Bishoop wrote:
"trainfan1" wrote in message
et...

Bishoop wrote:

"mark" wrote in message
...


I have a 225 ficht on a 26' v bottom aluminum workboat and at 6000rpm the
3 blade only gave me around 35mph and the 4 blade again at 6000 gave me
42 mph, I was amazed because I thought the 3 blade would give a higher
top speed.


Were they the same pitch and diameter?



Of course not.

Rob


I don't belive so either. With the facts as they were presented, the laws of
physics would have to be rewritten.

In probably 99% of all installations a three blade with the same pitch (all
other things being equal) will be "slightly" faster than a four blade.



I am no expert, But I think the 3 blade would run faster with equal
pitch. This is due to the added resistance of pushing the forth blade.
On my old cuddy (gee I miss it :-) I had a 17 on it and heard the boat
would plane at slower speed with the four blade. Merc suggested since I
was trying to keep the rpms the same to go to a 16 inch pitch four blade
as a direct replacement for a 17 three blade.

Tried it out and the boat did plane at a faster rate, I am not a speed
demon so I really did not try to see where the top end was.

Retired the four blade to the "spare" shelf as it made holding the bow
up rather difficult - ie the boat ran with the stern up high and
trimming it would not help.

Your mileage may vary, this boat had a wide stern for it's length and 18
degree deadrise at the transom.

Capt Jack R..