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Prop Sing

Category: Prop Shaft

Contributed by Kenneth Parnell

Summary: The prop on my NC33 makes a sound at 1400 RPM which seems to eminate from the cutlass bearing. The sound is not present below 1300 or above 1500. This sound has been there for the previous owner since he purchased the boat.
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I had her hauled to WA and before launching we changed the cutlass bearing and had the prop ballanced (local prop shop). Didn't eliminate the harmonic. I found broken motor mounts and the shaft rubbing on the brass through hull pipe.

Called Tacoma prop with this problem. Robert said "simple fix" bring your prop in and I will put a 45 degree cut on the trailing edge and eliminate the " prop sing." When he looked at it he said "looks like a Taiwanese one, but has to be original as it has European numbers on it.

Robert checked pitch and found 16", 16", 15 1/2". Said he would correct that because it would cause a vibration. When I picked it up he said that none of the blades were cut the same or had the same shape. He corrected that with his computer. Cost was $200, beats buying a new one.

The last thing he said as I left was to put it on without the key and mark the shaft at the front of the prop. Then install it with the key in. The key kept the prop from going on all the way by 5/8". I had to grind the key down until the prop fit correctly.

The prop nut and cotter pin fit in the original position but I had to re-drill the nut with the prop seated for the cotter pin to go through the shaft hole. The prop has been offset about .050" all these years from the factory.

You wouldn't believe the difference an efficient prop makes and how good it feals.