Johnb

I have one of these boats and have fought porpoising forever..
I run a 1150hp 540 (AFR 357CNC, matched cam, 14:71 @ 14psi)
34 5 blade (1.5 gear) spinning 6500rpm+... Did not get there over night. Larbe Tunnel tabs, raised drive (raised!) straight bottom, shifted CG and it is very sensitive to trim and power, The boat must be driven through the mph ranges and its transition points. Likes a good chop- On a glass surface I can make this boat porpoise at any speed if there is no acceleration event or if I do not watch the trim. The chop is more forgiving and the boat is a different animal.

tonyasz

Did the tunnel tabs make an appreciable difference. I understand they help on some cats. I am looking into installing them but have issues with swim platforms and exhausts and was wondering if results are worth the effort and expense. Also am relative newcomer and not familiar with CG-can you define for me. Thanks for the input.

tonyasz

Do you think the tunnel tabs made a difference?? thanks in advance!

GPM

What RPM are you running at top end ?

tonyasz

5100 RPM... 30 pitch bravo 1........... any suggestions?? thanks in advance!!

GPM

Have you tried a smaller prop and more RPM ?

tonyasz

We did use a 26P that a friend loaned us... As far as we can remember the porpoise was still there.. Can you explain how more RPM's would make less porpoise?? thanks in advance!

Brad Zastrow

Have you tried trimming the boat up? Cats need air and will porpoise if run flat.

GPM

Sometimes the torque load can affect how the prop carries the boat. With my DCB I usually run it up to about 50, raise the trim to where I run at top end, back off for a second and then hit it. It will porpoise between 60 and 80 if I run it up slow. The smaller prop would accelerate quicker and maybe run though your problem area.

plumb crazy

My buddy has a DCB we put a set of tunnel tabs on it and all the porpoise went away !!!! SIMPLE FIX LOW COST IT'S JUST MONEY.