Fwiw just about all of the data you see manufacturers throw around in advertising their boats ranges use data from the engine manufacturers. The boat test of the sea ray cited in post 69 does so as well. The data is somewhat useful but not as useful as a true propeller power curve which can better quantify the numerous real world variables all boats deal with while underway.
In my experience, very little of the data is based on what engine manufacturers provided. The post in 69 is based on a real test of the boat. The test information I cited earlier was all from actual tests. All the information I share in this regard is based on actual real world data. Yes, there are parameters. The tests indicate those such as "Acme 4 blade 23x26.5p, 3 persons, 30% fuel, 50% water, 50 lbs of gear, 78 degrees, 67% humidity, wind 15-20 mph, seas choppy."
Many of the boat and engine combinations have been around for a long time. Boats are regularly tested by boat manufacturers and by third parties. Now, for the information builders use in advertising, they do tend toward being conservative.
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