Boat speed and zero off

[bbirlew]

@Than_Bogans thread 'is slalom too easy' got me thinking about speed controll with zero off - specifically the a-c,1-3 settings.

Shouldn't it be the goal of the speed control system to maintain as close to the set speed as possible? It seems to me these settings are saying "you can drive any speed you like throughout a segment as long as you average the set speed at each ball.

I know that no system will ever be perfect, but isn't the intent of the rules to have a constant boat speed?

Thoughts?

 

[ral]

@bbirlew, this has been discussed ad nauseam in the past. Letters/numbers are not the issue, though, the algorithm phislsophy is.

 

The intent of the rule is constant speed over the bottom, but the only checking variable is time (the only precise enough in the past). Perfect Pass did a good job in getting an easy pull, comparable to a manual one (where speed is not constant).

 

Then came ZO revision N, first version, which effectively tried to get constant speed. Almost all skiers HATED IT. Gassing skiers to death was the constant complain. Then it changed to something that was more similar to PP, including a faster approach to the course. Revision N did have letters as well. As mentioned, letters are not the speed varying culprit.

 

 

[DUSkier]

@bbirlew no the intent of the rules is NOT to have a constant speed! It is to be within the range of times for a given speed. C settings are coming on and off within the tolerances just as A and B are.

[DanE]

@bbirlew Since no speed Control (or human) can accurately anticipate the various load applied to the Boat throughout a pass the speed have to vary a bit in order for the system to sense that speed needs to be corrected.

[mwetskier]

the constant speed requirement comes with a tolerance range since theres no possible way to get truly 100 per cent constant speed with a boat. maybe you could with a huge 1200 foot long hydraulic ram but that doesnt exist. so far zero off is the closest solution weve got because its totally reactive to the skier instead of just applying a fixed rpm increase over a fixed time period like pp.

[BRY]

@bbirlew, The original intent of the rule, with hand driving, was to be as close to actual as possible. The rule used to state this. No human could drive actual so tolerances were put in. Some drivers were good enough they could intentionally drive on the bottom end of the tolerances, which if I remember correctly was considered a rule violation (but difficult to prove).

PP came along and the ability to get more consistent rides and times. The ride quality varied less between good and not-so-good drivers. Properly set up PP gives very good times with significantly less deviation from actual than tolerances allow.

With ZO and drive-by-wire high HP boats it became possible to have the boat be nearly perfect to actual. This proved to be a brutal ride, like a non-stretch rope, with the instant throttle response. My understanding is "give" was put back in. Also my understanding is the ABC was done to try to make the "give" adjustable to different styles, so no one style had an advantage.

I did ski an early version with just ABC and a flat gate speed. A powerful ride, but I was the weird one and liked it. I really liked the flat gate speed, felt it made it easier for a slow and consistent gate. My understanding is the higher gate speed was put in at the time to better match PP which brings skiers in at higher than actual.

[ToddL]

ZO simply reacts to the lost speed due to skier force. The more the skier pulls the boat below the intended speed, the more ZO has to go faster than the intended speed to cancel it all out in the end. The letters and numbers just change the reaction time and abruptness of the corrective action.

 

The art of ZO is understanding those numbers and letters such that the skier matches the setting to the skier's style and desired timing/intensity of that corrective action.

 

The only way to get a "soft" pull on ZO is to minimize your force against the boat and to time its corrective action so that it comes while you are stacked and in your approach to the first wake. When that is ideal, the pull will feel consistent, solid, but not harsh.

 

In contrast, if you overload the boat with force or have it hit you too early or stay on you too late, the pull will feel harsh.

[bbirlew]

@toddL,

My argument is "shouldn't the reaction time be as quick as possible if we now have the technology to make it more accurate?"

I understand that skiers didn't like it, but why should that be a concern for upholding the 'intent' of the rule (to be traveling as close to 36 mph as we can) instead of bending them to make it easy for the Skier. Currently your boat speed might only be 36mph at 6 points in the course but you can still get "actual" times...

We can do better than that now.

Sorry if this has been discussed at length before. I'll go search the archives now.

[ForrestGump]

Why should it be as quick as possible? What would be the goal? the boat is already getting to each of those 134' 6" segments with an accuracy of .01 of second. Just because something is possible doesn't mean you have to do it.

[Than_Bogan]

@bbirlew I want to agree with you: the principle "feels" like it should be to get as close as possible to a constant speed. But skier experience fairly universally confirmed that doing so was less fun and harder on the body.

 

Barely related: I still believe that someday the control system will dynamically "do the right thing" for a given style without the "hint" of ABC, 123, and +. But that's a hard problem with little incentive to solve.

[bbirlew]

@Than_Bogan, it must be the engineer in me...

 

How about this:

Surely skiers found it easier/more fun/etc when the driver 'helped the skier' by varying side to side from the centerline of the course.

Should the driver drive as straight a boat path as he can, or should he 'help' everyone (or perhaps his favorite subset of everyone) such that he is weaving all over the course but still within tolerance.

The intent of the rules is to have a straight boat path... The tolerances are there to account for 'human' error, not as a way to bend the rules.

No?

[Than_Bogan]

@bbirlew But the big difference there is consistency and therefore fairness. Because ZO is controlled by an algorithm, it can assure that whatever "we" decide on as a sport is done universally at all tournaments. When a human is allowed to "help," then fairness is almost definitely compromised, as different skier/driver combinations will get different amounts of help.

[bbirlew]

@Than_Bogan,

Fair enough... However, if you were to design a 'boat path control system' - maybe some sort of pole sticking out of the water running on an underwater track - would you design the track straight or would you design it to curve closer to the balls but within the tolerances that were clearly intended to minimize human error because it would be easier (and therefore more fun?)

 

[ToddL]

The perfect system would predict skier force and timing, automatically sense skier force triggers, and immediately take only the minimal, necessary corrective action to maintain accurate times. All of this would be done without any skier selection of type of pull (no letters or numbers). However, that system does not exist and would be extremely difficult to build.

For the predictive part, it would would require collection a huge amount of data about skier tendencies at various skier weights, speeds and line lengths in order to build a enough data to predict skier force and timing. Even if we had all that data, the system would then need to be told some facts about the skier... Weight, current rope length, etc.

[BRY]

@bbirlew, The "actual" speed ZO was brutal, i.e. beats up hands, shoulders n so forth. Try slaloming with a spectra no-stretch rope, will give you some of the idea. So a little "give" is there, not to make it easier but to make it doable without pulling people apart.

 

"The tolerances are there to account for 'human' error, not as a way to bend the rules." You are years late on this by quite a few years for speed control. Was definitely an issue with hand driving. Less of an issue with PP but could still be manipulated. ZO doesn't allow that manipulation and its variation is way less than most, if any human, drivers can achieve.

 

"The intent of the rules is to have a straight boat path... The tolerances are there to account for 'human' error, not as a way to bend the rules." But with the best human drivers there is still some variation from actual, no matter how "tight" they may try to be. And there is possibility of swervey driving for some and not others or to enhance scores. Hence end course camera's for "R" tournaments. But an actual perfect drive down center is not possible right now. AutoDrive is on the horizon, I bet sooner than people think. Question to you, if the machine turns out to be able to drive a perfect center but that is shown to pull skiers shoulders out should we do it? Or if building in a little variance, less than the best drivers have now and essentially the same for everyone, makes it more "skiable" should we allow that variance?

 

[The_MS]

Speaking of tolerance, with ZO coming in very close to actual, why are the high and low tolerances still so liberal? Example is 55k giving you 16.78 under, 16.95 actual and 17.12 on the top. How great would it be to get 17.10 with a ZO pull?

[MattP]

@ms also why do we still call times after each pass? The driver/judge should look and if its out of tolerance call it in. If it is not dont. I have never seen a bad time from ZO.

[bbirlew]

@BRY,

I've been around skiing long enough to have skied through good and bad hand driving. My buddies and I experimented with making our own 'cruise controll system' back in the day, and I have had perfect pass since v2.0. My boat currently has zbox and I routinely ski behind zero off.

Unfortunately I don't believe I ever had the opportunity to ski behind the first attempts of zero off, but I would be interested from an engineering standpoint.

As to your question about boat path (or speed) and injuries/etc... Im not sure which side of the fence I fall on. I tend to think that if I'm not in the correct position to absorb whatever forces I'm up against, I deserve to be ripped out of my ski!

If I have my head down in hockey I will get hit... People don't just let me skate all the way down the ice with the puck because I'm not looking for them...

Fun argument. Again, sorry if this is re-hashed too much for some.

[ScarletArrow]

@MattP Agreed! Calling in times in a completely unnecessary w/ ZO.

[ForrestGump]

@bbirlew In 07 and 08 when ZO first came out, imagine hitching your rope to the caboose of a freight train driving down the lake at 34.2 or 36mph. You may think it an exaggeration, but I kid you not, that's what it felt like.

[BRY]

@bbirlew, No need to be sorry. I think the actual vs perfect argument has merit, just needs to be in the realm of where we are. Speed is pretty dialed in now that variances can be dialed in (or out) by the machine designers but not manipulated by the individual. Boat path is coming and the answer as to variances there may be different than speed.

My question about path/speed and injuries, to be more specific, is not for when you are out of position but for when you are. In man vs machine there is a point where the machine can pull the man apart unless it is built not to. So if even doing it right the skier gets beat up (pro's) and significantly worse if done wrong (yo-yo's like me). At that point I think it should be dialed back, particularly when it is still much tighter than before.

 

If you are playing hockey against a robot player that plays perfectly and is 230lbs, even if you skate with your head up, that robot player will hit you perfectly every time. Not a hockey player but I bet that accumulation of perfect hits you can't escape ends you pretty fast. Make that player 2300lbs and splat. Perhaps design in a little variance from perfect, maybe less than any human player ever, but some. Just enough it doesn't get you perfect every time, room to hang in there. IMHO, there's a challenge, there's a game to play.