Can somebody explain why some boats throw up more of a roost than others?
Beside the obvious horsepower answer, is it more to due with trimming the drives up higher?

i would think trimming.

X-dimension

HP doesn't really effect it. Under certain conditions a twin Bravo drive can throw a small roost.....otherwise it's rare for a Bravo boat to throw one. All of the surface drives throw water (arenson, #6, NXT, etc). The thrown water comes from the top 1/2 the blades being out of the water.

It's all drive height/x-dimension in relation to the water surface. The props have to surface to throw the water up and back.

All surface piercing drives will do it and Bravo's will do it if they are staggered with a high x-dim. Or if you over trim to the point where the props are coming out of the water, But you would be at a ridiculous trim angle to have it happen (trailer mode). At this point the props are just sending the thrust vertically and chances are you wouldn't be moving.

HP really doesn't enter into it.

I would think if a bravo is roosting, you are loosing propulsion as that water is being unused

No. If thrust is lost due to high prop height, it's usually a question of using the wrong prop, or in some cases, running way too high. Everything has its limits of course, no matter which drive and prop is used. If one disregard the issues with thrown blades and ruined drives due to harmonics ect, B1, Maximus, the semi cleaver Hering and Hydro props can easily run in the surface on a B1 drive. It has nothing to do with it being a prop for a Bravo drive or the drive being a Bravo drive. Get the gearcase and prop out of the water to reduce drag, that is what it's about.

Not only that, you will tear the helI out of the u-joints and destroy the drive.

If you wanna go fast, go high with a true surface drive. The rooster never lies.

Bravo1 / Hydro P5X. The tail lays down as speed increases.

rooster tail

Staggered drives with counter rotating props will usually throw a bit of water.

If your interested in huge tails, staggered engines and surface drives and as you trim "up" the rooster will become smaller.