fireboatpilot

32' Hydra Cat, twin 700hp Bandit 540's, Imco SC's, -2 shorties w/ 1 1/2" spacers and 1:50 gears, X dim is 2 7/8" above bottom spinning 4 blade 36P Bravo 1's top speed so far is 118 mph but hits rev limiters at 6K. I need more prop so I'm changing the lower gears to 1:35 so I can use 5 blades. I'm figuring I need to drop down to around 34P 5 blades to start testing props? Any thoughts, ideas? One other thing, with the Bravo props I get a serious porpoise starting around 80-85. I'm thinking the Bravos can't hold the stern lift?

IGetWet

Prop slip is pretty low for that high with 4 blades, 13.5 ish %. Maybe try some 34 4 blades first after the gear change to see where you’re at then. Things can get tricky when you change more than one thing at a time. You want to be 5700-5800ish rpms WOT?

Griff

First thing to do is try your current props after the gear ratio change to get a good baseline. The ratio change would normally equal about a 600rpm decrease with the same props, but your results will most likely be less of a reduction since you are hitting the rev limiter.

When switching from Bravo 4 blades to most 5 blades, with no other changes made, you would normally go with 2" less pitch on the 5 blades.