The max rpm on that engine is 4800 rpms.
I would not cruise for extended periods above 4000 as your fuel economy will
suffer greatly. Best cruise rpms for economy is usually about 3200 but you
have to decide based on your hull and the speed you like to go. Every boat
is different in terms of plane speed and ride attitude at a specific rpm.
I would hope the best cruise is not above 3500 though.

--
Tony
My boats and autos - http://t.thomas.home.mchsi.com



"scottht" wrote in message
...
I have a 1986 SeaRay 21' mid cabin cruiser. This boat has a 4.3
mercruiser V6. I don't have a hour meter on the boat buy I am told it
was low hours driven by a little old man I am wondering what sort of
RPM range that I should be cruising at and what is the highest I should
top out at. I certainly don't want to damage the old girl. I have also
noticed that the RPM's don't seem to be consistant when I have opened it
up in the past. Is that to do with current direction? Any help would be
appreciated. Thanks
Scott


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