Originally Posted by jwalker
John, I'm a bit lost by your comment. Do you imply that a light prop is likely to allow the clutch to chatter?
JW. A couple of things came to mind in my previous post as.
1. Yes, there is some chatter but this may be only with the power and loads that we use. The engineering on the plastic props, as you found, is not perfect. For example grab the blades and see how much movement there is between them and the hub.... a few mm as a norm on a pyra.
2. The actual engaging of the dog itself. We all know that on an OB we must make a positive action on the dog to avoid gear wear. The action is created at the control box and transmited to the gear box. However at the far end is the resulting action of the prop (with the integration of engine forces). Thus at the end of the scale is engaging a shaft many times with no prop on it. This will not give a "good dog" movement. Inbetween is a prop with poor bite such as a plastic prop.
What I am putting forward is that many only look at the engine side of the prop shaft .... the prop side must account for forces as well.
Now for the honest bit !
I studied for three years propellor theory as part of N.Arch but it was all for big slow boats. It was a long time ago, cant remember much and it was nothing to do with outboard props. !!!
Notwithstanding the above we are aware from 15 years of practical commercial experience that the combination of propping/boat/operator will define dog life. A prop with slip will cause problems on the dog.
To add complexity you must remember that on our operations we may have 100 gear changes per hour (in and out of caves and the "Bitches" etc).
ps. hows the boat coming along !