You will never hurt anything by leaving it in reverse.
Unless of course you own a Yanmar...
Advisory Number: MSA08-003:
DATE February 8, 2008 Dealers and OEMs
TO: All Marine Distributors
SUBJECT: Gear in Neutral While Sailing All MODELS:
All Sailboat Engines
We continue to get questions regarding the correct gear position while sailing with the engine OFF. This advisory is issued as a reminder; Yanmar requires that if sailing with the engine OFF (not running) the transmission shifter must be in the neutral position or internal damage to the gear or sail-drive will result. This damage will not be covered by Yanmar’s Limited Warranty. Please instruct customers and dealers who deliver the sailboat to the customer, of the correct (Neutral) position for the marine gear while sailing.
If the customer desires that the propeller shaft not spin while sailing, either a folding propeller, shaft break, or other suitable device may be used. However, Yanmar accepts no responsibility for the selection, installation, or operation of such devices. Please also refer to Marine service advisory “MSA07-001_Yanmar Sail Drive Propeller Selection” for additional information.
If you have any questions regarding this advisory please contact a Customer Support representative.
Yanmar Prop Position MSA (LINK)
The guy from Yanmar admitted that prior to 2008 they did not take much of a position either way in regards to reverse or neutral, hence the constant confusion on the forums when talking about Yanmar's.
This info does NOT apply to other engine makers.
For sure, I believe that with a 2 blade fixed prop locked in a vertical position you will have less drag than you would with it spinning.
You would not be the first to still be a disbeliever despite the data to the contrary, many still do. I have also tested a 16" two blade, the same way, and it too has more drag locked then when allowed to freewheel. This was also duplicated about a hundred times on my old C-36 which had a fin keel with a fixed Michigan 2 blade. I always sailed faster or the same speed free spinning than I did when locked with the original factory Michigan Wheel 2 blade. I never once observed the two blade prop add any speed when I locked it. Same on our old Cape Dory but that slug was just difficult to observe any minutia of effect either way.
If you want to know which is more drag simply align it vertically and if it stays there, by itself, when put back in neutral, than it is not causing more drag. If it starts to spin it is taking the path of least resistance. We know that towing a fixed two blade or three blade through the water causes more drag when locked. On our Cape Dory 27 even when set vertically in the well protected aperture behind the full keel it would still want to spin when put back in neutral. This simply means it is NOT as hidden behind the keel wake as people often assume.
Having the blades straight up and down right behind the trailing edge of the keel should really reduce prop drag and enhance sailing performance.
Problem is on most Ericson's the prop is not "right behind the keel" it is set back quite a ways. If it spins after locking it vertically it is just taking the path of least resistance. I have never observed what you have and I have studied this at great lengths over many years in many different situations.
I have heard the research saying a spinning 3 blade is faster than a locked one, but it seems odd to me, and you can't hurt the tranny by leaving it reverse.
Again, unless you have a Yanmar. The Hurth's can be left in either neutral or locked, but free spinning will always result in some minor wear on the cutlass and potentially the gear box. These Hurth/ZF boxes are splash lubed so they get lubed whether the engine is running or not..
I will leave the 3 blade drag argument to smarter folks than me, but for a 2 blade fixed, locked and vertical is fastest and safest for the engine.
Old tales die hard deaths....
From The Strathclyde White Paper:
"The experimental results confirm that a locked propeller produces greater drag than does a freewheeling screw (up to 100% more drag was observed, this being at higher speeds). Furthermore, for the freewheeling case, the magnitude of the hydrodynamic resistance is significantly affected by the amount of frictional torque on the shaft, low torque being accompanied by low drag.
Finally, a simple model of sailboat hull resistance has been used to illustrate the likely scale of the drag penalty due to various arrangements of trailing propeller. This shows that, especially for the case of craft having moderate or low displacement-to-length ratios combined with powerful mechanical installations, the impact on sailing performance of a trailing propeller is very significant indeed. By combining the
present findings with other more detailed techniques which exist for modelling hull drag, the influence of propeller drag on sailing performance should be substantially predictable."
