Prop Slip % With a Blackhawk?
 

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)

Prop Slip on my Blackhawk
 

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

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.

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

Prop Slip
 

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.

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.

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?

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.

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.

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

The Blackhawk is the worst drive ever built, why do you think they don't make it anymore? I had them on my p29 scarab and they were allway's breaking. I have never broken any other drive so I know it wasn't me. Do yourself a favor and call the people that build drive's for a living and ask them what they think.Plus I was told that they are not going to make the shafts for them anymore. I had Dean at the Bravo Shop look at it to see if he could do anything with it, pretty much told me to throw them away and put bravos on. When new they wouldn't put the on a carb motor because you have to turn the idle upto about 1600 to keep it from stalling.Props will be hard to find too.

Lapse... you are SOOOO wrong....

whatever do you own them

In 1996 Merc. had a race team called BlackHawk Racing, they used BlackHawk drive's. They Broke a drive every race. Entered 12 races dnf in all.

Owned one for 5 years, not a problem. Certainly not the best drive to load and unload because of the characteristics of the counter rotating surface piercing design, however; the Blackhawk is not the worst drive ever built by far! Boat designs and applications is what killed that drive.

Had a friend with a 22'Daytona 502 Black Hawk. It was an awesome package 91m.p.h. G.P.S , running 32 p., at 4900. Was a bit sluggish to get on plane. A little harsh going into gear. Very, very efficient.

With that said, it did have some handling quirks. When running on the sponsons only a crosswind puff would just move the boat a great deal. Not a little, a lot. It also did not want to turn at high speed. Almost had to drive it like a jet, apply power in the direction you want to go. It did spin out on a couple of occasions at a slow speed. My friend(Actually his wife!) got scared and sold it.
My opinion is that it was an awesome piece of machinery, the efficeincy was unbelievable. It needed external steering. Yes, Leach sent this one out without it. I believe that adding length to the skeg would make it handle better! The sound that the props and drive made were great. I wish he wouldn't have sold it.
Eric

[QUOTE]Originally posted by Lapse of Reason
[B]The Blackhawk is the worst drive ever built, why do you think they don't make it anymore? I had them on my p29 scarab and they were allway's breaking. I have never broken any other drive so I know it wasn't me.

Lapse,that drive was never designed to run on a big V hull period. I suspect you saw big air alot. The re entry is what kills bravo uppers. With twice the grab on re entry its not suprising that you broke them. The real reason behind the demise of the drive was cost and severe misapplication. If used on the right hulls,many more would have been sold.

[QUOTE]Originally posted by Airpacker

Quote:

---

Originally posted by Lapse of Reason
... With twice the grab on re entry its not suprising that you broke them. The real reason behind the demise of the drive was cost and severe misapplication. If used on the right hulls,many more would have been sold.

---

When you run drives as surface-piercing, each time a blade hits (enters) the water, it sends a shock through the driveline. With two props, the situation gets so complicated, you can wind up with some very nasty harmonics. As I understand things, the BlackHawk was not bad with smallblocks, but didn't survive very well with bigblock/heavy boats.

It's a similar story with the Volvo DPX. As long as the builders put 'em where Volvo said (submerged), things went well, but when they started mounting them too high, the aforementioned problems showed up. Since Volvo (and Mercury) couldn't keep the builders under control, they each pulled the plug on those high-performance projects, although the DPX is still around....

Blackhawk does look wicked bad, though, doesn't it? Do you get a double roostertail? :D

I don't think a 29 foot 6500# boat is a big V, plus it ran 350 mags not a real high hp motor. I live on the potomac river and didn't see much air at all.Yes they looked real cool and the boat drove great. The big problem with them was twice the prop suface, counter rotating running on the surface,witch we all know is harder on the drive, and it only had the same strength shafts and gears as the bravo. Do you think it is ok to put 1200 hp in front of a XR drive that would only be twice what it is rated for. It was a cool idea and if they did it with a drive like the BMAX it would last. If you look at the size of the shafts in the DPX drive they are a lot bigger than the one's that merc. used, that is why they last and are still around, but I think they rob more hp than they are worth and the props cost to much and are to hard to get. AirPacker said he had a high Xdim and I would geuss a big block a cat is allready hard on drive's. When Merc. started with blackhawk the target boat was mid sized v's with factory power, Like the p29 scarab, it was good for about 5mph. Just do yourself a favor and call the people that build drive's and see what they say. I bought one of my spares from The Bravo shop for 3k brand new in the box, they had a retail of 20k, He said if he didn't get rid of it now he was afraid he would be stuck with it forever. What boats was it the only drive offerd on besides the p29 or the donzi? I never saw it on a cat.

Lapse...

For the record, I do own a BlackHawk drive, two to be exact. One resides on my 97 Donzi 22 Classic. There is absolutely nothing wrong with that drive when set up properly. One of the Donzi's on Lake Winni, an X-18 has a 350Mag MPi setup, 1:65 ratio turning worked 31P's (32P) and he runs 77.8mph all day long, never broken, still under Merc's factory warranty.

I put a 1.5R Blackhawk on My Donzi, 454Mag MPI (385HP) and I turn my 27P's all day long at 75.2 mph. My drive is set too deep (stock Bravo location). Once I get the drive up 2" or so, I expect to see one or two extra mph.

Structurally, there is no real difference between a Blackhawk & a Bravo. If you launch a stock Bravo and get the props into the air enough you WILL break the upper gear set... its just a matter of time. Same goes for a BlackHawk. This especially pronounced on heavier boats, like the Scarab P-29. You need to drive it like an offshore throttleman... on the gas... off the gas...

With the new XR upgrades available from Merc, I think one could build a pretty bulletproof BlackHawk... Before you start trashing drives, you really ought to do your research...

If your Blackhawks suck so bad, why not just replace them with Bravo's?


Woodsy

I replaced the boat, I didn't want to put drives on that it didn't come with since it was 1 of 29 built. I did a ton of research talked to everybody that knows anything about outdrive's, I even talked to the guy that designed the Blackhawk at Merc. Racing. His statement(It was something new we were trying, it didn't work out as good as we hoped, thats why we don't make it anymore.)I am happy you don't have any problems with it, but your boat is much lighter than mine was and the 25 elimintor that started this thread. I do know how to drive. You are right there is nothing structurally diffrent really from the bravo, thats the problem because of the prop surface the Blackhawk has. I am also not some dumb ass who has no idea how things work, I am a ASE master tech, I own my own motorcycle repair shop, I have built motors(motorcycle) that have won national campionships, and have been racing motorsports for 25 years. Out of the 29 p29's built I talked to about 10-12 of them and they were all having problems some worse some not to bad at all, but all had drives break at very low hours. I didn't tear up the gears as bad as the shafts witch may be the weight of the p29, I didn't talk to the Donzi guy's so I don't know their story, but I did sell my spare's to a guy with a Donzi.blackhawk. I don't want to fight or get people mad I was just offering my advise, that's why we have this site. Everything I say is true and I trust the same with you, it is up to Airpacker to do his homework and make up his mind.

Lapse,which shaft did you break,vertical or one of the prop shafts?
As a side note,I have killed 3 upper gear sets in my bravo hp in 2 seasons(breaks off teeth) so I figure I don't have much to lose trying ther BH setup. Can't be any worse. I have one brand new pre production BH drive and 2 more parts doners just incase. I think I have to try it to see what happens. If needed,I have someone who can custom make me a vert shaft if I go through all 3 that I have.

I was twisting and breaking the input shafts and vert shafts, the prop shafts were fine. Dean at the Bravo shop said the input shafts were allready pretty strong but if he cut down his vert shaft and then have it rolled it would be stronger, but he didn't think they would hold up either. I havn't had a Blackhawk since 2000 so somebody might have the part's to make it last, that's why I said to call around to the drive shop's and ask. A XR drive or Teague may be better or a Bmax if you have over 700hp. They will be a lot more easy to change the Xdim with spacers than moving the whole engine up and down. Good luck.

Bravo I lower in Blackhawk?
 

Would it be possible to put Bravo I lower gears and shaft in a Blackhawk and then put a tall surface piercing prop on the drive? That would probably alleviate some of the stress that is put on the Blackhawk upper. Just a thought.

I'am not sure but would guess no, that would get rid of the whole point of the Blackhawk, the two counter rotating props. A XR or Teague drive with a two inch shorter speedmaster lower with nose cone and a cleaver prop would be a start.But when doing custom work like Airpaker is doing you never know what prop you might end up with, You might start with a 5 blade clever and end up running a 3 blade mirage.

The Blackhawk is basically a Bravo 1 upper with a Bravo 3 lower in it's own case. The reason they put them on 502 MPI motors was that motor was reproggrammed to idle very low to keep idle speeds down. Anyone that owns one knows what I am talking about!

I own a 1995 Donzi Classic with a Blackhawk drive. I would say the drive is just as strong as a Bravo. However, the problem is that when you do get air under the boat it will bite MUCH harder when entering the water.

Also, I will admit that they would not be well suited for Offshore racing at all. The high prop shafts would mean getting air a lot more than a Bravo which will lead to things breaking. However, for the "average" boater that doesn't get big air I think they work well. In a mid sized V they are about 5 mph faster than a Bravo and in Cats I have heard they can be over 10 mph faster! I heard of a 22' Eliminator Daytona that had a stock 502 and a 2-speed tranny hooked to a Blackhawk that was doing over 100!

The reason that they quit making the drive was the market was way too small. Some V-hulls had to be totally redisigned to make the drive work properly. Plus, it was one hell of an expensive package.

My advice to you is if you do get a lot of air under your boat be prepared to drive the s**t out of it. If you don't then hold it wide open and go!

I hope this helps! :)

Oh yeah, back to your original question I would expect 15- 22% prop slip depending on your hull.

Airpacker, I think Ted at Speedmaster had a blackhawk, last I checked.
After that, their are a pair of new 511cid Keith Eickerts, 727hp that would fit in.....

See you at the season opener.

RT

Rob,yes Ted has a used one. I already have 2 of those as parts doners in case I break the NEW NEVER BEEN RUN one that Raymond found for me at a great price. I don't think I'll bring my 25 to the boys boat weekend again though. That lake is just too small. I might bring my 10 foot cougar cub though if I get the resto finnished in time.