pstephens46; propeller and motor rotation

[99yam40]

there was a motor I had that the prop only locked in one direction and racheted in the other.
I though for sure it was this C40 Yamaha,either I was wrong or something has changed.

getting older my memory tends to slip now and then too

[dray0151]

I think it's a good thing most of us old guys with slipping cluthcdogs have all the other old guys with slipping clutchgdogs looking out for each other and reminding each other of things!!

[panasonic]

For your viewing pleasure...

https://youtu.be/hYPuB9nmS8E

[panasonic]

And this one....

https://youtu.be/vuAcrDFvApA

[99yam40]

well does that tell me if your prop shaft will ratchet in one direction and not the other while in gear or not

[panasonic]

well does that tell me if your prop shaft will ratchet in one direction and not the other while in gear or not

I think that depends on the particular L/U. They all basically work the same way (as shown in the video) but I believe some have dog clutch construction differences that allow them to ratchet...I think Rodbolt was talking about that in another thread.

The ones in the videos posted do no seem like they would ratchet as the dog teeth are very square on both sides. No ramp up one side of the tooth.

[pstephens46]

Why then did Yamaha design certain motors to detect reverse rotation and to take precautionary actions if and when they might? Which you say can't happen.

If Yamaha is incorrect about what they say in their service manual, what else might they be saying that is incorrect?

Have you reported this error to Yamaha US so they might convey it to Yamaha Japan so that a service manual error can be corrected?

Granted, it may certainly help to shut the motor down from ignition and injection side of the business if this CCW force is detected. But you could still get plenty of water in engine, correct? How would you know NOT to restart engine?

Look at this mess I have created.

[TownsendsFJR1300]

99YAM:

The forward and reverse gears have notches (elongated holes,square internal) for the clutch dog to engage.

The clutch dog should not slip/ grind (pop out of gear) unless there's an issue.

Either worn dogs, (edges rounded off) clutch dog NOT fully engaged (shifter issue), loose dog on the shaft (worn out), etc...

Those clutch dog "tabs" are sometimes "back cut". (I don't know about Yamaha OB's specifically). Back cut meaning once it's engaged, the more power you apply the more the back cut pushes the dog into the gear.

Pretty common in high HP motorcycle transmissions...

Posts where the op states he can't get full engagement but just clicking is exactly that. The dog is NOT fully engaging into the problem gear (often mis-adjustment of the shifter linkage-especially after a WP change). Of course if the issue starts by itself, there's likely other issues.


Question for Boscoe.. In your career with Yamaha, (or other experience), how many cases have you come across/heard of, concerning water forced into the exhaust resulting in any engine damage?

I suspect it's very limited with specific NOT normal operation by the captain...


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[panasonic]

Good for you.

Nothing wrong with being skeptical. Those that are sometimes need to see for themselves. It is what I do if and when needed.

I did not believe my Mama when she said the pot was hot. I 'spearmented to see for myself. She was right. Made a believer out of me.

This guy believes in you Boscoe and has filed for a patent to prevent it happening by installing a "Sprag Clutch" on the LU driveshaft so it cannot be back driven by the prop in any circumstance. The patent was only filed 2015 year. Look at the drawings.

United States Patent Application: 0170073056


Very interesting. Same concept as a sprag clutch on a helicopter main power output shaft, the engine can drive the rotor (prop) but the rotor cannot drive the engine, thus allowing rotor system to freewheel when engine fails and you can auto-rotate and not hit the ground so hard....

[boscoe99]

Granted, it may certainly help to shut the motor down from ignition and injection side of the business if this CCW force is detected. But you could still get plenty of water in engine, correct? How would you know NOT to restart engine?

Look at this mess I have created.

From the reports I had, the operators did not initially know their engines were damaged. After being hard throttled backwards and slipped it into reverse the motors died. When a start was attempted the motors would not either turn or they turned with lots of bad noises being made.

Seems to me that even with built in protection it does not always work. Now keep in mind it is the digitally con*****ed motors that have some self protection built in. The manually con*****ed models don't. The manuals are the ones that are most prone to being damaged when the operator mis-jockeys the throttle(s).

What happens in a modern car or truck today if the shift selector goes into reverse while the car/truck is traveling down the highway? I suspect the brains are smart enough to over ride the operators input. Need our flight test engineer fairdeal/pratt to let us know.

[boscoe99]

This guy believes in you Boscoe and has filed for a patent to prevent it happening by installing a "Sprag Clutch" on the LU driveshaft so it cannot be back driven by the prop in any circumstance. The patent was only filed last year.

United States Patent Application: 0170073056


Very interesting. Same concept as a sprag clutch on a helicopter, the engine can drive the rotor (prop) but the rotor cannot drive the engine.

You should know better than most that air loads can be used to air start an R2800 without the starter motor being used. Just activate the unfeather button and watch the propeller start to turn. If air loads can rotate an 18 cylinder motor using skinny propeller blades then imagine the loads being imposed by water. Even though the blades are much tinier.

[TownsendsFJR1300]

You should know better than most that air loads can be used to air start an R2800 without the starter motor being used. Just activate the unfeather button and watch the propeller start to turn. If air loads can rotate an 18 cylinder motor using skinny propeller blades then imagine the loads being imposed by water. Even though the blades are much tinier.

Air loads on a Cessna 152 prop would NOT crank over and start the engine.. A small 4 banger yet..

[99yam40]

From the reports I had, the operators did not initially know their engines were damaged. After being hard throttled backwards and slipped it into reverse the motors died. When a start was attempted the motors would not either turn or they turned with lots of bad noises being made.

Seems to me that even with built in protection it does not always work. Now keep in mind it is the digitally con*****ed motors that have some self protection built in. The manually con*****ed models don't. The manuals are the ones that are most prone to being damaged when the operator mis-jockeys the throttle(s).

What happens in a modern car or truck today if the shift selector goes into reverse while the car/truck is traveling down the highway? I suspect the brains are smart enough to over ride the operators input. Need our flight test engineer fairdeal/pratt to let us know.

I know that back in the late 60s a GMC automatic would lock the tires up.
not sure for how long, because I ****ed it back into forward

[panasonic]

Air loads on a Cessna 152 prop would NOT crank over and start the engine.. A small 4 banger yet..

Scott you are correct, not enough blade area on a 152 to turn that prop in the air. So if you shut her off in the air...you better pray the starter will work.

Bigger engines with much more blade area (more blades) can "air start" as Boscoe said.

[zenoahphobic]

Airstart in some instances. It would have been deliberately designed into the prop/ gearbox/ compression and so on and then tested and tested.
Remember air is very "elastic" and slippage is a useful phenomenon, aero engines can be brought up to useful rpms at a standstill (torque conversion); you can't do that with a boat prop much.
Rodbolt hinted on what I think why there seems to be Yamaha ( and Honda) concern about reverse rotation, is that there are a number of ways and instances, that an engine can be reverse rotated, and that is not a good thing, so the engine is designed to switch off. Momentary turns by hand be it flywheel or in gear prop shaft, even perhaps the prop being temporarily in contact with something whilst the boat going up and down stationery in heavy sea.
This is a continuation of that other thread,where I reckoned in that situation, at high speed slamming into reverse will see massive turbulence from cavitation and ventilation, because the water is not "elastic" torque conversion cannot happen, as it needs to, the mismatch of "gearing" if you like, in those circumstances would be extremely huge.