On Sun, 26 Feb 2006 20:43:43 GMT, "Injam"
wrote:

It would seem to me that in order to go faster the propeller would have to
spin faster.

Given your conditions of identical boats, props and gear ratios, that
is correct. The only other variable is "slip" and that should be
about the same unless the bigger engine is significantly heavier.

If you want to go faster with the larger engine you will either need
to run at higher RPMs or switch to a prop with more pitch, more blade
cuppage, or both.

There is an excellent book available on propellers if you want to
learn mo

The Propeller Handbook: The Complete Reference for Choosing,
Installing, and Understanding Boat Propellers by Dave Gerr.

Available at www.amazon.com