Texasmark
Supreme Mariner
- Joined
- Dec 20, 2005
- Messages
- 14,778
Re: Noisy Prop
River, The clatter is the clutch dog sliding over the sawtoothed F gear (slip clutch). For some reason, marine engineers, years ago decided that you need a slip clutch in F so that when you reduce the throttle on the engine, whatever the prop is doing in the water will have no effect on it.<br /><br />So, like if you are doing say 35 mph at 5000 rpm's and cut the throttle, the prop is still churning water at 35 mph, but the drive to it stops so they put in the slip clutch so that the engine can go to idle and later on the prop can catch up to (slow down to) the reduced rpm's.<br /><br />Same thing happens on farm tractors. They have what's called an "overrun clutch" such that if the load is going faster than the engine, (like the boat senario just mentioned) it's disconnected from the engine and won't drive you into a barbed wire fence or bar ditch.<br /><br />For some other reason, the same knowledgeable folks decided that R doesn't need this so there is no slip clutch function on R.....you are either in or out.<br /><br />I Don't buy the exhaust noise stuff. Exhaust doesn't have a clue what kind of prop (if any) you are running.<br /><br />Just had a thought. The reason you hear it on a SS prop is metal density. The SS is much more dense (heavier as a result also) than alum so that you have the same phenomenon with both props, you just can't hear it on the alum because it's not very dense and doesn't carry the sound.<br /><br />Now if the noise is caused by prop back drag (rattling the slip clutch); who gives a flip what the prop material is....prop drag is prop drag. All props drag; just so happens that you can't hear it on the lighter props.<br /><br />My 2c and I think it has merit. Open for ideas. Amazing what one can learn on here by just looking at things and applying a little common sense. I love it.<br /><br />Mark
River, The clatter is the clutch dog sliding over the sawtoothed F gear (slip clutch). For some reason, marine engineers, years ago decided that you need a slip clutch in F so that when you reduce the throttle on the engine, whatever the prop is doing in the water will have no effect on it.<br /><br />So, like if you are doing say 35 mph at 5000 rpm's and cut the throttle, the prop is still churning water at 35 mph, but the drive to it stops so they put in the slip clutch so that the engine can go to idle and later on the prop can catch up to (slow down to) the reduced rpm's.<br /><br />Same thing happens on farm tractors. They have what's called an "overrun clutch" such that if the load is going faster than the engine, (like the boat senario just mentioned) it's disconnected from the engine and won't drive you into a barbed wire fence or bar ditch.<br /><br />For some other reason, the same knowledgeable folks decided that R doesn't need this so there is no slip clutch function on R.....you are either in or out.<br /><br />I Don't buy the exhaust noise stuff. Exhaust doesn't have a clue what kind of prop (if any) you are running.<br /><br />Just had a thought. The reason you hear it on a SS prop is metal density. The SS is much more dense (heavier as a result also) than alum so that you have the same phenomenon with both props, you just can't hear it on the alum because it's not very dense and doesn't carry the sound.<br /><br />Now if the noise is caused by prop back drag (rattling the slip clutch); who gives a flip what the prop material is....prop drag is prop drag. All props drag; just so happens that you can't hear it on the lighter props.<br /><br />My 2c and I think it has merit. Open for ideas. Amazing what one can learn on here by just looking at things and applying a little common sense. I love it.<br /><br />Mark