There is some serious bull**** going on here. I'm not referring to you Dyno. But..Sonic seems to overestimate the speed of there boats. Ever since I bought my boat, I have been dissapointed with the tope end. Jay and others have told me that I should be faster than I am. 1998 31 with 454 mag mpi's 26 bravo ones. Top end is about 68 at 4,800 rpm. If you go through the math that equates to about a 13% slip. Other people with the same power tell me they are in the low 70's.

In the waiting area at the Sonic Factory. There is a Powerboat Mag write up of a test that they did on a 1994 31 with 502's turning 26p Intimdator QIV's at 5000 rpm. They say GPS speed was 74. Now, that equates to a slip of 9.8%, which, I say is bull****.

If anyone is interested, I have an excel spreadsheet that I pu together to calculate speed, slip. etc... Just email me

CP that sounds about right....so where do you think the BS is coming form....what i love is ad's saying they run the 90's with stock 500's...at the time is was a few mph over the world kilo record!!!LOL

Audacity posted a link with a speed-slip calculator check it out!!!Celtic I think they always pad there #'s a little....do you know what your X demension is?

No, I don't know what my x dim is. I do think that on my boat, I would need total hp of about 1050 to break hit 80mph.

I did see the 31 at the factory that has the 575 Sci's. It had 32p props on it.

Just by the prop selection they are running makes me think that they are a lot higher than I am....

CP sounds like you need a set of Pro Chargers!!!!

Actually, I am looking to sell the boat.

Whats next????Active Thunder?Pantera?that 35 looks way cool!!!

I was actually looking at a Formula 382 Fastech. But, now I am just looking to get out from under the Sonic because i may need to relocate.

Just back from Ft.L....ahhhh weather was good and even got some run time in...

Sorry about the late response but the x-dim should be 16". Minor mods were made to the 31 plug in the 90's but in essence it's pretty much the same hull. Jay,Bruce or Fred at the factory can give you the exact details...

Until they infused the hulls (2003) they were all hand laid so some weigh slightly more than others. The other biggie is in material advancements (which is true for all manufacturers) with the latest being the infused 3-Tex for Sonic. It is the strongest and lightest yet. As the technology continues to evolve it will get even better... The trick being of course to get as light as possible (fast) without reducing ride quality and handling.

Options on the boat can add alot as well... holding tanks,AC, frig's,TV's etc.etc. those puppies add poundage.

I've run a lot of different combo's motors/drives etc in the last couple years in this hull. Following are pretty representative of true GPS speed in flat Fresh Water running a typically optioned pleasure version with stock fuel injected Merc motors/drives without labbed props or infused hulls. Now of course weather conditions (heat/humidity), water conditions (flat/chop), water type (salt/fresh) are all gonna impact speed. That and the fact you sometimes just get a "stronger" motor from Merc...it happens.

454MPI 68-72
502MPI 72-75
496HO 78-82
500EFI 84-87
(caveat being with me driving, there are folks who could get more...)

The 575 boat mentioned above is one of mine and it does have 32 labbed props on it currently. It was hitting the rev limiter at 88.1 MPH so we don't know how fast it will truely go yet. There were two identical boats built with the exception of one having PFM chillers, AC and a TV/DVD installed and the other not. Todate we have tried a myraid of props both pitch,diameter, 3/4/5 blade etc, the sportmaster 2" shortie, shortie" made a lil' bit longer with a 1" spacer, replaced the blower upper assemblies (none of the original motors from Merc would push more than 3lbs of boost, this one change made for a quick 3-4MPH gain) and we still aren't there yet, just ran out of season up here hence why the one is at the factory. Before it's done we will probably try the new Merc 33p prop, maybe boxes and different drive ratio's...the fun just never stops.

To summarize, Audacity is absolutely correct in stating that you need current centerline data/numbers...then it's math coupled with experience.

The math is easy (angle calc, prop slip % etc) it's getting the experience of what has a higher probability of delivering the most bang for the buck and that is how this forum can be of value. Of course there is always that little problem of "pocket depth" to truely get to were you want but at least you can make informed decisions on how you get there and the sequence to take.

My first thought is your running the wrong wheels...personally I have wheels for different seasons and water conditions. What works in April may not work as well in August...I'm a big believer in labbed props but they have to be "custom labbed" for you there are several companies active here who do that.