Zero-Off not holding steady

[xrichard]

I'm looking at a 2017 G23 and the owner says that, at surf speeds, it will vary speed approximately +/- 0.2mph and that it only recently started doing this. Stationary on the trailer, the LINK display reads 0.2 mph.

He said the speed variance is not really noticeable in the boat but that he can hear the engine increase/decrease revs. Also, 1. it could be variance slightly more or less than 0.2--he hasn't paid close enough attention, 2. He isn't sure if it occurs at other speeds or in conditions outside of surfing, 3. no other problems with display--all seems to work normally.

Any thoughts as to potential causes? Seems like it could be a bad GPS antenna or a bad wire connection, but my fear is it could be indicative of a bigger issue.

[jjackkrash]

I've never surfed (we 3-event ski). But that's what ZO does is adjust the engine rpm to attempt to hold GPS based speed. It will adjust rpm going over waves, turning corners, in wind, and in response to skier input to keep the speed at the set speed. Jumpers and slalom skiers will make it absolutely drop the hammer. And the speed is never dead-bang perfect in my three sports as it is constantly adjusting. So I am not sure an RPM variance is a concern as that is a feature not a bug unless something else is going on or it is varying wildly for no reason.

I have no idea why it reads .2 stationary on the trailer. That might be a concern but maybe a software fix. Call a dealer and ask for possible causes and fixes.

[jpwhit]

Surfing doesn't put any skier load on the boat like 3-event skiing. And believe it or not, .2 mph is fairly significant variation for surfing. On my 200 or Prostar when slalom skiing, that kind of variation would be normal due to skier load. On the wake boat, when surfing it should be rock solid with no perceivable variation. That fact that it reads .2 mph on the trailer hints at a GPS issue. When surfing on my wake boat, I cannot perceive the least bit of engine RPM variation, much less a change in the speed reading. The exception being plowing through some huge waves. I think that's a case where I can hear some RPM fluctuations.

I'm going to discuss the two different version of Zero Off in this post because I don't know for sure which version you have. The 3-event Zero off and the Wake Edition Zero Off. The Wake Edition Zero is a subset of the 3-event version and only supports a single mode. That mode is just a basic speed control mode to keep the boat at a constant speed based on GPS speed readings. The 3-event Zero off has 3 modes. Slalom, Jump, and Trick. Trick is the same as the Wake Edition mode. It just keeps the boat at a constant speed based on GPS speed reading.

3-event Slalom and Jump modes are much more sophisticated. They use both the GPS speed reading but also uses accelerometers such that the Zero off can respond to skier applied loads more quickly. Also, for Slalom and Jump modes you "teach" zero off the exact geographic location of the courses via a process known as mapping the course. Then Zero off uses that info, along with current location info from the GPS to anticipate where the skier is likely to load the boat and to help is apply and remove power to ensure the buoy-to-buoy times stay within the acceptable limits.

There are two different generations of the 3-event Zero Off. If this were the first generation 3-event Zero Off, with the older dual Garmin GPS puck setup, the issue would almost certainly be caused by the GPS Week Rollover that happened in 2019. The Garmin 18x-5hz GPS pucks had a software bug that didn't handle the 2019 GPS Week Rollover correctly. The result of the software bug is unstable speed readings that cause speed surging of the Zero Off.

https://en.wikipedia.org/wiki/GPS_week_number_rollover

This is what the Garmin 18x-5hz GPS puck looks like and there would be two of them one on each side of the boat right in front of the windshield.

https://www.garmin.com/en-US/p/13195

The 2nd generation single ECI puck 3-event zero off was not affected by the 2019 GPS Week Rollover and upgrading to that is the recommended "fix" by Zero off for issues with the older dual puck system. To make a confusing subject even more confusing, the latest 18x-5hz Garmin pucks no-longer work correctly with Zero Off. The chip originally used to make the Garmin pucks is no longer made, Garmin switched to a different chip that doesn't work right with Zero off. That is actually what led to the development of the latest single puck 3 Event Zero Off which uses a single GPS puck made by ECI.

But I'm assuming this would most likely be the Wake Edition Zero Off with the single ECI puck for Wake Edition. I'm not aware of that puck having any issue with GPS Week Rollover. So it may be that your puck is just failing if you do indeed have the wake edition Zero Off.

https://www.nautiqueparts.com/produc...nc-r2-antenna/


And again, assuming this is a GPS issue is just an educated guess at this point. Clearly this could be a complicated issue to diagnose and get resolved. It also is possible to be an engine issue that is causing variations in engine power. Variations in engine output tends to wreck havoc with speed control systems.

This is likely way more detail about Zero Off than you wanted to know, but I covered it because it helps put into context why this could be a trick issue to get corrected. Personally, I would tend to insist the existing owner gets the problem resolved before buying the boat. Unless you're willing to take on what could be a real headache of an problem to get sorted out in exchange for a discount on the price of the boat.

[jjackkrash]

3-event ZO now has 7 primary modes: Slalom Tournament, Slalom Practice, Trick Tournament, Trick Practice, Jump Tournament, Jump Practice, and Speed Control Only. Tournament Jump also uses a mechanical switch. And with no skier behind the boat in any mode my set up will vary the RPM with a direction change, wind gusts, or going over waves/rollers.

All that said, I'll defer on anything surfing and how much variation is normal, and the above post is pretty accurate and has lots of good information. And having a bad puck is not uncommon.

[xrichard]

Thanks for the replies--lots of knowledge here