CBR

I'd like to know if anyone on OSO with a twin engine 30ish foot boat changed their X dimension, by how much, and what speed they gained.

I have a Sonic 1988 30SS and am thinking about raising the X by one inch. The boat is also getting Bravo I 24 pitch four blades fitted to the new Bravos and Scorpion motors going into it. Any other prop suggestions?

Thanks in advance.

tomcat

I raised propshafts 2", 30 Excaliburcat with TRS. This is what happened:

Before, propshafts 6.5" below hull

25 Mirage, 80 @ 5200
27 Mirage plus, 80 @ 4800, 66 @ 4000
29 Mirage plus, 78 @ 4300, 74 @ 4000
26 Bravo one, 78 @ 5000

After, propshafts 4.5" below hull

25 Mirage, 83 @ 5500
27 Hydro Q IV, 84 @ 5000
28 Bravo one, 82 @ 4800, 68 @ 4000
27 Bravo one, 82 @ 5000, 63 @ 4000

I would say that raising the drives gained 3 mph, but Mirage props would blow out, hard to plane with a load. Four blades were needed, slower, but got the planing back, little blowout with Hydro, none with Bravo. You lose ability to trim the bow as you raise the drive, not a problem with a cat where bowlift is by air, but you may not like it. Hydro had the least bowlift/ most sternlift. Was the fastest but I didn't like the way it felt, especially in calm water. All tests with props turning inward at the top, supposedly gives the most bowlift, maybe a bit more speed.

I would try a bigger diameter three blade at the raised position if I could find one. The 29 Mirage plus is 15" diameter instead of 14.5", but I don't have enough power to use it.

CBR

Great information TOMCAT, thanks!

Anyone else with a V hull raise the x in their boat?