Airpacker

Does anyone know what kind of slip percentage I can expect with a blackhawk turning 31's? on a fairly high X dimension(25 eliminator daytona twin step)

IHTFP

I'll give you the figures on my Donzi 22 Classic 502/Blackhawk, you can figure out the prop slip:

4950 RPM
31 Pitch Props
1.5 : 1 Ratio
80.1 MPH GPS

Let me know what you come up with

Airpacker

Those numbers come out to 20%slip...wow,kinda high. I guess I'll just have to wait and see what happens on the cat.

Whitey

How do you guys like the Black hawks. I am considering a boat with them on. Thanks Dwight
Ps the slip does seem high??

IHTFP

Yeah, the prop slip would be high for a submerged prop, but you have to remember that these props are halfway out of the water. I like my Blackhawk, it is quite a bit faster than a similiar boat with a Bravo. I would say the weakness of the Blackhawk stems from the tremendous bite that it has on the water. There is a lot of shock when you put it in gear. It is analogous to dropping the clutch on a 2 wheel drive car versus a 4 wheel drive car. The 2 wheel drive has less traction and is likely going to spin the tires. The 4 wheel drive has more traction and will probably transfer more of the shock to the transmission. Well, when you engage a drive with 2 props in the water, it is going to bite harder and put more stress on the internals than a drive with 1 prop in the water.

I plan on using the Redline Heavy Shock oil in the drive this year as well as limit the shifting in and out of gear as much as possible.

Airpacker

Re harsh shifting. I was considering wiring a bypass switch that would allow me to start in gear thus lessening the shift shock. It might help with drive longevity.

AZDominator

This may be a better example to use with your Daytona:
25' Warlock Cat
502/Blackhawk
29" pitch labbed to 30"p
1.5 gears
5000 RPM
79.6 mph
slip?

Cord

iTrader: (2)

air-you might want to reconsider wiring around the shifter. I was with a guy that had done that to save on the clutches. He was coming in and needed to shift quickly, but wasn't able to. The damage to his paint from the dock would have bought a set of cluches. Something to consider.

Airpacker

Cord,I would strictly wire it in as a switchable bypass. Switch on.neutral switch bypassed.Switch off,standard neutral switch operation. Wifey likes to take the girls out for rides in the cat,wouldn't want her to have to explain why she started it in reverse and twin propped a pontoon boat at the marina.
As for your reference, not too sure how wiring around the neutral safety switch would have prevented him from shifting though.

Airpacker

AZDominator,that works out to 16%slip. If I can turn my 31's to 5000rpm at 16%,I'll be runnin 93.6mph on a box stock 500efi package