Warlockkid

Hi all and thank you in advance for any input. I purchased a 29' World Class out of Havasu. The boat is beautiful it has a 540 with a Littlefield super charger and dual quad carbs. I was told it runs 940 horsepower and runs in the 100 mph. The first thing I had done was have a mechanic adjust the timing and the carbs the boat has a huge cam and the engine lope made it nearly impossible to park. It has a upper Imco X drive and a lover Bravo with a 30 pitch four blade Bravo prop. So far it has run out at 75MPH then it really starts bouncing in the back end of the boat. the boat seems to have great power it jumps on plane and accelerates hard. Do you think having the carbs and timing adjusted was a good move it seems to run a lot richer now at idle? also any suggestions on why this boat isn't going way faster?

Thanks Tom

Warlockkid

Here is a engine pic so you can get a idea.

Warlockkid

kidturbo

First question is what engine RPM it's turning at 75mph? Second is what are you using to verify the speed? GPS? Changing the timing could have lowered the power on the top end, while making it idle better.

The bouncing around at 75 sounds similar to a hull hook issues I experienced in my 21lxi around that same speed. I could get past it, but it took some practice and varied by how the boat was loaded and trimmed out.

Warlockkid

The rpm reads around 5000, and the reading is off of GPS.

kidturbo

Ok so you have 2 valid data points needed to start with. We can use BAM's prop calculator to figure the rest;

http://www.go-fast.com/Prop_Slip_Calculator.htm

With your current data, 5000R's, 1.5:1 drive ratio [most likely setup], 30 pitch prop, and GPS reading of 75mph we get:

Theoretical Speed: 95mph
Actual Speed: 75mph
= Prop Slip of: 21%

That prop slip is a bit higher than 15%-18% what I expected to see.. Mine ran 21% on a five blade 37P at 80mph. More blades and pitch, typically higher slip figures. Maybe someone with another 29 can chime in on their similar setup. But I can say for that boat to run 100mph with same prop and slip figures, ya gotta be cranking 6700R's. Highly unlikely.

I'd review the cam profile, and see where the torque range starts to falls off. That's gonna be most R's you can expect to be spinning. Just guessing, but you might have another 5-700 RPM left in that BB. Which gets ya up to 85Mph. Then your done with that prop and need to look at higher pitch options if you have the power to spin it. Also look at BAM's boat speed calculator for further estimates based off HP. http://www.go-fast.com/boat_speed_predictions.htm

Both tools are fairly accurate, enough to show you were you should be based off a few known figures.

28 V

Nice to see an offshore boat on the Lake...you'll need some wind and chop to have some fun ( I grew up there).
You're at 2200 feet elevation- not sure how your carbs are jetted if the boat is from Havasu or sea level. You may want to understand that first...I have twins so not sure of prop setups for singles- not sure there are any other owners at this site.
You may need less prop after tuning (experience here from sea level to Tahoe).
Is the bouncing chine walking from side to side- not uncommon for this hull at 75...maybe a bit less trim will help that...

Lane

2FastWarlock

Congrats on the purchase, I have the same boat and a similar set-up but nowhere near the horsepower you have. For reference, my motor makes around 550, I run a imco upper, with a sportmaster lower and I turn a Hydromotive 25 5blade with some diameter and pitch taken out at around 5400/5500RPM. With that setup I run a consistent 75mph all day long. I know the old F1 race boats liked to run a Bravo 1 28 4blade prop with the HP500s. With around 940HP, you should be able to turn a larger pitch prop than this. When you mention bouncing, mine would porpoise in fresh water around 65 but not in salt water. It would always come though it though with some trim and tab work.

Naughty Kitty

Guessing your at 1.5 gear ratio which would put your prop pitch, rpm and speed pretty much as expected. However if your puffing that kind of HP, you should be swinging a taller wheel or 1:36 gears.