[Public-list] Two vs.] 3 bladed prop

[Peter Hay]

  Phil:
  I have a Universal M4-25 diesel.  It came with a 13x7 prop which I changed
to 13x9.  The power was great and reverse even better.  However since I do a
lot of travel north and south in Lake Huron I spend a lot of time running
around 2200 rpm.  The two blade produced the above results but also very
annoying cavitation that sounded like bowling balls over 1600 rpm.  I bought
a used 12 x 7 three blade and the cavitation disappeared.  The reverse
thrust is still excellent (I can come into dock fearlessly).  Forward
acceleration is slower, albeit the prop will actually slip substantially if
heavy throttle is applied until the hull is up-to-speed.  Conclusion:  For
around the bay runs etc. I would stay with the two blade (which I have kept)
and for long distance the three is preferable.  Most of the problem comes
from the fact that two blades pass the deadwood at the same time and the
thirteen inch prop doesn't have enough tip clearance.

  Peter
  Rubicon #384
  Goderich, Ontario






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