How the heck does Speed control really work?

[Horton]

Does this sound right?

Based on gross weight, wetted surface area, engine package, prop choice, gear choice and a hundred other factors each boat reacts to a skiers pull a little differently. So at a given RPM or speed with cruse turned OFF if I create X pounds of drag, the speed of the boat will change Y.  Change boats, turn cruse off, go the same speed and add the same load; the change in speed will not be the same (Y+-). 

In other words if I turned Cruse off and ran passes without any throttle input after the pregates I would get a time that was slow but predictable. If I repeat in another brand of boat it would also be predictable but different.

Lets say the heavier boat is harder to slow down and more easily keeps constant speed and a lighter boat reacts more when a skier pulls. (This could be backward – just and example) Turn cruse on and the heavy boat need less throttle action to give a  good time.  

PP Classic was (I think) pure RPM based and ZO (I think) is pure Speed based. I guess Gazer is a hybrid but set that aside of the moment. If what I have said above it true then ZO should really feel the same from boat to boat.  Am I right that PP Classic has a number of adjustments to tune in a boat?

Just thinking . . . . . .

[DW]

I am not sure it would necessarily that predictable w/o cruise engaged.  You have to add the assumption that each pass is identicle for that to happen, water conditions do not vary and fuel load remains constant.  Water conditions alter the surface therefore the surface tension acting on the hull, fuel load will alter the fore/aft weight distribution therefore changing the wetted surface and inconsistent pulls will alter the moment the skier creates on the pylon that will also alter the boat attitude.  Granted, these are all small compared to 350 hp and 2500+/- boat wieght, but I think you get the drift.

Interesting thought on ZO effect on pull feel, I still think the various differences between boats will create a different feel among various boats.  ZO still has to be reactionary to a set of parameters, and can only react to changes from what it thinks it has to do.  I would still argue that different boats would change speed at a different rate, thus resulting in a different feel, due to system hysterisis and time lag effects.

[Horton]

My thinking is that if someone could define the pull profile of a typical short line skier. Then map an acceleration / deceleration profile from a specific boat. You would have a set of parameters that you would need to replicate when you changed boats. The map can not be in RPMs as each boat takes a different amount of throttle to accelerate or decelerate X mph. (I know I am only scratching the surface of the engineering needed)

 

In English: I want the MC to feel like the CC and to be able to send that map to PP so then can try to make a setting for the 2001 Infinity that I practice behind.

 

In truth I know that both PP and ZO have heard the cries from skiers like me and are working toward some solutions. Now we have to just wait. If my scores were not knocked down so far, this would be an interesting problem to think about.

[DW]

The pull profile would change due to line length and probably wind direction.  The more I think about it, it seems to me that the parameter that one needs to keep consistent across all boats / skiers is the hysterisis profile.  I think, and any other thoughts on this are certainly welcome, that the hysterisis of the system is what makes the pulls feel similar or different.  Sounds easy, but I think it is a pretty challenging task to get consistency across all variables.  I think the "best" drivers are just really good at controlling that variable, besides, they can anticipate.  Obviously it is, or else the ideal speed control would be on the market.

[Thomas Wayne]

I don't think a complete effort has yet been applied to any speed control algorithm.  The best drivers - as already stated - are skilled at anticipating the individual skier, but that is something they "learn" from the skier as they are pulling him/her.  Each skier pulls at a different moment and with a different amount of force.  How can a electro-mechanical system possibly do THAT?

And the answer is, probably pretty easily.  Suppose we had the option of putting a magnet on the 55m gates, and a utility in the speed control that would recognize that magnet.  Now, suppose the speed control could measure the force exerted by the skier during his/her pullout and also during his gate, and use that information to interpolate when and how hard that skier is likely to pull after the 1-ball - and after each subsequent ball.

Our slalom courses are functionally identical, and the speed control knows when it will be reaching the next set of boat gates.  Surely the initial data can be used to build an expected profile of the skier's actions throughout the rest of the course.  And, with the ability to check and adjust speed at 400 times per second, the system ought to be able to refine its skier profile as the run progresses.  16 or 17 seconds doesn't seem like a long time, but on the scale that PP or ZO are functioning it's a huge amount of time in which to adjust and make corrections.  All it would take is a company that is not too lazy to conduct the experiments and calculate the correct algorithms to make it happen.

 What skier wouldn't love a speed control that could truly control the throttle like a top senior driver used to?  Wouldn't it be nice to have throttle applied with the correct anticipation, rather than as a reaction to the skier?  It's certainly possible... it would just require what a lot of companies seem to be afraid of these days: some hard work.

Thomas Wayne 

[DW]

There are many controllers that have learing software.  As an example, the turbocharged Ecotec controller learns the environment upon start up and a short learning cycle, then will offer a better boost control algorithm than a purely open loop controller.  To get there from here, though, will take some hard work, time and money.

[Bruce_Butterfield]

<<<Open soapbox

A speed control to match the best manual drivers in the world was developed in 1997 and does provide a constant pull independent of the type or brand of boat. Accuski started out with the goal of matching the pull from the best drivers and gave a great pull to all skiers behind any boat. It even used a magnet on the 55m buoys as part of its control. I maintain that Accuski is still better than any of the other speed controls available today.

End soapbox>>>

Ok, that's all water under the bridge.

The real problem is the delay between when the skier's load is applied and released, and how fast the speed control can respond. A skier can apply and release an instantaneous load much faster than any GPS or rpm based control can sense it, let alone time for the engine to respond to it. Think of a slam dunk skier as an example - the skier has already released the huge load just as the boat is starting to respond to the massive hit. If a skier is nice and smooth and consistent, the speed control algorithm is relatively simple and friendly to the skier. If you have a strong, short line skier that is smooth on one buoy and has a short, hard hit on the next, the speed control response will be rather harsh. Attempting to consider all the variables such as hull drag, engine HP and torque, etc. simply compounds the problem and is what causes the response to be so different from boat to boat.

IMO, the simplest approach is the best - find the throttle setting that provides the correct average speed and NOT change the setting, i.e. set the throttle and leave it alone. A stronger pulling skir will have a higher average rpm and more speed swing than a lighter pulling skier, but the PULL from the boat will be the same. That is a much more level playing field than we have now.

If folks get upset about the speed swing, the far better solution is to increase the engine torque and use larger props. A turbo-diesel, gear reduction, and big prop will maintain a much more constant speed than any feedback control system ever will.

[Horton]

Heard tonight that the 2009 ZO has:

A Setting with subsettings 1, 2 & 3

B Setting with subsettings 1, 2 & 3

C Setting with subsettings 1, 2 & 3

Find your Letter and then your #. Claim is that I will not be able to blame the boat next year. Who's fault will if be when I ski bad?

[SkiRV]

So how is 9 different choices, instead of 3, going to make it any easier, if you still don't have access to ZO for practice?

And how does it fix the differences between boats?

[ForrestGump]

Damnit, unless I go buy an 07 or later boat over the winter, then I'm back to square one with ZO. I just now figured out that I like A and we've had ZO at tournaments since since Sept of 07.  Now I've got to figure out another 3 settings inside A? F me!

[LeonL]

Back to Horton's second post in this thread...................ZO software is boat brand specific.  No surprise to most of you I suppose.  But different is different.  Don't know what the nuances are.

[eleeski]

If I disagree with Bruce do I get probation? Oh well, here goes. My old American Skier with it's 250 hp worn out tired engine (it needed a different pitch prop just to make 34) was the sweetest slalom boat. It took a huge input from the driver to make times (Lisa's nickname was "the Hammer"). But everyone skied well behind that boat. My carburated Nautiques were OK but the latest 04 injected MC is really a tough slalom boat for me (Stan's 08 ZO MC feels much easier to me). I certainly do not prefer or ski better behind the bigger, torqueier (is that a word?) and stronger boats.

In today's world of high gas prices, going bigger and stronger is not the right direction. Quality reactive programming is easy and can match almost any desired speed profile (electrons move at almost the speed of light). You might be able to tow a little boat with something other than a semi. And still afford the gas to fill it. A twitchy little boat with a good speed control is better than a big torquer - and I'll probably ski better behind it.

Skiview and 2gofaster, you will have to beg or buy a few rides to figure out the number/letter setting that corresponds to something you can emulate on your boat. More choices means that you are more likely to find an acceptable match. That is a good thing.

Horton, forget ski tests. What we really need is ZO tests. I want MC and Malibu to feel like 08 CC ZO "C". Tabulate the number conversions and we'll have really valueable data. And nobody can get upset if you assign specific numbers.

Of course this still doesn't solve the problem of the thousands of Stargazer practice boats with no adjustments (and a toxic feel for me). When will Stargazer have some user parameters?

Eric

[Bruce_Butterfield]

Eric,

 I don't see much disagreement there.  Even with the Hammer driving, I bet you are still getting a pretty significant speed swing - and her throttle is in sync with the skier.  The key is that a 'really good' manual driver can anticipate slightly and match the skier's pull better than a speed control.

Yes, electrons move at the speed of light, but any reactive program is only as good as the time it takes to sense a change (GPS speed change, or rpm change) and the time it takes the ECM/engine to respond WITHOUT overcompensating.  It is those 2 delays that are the root of the issue - and the intent of my post was that the rate a skier can load and unload the boat is faster than either of those.

There is also a key difference with a "stronger" boat.  In general terms, horsepower is a measure of how fast a boat can accelerate.  More HP is important for the 'reactive control system'.  Torque is a measure of how much load an engine can take before dropping rpm (bogging down).  If you increase the engine torque, you will have much less rpm swing, and the job of the reactive control system becomes simpler.  A higher torque engine can also handle a prop with more surface area, so there would be less prop slippage, again making the job of the control system simpler.

[Horton]

Good thinking by all.

 

Let me clarify my original idea: If we could simulate a typical skier load profile at one speed / line length to create a baseline resistance curve. (Forget how we do this but assume we take ALL other variables out. Put aside that we all ski differently. ) We could do this is pounds of rope load or maybe you want to call it pylon drag, whatever. Those details do not matter as long as we all have the same high level idea.

 

When we apply Pylon Drag according to the Typical Skier Load Profile (TSLP), a specific boat will act pretty consistently with any one of the cruse options we have. So this gives us result for that boat with that cruse option. We would call this… Boat X, Curse Y, Response Profile or BXCYRP (ok I know that is stupid but I am making this up as I go)

 

I may have missed a parameter or two but if we had Standard Response Profile that then within some amount of deviation we would ask whatever cruse company to make each kind of boat match the Standard Response Profile.

 

I may have made this way too convoluted since I am making it up as I go along. I understand that a heavy boat with a lot of torque requires very different throttle action then a light low torque boat. Further more the bigger boat is most likely going to react differently simply because it takes more load to change its speed. I am dancing around the idea that I wish there was a mathematical definition for how a boat responds to TSLP.

 

---

I want again say that I am optimistic from what I have heard about 2009  ZO. I am told that with a ride or two behind each brand of boat with ZO next year I will have a feel that is close enough to the PPSG that I practice behind. A lot of skiers have pitched a fit and I think we have been heard.

[eleeski]

Torque X RPM = HP. At a given prop RPM more HP will deliver more torque. It takes more HP (and a bigger engine burning more fuel) to have a flatter or faster speed response.

I like the wild swings in speed. Like a jumper, in the pull I want the boat to accelerate - perhaps above the target speed. When I'm at the buoy, I want the boat running soft so I have more time to finish my turn and get in position for the pull. A profile like this is well within the response times of any speed control system and even a low power engine.

Historical driving patterns had wide speed swings. Engines in tournament boats were even smaller than my American Skier. Hopefully we are trying to copy the best drivers of the past with the speed profiles that the speed control mimics.

Stargazer and PP Classic (on normal 0) seems to be a flatter speed profile. I have a ton more speed at the buoy - and the resulting downcourse turn and slack. ZO and PP Classic (on kx- 10) seems to hit harder behind the wake and back off at the buoy - more speed swings. That is my prefered speed profile. More power or different programming to flatten out the speed will create a speed profile that is inconsistent with the past and hurt my skiing. Note that the response time is too fast for me with this profile.

ZO does need to satisfactorily emulate the PP Classic (normal 0) speed profile as this has strong historical relevance.

Knowing the speed profile (via radar gun?) for the various brands of boat and controller settings will give the skiers the knowledge to select the optimal settings. Present the data graphically. This is a reasonable exercise. One setting need not fit all.

John, Curse Y? I curse when I fall or miss!

Eric

[scoke]

Speed Control solutions recently pitched:

Phase 1: Steal Underwear.

Phase 3: Make Profit.

 

 

 

Seriously, too many variables to make the "feels" be the same from boat to boat. If a skier can feel the difference in WATER, they will always feel the difference from Boat to Boat pull.

[tsixam]

I might be on thin ice here, but I think some car manufactures have systems that learn how the driver uses his car and sets a profile for the engine and the gearbox to match those drivers driving habits. Would it not be possible for a speed control system to incorporate something similar? Using factors like Pylon drag (nice word) speed, weight torque and acceleration?

Tsixam

[Horton]

I have to use spell check to for the word esoteric so maybe I should not propose ideas that are a significantly esoteric. Where I am going is a way to try to make all boats feel the same or to at least quantify the differences.

 

My guess is that the boys at PP and ZO each have something like this all mapped out.

 

Eric,

I do not give a crap what you or another skier likes or dislikes. I just want us all to train and compete under the as similar a set of parameters as possible. Clearly there will always be wind, water, solar flares, feral chihuahuas that will prevent everything from being equal but we need to control what we can.

 

Scoke,

I have no idea what you are talking about but I am with you.

 

Sixam,

Yea maybe but I think we need to be able to mathematically define a typical PPSG 2003 Yellow CC without a tower before we start designing dynamic systems.

[scoke]

 

 

an all time classic:

 

 

 

[DW]

Eric,

To recreate your old boat, get an old small blade area prop or if you really want to go extreme, take a four blade and cut two blades off!  Won't matter too much how much hp or torque you have, it will be like an old '69 Camaro big block on skinny bias ply's.

[eleeski]

Ryan-Sandy's 69 Datsun roadster is very fun to drive. It gets you there, the girls smile at you and it gets good mileage. But I'm not sure it belongs back in production.

The 79 American Skier is a smaller lighter boat than the modern boats. It was appropriately propped and powered. When the engine got tired, repropping merely allowed the engine to produce adequate power. The boat skied great! I'd love to see it back in production.

I did replace my 97 Nautique 4 blade with a three blade. The only difference was a smoother trick table. The slalom pull was unchanged (after the PP was recalibrated).

John, the pull that I prefer is the historically consistent pull. I have liked pulls from the past. For several years, skiers have had choices to customize the pull. I reject any new speed profiles that differ from what we have had available in the past for the sake of giving everybody the same pull. My preference - as long as it is historically consistent - does matter. It scares me when my (or others') preferences are dismissed.

Eric

[PSM]

This is off-topic, but I have a question for you, Eric (or anyone else who may want to chime in).  We sometimes train behind my 88' PS 190, and recently put magnets back on the course.

What we find happening is that as boat goes through the gates at 36, PP does it's "gate-up" feature increasing the RPM's by "X" to compensate for the gate pull.  Unfortunately, this, combined with the skier pulling the boat down at that moment, is just enough to cause the carb's secondaries to open, producing a huge surge in the RPM's, throwing the skier way off.  Like 200 or so RPM's get thrown in, and the end times are way hot also.  We jokingly have been calling it the extreme Zero Off simulator

Is there anything we can do, either in PP or with the boat, to correct or offset this?  We'd like to continue using the magnets to get times, but don't want to have the large surge.  We were told to put skier weight to 0 and just increase the RPM baseline to compensate, as the gate-up feature uses skier weight to calculate the added RPM's, but we thought having skier weight at 0 may change the pull significantly.

Any thoughts?  Thanks in advance.

 

 

[9400]

Back in the day when all boats were carbed, we would disconnect the secondaries to avoid that "extra gas"

[PSM]

I've heard that before as well, but never did it.  Thanks for the suggestion.

Can you give me the overview as to how to properly disconnect the secondaries on my stock Ford 351 carb?  I believe it is the Holley 4160.  In addition, does the boat have trouble with pulling skiers up, or starting with these disconnected? 

I'm guessing you just disconnect the linkage on the secondary side of the bowl, but I just want to be safe.

Thanks again.

[eleeski]

If your prop is tired, re-pitch when you re-prop. This might get the throttle setting far enough away from (or into) the secondaries to stop the surging. I have disconnected secondaries as well. Another trick is to bend the linkage to bring the secondaries in earlier to avoid the surge. The American skier needed the secondaries, the Nautique doesn't.

Hopefully you can use reasonable PP settings after the fix.

Eric

[Horton]

I skied last night behind a MC with an experimental ZO with the 9 settings.

A Setting with subsettings 1, 2 & 3

B Setting with subsettings 1, 2 & 3

C Setting with subsettings 1, 2 & 3

The numbers put a cap on the  high end of the throttle input. (something like that) 

1= almost as much thottle as the old letter 

2= a little less

3= least

I ran a lot of passes but while I was fresh I used A2 and felt pretty good with it. With this number of choices I can see finding a setting for each brand of boat that feels enough like my practice boat.

 

[LeonL]

Horton, does this experimental version still insist on getting a 16.95 even though it may have a 1.79 at the 1 or a 7.16 at the 3?  I would hope that a software tweak would let it not try to make up time, just keep the same deviation.

On the Holley secondaries -- as my memory serves me the secondaries are vacuum operated.  The mechanical linkage only ALLOWING opening at some point.  Your best bet is to disconnect the vacuum pot (driver's side of engine) and then block movement of the vertical arm.  Or.....mechanically force them to open sooner to avoid the surge at the inappropriate time.

[tsixam]

PSM,

We had the same problem with our old SN with a Holley. But there is fix. Inside the vacuum house there is a spring that dedcide when the vacuum is enough to open the secondaries. This spring can be replaced with a stronger or weaker spring. If you talk to a speed shop they can help you to get the right set of springs and gaskets . Then it is just a matter of experimenting.

Tsixam.

[PSM]

Thanks for the input, Fellas. I'll hit up a speed shop for the Holley spring kit -- sounds like a real simple fix. The other thing is I have a nice, big Acme 3 blade prop on right now, so the RPM's that the boat runs at 36 are very low.

 

 

In the very short term, I may try throwing the stock OJ 3 blade on to see what that does to the RPM's, and where we fall in terms of the secondaries being open or closed. I'd rather the R's go up, and have the secondaries be open all the time at this point, as I think that's the move for 36. Sorry to mess the thread up.

 

 

How's the water temp up in NY, Ed?

[Horton]

Leon,

Don't know.

[JohnN]

I've been noodling this over as well and I think John's on the right track here.  Ideally, per the rules, we want a consistent boat speed.  From the skier's end we want that to be predictive like a good hand driver, not reactive like the current ZO.  It seems like the boat could have an ideal profile of power adjustment, or rpms, to maintain a consistent speed throughout the course.  The trick would be to adjust the curve based on speed feedback from the gps as the skier is skiing.  In other words move the curve sooner or later in time relative to the overall course time, as well as adjust the amplitude of the curve. 

This should get pretty close to the feel of a good hand driver who "learns" the skier as they perform and adjust to each skier.  It wouldn't compensate for the random "oh my god" big hit, but neither can a hand driver.  I think programming of this nature would be a great step.

 The ultimate, should the technology exist, would be to have a the boat learn how much throttle (rpms) it takes to resist a given amount of drag.  Then, use a very accurate strain gauge on the pylon to sense what's going on with the skier - the change in drag -  and react before the boat speed changes.  Kind of a super-switch. 

 Regardless of the specific solution, the profiles should have a learning capacity.  With differences in elevation, water, etc. the boats need to have much more flexibility in their controls than they have now, when they are dialed in for sea level power, temps and water.  As long as this is a wish list, real time wireless transmission of times or speed map to scoring would be sweet.  For troubleshooting, downloadable data acquisition of rpm, speed, sensor data during a set would be killer as well!

 Now, for the off season try to figure out a plan for testing the 9 settings during the 9 tournaments next year. 

 John

[Horton]

I don't know about the smart boat idea. I watched 5 minutes of the new Knight Rider TV show last night and I am not going for it. The chicks are smoken hot but....

I keep wondering into the crazy technical crazy ideas but the basic idea is if we put x amount of load on a boat for some lenght of time I want the responce to be the same from boat to boat. Why did I not just say that to begin with?

[Bruce_Butterfield]

Predictive algorithms and strain gauges will only make the response much worse. The 'prediction' will be different depending on if the skier is early or way downcourse. How does the computer know? The problem with using a strain gauge is you would also have to measure the angle of the rope - a 600 lb pull at the buoy will pull the boat sideways, but won't slow it down anywhere near as much as a 600 lb pull at the wakes.

Horton's idea of the same response behind every boat is what the control SHOULD be doing. Trying to factor in hull drag, engine size, prop, etc, is the reason the pulls are different. If the algorithm ignored those factors and only used change in speed and rate of change of speed as its inputs (like Accuski), we would get darn close to the same pull behind each boat. Any difference in pull would be precisely because the boat was different.

[JohnN]

Good point, I hadn't really considered the angle thought.  Wonder why a switch works, though.  Probably a sensitivity thing. 

 The predictive algorithm would just be a starting point and have some give in it.   The only reason for it would be to make the boat's job of adjustment quicker and easier so the boat doesn't get behind. 

 By response, do you mean rate of change of speed (either acceleration or deceleration) of the boat?  I think that's what we want to feel the same behind different boats as we load/unload the rope.  The problem is,  the boat needs to "know" that a change is coming before it happens or we end up with the current ZO, and the corrections come too little too late (or too much for some).  A good hand driver would feel the increase in pull and block or squeeze the throttle to prevent the boat from slowing.  If the pull would come early or late the driver would adjust the timing of the movement.  But, how can the boat know that, and, how much throttle to add or reduce to compensate appropriately?

you know it's getting cold out... 

John

ps - Not to hijack this into an Accuski thread, but doesn't Accuski have some sort of "predictive" algorithm?  Especially at lower speeds, without a skier there is a distinct increase and decrease in rpms as you pass each ball.  I didn't know Accuski used speed at all, I thought it was just rpm based. 

[Thomas Wayne]

The PP Slalom Switch is strictly an on/off system that triggers at a preset load.

The "predictive algorithm" system I proposed early in this thread would presumably be - as JohnN suggests - a starting point. By trial and error the system would learn how a skier is skiing in a sort of "artificial intelligence" manner, and could refine how and when it should adjust the throttle based on the skier profile as it is developing.

I realize "trial and error" sounds questionable, as if the skier is some sort of guinea pig, but given that the current system can make many hundred checks and corrections per second it shouldn't be as noticeable to the skier as it sounds. The existing speed controls make all the necessary corrections anyway, it's just that they do it in a reactive fashion only. My proposal is simply to create software that is "proactive", in that it begins by following a known standard load-and-release pattern, but very early on it "edits" that pattern to more accurately reflect how the skier is actually loading and releasing.

Surely we can take a cross-section of skiers and determine some sample load-and-release patterns. If nothing else, we've got great footage of Marcus Brown and Terry Winter skiing various line lengths while being tracked with a strain gauge. How hard could it be to gather a few more samples and build 3 to 5 basic profiles, which the system could refine based on data developed during the skier's actual performance?

In a sense the system I'm proposing is both reactive AND proactive, in that it adds and removes throttle based on a predetermined algorithm (proactive), but it constantly adjusts that algorithm to match how the skier is affecting the boat speed (reactive). Instead of putting in a skier's weight before his set you would put in his choice of starting algorithm (have "A", "B" and "C" been spoken for yet?) and an identifier, such as "Bruce". Thereafter the boat will develop and use it's most recent "Bruce" algorithm until a new skier identity is input, or the "Bruce" identity has been cleared or reset. That way "Bruce" could ski a later set with the same modified algorithm, which remains in memory until cleared. Of course, this "Bruce" algorithm would continue to evolve during every run.

Perhaps, much like a Concept II rowing machine, the speed control could accept a "smartcard" that would already have "Bruce's" proven and preferred algorithm stored on it. So now when it's your turn to ski you hand the boat crew your handle section and your PP/ZO smartcard and you're ready to go.

Just a little futuristic thinking.

TW

[roda]

 

I'm thinking in totally the opposite direction. I say you set the rpm and then don't change it. Let the boat speed vary. To qualify as an official towboat it has to be able to run a pass with a sled to a specific tolerance w/ the RPM fixed. That is the baseline, everyone has to deal w/ it. Lighter skiers would get faster end of tolerance times and bigger skiers would get slower end times. No processors, algorithms, reaction times to deal with. KISS. If you wanted to make it a bit more complicated (and arguably fair) then have several sled weight baselines that a skier would have to use based on his/her weight. Don't most other sports have fixed equipment to deal with?

 

 

[JohnN]

Set rpm would be a pretty big speed variance, wouldn't it?  At 1 lb per rpm approximately it would put my speed 1mph slower than my 10 yr old for the same set point of 34mph. I don't think you could get near tolerance with today's boats.  Of course if you add in a skier weight factor  to eliminate that issue you pretty much have pp classic or accuski. Not a terrible thing, IMO /vanillaforum/js/tinymce/jscripts/tiny_mce/plugins/emotions/images/smiley-wink.gif.

 John