3 vs 4 blade

Jody, What do you think about my application, 13x12 or 13x12.5?

I've been considering a different prop for our Malibu Sporster. It has the 310 carb engine. Manual states red line is 4800. It turns 5050 with even 3 people in it. It's got way more hole shot than it needs. I'm thinking a little more prop would be just as good or better all around and may increase top end slightly and better fuel economy for cruising. Does that sound right to you?

Riley what is on the boat now? And what did the boat come with? If you are happy with the current performance but feel the revs are to high you may want to consider adding some cup to your existing wheel.

Tim I am sure OJ has a prop for ya but with the amount of extra HP you might want to consider going to steel racing/high performance under water gear. Going over the 60 mph mark with stock brass componets may be a recipe for disaster. Though keep in mind I did run my flat in the 80plus range with brass under water gear! But!!! No more! As far as propellers go you may need something as high as a 15 pitch but when the time comes just let us know what you feel you want and we will make it happen,at least get you some product to try out and play with.

TRBenj wrote: Jody, whats the danger with the brass components?

Jody , I guess Tim has never seen nor had the good luck to "chunk a blade" at speed.Not for the faint of heart, insert enough HP and NiBrAl will fail. There is a lot going on under the water that we never see nor think much about , TILL !!!!!!

Tim I am not sure what the Barefoot 454 motors were rated at maybe 330?? a little more. But if your calculations are in the 470 hp range spinning a prop at 5500 RPM then some reinforcement and re-thinking about your project may be in order. I know I would not run a Nibral wheel with those numbers. I would also at least reinforce my backing substructure that my strut is fastened to.

This one would be rather overkill but I hope you understand.
Kinda like putting 500hp in a car that came with 300hp and not doing anything with the stock rear end. At least on land when the drive train goes away the car stops and we walk away. Ever throw a blade on a prop at High RPM?

Fl Inboards wrote: east tx skier wrote: For comparison's sake on blade area, here's my old Acme 541 next to a comparable OJ XMP 13x12. Acme has a throwing star thing going for it. I see these are left hand unless the picture is inverted would any of the two be for sale provided they were left hand? And not Gold plated! LOL!!!

They are left hand rotation. The Acme conveyed with the sale of my old MasterCraft and the OJ was on loan from Eric so that I could run a little side by side comparison with them back in 2005.

/edit. Just caught the "plated" joke. Well played, sir!

Fl Inboards wrote: Tim I am not sure what the Barefoot 454 motors were rated at maybe 330?? a little more. But if your calculations are in the 470 hp range spinning a prop at 5500 RPM then some reinforcement and re-thinking about your project may be in order. I know I would not run a Nibral wheel with those numbers. I would also at least reinforce my backing substructure that my strut is fastened to. This one would be rather overkill but I hope you understand. Kinda like putting 500hp in a car that came with 300hp and not doing anything with the stock rear end. At least on land when the drive train goes away the car stops and we walk away. Ever throw a blade on a prop at High RPM?

I think the builder expects that motor to live at very high rpm's, very nice. Dry sump motor, shaft mounted rockers with their own oiling circuit, what kind of numbers does that thing put up?

My brother in law runs a 7 liter hydroplane, 468 in., small carburetor, 13 or 14:1, turns nearly 8000 rpm's. Other boats in his class turn over 8 grand. 8-9 hundred hp. direct drive 12 x 24 ish props,

Fl Inboards wrote: Tim I am not sure what the Barefoot 454 motors were rated at maybe 330?? a little more. But if your calculations are in the 470 hp range spinning a prop at 5500 RPM then some reinforcement and re-thinking about your project may be in order. I know I would not run a Nibral wheel with those numbers. I would also at least reinforce my backing substructure that my strut is fastened to. This one would be rather overkill but I hope you understand. Kinda like putting 500hp in a car that came with 300hp and not doing anything with the stock rear end. At least on land when the drive train goes away the car stops and we walk away. Ever throw a blade on a prop at High RPM?

Most BFN's came with the 330hp 454, a handful with the 340hp 460, and some with the HO 454 (390-425hp), though Ive never seen one of those with my own eyes. With a 600+ lb overweight, soggy structure, bent fin, misaligned powertrain (riding on the log as it turns out!), severely pitted rudder port and tweaked strut, running up to 56+ mph was a pretty mundane event. We've fixed the issues with the running gear and solidified (and lightened) the structure, as well as added a handful of hp up top. Id love it if our changes gave us a handful of mph and an improved holeshot, but Im not expecting to see 70mph or anything.

Ill ask again (because I dont understand!), is it the HP (or perhaps torque), speed or RPM (presumably prop RPM, not engine RPM) that I need to be concerned with? Or is it some sort of combination? I dont believe Im entering into unchartered territory, but perhaps I need an education. There seem to be plenty of ski boats with equal or more hp (Python powered Nautiques and 6.2L Malibus come to mind) that have more cubes and torque with comparable hp to what Im planning to be pushing- and those run nibrals. Billy and Alan have both spun their 330-380hp SBF's 5500+ RPM with nibrals. Those 2, as well as Joe, Reid, Marshall, etc have all flirted with the 60mph mark, all with nibrals. I dont *think* Im flirting with disaster at 455hp @ 5500 RPM, but I could be wrong. Im not opposed to trying other props- got any suggestions on what to look for and where?

As far as the strut "underlayment" goes, I assume youre referring to the hull? The bottom of the keel had a pretty beefy layup, but we reinforced it with 3+ layers of biax nonetheless. It is also getting an aluminum backing plate/bracket for the steering clamp.

Torque and rpm both have a say, rpm makes the blade want to fly off.. bigger (size and pitch) blades and the torque to turn them causes the flex that reduces the ability for the blade to hold on when the rpm makes it want to fly off. I dont really worry about my 4 blade nibral prop that I turn with my engine running at 6k rpm.. but my prop is only turning at 4900 rpm.. you are talking about a running 3 blade with 33 percent more loading per blade and running higher prop rpm... starting to push it..


I hate to talk about any of this on this thread because the original poster really would likely be most happy with a an appropriately sized 3 blade cnc nibral prop..

Tim Just trying to help with a little caution, The water gets like concrete over 60 and anytime maijor performance gains are to be had in a boat always second guessing and second or even third re-measuring for saftey sake is necessary. You mentioned Python motors but like Joe pointed out they are spinning 25% less then motor RPM at the prop. 5000 plus RPM I would not try and spin any nibral but to each their own. Glad some beefing up around the strut was done. I am not sure where the thinking that just because a prop is a cnc it will be less likely to self destruct and let go, remember they start life as a casting just like any other nibral prop and can have wrong material % cast in them also. I have seen ACME as well as Federal and OJ loose blades. But a Steel prop is far less likely loose a blade at those kinds of RPM's.
I think if you are building a 470 HP 454 motor it kinda throws skiability out the door, will it not? High idle to compensate for the cam lope, fuel consumption will increase. Dont get wrong I think the build is cool as hell but 470 HP in a direct drive for skiability? Your not going to find a prop that does every thing well but will find a prop that you can live with under most conditions.
Any way when the time comes that you want to experiment let us know and we will send you product, if you dont like it send it back! Is the shaft on your barefoot 1" or 1.125? Either way I am sure we can get you into a C&C wheel if that is what you want.
Cheers!

Fl Inboards wrote: You mentioned Python motors but like Joe pointed out they are spinning 25% less then motor RPM at the prop. 5000 plus RPM I would not try and spin any nibral but to each their own.

Hence my repeated questions above! Sounds like its the prop RPM that I need to be concerned with above all else (hp, tq, speed). Like I mentioned, there are several guys here (Billy, Reid, Alan) that are turning 5000 RPM or more (prop RPM). I guess Ill find out if 5500 causes issues or not when we launch!

Fl Inboards wrote: I am not sure where the thinking that just because a prop is a cnc it will be less likely to self destruct and let go, remember they start life as a casting just like any other nibral prop and can have wrong material % cast in them also.

I made no such claim- I want a CNC for the skiability and smoothness. I have no idea if Ill have strength issues with it or not. Ive got a 14x16 SS OJ (3-blade) that I really didnt care for on my '90... maybe I should consider getting it cut down for the BFN?

Fl Inboards wrote: I think if you are building a 470 HP 454 motor it kinda throws skiability out the door, will it not?

I sure hope not. Comp says I should still idle ok. The powerband below 3000 is really very similar to what it was before the new cam/exhaust/etc (370hp @ 4500 RPM), all the newfound power is above that point- so with the weight loss, holeshot should improve (assuming I dont need to put on a wheel with a bunch more pitch to keep the revs in check).

Fl Inboards wrote: Any way when the time comes that you want to experiment let us know and we will send you product, if you dont like it send it back! Is the shaft on your barefoot 1" or 1.125? Either way I am sure we can get you into a C&C wheel if that is what you want.

Sounds good! We've got a 1" shaft.

TRBenj wrote: skicat2001 wrote: Yall confuse me. I was thinking switching to a 4 but everybody on here said stick with the 3. Go with the 3. Now yall are saying 4. Huh! Have to rethink here then. You need to re-read this thread. Very few people would recommend a 4-blade for your application.

Skicat, how and what for do you use your boat?

I grabbed this quote from the above mentioned thread:

Luchog wrote: I always wanteds to see a comparison between the 542 and the 4 blade 208...

I already have the 208 and I'm happy with the all around performance, but I don't know anything else, my boat came with it. I use it primarily for open water slalom and occasional wakeboarding but no ballast.

Are you likely to see the same kind of really eye opening difference going from a 4 to a modern three blade that you would see going from an old 3 blade to a modern 3 blade? With equivalent pitch etc.

skicat2001 wrote: Yall confuse me. I was thinking switching to a 4 but everybody on here said stick with the 3. Go with the 3. Now yall are saying 4. Huh! Have to rethink here then.

Buy a 4 from Jody immediately!

My main question is which one out performs the other. It doesn't matter whether I myself is going
For a cruise, or having a ski day with a couple of buddies or pulling my nieaces on the tube. Which blade out
Performs the other.

what was there first, the chicken or the egg?