We usually sail our C320 with the transmission in neutral with the prop free wheeling. Obviously there is less drag but can it do any damage to the transmission or wear out prematurely over time?
Neutral or not ?
- Thread starter Brahmany
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According to Eric Hiscock (RIP) There is less drag when the prop is locked. Since Eric, in his day, was an athority on all things sail I accepted his advice. I would like to know if he was correct and how it was determined.
Best regards,
Charlie
Best regards,
Charlie
The answer lies not in Hiscock, my friend, but in your transmission manufacturer.
What do the instructions for YOUR transmission say?
Mine says this: http://www.c34.org/faq-pages/faq-transmission-position-sailing.html
Find out what transmission you have, read the instructions, and follow them.
[This ? gets asked about twice a month. Like this:http://forums.catalina.sailboatowners.com/showthread.php?p=653035&highlight=transmission position]
If you are ONLY concerned about the drag, Maine Sail did a workup on that and should be on his website: http://www.pbase.com/mainecruising Or search on this website for "prop drag" and more "transmission position" posts.
What do the instructions for YOUR transmission say?
Mine says this: http://www.c34.org/faq-pages/faq-transmission-position-sailing.html
Find out what transmission you have, read the instructions, and follow them.
[This ? gets asked about twice a month. Like this:http://forums.catalina.sailboatowners.com/showthread.php?p=653035&highlight=transmission position]
If you are ONLY concerned about the drag, Maine Sail did a workup on that and should be on his website: http://www.pbase.com/mainecruising Or search on this website for "prop drag" and more "transmission position" posts.
Brahmany,
Stu is absolutely correct. My transmission specifically requires sailing in neutral, but that is what the owner's manual for my engine/transmission states. You need to check yours as each one has their own specifications.
Yes there is less drag in neutral, but that is not the only factor, far from it!
Good luck,
Tom
Stu is absolutely correct. My transmission specifically requires sailing in neutral, but that is what the owner's manual for my engine/transmission states. You need to check yours as each one has their own specifications.
Yes there is less drag in neutral, but that is not the only factor, far from it!
Good luck,
Tom
Where is your proof that there is less drag in neutral? Nothing on the web supports that idea. One example of many: http://www.answers.com/topic/propeller-drag . And why would you want the gearbox working and the accompanying noise unless you were sure? Stu's Hurst example simply states not to lock in "Forward"(possibly because it does not lubricate well when running in reverse). Tom writes that his manual requires neutral. I think we would all want to know what manufacturer requires that. And why would also be good to know. Those of us with folding/feathering props always lock in reverse. Before I had one I still locked in reverse.
Nothing on the web? There are actually two white papers, one by MIT & one by the University of Strathclyde Ocean Engineering Dept. There was also a test were a UK mag, Yachting Monthly, towed actual sailboats through the water, using a strain gauge, and found more drag locked. All of these articles/white papers studied sailboat props specifically.
I also tested a three blade Michigan Wheel 16" X 12P, the same kind shipped as standard equip on new Hunters, and found drastically more drag while locked than when allowed to spin. Depending upon the prop and the pitch there can be more drag with it locked and there is data out there on the web to that specifically studies and addresses this as well as in print mags such as Yachting Monthly..
[ttyouyube]http://www.youtube.com/watch?v=jI-UG9RSlJo[/ttyouyube]
It would be best to default to your specific owners manual for the gear box position while sailing. Mine is almost always locked in reverse but it can also run in neutral safely....
No data on prop drag???
Where is your proof that there is less drag in neutral? Nothing on the web supports that idea.
Nothing on the web?
In addition to Maine Sail's posted experiments in directly measuring prop drag, I posted some personally documented experimental drag results on vessel performance under sail
http://forums.sbo.sailboatowners.com/showthread.php?p=592335&highlight=Persephone
supporting the old USN study (David Taylor Model Basin report, as I recall) that said 2-blade props exhibit slightly less drag when fixed, and 3-blade props exhibit minimum drag when free-wheeling.
I've posted these experimental data before, but they seem to be ignored by theorizing that confuses drag in incompressible fluids (water and ship propellers) with that in compressible fluids (air and airplane propellers).
"Counting the number of teeth in the horse's mouth" I find a lot more straightforward than solving Navier-Stokes equations
However, my cone-clutch transmission permits free-wheeling; not all transmissions do. Be sure to check with your manufacturer.
Fair Winds,
s/v Persephone
PS: the 6,000nm of free-wheeling mentioned in the referenced posting is now 7,200nm - no ill effects apparent.
The clutches in many small marine gear boxes are two tapered cones. One slides along a shaft to engage with the other. You engage them with the gear and the thrust then pushed them tightly together. If you put the gear in forward and then pull the shaft through the water, there may be enough play in the system one of the cones is pulled on enough to reduce the pressure and allow the clutch to slip. It will then quickly become glazed and may start slipping in normal operation. It's then going to need to be rebuilt.
If you read more closely you will see that I did not write that "there is nothing on the web". Rather I wrote that nothing on the web supports the idea that free-wheeling causes less drag. I should have been more specific to state that there is as much on the web supporting fixed as there is supporting free-wheeling. Either way I am glad I have a folder and have to lock in reverse. So I do not have to wonder. 
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