As no one else has offered a reply heres my 2p's worth but I'm no expert....
I believe that each prop pitch inch equates to about 200-300RPM. So you
could in theory drop at least one size down from a 17" pitch (end of the
part number). This should raise the max RPM closer to 5000 at WOT. This is
very dependent on many factors and care should be taken to observe the
engines maximum RMP. In my own experience changing the prop size does not
always result in the expected and there seems to be as much 'black art' to
this as science. The rev counter could easily be a few hundred RPM out and A
mis-balanced or slightly damaged prop can make all the difference. If there
is even the slightest nick or bend it is worth getting it fixed and as most
most prop repairers will increase or decrease this pitch by an inch or so
without an additional charge. It may be worth sending the worst one off to
try it. If you find it's no better you could always keep it as the spare.

try
http://www.proprepairs.co.uk/Steel_Developx.html
or
http://www.miwheel.com/MIWheel/produ...board/main.htm

hope this helps


"Mark" wrote in message
...
can someone please help with the following query regarding propeller
specification.
On our RIB is a mariner 100 outboard, we are told the engine will only
make
100hp at 5000rpm, so have just fitted a rev counter, we now find that the
engine is only achieving 4400 rpm with anow weight load on the boat in
river
conditions, therefore we believe the propeller on the boat to be
incorrect.
The current prop has the number 4877344A4017P on it but we also have a
spare
prop with a very slightly different no ie. 4877344A40L17P, these numbers
do
not mean a lot to me personally, but I am sure they witll to some people,
we
assume we need a slightly smaller prop to achieve 500rpm, but any advice
would be greatly appreciated.