What Prop To Start With
 

I repowered :cool-smiley-027::cool-smiley-011::party-smiley-004:
502's na/ 550 HP each / TRS Drives 1.5/ 31ft Scarab II.
and was running 25 pitch 4 blades choppers.
Turnin 5200 RPM @ 73 MPH

Now I have Twin 31 ft. Scarab II
555ci na/ 700 HP each / TRS drive 1.5,
I don'nt think I should even attempt to test with my old props?

Where should I start, What pitch? I want to spin 5600 RPMS? Should I go with 5 or 6 blades?

I really would like something that picks the nose up a little more or will the pure increase in HP make this happen.

These should help greatly. But borrow all your buds props you can for testing.

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

http://www.rbbi.com/folders/prop/propcalc.htm

After doing some calculations with the 2 links It looks like you will need about 2" more pitch. Since you are turning more RPM I would try the props you have. If your slip is @ 10% that puts you @ 79.5mph. If you are not satisfied there you could have the labbed and an inch of pitch added.

I agree. use your current props as a starting point.
If you have a rev limiter set @ the 5600 rpms you peak at, you will be able to estimate how much throttle is left when you hit 5600, if any.
5 0r 6 blade props will raise your stern, vs your bow, in most designs. Carder

What did you say? I was just watching her!!! Tell her to take it off!!! Thanks for the information!

31scarab31, I have allmost the same boat. Mine is a 79 sport300. I have 2 540's,trs. I run hydromotive quad IV X props 26 pitch at 5900rpm=89.9mph. The x prop will lift the nose of your boat which is what they need. Cleaver style props raise the stern and that boat won't handle well. Brian

4 Blade choppers? Hoss?

With the upgrade in HP and the increase in rev limit, your current props are the best test platform. You will most likely need 1.5 more inches in pitch

Gentlement, thank you for your knowledge. Once I get the official numbers with the props I have now, should I get back with you? Again thank you for your input!!!

Brett, what is the price of the 4 blade choppers?

They aren't currently available. We would custom make thm. We would need to discuss the set up to quote a actual price.