving. Every site I've been to seems to indicate that when tests are actually performed, the freewheeling prop creates more drag and slows the boat down more than a fixed prop.
This question comes up frequently on many forums. The answer seems to be that leaving the prop in gear or letting it spin depends upon the transmission (as has been said here, again) and what the manufacturer says about it possibly damaging the transmission, or not. Another question related to this has been broached here: which creates more drag; a freewheeling prop or one that's not moving. Every site I've been to seems to indicate that when tests are actually performed, the freewheeling prop creates more drag and slows the boat down more than a fixed prop.
Sorry, Paul. Freewheeling prop has less drag. pro
I repeated this experiment many times: While sailing at less than hull speed with the transmission in reverse, I would shift into neutral. The prop would immediately start to spin. The speed would noticibly increase. I would then shift back into reverse. The prop would stop spinning and the boat speed would decrease. Happens every time. Explain it as you will, the prop exhibits less drag on the boat when it is freewheeling than it does when is is stationary, locked in gear. As long as your tranny will stand it and the vibrations / noise of the spinning prop don't drive you buggy, from a strictly speed under sail perspective, you are better off letting the prop freewheel than you are having it locked in one position. Of course, the best answer is to buy a folding / feathering prop and ignore all this chat about freewheeling vs fixed being faster. Steve Alchemist C-30T #4764 Alchemist C-320 #909
I repeated this experiment many times: While sailing at less than hull speed with the transmission in reverse, I would shift into neutral. The prop would immediately start to spin. The speed would noticibly increase. I would then shift back into reverse. The prop would stop spinning and the boat speed would decrease. Happens every time. Explain it as you will, the prop exhibits less drag on the boat when it is freewheeling than it does when is is stationary, locked in gear. As long as your tranny will stand it and the vibrations / noise of the spinning prop don't drive you buggy, from a strictly speed under sail perspective, you are better off letting the prop freewheel than you are having it locked in one position. Of course, the best answer is to buy a folding / feathering prop and ignore all this chat about freewheeling vs fixed being faster. Steve Alchemist C-30T #4764 Alchemist C-320 #909
I don't think so...
As a pilot the first thing they teach you to do when you lose an engine is to slow down enough to stop the prop from spinning, to reduce drag thereby giving you more gliding distance. I have long ago forgot the physics behind it, but they apply to fluids so I would think that the theory would also be correct in water.
As a pilot the first thing they teach you to do when you lose an engine is to slow down enough to stop the prop from spinning, to reduce drag thereby giving you more gliding distance. I have long ago forgot the physics behind it, but they apply to fluids so I would think that the theory would also be correct in water.
It would really be great ...
if there was some more testing available to support a conclusion either way. This question comes up a lot, and I've always thought the conclusion was that prop stopped is best (from the performance and drag perspective). Alchemist's tests would seem to refute this. If I understand the physics correctly, I'd have to conclude that stopped would lower the drag. However, this wouldn't be the first time that empirical data refuted a theory. So, anyone know of any significant test data?? -Smitty
if there was some more testing available to support a conclusion either way. This question comes up a lot, and I've always thought the conclusion was that prop stopped is best (from the performance and drag perspective). Alchemist's tests would seem to refute this. If I understand the physics correctly, I'd have to conclude that stopped would lower the drag. However, this wouldn't be the first time that empirical data refuted a theory. So, anyone know of any significant test data?? -Smitty
Valid testing
For tests of any sort to be valid all variables must be absolutely controlled and repeatable with certianty. That means wind speed, current, sea state, instrumentation, etc, etc, etc. There also needs to be several modes of measurement and in deed several different measurements. No offense to Alchemist, but some guy putting his boat in gear a feew times and looking at a knotmeter is hardly a scientific, repeatable test that could stand up to any acceptable standards of testing at all. Having said all that, I prefer putting the tranny in reverse so that I don't have to put up with the vibration and I don't wear the cutlass bearing. If either way caused me to go 1/4- 1/2 knot faster or slower I wouldn't care in the least. An extra 12 miles per day would get me to California to Mexico about 12 hour sooner... and that really isn't the point of sailing for me.
For tests of any sort to be valid all variables must be absolutely controlled and repeatable with certianty. That means wind speed, current, sea state, instrumentation, etc, etc, etc. There also needs to be several modes of measurement and in deed several different measurements. No offense to Alchemist, but some guy putting his boat in gear a feew times and looking at a knotmeter is hardly a scientific, repeatable test that could stand up to any acceptable standards of testing at all. Having said all that, I prefer putting the tranny in reverse so that I don't have to put up with the vibration and I don't wear the cutlass bearing. If either way caused me to go 1/4- 1/2 knot faster or slower I wouldn't care in the least. An extra 12 miles per day would get me to California to Mexico about 12 hour sooner... and that really isn't the point of sailing for me.
Locked will have less drag .....
For the drag 'component' that is due to 'shape profile' (projection of frontal area - impact) there is no difference in the drag component if the prop is spinning or not - as the area of the shape of the prop doesnt change. But, since a fluid has viscosity (the resistance to flow) a spinning prop will be in contact with more (mass) of water and therefore a spinning prop (traveling a greater distance 'through' the fluid) will react against more total 'viscous shear'; hence, more total drag. The analogy would be for a boat moving headlong against a fast current vs. moving through still/non-moving water ('relativistically' speaking) - the 'skin friction' will be greater through the moving water. Simple speak - the spinning prop comes in contact with MORE water; more contact = more friction. Doesnt matter if the prop is in air or water or some other 'fluid'. A spinning prop has more drag than a stationary prop.
For the drag 'component' that is due to 'shape profile' (projection of frontal area - impact) there is no difference in the drag component if the prop is spinning or not - as the area of the shape of the prop doesnt change. But, since a fluid has viscosity (the resistance to flow) a spinning prop will be in contact with more (mass) of water and therefore a spinning prop (traveling a greater distance 'through' the fluid) will react against more total 'viscous shear'; hence, more total drag. The analogy would be for a boat moving headlong against a fast current vs. moving through still/non-moving water ('relativistically' speaking) - the 'skin friction' will be greater through the moving water. Simple speak - the spinning prop comes in contact with MORE water; more contact = more friction. Doesnt matter if the prop is in air or water or some other 'fluid'. A spinning prop has more drag than a stationary prop.
Maybe...
Perhaps the engine was running when the tests mentioned below were done? In that case, sailing along with the engine in reverse and then shifting to neutral probably would make you speed up.
Perhaps the engine was running when the tests mentioned below were done? In that case, sailing along with the engine in reverse and then shifting to neutral probably would make you speed up.
Test data ...
Each prop is different. The blades have twist and pitch. These combine to give an optimum speed and RPM. If your prop freewheels at it's design speed the drag will be lower. If it freewheels at a higher speed the drag will be higher. Another variable is the friction of the drive system. The drag goes up with the square of RPM, if the system is drag free, the total drag is a function of prop design. A fixed (non-rotating) prop blade will have a CD of around 1.1 The blade will have a CD of about .08-.1 when aligned with the flow (at design speed or feathered). If the system has internal friction, the blades will have to generate lift to overcome the friction and that ads induced drag into the picture. My two "real" data points are a Michigan Wheel 12x6 2 blade and a Campbell Sailor 10x6 3 blade. The 12x6 2 blade has more total blade area and has a higher blade area ratio to the 12" dia circle than the CS 3 blade. The boat was slower with the the 2 blade freewheeling compared to stopped. The 3 blade doesn't freewheel as fast (should be the same since pitch is equal) and is only slightly faster when stopped. I've read about systems that un-couple the prop shaft from the engine and use a large diameter pulley on the shaft so the prop can turn an alternator while under sail. I suspect that boats that have low prop RPM at cruising speed *might* be faster with the prop freewheeling, while those of us with little "egg-beater" props turning at high RPM are better off with the props locked.
Each prop is different. The blades have twist and pitch. These combine to give an optimum speed and RPM. If your prop freewheels at it's design speed the drag will be lower. If it freewheels at a higher speed the drag will be higher. Another variable is the friction of the drive system. The drag goes up with the square of RPM, if the system is drag free, the total drag is a function of prop design. A fixed (non-rotating) prop blade will have a CD of around 1.1 The blade will have a CD of about .08-.1 when aligned with the flow (at design speed or feathered). If the system has internal friction, the blades will have to generate lift to overcome the friction and that ads induced drag into the picture. My two "real" data points are a Michigan Wheel 12x6 2 blade and a Campbell Sailor 10x6 3 blade. The 12x6 2 blade has more total blade area and has a higher blade area ratio to the 12" dia circle than the CS 3 blade. The boat was slower with the the 2 blade freewheeling compared to stopped. The 3 blade doesn't freewheel as fast (should be the same since pitch is equal) and is only slightly faster when stopped. I've read about systems that un-couple the prop shaft from the engine and use a large diameter pulley on the shaft so the prop can turn an alternator while under sail. I suspect that boats that have low prop RPM at cruising speed *might* be faster with the prop freewheeling, while those of us with little "egg-beater" props turning at high RPM are better off with the props locked.
Sorry Dennis and RichH, but you're analysis is
flawed. Dennis: An airplane stops its prop from spinning by feathering the prop, thereby reducing the surface area to essentially that of the leading edge of the prop, and therefore is totally unrelated to the problem at hand (that's why people purchase folding / feathering props). RichH: A stationary, NON SPINNING prop has an apparent surface area that is proportional to the actual surface area projected to be parallel to the flow of the fluid (this will be somewhat less than the actual surface area, but MUCH MORE than the surface area of the leading edge of the prop. A prop that is free wheeling can't spin any faster than the water will turn it (conservation of energy and momentum etc), and it will be less than that depending on the friction of the transmission, bearings, etc.) (otherwise it will be providing thrust, not drag). If a prop is spinning AT THE SAME SPEED as the water, it will have essentially the same apparent surface area as the leading edge of the blades. To understand this, take two streams, both the same distance from the center of the prop, but next to each other (say 1 mm apart). If the prop is fixed, stream 1 will hit the prop and be deflected. Stream 2 will hit the prop slightly later, but 1 mm ofset along the same concentric circle from the center of the prop (the prop does have a pitch after all), but when it does, it will also be deflected. This is form drag. If the prop is free to rotate, when stream #1 from above hits the prop, it is deflected slightly, and pushes the prop away by inducing rotation. The second stream may or may not still hit the prop because the spin induced by stream #1 has moved the intended target away. In this fashion, a free spinning prop can aproach the apparent effective surface area of the leading edge of the prop, but not actually reach this ideal due to system friction. Before you theorize, perform the experiment or do the math. A feathered prop has the least friction / drag, a free spinning prop has more friction / drag than the feathered / folding prop, and a fixed prop (assuming the same prop / boat combination as above) will have the most friction / drag. The ONLY case where a fixed prop may have less drag than a freewheeling prop is if it is mounted in an apperature where the deadwood around the prop essentially hides the prop from the water flow as long as it is alligned with the hull / keel. To convince yourself of this, take a toy windmill / whirlygig. Tape the spinner (prop) to the shaft to prevent it from spinning. Mount it in a block of wood. Glue the wood to the roof of your pickup truck. Drive around your neighborhood at a set speed. Measure the angle of deflection between the shaft and the block of wood using a protractor. Now, un-tape the whirlygig and let it freely spin. Repeat the experiment. Better, use two whirlygigs. Tape one and let the other free-wheel. Reverse the tape job and repeat. You will find that the free rotating whirlygig will have less deflection in the shaft than the locked whirlygig. That is related to drag caused by the whirlygig prop and is exactly the what we have been discussing. I reiterate. A free wheeling prop will ALWAYS have less drag than a fixed prop. A free wheeling prop may or may not be suitable for your boat based on engine, transmission, bearings, etc. And Liam, I'm a good enough helmsman to detect when a change in sail trim (or prop rotation), has affected the speed of the boat. I suspect that you are too. Perform the experiment before you trash it. It works EVERY time. (but you must be below hull speed as prop drag is minimal when compared to other forces acting on your boat and probably undetectable) Steve Alchemist C-30T #4764 Alchemist C-320 #909
flawed. Dennis: An airplane stops its prop from spinning by feathering the prop, thereby reducing the surface area to essentially that of the leading edge of the prop, and therefore is totally unrelated to the problem at hand (that's why people purchase folding / feathering props). RichH: A stationary, NON SPINNING prop has an apparent surface area that is proportional to the actual surface area projected to be parallel to the flow of the fluid (this will be somewhat less than the actual surface area, but MUCH MORE than the surface area of the leading edge of the prop. A prop that is free wheeling can't spin any faster than the water will turn it (conservation of energy and momentum etc), and it will be less than that depending on the friction of the transmission, bearings, etc.) (otherwise it will be providing thrust, not drag). If a prop is spinning AT THE SAME SPEED as the water, it will have essentially the same apparent surface area as the leading edge of the blades. To understand this, take two streams, both the same distance from the center of the prop, but next to each other (say 1 mm apart). If the prop is fixed, stream 1 will hit the prop and be deflected. Stream 2 will hit the prop slightly later, but 1 mm ofset along the same concentric circle from the center of the prop (the prop does have a pitch after all), but when it does, it will also be deflected. This is form drag. If the prop is free to rotate, when stream #1 from above hits the prop, it is deflected slightly, and pushes the prop away by inducing rotation. The second stream may or may not still hit the prop because the spin induced by stream #1 has moved the intended target away. In this fashion, a free spinning prop can aproach the apparent effective surface area of the leading edge of the prop, but not actually reach this ideal due to system friction. Before you theorize, perform the experiment or do the math. A feathered prop has the least friction / drag, a free spinning prop has more friction / drag than the feathered / folding prop, and a fixed prop (assuming the same prop / boat combination as above) will have the most friction / drag. The ONLY case where a fixed prop may have less drag than a freewheeling prop is if it is mounted in an apperature where the deadwood around the prop essentially hides the prop from the water flow as long as it is alligned with the hull / keel. To convince yourself of this, take a toy windmill / whirlygig. Tape the spinner (prop) to the shaft to prevent it from spinning. Mount it in a block of wood. Glue the wood to the roof of your pickup truck. Drive around your neighborhood at a set speed. Measure the angle of deflection between the shaft and the block of wood using a protractor. Now, un-tape the whirlygig and let it freely spin. Repeat the experiment. Better, use two whirlygigs. Tape one and let the other free-wheel. Reverse the tape job and repeat. You will find that the free rotating whirlygig will have less deflection in the shaft than the locked whirlygig. That is related to drag caused by the whirlygig prop and is exactly the what we have been discussing. I reiterate. A free wheeling prop will ALWAYS have less drag than a fixed prop. A free wheeling prop may or may not be suitable for your boat based on engine, transmission, bearings, etc. And Liam, I'm a good enough helmsman to detect when a change in sail trim (or prop rotation), has affected the speed of the boat. I suspect that you are too. Perform the experiment before you trash it. It works EVERY time. (but you must be below hull speed as prop drag is minimal when compared to other forces acting on your boat and probably undetectable) Steve Alchemist C-30T #4764 Alchemist C-320 #909
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