proping my cat
 

Now that I finally got the extension box hung, I'm trying to figure out what my boat will be needing for props. Here are statistics:

26' Firehawk cat simular to a AO
single step, 12" notched transom
The center sponson is about a inch below the outer ones.
I have a 12" adjustable extension box that is set back another 1.5". With the box all the way down, the prop is centered on the bottom. I can go up another 2-1/2". The bottom also has some major rocker built into it!
The drive is bravo 1 with a 2" imco shortie
The engine is a 600hp 540

First of all, I really need to figure out what this thing will run. Mfr says close, if not over 100. Dealer says mid 90's. I dunno. What's your guess?

Second what do cats like mine like for props? Because the drive is surfacing, am I in the cleaver range? How much rake do I need? How much pitch?

Cord;

What kind of extension box are you runnning? What is your drive ratio? Assuming you are running 1.5 gears it would be hard to go wrong starting with a 26 Bravo. My guess on speed is low - mid 80's. :) Unless you have a very light hull...not real familiar with Firehawk. let us know how it turns out.

Where are the pics:D

It's a stellings box. The drive is a 1.5

Florida, you're not the only one that's been bugging me for pics! I'd take a couple now, but it's overcast and they'd be kinda drab.

Where exactally is your prop relative to the bottom of the center pod? Even with it OK, a bravo prop will work well. A 28" turning 5500rpm and 8% slip is about 90mph. The old saying TEST, TEST, TEST. Run what you brung- what do you have? You will need between a 26 and 30". Try anything and the guessing is much easier.

I'm using a 26 Bravo with
 

1.36 gear. 5300 to 5600 depending on weather. 540 with about 625 at the prop. I would think you would need a 28 to a 30 with a 1.5 gear. 26 would give you a lot of r's. Close to 6000 :rolleyes:

Right now the prop is exactly centered on the bottom of the center pod. I can still go up 2-1/2". The only prop that I currently have is a 24" bravo 1. Naturally that will be too small. :D

I have a back issue of Hot Boat where they tested the cat with a 650 hp engine and got 98 with a 32" prop and 1.36 gear. I know that the mfr spun the snot out of the engine (700+) and put a shortie lower on for 107. This was without a extension box. Why do those numbers seem optimistic?

I have a 2600 American Offshore NSX and am currently using a 12 inch extension IMCO Box, SC drive with a 2 inch shortie, 1-34 gear ratio, and a Lab Prop. This set-up increased my speed approximately 14 mph. This may work for you too.

Iwould try a 30 bravo one,you should run 100 mph

cat-have you experimented with any other props besides the bravo? What were the results? How much hp you running? It must be quite a bit because of the drive ratio. Finally, what is your prop height in relation to the bottom?

I think you will really like the Shorty Drive and extension box. I have not tried any other props, however I turn a 32 Bravo One Lab, 5800 RPM's. I currently have 786 HP and my prop is one inch above the bottom.