I dont want to calculate speed. I asked the question this way because I knew
someone out there had the formula.
I want to ensure that my new boat has the correct prop fitted. I can have
the speed recorded by GPS, I will know the prop pitch and gearbox ratio and
maximum engine rpm. With all of that I can calculate slip and make a
decision on the prop.


"Peter Aitken" wrote in message
om...
"Woodchuck" wrote in message
...
For me, it works very well as my props have about 8% to 10% slip and
it's
verified by GPS. But then again I'm running a hi-performance boat over
100mph. The props I have are Mercury stainless steel lab cleavers. Most
average consumer props have alot 15% slip for stainless steel and near
20%
for aluminum. The calculation provides a good starting point when you
want to change pitch, RPM, mph, etc

No one has asked the obvious question - why would anyone want to calculate
boat speed this way?

--
Peter Aitken