What RPM does your GT40 powered Ski Nautique run at WOT?

[Fast351]

Mine runs about 5400 RPM. Was perusing the manual, and it said:

 

MAX (Intermittent)RPM 4,800

Continuous cruise RPM’s (max) 4,000 - 4,200

 

Obviously at ski speeds I never get close to that (although it does turn about 4K at 34.2) but I'm wondering if I should consider a reprop. Near as I can tell it has the stock OJ prop on it although I understand that the Acme 422 is the preferred unit for this boat. I'm not really all that anxious to spend the money and especially recal my now perfectly dialed PP.

 

If you have one of these boats, especially with the OJ prop, what do you see?

 

Thanks!

[DanE]

I have the new CNC OJ prop, turns 5000 @wot. I don't exeed 4000 even @ 36 mph.

Original cast OJ turned more rpms as I recall it.

[paco]

If your prop is original, it's damaged in some way. No way I'd push it to 5400. They are tough, but your asking for trouble. I'd call Eric at oj and see what he . He may be able to repair or tweak yours a little. 4000 is not terrible, but you'll shorten your engines life at this range. Mine is propped fairly low as I turn 3600 at 34.2. I'd try to stay 3800 or lower.

 

After changing, all you should have to do is recalibrate each speed, but i do understand not wanting to change it.

[TallSkinnyGuy]

Theoretically your wake will get softer at the same speed if the RPMs are lower, so it might be worth the re-cal effort just to get softer wakes. One of my ski partners has that boat and engine and his WOT RPM is 4800 at 2000 feet elevation.

[oldjeep]

How fast is the boat going at 5400RPM?

[Fast351]

Maybe 48ish? Haven't verified with GPS, but the Faria paddlewheel speedo is accurate +- 1MPH all the way from 5-40, so I have no doubt it's close. I will check it tonight because now I'm curious. That's with 2 people, a rope and a ski, a couple lifejackets, and not enough gas to get you across a 2 mile wide lake in the boat.

 

I love the wake behind my boat, I ski mostly 15off at 34, occasionally shorten to 28 just for entertainment purposes. My wife says the wake is significantly larger at 32MPH 15off than @dtm8119 's 94 PS190. If only for that reason, I wouldn't mind softening the wake some.

 

So if I were to get a new prop, I understand the Acme 422 and 668 are popular (with the 668 having lower RPMs due to more cup) and the OJ 428 as well. Any others I should look at? I've heard 3 bladers are coming back into style for these boats. This boat is ONLY used for skiing (OK an occasional idle around the lake) but never for trick/jump/tube/whatever, so soft wake is the only thing I care about.

 

 

[DanE]

OJ 428 is a firmer pull than the Acme 422.

422 is smoother.

[slow]

4800 rpm at 44 mph 2000ft elevation

3625 rpm at 34mph

[TallSkinnyGuy]

@Fast351 My understanding is that 3-blade props tend to work best with 1:1 transmissions whereas transmissions like yours (1:1.2ish?) and the MC Powerslot 1:1.5 tend to perform best with a 4-blade. I'm sure Acme and OJ could guide you right. Before talking to them you'll want to have all the dimensions of your prop and the RPMs on your boat at WOT and a couple skiing speeds.

[BraceMaker]

I think 3 v 4 changes a lot with CNC props. The running surface of the the blades is very well optimized in both products and both companies will hedge bets.

 

I like the 3 blade oj.

[Fast351]

 

So here is the stock prop. OJ Legend 13x16. I think it's their part# 1251.

 

Speeds:

3810 RPM, 34.2 MPH

4030 RPM, 36.0 MPH

5180 RPM, 46.0 MPH (WOT, GPS indicated).

 

RPMs were taken from the PP tach, not the Faria analog one, which seems to run a couple hundred high (so it's not AS bad as running 600 over redline, but still 400 high).

 

Again, this is a 2001 (MY) Ski Nautique, GT40 1.23:1 trans I believe.

 

 

 

[aupatking]

Brother, I put a new 422 on mine 2 years ago. Just bought another. Mine runs real close to 100 RPM per MPH. I think mine at 34.2 may turn 3430-3430. Even thinking I hit nothing in the river, I put a new prop on after that long and the vibration I didn't even know existed, was immediately obvious, but gone

[aupatking]

Oh yeah, I ever catch anyone, ever, running my boat at 4,800, I'm whipping their @$$

[Fast351]

Eh, it's a 351. My race engines endured far worse which is why I never even noticed the higher RPM. I spun that thing to 7200 regularly (of course that was short periods of time, not crossing a lake for minutes straight).

 

Thanks for the advise tho. I could live with a 400 RPM drop, that'd be nice.

[LeonL]

You should get an Acme 422. That's the stock prop for 2002 and up for 196 SN. You'll be happy with it. Much smoother than what was on 2001 and back boats.

[paco]

Glad to see you're not turning the full 5400 you thought, but that prop should turn a lot lower rpm! That's assuming of course that your transmission is a 1.2?:1 gear reduction. My bet is it's damaged, may not be noticeable as far as vibration, but it's definitely not right. Could've been repaired poorly? We just went through thot same thing with my ski partners boat. Repair shop got the cup wrong and rpms are around 500 higher than when the prop was new. Send it to Eric at OJ props. He'll make it like new again.

 

I'll second the fact that the faster a prop turns, the more it will diminish the wake. This happened on the boat spoke of!

[wtrskior]

I was going to suggest checking to be sure you're getting the correct rpm reading from the engine but the revised numbers look better

[Fast351]

Talked to Acme today, and on their recommendation ended up getting an Acme 422 on order. I did ask about the 668 (basically identical to the 422 except .150 cup instead of .105) and their response was "sure, it'll work, but it was specifically designed for the higher HP engines that came later".

 

Can't wait until the new prop comes in. I'll give you guys a back to back review.

 

I will probably get the OJ prop redone and just hang on to it as a spare. Shouldn't ever need it but you never know.

 

[Fast351]

 

Out with the old, in with the new!

 

 

Old vs. new baseline RPMs, and a BIG improvement in vibration (or lack thereof).

 

Win win!

[rockdog]

Yep, I'm running the 422 on my '97 with GT-40 and also ski partners '05 with Excal. That prop is perfect for both and it runs right around the 3400rpm.

[A_B]

My '99 SN ran just under 5k rpm and was around 47 mph. I think 34 was around 3450 rpm give or take a little with a 4 blade OJ. From my PP days. Was very fast out of the hole.

[TallSkinnyGuy]

Your skiing speed RPMs really dropped a lot. Did you notice any difference in the shape or softness of the wake?

[Fast351]

Maybe if you use your imagination a little bit :smile: To be honest, the water conditions from yesterday to today were different enough that it was hard to tell. My ski partner said at 28 off there was no difference. I was skiing at 15 off, and it maybe was a hair softer (maybe) but not enough that you'd say "WOW what an improvement". Both at 34.2

 

The boat is quieter and vibrates less though, so for the driver its a better experience.

 

[Teddy]

I'm at about 3,000 feet and currently run an OJ Legend 13 x 16. I think the prop is original to the boat. My numbers were 4700 rpm off my Perfect Pass reading and 42.7 MPH.