Acme 906?

['99 Python]

Anybody have any info/experience with the 906? It would be going on my '99 Air Nautique DD w/502. Just very interested what the 19 pitch would feel like. Torque is not an issue. I'm the second owner of this boat, but i believe the factory issued prop for this boat is 14x18? Please correct me if I'm wrong. It's time to get a new prop for this season, and i like the 14x18, but i feel like i can shatter the 50 mph barrier easily and not give up much, if any, holeshot. As you fellow Python owners know, there isn't much info available anywhere for trial and error products for our boats, and just want to get some insight on what you guys think would be pros/cons of the 13.5x19 vs the 14x18. Also, I'm a former lifetime I/O owner, so the whole cupped thing is relatively new to me as well. Currently with the 14x18 factory setup, on the PP, the boat will match mph with rpm. It just about tops out around 48 mph @ 4800. Any insight/help would be awesome guys. Please school me. Thanks for your time.

[bchesley]

I just replied to another thread that you posted in so I won't retype everything. Do yourself a favor and call ACME. Tell them what boat and motor you have and they will get you the right prop. They did for me and I couldn't be more pleased with the results. I tried everything under the sun before I called. Could have saved myself some time.

Brad

['99 Python]

Will do. Thanks.

[TRBenj]

What makes you think you should be able to shatter the 50mph mark? The 502 Ski Nautique was only a 50-51mph boat from what I understand. Add a few lbs and more drag with the bigger hull and 48mph seems pretty close to what you should expect.

I dont know the motor specs off hand, but I would expect that motor to be making the most power right around where its spinning now (4800rpm). Deviating significantly from that optimal range (where the engine makes its peak hp) will only slow the boat down. Going from a 14x18 OJ to a 13.5x19 Acme is going to drop your RPM's significantly. I wouldnt be surprised to see you lose 400rpm. It'll come out of the hole slower and you will probably slow down, since limiting the engine to 4400rpm is keeping it from making its full hp.

From what Ive read and heard, the direct drive Python boats came with 18" pitch props. I thought they were 13x18, at least on the Ski Nautiques. The Sports may have had a little more hull clearance to allow for the larger wheel.

Dont worry too much about cup. Its useful in a very small range (0-.200). Most ski boat props will have somewhere between .080 and .110 cup, with a few that have up to .150. Having more cup is like having more pitch (it will turn fewer RPM's), without all the tradeoff in holeshot. I believe that it makes the prop more inefficient though.

Just a guess, but I would expect the 380 (13.5x17) or 800 (13.5 x 17.5) to improve performance a lot more than the 906 would. Acmes tend to "act" slightly larger than their measurements suggest, versus an OJ of the same size. The goal would be to find a nice Acme prop that allows you to turn in the 4800-5000 range. That is what will get you closer to the 50mph mark.

['99 Python]

Awesome. Thats the info i was hunting for. Thank you very much. I was backwards on the Acme pitch "feel". In a nutshell, it just feels as if she runs out of prop way before she's runs out of power, leading me to believe she's not reaching her maximum potential (max rpm in relation to max hp). The 50 mph thing would just be the bonus of finding the perfect prop, it's not a goal or anything. Just trying to achieve "perfect" harmony, if you know what i mean. Thank you for your help and time.

[TRBenj]

I think youre thinking about it a little bit wrong. If the motor can only pull the prop 4800rpm, then youre not "running out of prop". That would be a better description if the motor was over revving, and the prop was not able to push the boat forwards efficiently. Its actually doing an ok job of keeping the revs in check, so it appears to be an appropriate match to the powertrain.

Thats not to say that a modern CNC Acme wouldnt be a good step forward in terms of performance. It will have more blade surface area so holeshot should improve (if the pitch is comparable, which I would expect the 17.5" to be, as compared to the 18" OJ. It will be more accurate and a bit smoother, too. If you can get the revs up just a *touch* (shooting for 4900-5000) then I wouldnt be surprised to see the boat hit 50mph. Ive found that Acmes are pretty darn efficient, in terms of turning RPM's into speed.