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I don't think running it up to WOT, while tied to a dock, is the same as being underway. The momentum of the boat will reduce load on the prop a little. The prop is pitched for being underway. Kinda of like starting to peddle in a high gear, after a few turns it's a bit easier. Not terribly surprising that a cleat let go.
 

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I don't think running it up to WOT, while tied to a dock, is the same as being underway. The momentum of the boat will reduce load on the prop a little. The prop is pitched for being underway. Kinda of like starting to peddle in a high gear, after a few turns it's a bit easier. Not terribly surprising that a cleat let go.
This is correct and ALSO a test of the prop "design"... pitch etc. WOT at idle would test the cooling, and mounts for example... that the governor is properly set.

This makes me think... about motoring. Is it important to determine in a sea trial what speeds the boat achieves at various RPMS... ie "cruising speed" ... hull speed... idle speed (slow as possible)... in reverse?
 

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Is it important to determine in a sea trial what speeds the boat achieves at various RPMS...
I don't know how important it is, because wind and wave conditions can impact these. My last survey did record them, however.
 

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Discussion Starter · #84 ·
Reference the cleat, I had the boat tied to pilings on both sides at the bow and the stern, but I also had a midship line to this cleat that I used to pull the boat over to the dock. When I put the boat in reverse I did not realize that all the load went to that line first. The area around the cleat bolts was partially rotted and so the cleat just ripped out of the piling. As you said, not surprising, except to me at the time.

I plan to run my WOT test again on open water soon, to see if that resolves the max RPM issue. I have in my notes, somewhere, what speed I can reach at what RPM on a calm, day. I also roughly determined how much fuel I use at the lowest setting to reach around 7 knots which is hull speed for a water line length of 29.6 ft. But this changes based on sea and hull conditions (recently cleaned vs dirty), so it is hard to repeat.

Anyway thanks again for the discussion.
 

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Hey,

Very brief point: The Tachometer on a diesel may not be accurate. There are no spark plugs, so no pulses to count. Instead the tach is adjusted somewhere by someone and that's that.

Barry
 

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The Tachometer on a diesel may not be accurate.
That's right, one should buy a laser tach. They are not expensive at all. You put a reflective piece of tape on one of the external rotating parts of the engine. The crankshaft pulley often has a weight on the outside, with a flat space. Point the small laser at it, while moving, and it instantly counts the rotations by the reflection going by.
 
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