The formula is:

rpm x prop pitch
------------------ x efficiency(slip) = speed mph
1056 x gear ratio

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com
"Barry" wrote in message
...
Hello,
This has probably been flogged to death but I am going to ask anyway.

What is the formula for calculating boat speed?

From memory the propeller pitch, engine rpm a reduction for slippage and a
couple of other things are needed.

I did have the formula on the computer but a recent crash of the system
caused it to be "misplaced"

Many thanks..