What they have now is simple. If the driveshaft turns, so does the impeller in the pump, (assuming the rubber vanes are still attached to the hub) and it should make water. Electric pumps are not a good idea on any engine IMO. You simply become more reliant on another electrical device to work. I like mechanical and keep it simple. I get your point about the rubber giving up the ghost.
Corrosion and weight issues I suspect is why they went rubber. That and the fact that they required a pump that will self prime at idle speed of around 400 to 500 RPM, yet run up to 6000+ RPM. Centrifugal pumps will loose efficiency at some point and would need to be slowed down or run the risk of cavitation. IIRC displacement pumps are better suited for the huge range of operating RPM's. Some additional demands are that it must be capable of pumping sand and small debris without running the risk of clogging a vane as is in the case on some centrifugal pumps, must be capable of running dry for brief periods, must fit within the confines of the lower unit so it would need to be small but I don't see why they couldn't work out those issues. So in the end I would say, I don't know. GOOD QUESTION! The answer might be planned obsolescence or the answer may lie in the text above, or be completely unrelated. Interesting that no modern outboards have any "different" designs. The Japanese are some very smart folks. You would think they would have a better mousetrap by now.
On a 2-stroke I would say they don't have a different water pump becuse they can't drive it off the cam.. LOL! IDK!! Grasping at straws.
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1996 -19' NV Flats 115 Mercury 4-stroke
1983 -20' Wellcraft Center Console 250 XS
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