Prop Ringing

[kbmab]

87 Pearson 303, Yanmar 2GM20F with KM2-C trans. Purchased in 07, third owner, previous owners notes from Yanmar Seminar indicate reverse gear while sailing, stopping to engage, neutral to start. Have sailed fine for the past three years ok. Moved to new marina after launch in spring, needed hauled after being at slip a couple weeks, and noticed pink prop, zinc was good, cleaned up well, added a zinc guppy to shaft, for peace of mind. Sailed fine all summer, hauled to check and clean bottom/prop, bottom good, prop had fuzzy growth, and no sign of pink, left for 3 weeks sailing down the bay. While sailing, 4 1/2 kts and up, noticed ringing sound from shaft area, shaft did not turn, which was what I suspected at first, shift to neutral, ring gone. As the trip went along, ring seemed to increase to the point was apparent in cockpit. Only occurred locked in reverse. Comments?

[Jurgy]

No clue on the ringing - but I have another question. My O'Day 302 has the same propulsion set-up, and as a newbie to in-boards, why lock the shaft while under sail ??

I can feel the prop/shaft turning as speed increases, and it seems freewheeling would be less drag.

Your thoughts ?? Thanks

[jrd22]

Letting the prop freewheel can damage the transmission because there is no lubrication if just the output shaft is turning. I believe Yanmar is one that needs to be locked in reverse.

[MacGyverRI]

1, The ringing may be cause by play in the Cutlass bearing and it's bouncing around in there.

2, You lock the shaft (extended cruise) to prevent output bearing wear in the transmission. It's like taking a drive shaft off an old rear wheel drive car to tow it any distance if you can't leave the motor running to keep the gear oil lubing the trans. bearings.

[Jurgy]

Thanks guys -

I will lock the shaft in the future. It is just one more piece of knowledge that comes with time and listening to others.

Tks Again

[Maine Sail]

As always be careful with what you read on the net.

Yanmar specifically advises NEUTRAL and NOT reverse when sailing.

[Jurgy]

Again my thanks -

A quick Google search even found the Yanmar Advisory - MSA08-003.

Here in the Midwest - those of us that have not yet winterized - will be busy come Thanksgiving weekend. Hope everyone else has good weather for end of season chores.

[mitchbrown]

Yanmar recomends neutral when sailing for a specific transmission but im not sure which one it is. I have a 2qm20 and its been used in reverse for 30 years with no problem. A spinning prop has the effective resistance of the circle it spins in and a locked prop has only the resistance the size of the blades. Im not sure what the reasoning behind yanmars new put it in neutral policy is but when i read it, it didn't really make sense.

Mitch

[Maine Sail]

Originally Posted by mitchbrown

Yanmar recomends neutral when sailing for a specific transmission but im not sure which one it is.

Yanmar recommends neutral for "all sailboat engines" & their associated transmissions.

Yanmar Gear Position (LINK)

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.



The guy from Yanmar that I have spoken with 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. They did however have so many issues caused by locking these boxes in reverse that they came up with a warning and official position or Marine Service Advisory as they refer to it.

This info regarding Yanmar does NOT apply to other engine makers!

Originally Posted by mitchbrown

I have a 2qm20 and its been used in reverse for 30 years with no problem.

Many others have too and probably been lucky they have not suffered gear box problems.

Originally Posted by mitchbrown

A spinning prop has the effective resistance of the circle it spins in and a locked prop has only the resistance the size of the blades.

This has been show to be NOT true many times over. MIT, The University of Strathclyde Ocean Engineering Program and Yachting Monthly all studied this exclusively with sailboat props. They all found and were in complete agreement that a locked prop causes MORE drag not less.

I also studied this and made a test jig and actual video to show the very large differences between locked and free wheeling. Helicopter analogies, which started this myth, do not apply to a typical fixed sailboat prop moving through a denser fluid at 4-7 knots.

YouTube - Prop Drag Test Movie

Originally Posted by mitchbrown

Im not sure what the reasoning behind yanmars new put it in neutral policy is but when i read it, it didn't really make sense.

Mitch

The reasoning is quite simple, to prevent damage to the gear boxes. It is long known that when locked in reverse the Kanzaki's could bind up and not go back into neutral before starting the engine. The engines often had to be started in reverse then quickly shifted to neutral.