Sonic30ss

I have a Sonic 30ss with Small blocks and Alpha SS drives.
I had a highly recommended shop "lab' my props. They are Mirage 14 3/4 x 21. I was told they were not a true 21, so they were repitched and cupped considerably.
My problem was related mainly to getting on plane, because of the high X of the drives, and they are both right hand, it takes a lot of finesse, and many times the props will slip so bad that I have to stop, let them rebite and try again.
Guess what it did not work it actually seems worse, funny thing in the salt they work pretty good, no issues blowing out, as soon as I get back to the river the problem reoccurs. Am I nuts ? I've tried every adjustment or combination of adjustments for drives and tabs. The best is drives all the way in and tabs all the way down, as the boat builds speed around 13-14 mph raising the tabs slightly.
Thanks for any input

throttleup

It sounds like you may be struggling with the 3B propellers. Can you give us some details about the boat, motors, drives and props, please.

Julie

Sonic30ss

Julie-
Sonic 30SS Same as a 31 SS aprox 7000-7500# ?, EFI small blocks aprox 320-340 horse, Alpha SS(semi-surface piercing) drive 2'' shorter than std Alpha plus nose cone 1.50:1 ratio all new gears and bearings, props 14 3/4 X 21 supposedly repitched and matched to 21'' pitch, added cupping, and polished by Big name shop (in my area anyway). Engines would spin to 5500rpm before work, Engine WOT 5200 by the service manual. I have not made a high speed run yet this year.
Joe

throttleup

What year is the hull?

Do you have the WOT RPM and MPH via GPS numbers? I would like to run thru some theoreticals.

Julie

CMG

Joe, get a hold of Sonic 28 (Paul) - he has a 30 w/ ss's and small blocks. I am sure he has tried different set ups , he is trading in towards a new 35 any day now.

Sonic30ss

Julie- 1987 hull, I'll get some WOT #'s this weekend, just got back from changing the break in oil so I'm ready to rip.
CMG thanks I'll PM Sonic 28

throttleup

Safe Testing!

Julie

Sonic30ss

Update- I blew a motor while testing So I did what any self respecting speed junkie would do. Bought two newones and replaced them I just finished testing today
1. the whole problem with getting on plane was NO power, I can jump out now with no trouble at all
2. Saw 59.2 on GPS @ 4800 rpm engines can go to 5200. I ran one of the prop slip calculators can my slip really be 9.5%? is that too low?
Boat was FULL (160gallons) of fuel so I guess 8000# +/-
Engines are rated @ 325 horse, but I have GLM manifolds and Imco risers, so I may be making a few more ponies.
Thanks in advance

DUH I forgot to ask the question! Should I rework the props to pick up more RPM, say 300 or leave well enough alone?
Also I ran with full fuel, six people, and gear for an overnight, @ 56 mph +. I've got to figure I was close to 9500#, the boat ran the best ever, why did I only lose 3 mph with all that extra weight ?

bbladesprops

Depending on what the props pitch read at, your slip numbers are conciderably above average. If they are 21 pitch, Your under 7%. 22 pitch = 11%, still very good.

Are you sure your tach is accurate?

throttleup

Sonic30SS,

Well it sounds like you had a tough weekend of testing ...sorry to hear about the old motor! But obviously that wasn't keeping you off of the water. Gotta love a junkie ...

You stated that the engines can go to 5200 RPM, is this were the peak HP is produced? Of course if your goal is max top end then you need to prop for 5200 RPM at WOT. If you have not opened her up yet then of course we will need to run your numbers after you do so. If indeed you opened her up to 4800 RPM at WOT then you will need to adjust the propellers to achieve your goals. Give us a little more info and we can get started.

Julie