Wish I would have done this years ago, even with the torque of the 575sci. Would load the hell out of the motor and drive and wouldnt slip the prop at all. On my old 2.5 outboard stuff the overhub type prop ventilation was like a revelation! I am feeling the same now.

I'll have to try that before I have some made, that's a pretty good idea! Did you make it up kind of like the 3rd pic you posted?

I think I'm getting real close to the right prop, I'm just waiting on a call back from Bblades to maybe try a 30p, but just not sure if I can get up with it. If the simple setup you did with the hose helped that much I should be golden! Did you only run one 1.75" hose, and was it just set off to one side in front of the prop?

I'll get pics, I run a left hand prop because my boat runs flat at lower speeds with it. The top of the tube I zip tied to the right (stbd) side of the drive shower hose by the top cap and steering ram mounts. I ran a hose clamp around the back of the trim cylinder and another through it and around the bottom of the hose. The 90 hooks around the cav plate and ends 1" away from the prop.

My new plan after looking at it last night is to run the tube directly thru the stainless imco cav extension plate, with a bung on top for a hose.

What is the exact problem that the vent tubes solve? Does the air create a pocket, so to speak, to allow the prop to spin up?

Cats typically run much higher pitch prop than V hulls of the same power and size. It is to slip the prop and help the motor rev into a higher power RPM.

I only ran one from the back of the top cap straight down and the 90* bend hooked under the cav plate and is about 1" from the prop. I verified that the ID is 1.75". Had the boat out last night and i liked the way it came on plan. Still will experiment with a smaller tube to see if it will give me more bite.

Got it. Thanks. :) kinda like slipping the clutch in a car with tall gearing.

Yes. Slipping the clutch will at least get you going.
The tubes allow air to break the high pressure water off the blade faces creating a initial high rpm to get the boat moving. The high rpm will create a slight launch as the blades re-load. Once the boat is up the vent tube are non-effective because there is no longer a direct line of air to water to prop. There is now a air gap between bottom of cav plate and the water itself.

Brett

Well I got to try a 1.75" radiator hose, WOW what a difference! It still loads up for about 10 sec or so but after that it's like a rocket!

It seems to maybe slip a little much with 1.75" hose, but I'm going to try it with a 30p first before I down size. Just having to wait on a 30p to become available from Bblades (cough cough Brett) before I can do more testing.