Eggsuckingdog is right. Your prop probably has way too much pitch and to forget about diameter. When choosing a prop, instead just concentrate on pitch and prop model. If you post the serial number off the prop we could probably figure out what you have. If the last three characters happen to be something like 21P that would tell you that you have a 21 pitch prop for example.
Not only do you probably have way too much pitch, your engine could be mounted too low. On my other boat, I just remounted the engine and tested this weekend. My anti-ventilation plate was 1-inch below the the bottom of the hull. After remounting the engine 1 bolt hole up (3/4 of an inch), I gained 250 rpm and 2-4 mph and it is actually still mounted too low. That is a pretty big performance gain with no change in prop. Btw, those Mercury lifting rings they sell on ebay for like $15 work great for remounting an engine if you end up having to do that. With a cheap Harbor Freight hoist, it made remounting the engine a 1-man job.
Do a search on CSC as there are a zillion prop threads.
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10-02-2012, 01:30 AM
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