[alberg30] Diesel Prop Size/Pitch

[Peter Hay]

During some of the discussion on props for A4's I noticed that the preferred prop size is an 11".  I currently have a 13 x 7 on my Universal 25hp diesel.  From what George has said in the past and what I have learned since, that is very much under-pitched because the diesel tranny has a 2 to 1 reduction.  I have been told that a 13 x 11 or 13 x 10 would be better.  The problem is that with a 13" prop I have only 1/2" at the top and 1" clearance at the bottom.  Although the engine runs great I have a distinct "bowling balls in a barrel" sound that only occurs when the engine is in gear.  At first I thought it was a motor mount, but I have fixed that problem and checked the alignment--all OK.  Is my problem too big a prop causing cavitation or will the problem lessen when revving less with a greater pitch?  I am willing to change the prop but not sure what to do.  Has anyone experience with this problem? 

Peter Hay
Rubicon KC384
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