prop issues....
 

I am perplexed on what to do.

Twin 350 mag MPI motors with ProChargers, 5 psi kit.
Bravo drives 27 pitch Mirage plus props (untouched)

Did a small amount of testing on saturday for the first time with the Prochargers. There was a regatta going on so I had to keep it to a minimum.

Boat comes up on plane fine, as soon as it does the props blow out of the water. Runs really good through the mid range but will blow the props at any time if too much throttle is used. I did three short WOT blasts, none long enough to get an accurate top speed. The rpms went easily over 5000 rpm at 76 mph (GPS) on a short run. However it just feels like there is no load on the motors, almost like it was on the verge of blowing the props out at wot.

All the testing was done with 4 adults and 100% full of fuel. (100 gallons)

Is this purely a case of not enough prop?

Re: prop issues....
 

I would highly recommend going to a 4B propeller for your application witht he upgraded power. This will hopefull calm down the blow out if not eliminate it. You will need a WOT RPM reading to determine the appropriate pitch.

Julie

Re: prop issues....
 

Julie,
How does a four blade pitch compare to a three blade? I think I recall from a past post of yours that when using the calculators that a 24 four blade is being used then use 25 for the calulator, do I have it right or is it the other way around? I am just using 24 and 25 as an example.

Thanks

Re: prop issues....
 

Good Morning,

First a couple questions. Who makes your hull? What is your X dimension?

Your boat does come up on plane "ok" and you like the way the props handle cruise. 4BL props may be a best case set up. However, there would be a small amount of work that could be done to the existing props to make them handle the power better.

Re: prop issues....
 

I just looked at your profile and saw the boat is a Scarab. Still wondering about your X.

The 3 blades are closer to true pitch than the Bravo 1 series.

Re: prop issues....
 

1998 Scarab 29 stock X dimension.
It just feels like there is no load and the rpms are too high. I did not even run it long enough to make 5 psi boost, boost should only come in when there is a load I would assume. The boat chine walks at high speed but the K planes settle it down. I can't really say on cruise, I really did not have enough time in the boat. I have a minor fuel pressure problem and the RPMS were too high at wot even in a short run.

I originally had 23 pitch props on the boat prior to the Prochargers.

Re: prop issues....
 

Maybe some more seat time is the best thought right now. Also getting the fuel system problem taken care of so you can be comfortable with your test sessions.

Re: prop issues....
 

I agree, the fuel pressure issue is what stopped me from testing more the first time. I think I have that all taken care of now. once I have more data I can start figuring out what I need.

Re: prop issues....
 

With Bravo I propellers you will decrease 1 inch of pitch when using the sllip calculators. Once you reso.lve your fuel issues I am sure we can get you dialed in.

Julie