1995 Ski Nautique Prop Choice

[Westlotorn]

I am looking for options with my prop choice, this is a 95 Ski Nautique with the EFI 351W PRO BOSS engine.
1.23:1 trans.

I Currently have 2 props, both are 14 x 16, one 3 blade spare that I have not run, and an OJ 14 x 16 4 blade with 696 stamped in it.

The 4 blade gives strong acceleration but the boat tops out at 45 mph at 5,000 RPM.
At 30 MPH it is at 3,500 RPM.

I would like to have a lower RPM cruise speed. I wonder what props have been tried and how you liked the result.

My days skiing the course are over so just pleasure work now. I am not in any hurry, summer is a long way off.

Thanks for any shared experience.

Mark

[TRBenj]

Acme 422 (12.5x15.5) is the tried and true choice on that hull/engine combo. The 224 (13x15.5) is also comparable in size and performance. Either choice will outperform a hand finished 14x16 by a substantial margin.

I may have a 224 from my collection that I'd consider parting with... PM me if youre interested.

[Westlotorn]

My goal is lowering the RPM's, if I could cruise at 30 with the tach down to 3,000 or a little less I think that would be good for me.

The powerful hole shot many need for short course work is not needed for me. The engine seems to have plenty of power for a larger prop. If larger ( 14 x 17.5 maybe ) type props ruin the ski wake I would like to know that also. My ski time now is at 15 off.
I am trying to avoid spinning the engine 3,500 to 4,000 RPM as I drive 4-6 miles getting to our ski beach.
(I know I could slow down but who wants to go 25 mph when you could be going 35)

Thanks

[TRBenj]

The 500rpm differential between speed and RPM at skiing speeds (30mph @ 3500rpm) indicates that the prop being used to produce those numbers has either been altered from the original 14x16 dimensions, or is extremely tired (and flexing). Most likely the former, as the problem would be exacerbated at higher RPM, whereas your numbers are consistent at the 2 speeds.

A true 14x16 should run right around 1:1 at skiing speeds (30mph @ 3000rpm), and only overturn slightly at WOT (46-48mph @ 4800-5000rpm) on that hull. The 2 Acmes in question will run very similar numbers, as they are essentially sized as stock replacements.

Something like a 14x17.5 prop would perform horribly- adding 1.5" of pitch is very extreme... and youre most likely running a 14x15 right now (or possibly less). While such a prop would reduce RPM significantly all across the board, the boat would be significantly slower out of the hole AND up top. It would also put more stress on the engine and transmission, as you would essentially be loading up the drivetrain with the taller prop. Definitely not recommended.

Long story short, the prop youre running now is borderline junk, and even if it were brand new, the Acmes I suggested would still offer superior performance.

[Westlotorn]

Thanks for the great information. Maybe I should install the factory 3 blade and see what it does, I never tried it since they both had the same 14 x 16 stampings I assumed very similar performance would be had. I would be happy if I picked up 4 -5 MPH and the RPM at 30 was down to 3,000. That is what I hoped to achieve.
I will share that the current prop 14 x 16 4 blade does have incredible acceleration but it revs very high. I can see it has been repaired so it may have been re cupped also.
I just purchased this boat, it has only 100 hours on it so the OEM prop is probably like new. The 4 blade is an OJ and has been used and abused by the previous owner.
Do the newer CNC blades give that much more performance?
I would like to learn a little more before buying, what condition is your 224?
I always assumed the 14 x 16 would move the boat 16 inches in one rotation, that is why I did not consider a prop listed at 15.5 per rotation. There must be lots more involved. Thanks again.

[TRBenj]

It is highly unlikely that you would gain 4-5mph with a prop change, even if your prop has been repitched as I suspect. That would be the equivalent of a "magic bean"... 2-3mph is about the best you could do- and thats if you have a fast hull. Its highly likely that you will only pick up a little bit (1-2mph) as 46-47 is about right for a Proboss NWZ SN like yours. But, running 30mph at 3000rpm is pretty much a given if you choose the correct prop (like the 422 or 224). But yes, overall performance will be night and day when comparing any old school hand finished prop to the new crop of CNC wheels.

The slight difference in the size listed (14x16 vs. 13x15.5) and the fact that they perform equivalently (at least in terms of speed vs. RPM) has to do with 2 things, for the most part. 1)Prop sizing varies from manufacturer to manufacturer- some round off their dimensions to the closest integer and 2)Acmes have a LOT of blade surface area, which allow them to act like a slightly larger prop than their dimensions imply.

My 224 is very slightly used (~20 hours) and is in as-new condition. No imperfections to speak of. PM me if you want to discuss.

[Lewy2001]

ACME 422 12.5 X 15.5 on the Left and OJ 4 Blade Legend 13 X 16 on the right.

As Tim states the numbers are somewhat rounded off. The 422 actually looks larger in diameter.

[Westlotorn]

Thanks for the pictures, advice and help. It sounds like the 422 is the prop of choice for most here.

If I could drop my RPM from 3500 at 30mph to 3,000 at 30 mph I would consider the prop change a success.
My engine feels really strong, I am sure it could comfortably pull a better prop.