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Herring prop, broke or hit something?

Old 09-28-2020, 12:14 PM
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Default Herring prop, broke or hit something?

We did a run down to the inlet and the waves were 6-7' I fell off plane going into the waves because I was going a bit too slow. Tried to get back on plane and didn't like spinning the props as much as I did so I backed off and cruised out further to get past the inlet waves. Turned around and got back on plane. Had a brain fart and was on the wrong side of the submerged jetty, more then 15' away from it. Turned around went back through the inlet. Cruised back and opened her up hit around 100 and got air about 3-4 times no vibration at all, then slowed down to around 60-70mph for about a minute and all of a sudden vibration.. I dropped the throttles immediately and had a lovely 2hour 7-8mph cruise back to the ramp on the other engine. My friends were in their boat too and my one friend thinks I hit the jetty. I saw that jetty and knew I was safe and far enough away. He thinks I hit it but I wasn't close enough and felt nothing and the boat performed like always after my brain fart. And if I did hit anything even something in the water after my high speed run wouldn't the other blades be messed up too? I'm thinking I cavitated the props too long and they heated up and caused a stress fracture or did the blade just snap off? But how could the blade fold in the direction of propulsion? It's like it bent in to create more pitch? I did use that engine to dock but I doubt low speed would bend the prop in reverse? Thoughts?




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Old 09-28-2020, 12:35 PM
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Fatigue break; not s strike. A strike would have have damage to skeg or other blades. When props lose a blade, that's exactly how they look.
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Old 09-28-2020, 12:48 PM
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I've had that happen with a bravo prop. I felt vibrations, when I stopped the blade was still there, but had a crack 3/4 of the way across the blade. By the time I idled back to the ramp, the blade was gone.
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Old 09-28-2020, 03:01 PM
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How did the broken blade bend IN to create more pitch?
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Old 09-28-2020, 05:50 PM
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Appears the blade failure initiated at the "pit" at center of "beech mark" at the discharge or aft end on pressure side of blade. As the prop rotated the partial section of blade carried the complete load on a reduced cross section. The remaining section curled in and deformed until it eventually yielded and failed (in shear?). Sample beech mark. See yours now?



Last edited by 28 V; 09-28-2020 at 06:01 PM. Reason: sp
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Old 09-28-2020, 06:03 PM
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Originally Posted by 28 V View Post
Appears the blade failure initiated at the "pit" at center of "beech mark" at the discharge or aft end on pressure side of blade. As the prop rotated the partial section of blade carried the complete load on a reduced cross section. The remaining section curled in and deformed until it eventually yielded and failed (in shear?). Sample beech mark. See yours now?


Ahhhhh excellent thank you now I understand why it curled in
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Old 09-28-2020, 06:31 PM
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The discoloration may indicate it was cracked for awhile...maybe inspect same area on the other prop?
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Old 09-29-2020, 08:49 AM
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Originally Posted by 28 V View Post
The discoloration may indicate it was cracked for awhile...maybe inspect same area on the other prop?
I didn't see any cracks or bends before launching on that prop, the starboard prop had a minor bend.
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