Zero Off and Reconditioned Propellers

[MARK-S]

ZO and rebuilt or bent props do not get along.

[swc5150]

That's good to know! I've only had PP, and have not dinged a prop, so I wasn't aware of that. How is PP with a rebuild?

[MARK-S]

I never had any issues with PP, so I would say none.

[swc5150]

Cool, thanks! Sorry for highjacking the thread!

[Craft]

ZO and rebuilt or bent props do not get along.

Why wouldn't a rebuild work?

[MARK-S]

Not sure and it is only theory at this point, but I know that I skied behind 3 196s this summer that were putting out 16.95 every time, but I could not run 35 ever. All 3 had rebuilt props on them. On one of them there is a skier that runs 38 with his eyes closed and on his home lake, he could barely get out of 35 and never got past 3@38 in 6 tries. After talking to lots of 196 people, there were many reports of very strong ZO pulls behind rebuilt prop 196s. I skied a 196 with rebuild the first weekend in Oct and could not ski a lick behind it. The next set was behind a new prop 196 and I almost had a practice PB.

[2gofaster]

Very few prop shops have the bucks for an Acme prop. It's not just 196s. There is a MC197 down here with a different prop on it and it feels like you're being pulled by a runaway freight train.

Stargazer doesn't like props that allow more engine rpm than what would typically be called normal. It doesn't make it a harsh pull. Instead it makes it really touchy on acquiring control and over-running speed.

[Craft]

Not sure and it is only theory at this point, but I know that I skied behind 3 196s this summer that were putting out 16.95 every time, but I could not run 35 ever. All 3 had rebuilt props on them. On one of them there is a skier that runs 38 with his eyes closed and on his home lake, he could barely get out of 35 and never got past 3@38 in 6 tries. After talking to lots of 196 people, there were many reports of very strong ZO pulls behind rebuilt prop 196s. I skied a 196 with rebuild the first weekend in Oct and could not ski a lick behind it. The next set was behind a new prop 196 and I almost had a practice PB.

I guess I didn't realize reworking the prop would change its integrity so much.

It'd be great to hear some confirmation from someone that's skied ZO behind their own boat with an oem acme prop, and after rebuilding it.

Obviously the manufacturers prefer replacement.

[ScarletArrow]

This is news to me. When I dinged my prop early in the summer I put a new one on. When I had an '07 (in 2008) I put a reconditioned prop on...but I think everyone was too busy adjusting to ZO to take notice if there were any differences.

[2gofaster]

It all depends on who's doing the prop work. From what I've seen, differing props make a big difference in the pull characteristics with ZO. I think a lot of it has to do with the cup people put on. Increasing cup will generally lower rpm. But where in the torque curve does that move the rpm at a given mph? It's pretty much a given that almost all ZO development has been done on a TSC3 hull with a 422 Acme with .105 cup. Anything else changes things. Just like if you rebuilt the EX343 with a lighter reciprocating assembly to increase throttle response and allow the engine to respend quicker. That would KILL a skier, I would bet.

[scoke]

I hope our boat was the "seed' boat that inspired you MS. haha.

We are very much inline with the same thinking as MS. The engine has 700 hours on it, 2007, but there is an excessive noticeable "strength" to it. It's a very stiff and not so forgiving boat.

The prop on it is an Acme 422 rebuilt. Our spare prop is another rebuilt prop from Acme. But the glitch is, Acme rebuilt both props. So you can add that to your list of info maybe. A prop can only get so close back to the original CNC out fresh from the factory.

Our plan of action now is to take the 422 to a local high end prop guy, add cup to it and see where that takes us. Also, check the cup measurement beforehand and see if it got tweaked in the rebuild.


Shane, that .105 might be a typo as the 668 is .150 and the 422 .015, I could be remembering incorrectly but i've got the cutsheets on another computer so i'll check.

We also talked to several other engineers and one of the theories is at slower speeds/line lengths it's probably not going to be as noticeable but once you get to 32'+/34mph-36, due to the rpm swings being in shorter bursts, that's when the skier is going to feel it.

[2gofaster]

Shelby, I'm positive the 422 is a .105 cup as it comes new. I'm looking at the box that my last one came in.

[scoke]

ok great, good info, thanks.

I am wondering if some of the cup is lost in the rebuilding process and if it's not specifically added, it's felt.

[2gofaster]

That's entirely possible. What rpm do you turn 34 and 36 at? I can compare it to mine and Mike's. You should be pretty **** close. If you truly have .015 cup, you'd have a minimum of 100rpm more rpm.

[DanielC]

I am going to throw out another idea. I might be off base, but there is a possibility my idea could be a factor. Also note that I an a show skier, and not a hard core slalom skier. I admire you guys doing this. I have ran a best of 6 at 30 MPH, 15 off. My boat does not even have either speed control system.
I do use a handheld Garmin GPS72 for a navigational aid. It can display the speed, and I use that function to adjust my Airguide speedos when they need it, and it serves as a backup when both speedos quit working due to a pitot clog.
When I am traveling in my boat at a constant speed, with a constant load the GPS speed displayed is almost always wavering a little, even thought the RPM is constant, and the Airguides are constant. The GPS speed displayed also lags behind the actual speed of the boat, both speeding up and slowing down.

The GPS system was not designed to provide accurate speed, to American citizens driving a boat. It was designed to provide accurate location to the military, for targeting purposes. Because it uses time to get a fix, it can calculate how fast you were going. Yes, I meant to use the word "were". In order for GPS to give you the speed, it has to get a position fix, get second position fix, calculate the distance moved, and calculate the speed based on the time it took to travel that distance. GPS devices then can display or control the speed based on the average speed it took for the last two points it sampled, or got a fix on. Because of this, a GPS based system is always reacting to the speed you were going, not the speed you are actually going.

I would think a GPS based speed control system built for a ski boat can "know" exactly where the course ends, and therefore know what time it has to arrive at that point, and would be able to adjust the speed to get there, at the exact time required, to give you the "perfect" 16.95 second pass, but I would question the boat is actually traveling at a constant speed to get there. It is entirely possible the system is trying to make up time, especially as you near the end of the course.