How does prop size and pitch effect wake?

[wotan2525]

Have an old and inefficient 14x14 that I have been using for the last 2-years. It's really the prop I've used to dial in everything about my surf setup and it's been REALLY good all summer. Unfortunately, my roommate wrecked it last weekend so off it came and on went my Acme 13x12. This was originally a 13x11 but at some point I had it repitched to a 12 (and I can't remember why.)

I assumed the 14x14 would be a better surf prop but the difference in surface area between the old 14" and the Acme CNC 13" is HUGE. The 13" has so much more surface area that it's crazy.

So... help me figure out why the following happens. Everything was weighted and setup the same except for the prop.

13x12 Acme CNC Prop - Best surf speed 3000-3100RPMs - Wave is crazy long but doesn't seem to have the "push" or the volume of the other prop. Was not effected moving people/weight front <-> back.

14x14 Antique - Best surf speed 3500-3700 - Wave is BIG (above waist high) and has tons of volume but not nearly as long. This wave seems very sensitive to weight in the front of the boat (moving people around.)

[tre]

I don't know how accurate you speedo is but I assume it is not since you are talking RPM. My simple guess is that you were going 1 or 2 mph faster with the 13x12 prop because that will lengthen the wake. Try slowing down more and I bet your old wake will return. The RPM differences are due to the different prop (sounds like you know this). We set our perfect pass at 11.4 MPH for surfing and less than 1 MPH speed difference makes a huge difference in the wake. I just think you need to find the proper RPM to get the same boat speed as the old prop. It is possible the new prop will not hold the same speed you went with the old prop since the RPM is much lower with the new prop.

[wotan2525]

I'm guessing that the speed is a little bit different but since we're riding RPMs, we ride by "feel." We don't determine the right speed to surf at until we get in the water and even then... every rider seems to like it a little bit different.

I can tell you that, without a doubt, the wake would not have been the same had we slowed down or sped up. I'm still completely baffled as to how the pitch and shape of the prop effected the shape of the wake.

Still not sure which one I prefer, either. The 13x12 actually makes it easier to drive a boat weighted for wakeboarding (but until I get adjustable trim-tabs, my trim tab will stay in the down position and it completely flattens out the wakeboarding wake even when we are loaded down with 2000+ lbs.)