Sonic30ss

Now that everything is working great, it's time to start messing around.
I have a Sonic 30 SS with Alpha SS drives, and Small blocks making around 320 horse.
I'm running Mirage 14 3/4 X 21 props that I had worked on by Hale in CT. They matched the props(apparently the pitch was off) and added a bunch of cupping, (my complaint was hard to get on plane). Now the boat pops up great, and the mid range cruise is awsome. They are showing a slip of 4% using new tachs and GPS for speed. I've run a best of 62 MPH @ 4900 RPM. My question for the prop gods is, do you think I can get more top speed without sacrificing too much down low and in the mid range? Thanks

throttleup

With 4% slip not likely. If you truely have that low of slip I would leave it alone. Unfortunatlye though a Sonic is not capable of such low slip. You are in cat territory that low. I would verify your data and re-calculate your slip.

Julie

Pat McPherson

Hey Sonic,
I bet after the mods Hale did, your props measure more than 21p.
My experence with working with the guys at Hale is that they are great for reworking to stock spec.
I know their sign says "we make fast boats go faster", but lets just say that their mods never made any of my boats go faster...
We had a 28' Cig with about the same power as you are running. The fastest props we ran were 21p cleavers but the boat was slow out of the hole.
21p Mirage props worked well and 21p Turbo Vectors worked great. With the Turbos that boat topped out at 60-62mph at 5000-5200rpm.
You may want to try some stock 19p Mirage plus or 21p Turbo Vectors. I think you want to spin those small blocks 5200rpm for max speed...

Sonic30ss

Thanks for the info Pat
Julie I will recalculate again and see if the numbers change

Sonic30ss

Something is not right, may be as Pat said they changed my pitch. I did a mid range test yesterday 3400 rpm, 40.3 mph
I had to be around 9000# full fuel (160 gal), 500+ pounds of people, full cooler etc.
I tried the Bam calculator and the slip came up infinity,and theoretical speed was 46mph, what am I missing?

throttleup

Try to get the pitch from Randy and Hale.
Verify your tachs (main culprits for bad info)
Calibrate GPS unit
Verify Gear Ratio

Then baseline your props again and hopefully we will discover what info is inaccurate.

Julie

Sonic30ss

Julie
Pitch 20.2 (They are cupped quite a bit)
Dia. 14.75
Tachs are both brand new and read exactly the same but I will try another.
GPS- I will bring a hand held to compare
Drive ratio is 1.47:1 with the new gears
Thanks for your help

CBR

I have a Sonic 30SS also, with Scorpion 350 HP small blocks cranking 5200 RPM, counterrotating Bravos and lab finsihed 26 pitch props. Best I ever saw was 73 MPH, so I'd be happy with those numbers and leave it alone.

Pat McPherson

With a 20.2" pitch, 1.47 ratio, and 3400rpm engine speed, the thero speed would be 44.2mph.
At 40.3 you are at 9% slip.
Sounds like she's running good to me.
I still say if you want to eak out a little more, you will need to spin those small blocks 5200rpm.
19p Mirage plus would be a prop to test IMO...

Sonic30ss

Thanks everyone for your input, I guess it is running pretty good. Maybe if I can find a set of those 19p Mirages to try before I buy. Anyone in our area do that Pat?