The TLDR of this article: You should be in Neutral gear while sailing.
There is a common discussion among sailors on what gear you should be in while sailing. You have turned the engine off, raised the sails and are crusing along. Should you be in forward, neutral, or reverse? The issue is that water is flowing across the propellor, which then can potentially turn the shaft, which then turns gears in the transmission. Almost everyone agrees that being in forward gear is a bad idea. This just wrecks the transmission. So that leaves neutral or reverse. In neutral, the prop freely turns as the boat moves, but the transmission is disengaged. If it is in reverse, then the prop is held in place by the transmission. Some people don't like the sound of the prop and shaft turning. The problem is that if it is reverse there is pressure being applied the the transmission, which causes wear and tear. This is what Yanmar says:
Advisory Number: MSA08-003 DATE: February 8, 2008 TO: All Marine Distributors, Dealers and OEMs SUBJECT: Gear in Neutral While Sailing 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.
So they give the alternatives. You can have a folding prop, shaft break, or other suitable device. If you have a folding prop, the gear still must be in neutral. The prop being folded will cause the shaft to spin minimally. If you have some kind of shaft break, then potentially the prop can be locked, because the shaft can be disconnected from the transmission.
While the advisory above is for Yanmar engines, I don't see how it doesn't apply to all makes of engines. Having just spent thousands of dollars to get the transmission on Achernar rebuilt, we are going to do everything we can to protect our investment.
