Cat props
 

Ok, I want to do some research on what is working for other people. My application is a 26' Firehawk catamaran. It's a center sponson, single step, notched transom cat that is simular to the Talon and American Offshore cats. I have a 600hp big motor, Imco 2" shortie drive and a 12" setback Stellings adjustable box. The center of the propshaft is currently set about 3/4" above the center sponson. With a Bravo prop the boat planes out with absolutly no slippage. Because of this, I'm thinking that I can go higher with the X. I finished the boat late last year, and really don't have much seat time. Our calcs show that if I can turn a 30" prop that the boat will go 100. If I have to step down to a 28", I'll be in the mid 90's.

My question to the board is what prop works for you? I know that the Bravo 1 is a easy winner. I currently have a 30" stock B1. But what about cleavers? Hydros? (I'm leary of Hydromotives having broken one) Be sure to include info on your combo, slippage, pitch/type, handling characteristics, and of course speed. Thanks!

Spinelli's seem to be fast on cats with low "X" dimersions, the only issue is finding one now. ;) I have a 26 Carrera cat that had a very high "X" (only prop that would plane was a bravo and it broke loose) I put an Imco box on very late last year with no real time to experiment before winter. Before the box my slip was around 12.5%, after the box my cruise speeds were essentially the same but planning was much easier. Motor is NA 632", 900HP.

Before box results;
30 bravo @6100 101 GPS
28 bravo @6500 98 GPS
30 Bravo @6700 108 GPS (175HP NOS)

To see 100 with a 30" Bravo thorugh 1.50 gears you'll need to turn ~6000 rpm. @12-13% slip. A 26" Bravo would need to turn 7000+ in the same scenerio.

HTM Sr-24 boat likes 4 blade Hydro 27 pitch props best. With a 540ci motor, Bravo 1 1.36 gears, nose cone, IMCO drive extension it ran 93. With a 500 hp motor it ran 87 with a 26 pitch prop.

You didnt say what gear set you have I put my little motor in a profile cat this winter just to see how fast it would run it has a Imco sc drive std.lenght on a 3' imco box with 1.5 gears with a bravo 32 turning 5500 the boat run 94.6 mph on gps this was full of gas (120 gallons) and two people I dont think my motor makes as much power as yours so if you have 1.5 gears I would think your 30 would be to small. but I run the boat for less than 2 miles I just had to see the differance between my v-hull and the cat.
Eric

jd-do you know what you x-dim is? The box should help with planing. Are you thinking of a Spinelli cleaver? Man, think of the speed of you could just get those slip numbers to come down! Assuming a 1.5 drive, it calcs out at 116mph. :cool:

KC-what kind of power do you have? Does the hydro surface? I feel that my old hydro broke because it was surfacing-so I'm really reluctant to try another.

EWB-I have a 1.5 gear. When I calculate your slippage, I come up with 17%. Is this correct? I don't know what your hp or boat is, but if was a small single engine cat, a 32" @ 5500 should get you over 100.

On the 540 I would guess in the area of 550hp never had it on a dyno and it was abit mild. I have had zero problems with the hydomotive prop. I had more of a problem with prop shafts.

I take it that you're breaking them? I've heard that on a surfacing application that the Bravo will chuck it's shaft with as little as 500hp. Something that I'm a bit nervous of.

Put hard shafts in...I've never broke a prop shaft in 3 yrs. Now gear floors are another issue.:rolleyes: I've seen many Bravo's sling blades that were "surfaced", labbed and non labbed.

That is what solved my problem with prop shafts. Sucks was breaking the shaft off in the water with a brand new prop on it.

Its a Profile 28 with a stock Bravo 32 the motor is a 502 with a 250 powercharger and Nickerson carb I have know idea how much horsepower it makes the prop shaft is even with the bottom of the boat the motor run my H2X 24' v bottom 82 on gps with a labbed bravo 30 at 5000 I dont know how heavy the cat is but I would think it would be more than H2X ether way the cat is faster with the same power even though its 4' bigger.

Cord,I run a 25 daytona 2 step with a 500efi and bravo 28 stock through 1.5 gears at 5100 rpm. It runs 84mph light with this set up. Never broke a shaft or a blade but gear sets..well. I tried a hydro and the boat was a bear to plane off. Looked at a lot of clouds waitin to come over the hump. Tried a mirage plus 30 and it almost wouldn't plane but picked up 1.2 mph on top. The drive surfaces all the time so I surmise thats why I break gear sets too often. Actually just came across a preproduction blackhawk drive through a connection at Mercury's training school last week( major deal :) ) and found a set of 29 and a set of 31 lab props for it so as soon as the ice melts(maybe by April this year) I will be doing some testing.

Air-if you prop it right, you should be into the low 90's with the BH. Would love to get into one, but I just havn't been able to get a deal to happen. Please keep me up to date with your testing!

Cord;

116 is with "0%" slip. Very rarely can you get under 10% with a bravo style sterndrive particularly a single with a center pod.

Yea, I knew you were going to call me on it. Everytime I try to edit a post the computer crashes, so I wasn't going to chase after that little omision.

CORD,26 FT CAT 840 HP IMCO DRIVE 1.36 GEAR VERY CONSERVATIVE X-DEM PROP SHAFT ABOUT EVEN WITH BOTTOM CENTER SPONSON 32 4 BLADE BRAVO STOCK RUNS 108 AT 6K RPM TRIED HYDRO 30 5 BLADE BITES HARD-A LITTLE HARDER TO PLANE NO SPEED INCREASE BUT FEELS MUCH LOOSER-MORE STERN LIFT DIDNT LIKE IT..WANNA TRY 32 LAB 4 BLADE