Does the hull impact the efficiency of the propeller?

That is, if a certain motor with a certain propeller pushes
a fiberglass boat at 90% efficiency, will that same motor/
prop drop to 85% (say) efficiency behind a pontoon boat?

Or, would it just turn that much slower, at the same
efficiency?

--
frosty

tony thomas wrote:
1. If you are wanting to know what a different prop will do for your
speed. Most know that a 2" pitch change will be about 300 rpms.
2. If you want to know how accurate your speedo is. I have found
that most aluminum props are about 85% efficient. Performance SS is
about 90%. A High performance prop like a Merc Lab, Mazco, etc.
are about 92%.
These are just examples. I use the formula all the time. When
someone says they have a 150hp engine that is turning 5500 rpms w/ a
22 pitch prop and running 80 mph you know they are lying. 61.27 is
theoritical and w/ a good prop at 90% they would be at 55 mph.
Now a lot of speedometers will show 80 mph. Without a GPS the
formula is the only way to really know.

"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

"Peter Aitken" wrote in message
om...
No one has asked the obvious question - why would anyone want to
calculate boat speed this way?