The motor is indeed a 2+2. I've got it tuned pretty well, so the transition from 2 to 4 is "ok". It switches to all 4 cylinders at right around 2250 which is just where you want to be when you're off plane just poking around.
My wife always thinks the motor is failing.
I did some research and found what seems to be a way to determine pitch on an unmarked prop. Its not 100% mathematically accurate but it got me in the ballpark.
Using it I ascertained that my unmarked prop appears to be a 13x17.
Heres what I found:
Quote:
Pitch can be measured as circumference x slope,where circumference = diameter x pi, and slope = blade depth divided by width.
It's easiest to measure the depth and width at the hub - in the picture below I drew a yellow line to represent the depth measurement and the green line is the width.
If you measure at the hub, then use the hub diameter in the formula. The actual prop diameter is twice the distance from blade tip to center of hub, but it's extremely difficult to measure width and depth at the tip.
My prop for some reason had no markings, but I suspect it's a standard size for the motor (13.75 x 17). I measured the the depth/width as approx 4/3, and the O.D. of the hub is about 4, so 4 x pi x 4/3 = 16.8
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So maybe my prop is OK for the SF18 and I'm just being fussy, I dunno.
Maybe the no-name prop has poorly designed blades, or maybe the boats overloaded and I need to lay off the french fries.
I'm going to see if I can borrow a 13 3/4 x 17 Black Max and a 13 3/4 x 15 Black Max from Nauset Marine and do some benchmarking.