Zero Off and Reconditioned Propellers

[j2nh]

Zero Off speed control does not use coordinate position to determine speed. Zero Off uses the radio signal that is sent out from GPS satellites and measures the doppler effect to determine speed. The accuracy of the displayed speed is dependent upon the sampling rate of the unit measuring the speed. A hand held Garmin might sample once or twice per second, hence the lag, while ZO measures in the hundreds per second and eliminates the lag.

[DanielC]

You may be right, can you point me to more info on the process GPS uses?

[j2nh]

You may be right, can you point me to more info on the process GPS uses?

This is a pretty good one that I had on file. There are some other good ones on the net if you do a search.

[DanielC]

Thanks for the article. I did not read the entire article, I skimmed it. Nor do I understand all the math in it. I could be wrong, or I missed it, but it appeared that the article was talking about one brand or type of GPS unit the company makes, and it did mention at the end in the conclusion that to achieve the accuracy described it needs speed events longer than 20 seconds.
We both know how long a slalom run is.

OK, here is another idea. About a year ago, I took a class on fuel injection and emission systems for automobiles at the local community college. I wanted to understand more about my boat, how it works, and the car I drive. I pretty much took a whole auto mechanics program there when I got out of high school. At that time, cars had carburettors, and most still has points inside the distributer. I wanted to update my knowledge.
One of the things mention in the class is that the the modern computer used in a car is adaptive. It learns the values the specific sensors give it in normal operation, and compensates for that, and optimizes the output parameters to make your engine run cleaner, and it also adjusts the outputs to compensate for component aging. We learned that you sometimes have to reset the computer, when a bad or poorly operating sensor is replaced.

I am just offering ideas on why a ZO equipped boat becomes harder to ski behind when the propeller is repaired. I am just a show skier, and driver, and my speed control is in my right hand, but show skiing does not require the accuracy that running a slalom course requires.

[j2nh]

DanielC
Two ways to measure speed with with GPS:
Speed as a function of GPS positional measurements (trackpoints). Most GPS units sample at a rate of 1 per second (Garmin handheld).
or
Instantaneous speed measurement as a function of the doppler shift of the GPS radio carrier signal which is completely independent of the GPS positional information.

Zero off uses the latter and samples at a much higher rate thus eliminating lag.

How the instantaneous speed is integrated into the boats computer is based on proprietary algorithms developed by Zero Off/Econtrols and I would suspect that you are correct that changing a variable, in this case the prop, is what changes the feel of the pull.

[DanielC]

J, have you noticed any of the above problems that started this thread with your boat, about it becoming more difficult to complete the course with a rebuilt propeller?

[2gofaster]

Daniel, it's not that it becomes difficult to complete the course. It's that the pull becomes noticeably harder or more harsh. With ZO, there is an allowable deviance of .02 seconds through the course. When the skier pulls down the boat the ZO will instruct the efi to accelerate. This rate of accelerate back to baseline is what makes the pull feel harsh. If you do something that allows the engine to accelerate quicker, the skier can feel that.

[Craft]

I don't understand why ZO doesn't utilize a slalom switch like PP. A jump switch is required with ZO, and there's only one significant point (two if you include counter cuts) where the timing of the pull is communicated to ZO. In slalom, there's six.

[MARK-S]

Its the only theory I have. It cant be the skier, right?

[DanielC]

Here is another idea. The horsepower is raised on both the 5.7 and the 6.0 engines, but they still have the same redline, about 5000 RPM. In order to get a horsepower increase at 5000, the RPM the engine produces it's peak torque has to be moved up in the RPM range. This is done with different camshaft, port tuning, and many other factors, but these changes also cause the engine to lose torque at a lower RPM. These changes also make the RPM range the engine produces maximum torque smaller.
If the speed control system is calibrated at a specific RPM, having the engine run at a slightly higher RPM could put the engine at a speed where it produces more torque, and therefore it would be more responsive.

[Craft]

Here is another idea. The horsepower is raised on both the 5.7 and the 6.0 engines, but they still have the same redline, about 5000 RPM. In order to get a horsepower increase at 5000, the RPM the engine produces it's peak torque has to be moved up in the RPM range. This is done with different camshaft, port tuning, and many other factors, but these changes also cause the engine to lose torque at a lower RPM. These changes also make the RPM range the engine produces maximum torque smaller.
If the speed control system is calibrated at a specific RPM, having the engine run at a slightly higher RPM could put the engine at a speed where it produces more torque, and therefore it would be more responsive.

Huh? How does this tie into reconditioned props not working as well as oem?

I personally don't need any more responsiveness from my 5.7L. It's just fine. I think the ZO already works the whole range of torque when the system is engaged and the throttle is pinned on my drive-by-wire boat. No?

[2gofaster]

Yes, Craft.......as long as you have the throttle pinned, ZO has full use of the torque. The difference is how quickly can the engine accelerate. IMO, that's why boats feel different with different props. If you allow the engine to accelerate faster, the pull will feel harder. Or if the selected prop puts the engine at a point in the powerband where the engine is less effected by the skiers load, the pull will feel harder.

[scoke]

Hopefully sometime soon i'll get this prop to the prop guy. $45 to add some cup to it. I am curious if he can measure the cup on it etc See what he thinks.

Maybe it's cup is below the factory .105?

I doubt some of the near-perfect brand new props are more than the .105.

[Craft]

What about using a 3-blade prop instead of a 4-blade with ZO? Seems like the transitions would be smoother.

[2gofaster]

I wish I still had the 470 acme 3 blade from my 2005 to test with. I knew I shouldve kept it when i sold the boat.