Originally Posted by StuM
1. Shape/pitch and cross sectional area of a boats prop as a proportion of the swept circle compared to autogyro, helicoptor rotor or fixed wing prop. Even a two bladed prop takes up a lot more area than the others and has a greater pitch.
2. Relative density and resultant drag between water
3. Completely different airspeed/boat speed and rotation speed of the propellor
You just can't draw a valid comparison between the two situations.
Spot on mate, spot on!!!!!
Lots of folks think that a prop is a prop is a prop.
The only real similarities between a a/c prop and a marine
screw is that they both spin and both propel. Beyond that, they are two totally different animals
in completely different environments.
It hard for folks to get their head
Now if I may bring this thread full circle and back to the topic at hand (sailing with tranny in gear
or neutral), I have been following this thread (along with many others on the subject) very closely.
Because, as it is now becoming very obvious, I have been taught wrong and have been given a healthy dose of misinformation.
All the way from great grand pappy, through all of my mechanical repair and design education and personal experience's, it has been drill in my head
that you don't spin what you don't need to spin!!!
I.E. keep the shaft stationary when not motoring.
I have always done, observed and even instructed folks to do the same.
It seem that I was/am wrong!
Okay, I can accept that a few blown, locked up, striped..etc, trannies could just be operator error or lack of maintenance
. I think that over the last few weeks I've read or heard of, about a hundred and a half that have failed. 150 out of how many ten's of thousands that were built, seem to be a small amount of failures.
Okay I can live with these numbers. After all I would like to think that I take care of stuff better then most.
has issued SB after SB on this very subject. I think that they are up to three or four now. At first, I thought they were just SMA's (save my ass's). But after reading, what the third one, it is apparent that Yanmar
has a design flaw! To be fair, it's not only Yanmar, but all of the manufactures seem to be drinking the same Kool-Aid.
Okay, I've spent $6k on a new tranny, and now you want me to spend another couple of grand for a shaft lock, just to keep the wear & tear and noise
down. Why the hell is a marine transmission
not designed to allow it to stop the shaft spin in the first place?!?!?
My question is why do we as consumers keep putting up with this crap.
I still think that it is a bad idea to let the prop shaft free spin for hour's/day's/ week's at a time. That can't be good on the bevel gears. So I guess I'm now looking for a shaft lock.
----END of RANT-----