Re: Trim operation question
OK the reason I am totally struggling with 13 pitch is your speed and RPM numbers. A propeller theoretically goes forward in one revolution the "distance" of your pitch. This theoretical part is based on it going through a solid, which of course, water is not . . . Imagine a cork screw driving into a cork, you spin it once 360 degrees and it travels through the cork so far, that is pitch. However, again, water is not a solid, so it cannot get 100% of its "pitch" in forward motion, it "slips" some. The amount of that slippage is called "slip". OK, it is basically impossible to have no slip, many boats have as much as 20%, some down near 8%, which is outstanding.
OK with the above noted, your OMC 400 with a 4 cyl 140 bhp engine should have a 1.71 gear ratio. The fact is that with a 1.71 ratio and 4000 RPM, and a 13 inch prop, and 32 MPH result, you would have to have a negative slip number. Basically the boat is going farther than 13 inches with each revolution of the propeller. This is more impossible than no slip . . . So like really impossible. So one or more of our numbers is/are wrong. Either the tach is wrong, or the ratio has been changed, or the pitch is higher, or the GPS is wrong. Out of all of this, I trust the GPS the most . . . I would check the tach with a "shop" tach first. If the numbers are correct, then that pitch is at least 16 inches . . .
