600hp 22' Scarab XR/-1 propping
 

I've ran a stock 30 Bravo, and a labbed 28 bravo. Both props around 78 mph the boat really starts moving around. I think I need more bow lift, as I think I'm feeling bow steer. Any opinions?

What rpm are you turning both props, and where does your engine make peak dyno horsepower? This will help us figure ouv what is going on.

The 30 about 5k, the 28 about 5200. The motor is still pulling but I'm forced to let off due to general respect for my own life lol.

What rpm do you desire to turn the engine up to? How far are you trimming the drive out at 5-5200?
We will have to consider possible test propellers for you.

Brett

I have a 525efi on it, with a -2 imco shortie and still didn't find the prop for it :-( plenty of stern lift above 70mph!! Best I ran till now is 78mph with a hydro P5 30 pitch @ 5100 rpm but alot of bow steer,stern lift and china walk that i have to pull back. Then i tried a Bravo but plenty of china walk with a 4 bladed. P5x plenty of slip and very slow accellation. Any idea would help??? But i would like to know if a hydro P5 can be worked on for plenty of more bow lift

Your drive is too short, causing most of your problems. You need to try a 1.5" spacer

Modifying your propeller may become a requirement.
Spacers are options too but I would want to talk to you more about that first.

We have a spacer plate test program too. You can test spacers without having to buy them.

Brett

I tried the spacers already, and it didn't improve anything. Just for your info the prop shaft is 4" below the pad.

Harry

!!!!

Ive got a buddy that has the same boat as you with no drive modifications, its a stock Bravo 1 at stock Xdim.. Hes running less HP than you and turning more RPMs than you and runs 78 on a stock 28B1. He ran low 80s on a mirage 25P but the boat got too squirly. 78 to 80 is all that hull likes before it starts getting squirly, unless you have trim tabs.

Dharry is your prop shaft 4" below pad with a shorty on it?
When putting big power in a lighter boat the more pitch you use, is going to lift the transom. My advice turn more rpms. I have always run 6000 rpm range. It seems to have less stress on the drive because of less load, i have never broken a drive with 825 hp behind it well in front of it. On a 30 ft single engine scarab. The more the angle (pitch) is added the more the blade is sideways like a paddle wheel which is lifting as well as pushing.

Thanks for the info. Yes it's 3.3/4 " to be exact below the pad with a -2 shorthy. But since the 525efi is stock the rev limiter is at 5250 rpm, so do you suggest i'll go for a 1.36 gear ratio???

Yes i do have trim tabs and also full hydraulic steering

!!!