I see outboard and even tunnel boat I/O people raise the X-dimension so high, they are essential running their drives as surface drives for extra top end speed. They couple this with a Speedmaster type lower to lower drag and give the prop better flow. I rarely see that done for offshore, though. Anyone have any idea why not?

Michael

The Bravo was never designed to be a surface drive. It can't handle coming out the water constantly. Also, props built for Bravos are not built to be surface piercing. Prop slip goes up, the blades crack and often break off.

"I saw it on the Internet, I'm pretty sure I can do it".

That's a pretty convincing argument you put out there Griff.

Are the higher hp Mercury outboards are designed to run in a surface piercing state? It seems like it is done a lot.

Michael

What Griff said is correct about the Bravo style drives. My prop is surface piercing and so far I have thrown blades on three different props in three seasons.

Wow - scary. Any damage? Were they all stock props or modified/lab'd?

Do you have a shorter X-dim or do you just launch off waves as much as possible?

There is also the hamonic impact on the gears. The vibrations created when the drive is surfacing travels through the gears as well. On all acounts, it's hard for both prop and drive. When it comes to outboards, the power is often substancially less than on boats running surfaced Bravos. Which kind of prop also plays a factor. When you see outboards running completely surfaced, they run either Cleavers, Choppers ect. that are build for it. When all is said and done, outboards also has their problems with making the lowers last in larger surface installations. Just ask the guys running twins to quads on 25-35 foot cats.

I just got an email from a guy who is running his Imco SC (XR equivalent) with the prop shaft 2" below the hull line on his 21' Daytona, using a Bravo 1 prop. He has a friend who is 1/2" below hull line, with the same prop. Both report no problems so far. I keep wondering how they are getting away with this. One is running 670 hp at over 119, and the other almost 800 at over 130. They do run in calm water, and, of course, the boats are light, comparatively speaking to your typical offshore V-hull.

Michael

I gonna try this in a few months whit 560hp in front of it




Prop shaft is above the bottom it works very well on the classic donzi's

with 560hp,you'll still have to be ''polite'' ,as those were designed for 400-450hp max...good luck