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Richard Casady

On Fri, 13 Feb 2009 07:29:13 -0800 (PST), wrote:

On Feb 13, 9:43*am, HK wrote:
Richard Casady wrote:
On Thu, 12 Feb 2009 20:46:13 -0500, D K
wrote:

The one thing I know for sure is the F90 is best
suited for a three-blade prop rather than a four.

Three is always more efficient than four. Four blades is a way to get
the blade area in a smaller diameter, if you lack space.

Casady

My admittedly limited experience with Yamaha taught me that the company
is pretty damned good matching up engines, props and boats, and that a
good dealer is also a valuable resource in prop selection. When I took
delivery of my 2008 model boat, the boat factory had just changed the
prop it spec'd for the boat and engine combo, upon a suggestion from
Yamaha. The factory sent me copies of performance print-outs for several
props. I was able to almost exactly duplicate the performance on the
factory print-out.

Almost every outboard boat I considered has performance sheets available
* from the engine manufacturer, and those sheets specify props.

Really? How did they know your exact requirements as far as weight,
loading fore and aft, etc.?

They give you one in the middle of the range of props that are
individually ideal for one of the varying conditions. My sprint car
has a quick change rear axle. You can change the gear ratio in a
couple of minutes. There are three brands around, and they all have a
magnesium case. Stuff is brittle, but there are no impact loads. They
have variable pitch props for ships and planes.

Casady