1990 38 Fountain. SSM IV drives. Propshaft 1.5" below bottom.

Engines making 750HP@5500, 800HP@6000.

So far, I tried 17x29 4 blades. 5500 get me to 83mph.

17x28 four blades, supposedly added cup by merc, 5400 gets me 85mph.

Boat needs to be trimmed quite a bit to free up the hull and pick up some speed.

It seems I may need to step down in pitch, to get engines up in RPM a bit more. Also, since I have to use a lot of positive trim, the fact the bullet of the drive is no longer at a efficient angle, is probably scrubbing speed. I assume more rake would help here, only problem is, some new high rake merc or herrings really aren't in my budget. Would a 16.5 diameter get a little more bow lift?

Any thoughts here?

Hello,

What is your gear ratio?

It looks like the 28's with the bigger cup have the lower slip % (hooked up better). 29's are slipping quite a bit.

Decreasing the diameter will decrease the stern lift and can induce better bow carrying help.

Brett

Sorry, 1.5 ratio Brett .