Ok, by way of further information. The two British Seagull outboards I have both have identical impellers. They run off the drive shaft just like the rubber ones do, and in fact are mounted in the same place. The difference being that they are in a centrifugal pump housing instead of a positive displacement type like the rubber ones are. The pump body is stainless steel and the impeller is made of some kind of hard plastic. I would hazard a guess that it's nylon. Point being that they work the same way off the drive shaft. This is what one looks like:
http://www.ebay.com/itm/British-Seag...item4183e342a7
I understand that at high revs the rubber impeller collapses , but I would think that with the proper ducting of incoming water there really wouldn't be any cavitation problems with a centrifugal impeller. As to the self prime feature, if the pump is designed to be submerged when the engine is in the normal operating position I don't think that would be an issue. I fully understand that they have been making outboard engines with rubber pumps since Ole Evinrude invented the outboard in 1907, but that doesn't mean there aren't other pumps that can do the job.
So, except for the fact that they sell a new pump to everyone once a year thereby guaranteeing themselves sales... I say again... What is a factual reason for the use of a rubber impeller?
__________________
1987 V20 w/1987 150HP Yamaha on a Shoreland'r Trailer
1978 16.5 Airslot w/1996 120HP Force on a Four Winns trailer
1996 V21 w/1993 200HP Mercury on a Shoreline Trailer
All towed by a 5.7L Hemi Durango.
If God didn't have a purpose for us we wouldn't be here, so
Live simply, Love generously, Care deeply, Speak kindly.
(Leave the rest to God)
Silence, in the face of evil, is itself evil. Not to speak is to speak, not to act is to act. God will not hold us guiltless.