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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #11  
Old 05-30-2005
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FalconEddie is on a distinguished road
Should transmission be in gear when sailing?

While the reasons for putting the transmission in gear are correct, in my humble opinion, but reinforced by a lifetime as a mechanic and the past 20 years as a marine mechanic, there is another good reason that I read some 20 or so years ago in Practical Sailor, which I tested myself.

The report had to do with conflicting theories of drag from the propellor, and this is what they found:

A free-spinning prop quickly enters it''s intended range of efficiency where it gets a full mechanical grip on the water. If the props RPM''s 200 or 300 or even 400, imagine how hard you would be working to do that by hand. That''s horsepower and it translates into considerable drag. They had numbers. I forget them.

A locked prop produces some drag at slower speeds that is a tiny bit higher than a slowly spinning prop, but once you start making more than 3 knots, the spinning prop makes more drag. At speeds approaching five knots, locked props begin to cavitate, significantly reducing drag. Yes, there''s still drag - you don''t get cavitation without pumping horsepower into it, but it''s far less than a fully spinning prop that has a secure grip on the water your trying to slip through.

Just my 2 cents.

Fair winds and fine seas, all.
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  #12  
Old 05-30-2005
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Should transmission be in gear when sailing?

I conducted an experiment that convinced me that at least on my boat, a locked prop worked best. While under sail (engine off) I engaged and disengaged the tranny (in reverse). Regardless of sailing point, the boat speed (measured by GPS) increased by about 10% whenever the tranny was engaged.

My prop at that time was a fixed three blade well suited for the engine''s optimum operating RPMs. I have since replaced it with a folding two blade, so I don''t worry about prop drag anymore. ;^)
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Old 07-11-2005
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Should transmission be in gear when sailing?

I always put my engine in reverse when sailing for both the wear and drag reasons noted previously. The reason you use reverse as opposed to forward is that this takes up the gear lash (the small amount of "slop" before gear teeth engage) and the faces of the gear teeth engaged are the same ones as when you are going forward under power. Wouldn''t make much difference if you were in forward but to me this is the tie breaker by putting the gearbox under the stress conditions it sees normally.

Note. I also put the gear in reverse when docked or moored. The same propeller spinning can happen from current. I have never noticed shaft spinning while at my summer mooring probably because the current isn''t too bad. However, when I''m launced into the Connecticut River in the spring there is a steady 3 knot current. Put the transmission into neutral and I can hear the propeller spinning. I make sure that gearbox is in reverse before they launch. Would hate to see what days and days of 24 hr./day spinning would do to my gearbox.
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Old 07-17-2005
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Should transmission be in gear when sailing?

It''s 100% the functiuon of the transmission and not anything to do with the engine or boat manufacturer.

I have a Hurth transmission and it goes in gear and in reverse while sailing. As far as I know all Hurth transmissions art like this and all sail drives don''t have to be. After that you are on your own.
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