I think he is talking about straight bottom Formula's. Nobody on here has done it, or at least posted about it. That is why I was hesitant to bite the bullet.

There is plenty of info on OSO related to straight bottom hulls with high X. In about in 2000-2002 the -2 Imco lowers became available that turned out to be a relativity inexpensive way to raise the X on an existing hull. The Bravo 1 props then allowed the new factory boats to have a much higher X which provided more speed. If you search back about 10 years and you should be able to find numerous threads about -2 lower info on older straight hulls from Wellcraft (Scarab), Formula, Cigarette, Checkmate, etc. The stepped vee hull manufactures led big time by the master marketer Reggie Fountain took most of the credit for the speed. In reality a large part of the speed came from the Mercury Bravo 1 props, coupled with high X dimensions (just rigging) and lighter lay-ups and some with cored hulls that increased speeds.The ventilated hulls did add speed (2-4 MPH?) on some boats but not significantly compared to the other changes. There are lots of old guys that know more than me, maybe some with add to this post of correct whatever BS I have posted.

I was reading some of your old posts about the marketing factor of the stepped hull and that most of the speed gains were really from higher x and props. It's funny how much power marketing has. There is certainly more than one way to increase speed, and I would rather make my boat more efficient, than just keep throwing more power at it. At which point drive durability starts to become an issue.

Exactly. Why throw power at a problem when you may be able to increase efficiency. Why sacrifice engine reliability and drive reliability when things like less drag and less weight can do the same?

I have more research to do on the subject, but what worked on a straight hull Fountain with a different X than I have is not always directly comparable. In addition, there are many more props available today than in 2000, more than just the Bravo 1. Who knows how these props available today would have changes the results 15 years ago?

Yes, I have noticed the speeds on the 336 are similar to the 311, even though the 336 is a tad heavier and longer. I have 450hp 454s from Mercruiser, basically an HP500 carb but in a 454 instead of a 502. Cam and everything else is the same. Normally I run about 67 with a full load of people and a good amount of fuel, 71 is with a very light load. Plans I have for sure are to get a set of aluminum heads next year and shave some weight in the ass end along with bump the hp up to close to 500. I never plan on running more than 500hp.

Right now I am running 23" Rev 4 props which handle great, and give me the same top speed as Mirage Plusses. Really I would like to have a solid 74-75mph boat regardless of load, and I will be happy.

How far is your driveshaft below the bottom of the boat right now?

Several years ago I raised the X dimension on my Apache. I gained 4 mph on top and over 6 mph mid-range. It was still at a conservative setting (5") below the bottom. I took the cheaper route (form me) and filled the transom and raised the X. Whole job cost me around $2K but MANY hours of labor. As a pleasure boat, I'm not sure I would go any higher than 4" below the bottom so you don't have planing problems.

http://s706.photobucket.com/user/Fun...sion%20Project

When you measure do you just run a straight edge forward and measure straight up to the hull? What if you have a notch do you measure to it or to the main hull? My notch is a few inches IIRC

I measured my prop depth today- I'm currently at 7" below the hull. So with the Sportmasters I'm going to be at -5".

Your engines are very similar to mine as is your current speed. My engines are HP 450 clones, except I used the 741 cam instead of the 731 cam. Last summer I was spinning a Bravo 1 Merc labbed 25 pitch @ a 5200 rpms. Top speed was 70/71. If your drive depth is the same as mine, you could most likely expect the same results as me if you installed shorter lowers.

Are you sure they are 25" pitch? Bravos only come in even pitches. I am out of prop at 5300 at 70, which is fine right now. Rev4's tend to run like a prop with more pitch, Bravos like a prop with slightly less pitch than their rating.
Once I get back to the US I will measure to see my drive depth