Hmmm.........
 

Sounds like we are getting a little
closer to reality, X-dimensions, junk
speedo's.

Cougarman

I've never put any stock in my speedo...its barried at 80+ when running 74 on GPS but the tach I've never suspected to be wrong........if it was off significantly I think I would be able to hear it......

http://www.boatramp.com/prop_applet/...erAppletG.html

play with the math and let us know what you come up with
chances are the tachs are correct or w/in 100rpms.

Looks like for the #'s to work out I'm running closer to a 25 pitch prop.....thats if the #'s are right.....what is an exceptable % of slip?13-15?????

well lets just say a FULL blown F2 race boat will be in the 11-13's....what # does it say on the side of your props!??

23.....

well....let's say you changed the original gearing to 1.36 and turned your 23's to 5100....at 74 mph ....that under 10% loss...better than any v hull i know. are these the same props you used prior to your engine mods/rebuilds?

do both of your tachs read the same at WOT??

both Tachs read the same and no I havent changed props since the engine up grade...I did have one toughed up after I hit some sh@#......

what was your max RPM at WOT prior to??

cant recall exactly.......4600 I think...

man i have no idea what you have even with 1.36 gears and calculating the same losses put you only at 70mph...nothing ads up or even close...if you can't run this boat before sping??...don't do a thing til ya get good data....pull it down with us on the 14th to FL/KW for the worlds!! just keep down there and go back for x-mas!

I wish I could.......but it will be spring before I can do any more testing....I just took an old PB magazine that had some test #'s with the 496ho, 7 different boats running the same motor, same drive ratio, using the link you gave me they had anywhere from 10-19% slip the worst being the 19% is a Warlock 29 world class worst slip, best top speed #'s. the least ammount of slip was a 275 Baja at 10% but running almost 10 mph slower and they were running the same prop I run, go figure....no slip but the Dog dont Hunt!!!

foget what you read there! they ONLY thing that matters are your #'s in the real world....i'll help ya the best i can next season...call me anytime...if dial in work is what you want we also do that!...but a few questions here and there....NO PROBLEM!!!

Hey Audacity, which motors are going in the new 38ZR? 500s or 525s?

525's mercs...also using the smart craft computer system/display....they should be going into it today!...the engine room was painted yesterday. why??

Just curious. The 525s are awesome.

we shall see...lets hpe they stay together!!!...better yet, lets hope we can keep a drive together!!!!!the weight is going to kill us!!

hey Joe get your own post!!!!just razzing you Dude!

yeah yeah yeah!

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.

30ss
 

Having read all of this I was a little confused.

I have a 1991 30SS with 7.4’s that has always shown 74 plus on the Speedo. This year I found out that that respectful 74 is actually a reasonable 65.7 on GPS. I am sad to admit that after 11 seasons I dropped a valve and I’m in the process of a rebuild.

My point is that stock eleven year old 7.4s are running 65.7 on the Chesapeake Bay. I’m sure you can imagine the amount of clutter one gathers over 11 seasons in the cabin. She’s not real light.

I feel real good about the speed and overall performance of the Irish Mist after all these years. I had a friend with a 30 SS with blown 850+ (he would never tell me exactly what) that wouldn’t go over 92. Jay told him that that was all the hull was capable of.

CelticPride - maybe you should try some different props. I had my 35 with the same power up to 67.1 on GPS with 25P 3 blades and 66.7 with 24P 4 blade hydros. (in fresh water) I have been told that the Bravos are for bow lift and the Hydros are for stern lift. Maybe you need Hydros. If you can borrow some different props, I don't see why you couldn't break 70 mph.

HTH

BN...dailing in 4.5 mph from prop is not a reasonalble goal with his set up....and as dano stated; diferent prop for diferent conditions...people most of the time only look at the top end number as a referance for an increase in performance....while all too often they have slashed their cuising speed by 5 mph and cruising MPG just went to ****!...this is where the poeple that REALLY know what there are doing are seperated from the ones that think they do.....example....my top end props are 2 mph fast and accelerate like there is no tomorrow over my cruising ones....my cruising props are 8 mph faster at 4000 rpms and my fuel economy is amazing!

BN, I actually am no that concerned with what I get for a top end. The boat runs excellent the way it is and I spend most of my time int he 3400 to 3600 rpm range anyway.

Have any luck sellng your boat? I am trying to sell mine as I may be forced to move back north forjob reasons.

audacity - I realize that there are more things to consider than top end. I was just giving honest results in real world conditions. I opted to run the 4-blades all summer because the boat planed better, was more efficient etc. But of course I had to gps them at top end. :D


CelticPride - no luck yet. It's winter up here so I'm going to have to find someone down your way to buy it. I'll make a winter special if you know anyone.

shhhhh.....i find myself hitting the recall toggle to see what we ran too sometimes :)

Irish Mist,

Sharp lookin' boat! I guess you found out that a GPS can really hurt the ol' ego. Are the 7.4's the 330hp engines? 65.7mph is still pretty good.

Dyno/Don,

When you're doing a water test next spring I will go out in my boat and we'll both run along side each other and compare the numbers on each of our GPS's. That way maybe we can narrow some of this stuff down a little better. Can you believe that I'll actually have my boat running for the spring? Who knows---maybe your boat will out run mine!-----then we'll ALL really be scratchin' our heads! :)

Dyno's 31SS with 330 engines ran 65 mph on my Garmin GPS 95 on the prepurchase sea-trial. We did two runs, one upwind at 66 mph, one downwind at 64. After the engine upgrades the boat ran 75 mph on my GPS. You can say and think what you want but this boat ran the 75 Dyno said it did. Personally I think his tachs are reading 200-300 on the low side.

ok then...for your sake please look at the math...the boat had an engine upgrade, used the same props and got 10mph?...by the way do the math with 400 rpm added for error on the tachs...so both tachs have the same error??