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Who thinks the boat speed should be constant?


ozski
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So we have the technology and HP to deliver a pretty flat pull without the speed control gassing and letting off the way it does, scores would go down and some if not all skiers would be disadvantaged almost certainly. 1 type of pull and 1 setting removes the arguments and to some extent the differences between boats, the current slalom and jump world records would probably stand for a long time to come Is there any real upside to a more linear pull? Is ZO gassing cheating? think about how much a jump boat hammers when it goes on the switch. How much HP do we actually need with a slalom boat anyway? Should they cap HP and boat size at some point? Are we seeing more injuries with the bigger more powerful boats?
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Interesting topic. As long as the skier pull is inconsistent the boat is going to be reactionary. I'm not sure how much flatter the pull can be. Perhaps it could be much flatter I don't know. If it could be more consistent from boat to boat an engine to engine I think we would all agree that's a good thing.

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That flat pull was produced and “tested” way back around the early 90’s I think, and everybody hated it from what I’m told. Supposedly it kept the speed it was set and that was it. But skiers were used to hand driving, so it was quite a shock I’d imagine. The creator of that system traded the technology to Correct Craft for a newish boat....I believe it was a 1991 hull with a newer engine.

 

 

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Before this thread gets too carried away does anybody know what the actual speed swing is with zero off. Don't make me call Will Bush and ask. please.

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The only way to eliminate any surge would be to replace the boat with a rail moving at a constant speed akin to a cable tow.

 

I think the boats/drivers/technology do an amazing job. Think about it, you have a 2000lb mass bring pushed through/over the water by a small bit of metal screwing through a viscous material with a variable load trying to slow it down and pull it side to side.

 

To control boat the speed (using tech) based purely on a load cell and a gps sensor and keep it within say 1/2mph is pretty stunning. An experienced driver can do similar, but they have so many more data references, (feel, sight, preemption etc) and takes years of practice.

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I can understand why people did not like a flat pull might as well have a rsj/building steel to connect you to the boat, I would imagine if there was no give at all in the line/boat there would not just be sore backs but a fair few badly damaged backs, for me there has to be some give, we are not super human, I know some people think they are but in reality our bodies can only with stand so much force.
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What exactly do you mean by a flat line pull? If that means that the boat will put out the same amount of power throughout the pass with no gassing that will be the exact opposite of constant speed.

Constant speed on the other hand will require more gassing than what we have now and some way to make the soeed control to anticipate change in load for a quicker response.

I suspect constant speed control would feel like crap.

 

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Radar plots will show a good hand driven pass, which PP, Accuski and ZO all emulates, looks like a sine wave with .6-1 mph variation.

 

If you could get a constant speed ( our calculations at the time was 500-600hp), expect to lose 2 or more passes, and would experience more crashes and injuries. Anyone who advocate a constant speed does not rely understand the physics of skiing.

 

If you want to look at speed variances, analyze jumping where they vary 2mph, (increased speed to ramp) distances would fall at least 20 feet with a constant speed. Jump boats need high HP, because they are increasing speed all the way to the ramp.

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@ozski

 

My definitions.

 

Constant speed - engine applies instantaneously enough power to fully counter any force applied to it in order to hold acceleration in equilibrium. Sort of ZO but A1+++

 

Constant power - basically fixed rpm down course where engine power output is limited to a fixed amount.

 

Currently of course it is neither, the second of those is "flat" engine wont make a peep but the speed will drop unless you swing a big steep prop and have a heavy boat because momentum.

 

The first is instant response flat speed, the second is flat engine response.

 

The only way to have both is to have such a surplus of power, momentum, and grip that the skier becomes negligable to the syatem.

 

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@BraceMaker So true on your last sentence, as in hook a ski rope to a Carribean cruise ship and your pulls will go unnoticed.

However a fixed rpm is not the same as constant power output, to achieve a constant rpm the power output has to vary as the load does.

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Several issues on this topic that are frequently misunderstood:

 

1. The old PP speed based system used the air pressure speedo that had a very significant lag. The speed swing was actually more and was out of sync with the skier. That’s what made it suck

 

2. In any feedback control loop, there will ALWAYS be some amount of delay between the skiers load – that causes a reduction in speed – and the engine response, that causes an ACCELERATION to get the boat back to “constant speed”. It’s the acceleration that makes the pull feel hard. The GPS based system has a relatively short delay, but it still has to accelerate after it senses a reduction in speed.

 

3. Whether its hand driving or ZO, the “goodness” of the pull is determined by the timing of when the throttle is applied. If the throttle is in perfect sync with the skier, the pull feels great. But out of sync really sucks

 

4. When the skier loads the boat, 2 things happen to reduce the boat’s speed: 1) the engine rpm will drop due the load and 2) there will be prop “slippage”. (that’s not the actual effect, but is sufficient for this discussion)

 

5. If we have to rely on high HP and quick reaction feedback control, we will continue to have these problems that some skier won’t like. The quality of the pull is 100% determined by the math coded into the system.

 

IMO, the better way to get closer to a constant speed system is with a very high torque engine, like an 800 ft-lb turbo diesel, with a huge prop (or 2). With this system, when the skier loads the boat, the rpm drop will be next to nothing (the engine won’t notice the skier) and with much more prop surface area, the prop slippage will be much less. The job of the speed control gets very simple and will need very little additional throttle input. My theory is that with this setup, the speed swing will be very small and the pull will be awesome.

 

With regard to jump, the jumpers WANT acceleration. Slalom skiers don’t.

 

If it was easy, they would call it Wakeboarding

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A switch is probably the best addition to mitigate a proper reaction from the boat. Quickest to apply or release added force and base the required force on skier "pull" ....added to existing ZO settings would perhaps narrow the amount "gassing" time and soften force
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Switch yes, my mechanical steampunk contrivance would be a pylon linked to a hydraulic control system similarly to draft on a tractor. More drag on pylon would up shaft rpm while engine rpm runs fixed. Variable transmission going opposite direction on engine where a heavy flywheel with viscous coupling stores energy during low demand and feeds it back during high load. Even so far as revving up engine and flywheel prior to engaging the transmission such that the skier load on the pylon during pull would engage extra pull speed.

 

Just fun to consider how it would be if we didnt have V8s

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Constant speed is pretty impractical with the boats we have. What would be a step forward is the same pull behind different boats and engines. My understanding is this would be a software and zero off hardware solution. I assume every new boat on the market has plenty of horsepower to get this done.

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Agree with Horton, the same or similar pull would be a significant improvement. I do not think any hardware would be required, but tweaking each boat/ engine combination so that the radar plots of speed response would match across the boats/engine. Accuski was orginally designed to emulate the radar plots of some of the best drivers, pulling Guy Haggard, myself and other. Then Andy Mapple who would quickly describe what we thought was good, but wasn’t to him.
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Wasn't that kind of what "trick mode" was that everybody seemed to love? Not exactly of course, but a move closer in this direction?

 

Apparently not, or else we wouldn't really be having this discussion so...anybody have a good explanation as to where my thinking is wrong?

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@escmanaze Sure the new "trick mode" seems to rev higher than previous modes but for us that is not " in the know" that really doesn't tell the whole story.

Hypothetically you could achieve this behaviour by softening or delaying the initial response thereby creating the need for a higher response, or you could just have a firmer response with more down time on the throttle making you more free of the boat.

Only the in crowd really knows what's going on.

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@escmanaze trick mode simply allows the boat to add more revs when the system decides it is time to add revs. I am not sure if that means less of a speed swing but it does mean the boat speed is closer to actual more of the time. (make any sense?)

 

Thinking about this I think it does mean the speed curve is flatter. If not someone will correct me.

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@Bruce_Butterfield Well said. But, in absence of 800 ft-lb. boats for now, what if ZeroOff could anticipate when to apply a slight "thumb pressure" on the throttle to be ready as the skier loads the line. Maybe this could reduce the stronger response that comes after the skier loads the line?
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I think dealing with slack would be a huge issue behind a (theoretical) constant-speed boat. My reasoning is that a traditional boat is able to run up the speed a bit when the line load is decreased from skier edge change into the buoy (especially if running ZeroOff "A"). This slight overspeed helps to reduce or eliminate slack for the skier. So not only would a skier behind a truly constant-speed boat likely have more potential for slack thru the turn, but the hit from any slack in the line would be much harder if the boat is not going to lose any speed at all- compared to the current reality where the boat takes at least part of the hit and slows down- and makes up for it more gradually (depending on speed control setting, but there is at least some latency with any setting).

 

 

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@Tom351 actually it is the opposite.

 

We’ve already been down that road before:

 

REV-K version of zero off back in late 2006 early 2007. There was only one guy that could run buoys on that version and he designed the system. It held constant speed no matter what. He had to change the system shortly after. Sadly he died in 2015.

 

There was a new 196 owner in orlando who got the new ZO as it was rolling out. I skied with him, he was in tears. He couldn’t run a pass (28) behind his new boat as it was brutal. I personally was down 9 buoys or so on that same boat. Driving it, it sounded lined a freight train. NEVER changed rpms therefore you never got slack as it was always on you. 16.95 and 34.2 from gate to gate no matter what.

 

Now what is interesting is trick mode, Sounds the opposite. It’s got wild swings of rpms but feels awesome to the skier. I’ve got video around here somewhere that has decent audio too as the boat crew thinks the skier is going to die but it’s very forgiving.

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"for every action there is an equal and opposite reaction...."

 

I would put this idea in the "be careful what you wish for" pile. If this were somehow achieved, undoubtedly there would be technique and equipment changes required. they may not be what you really want.

 

If larger props and higher torque engines were used, you may well get (near) constant speed, but the wakes may worsen. changes like these may make learning more difficult for those just getting started in the course, ultimately hurting the sport.

 

To my eyes, everything has improved immensely in this sport over my lifetime. Skis, boots, bindings, boats, engines,ropes. Heck,even gloves are better.

 

No need for much change at all.

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Speed swing makes slalom feel right. History had observed speed swings of 1/2 mph on the heavily damped airguide speedometers in the time of hand driving - in reality it was more. How much and when a driver responded to the speed changes determined how good the driver felt. PP gained acceptance when its RPM based reaction matched hand driving. The options of KX and PX (and the switch) let skiers "choose their favorite driver". ZO put too much focus on perfect times - it feels like when the good drivers were mad at you so they gave a right on time. Still big speed swings but perfect times and speed responses timed perfectly.

 

Jumpers have had huge speed swings. Low power boats with big aggressive jumpers just couldn't make in tolerance time without overspeed. Once the technology to accurately measure speed came available, the option was to radically change jumping or codify 2 mph speed swings (previous rules were 1/2 mph). We now have "fast second segment" or "return to baseline" to account for real life speed swings.

 

Trickers like a steady speed. We use spectra ropes because we can feel the variations from rope stretch. In the old days, we would remove the big damper tube from one speedo to make the speedo more reactive. The paddlewheel on PP was magic for maintaining speed. ZO accelerometers are equally good and C3+ takes speed variations out of the picture - for how hard trickers typically pull. I still see the speed readout vary by .2 mph during a normal trick pull.

 

Real life has variations in speed. Sometimes minimizing those variations is good. Othertimes it feels terrible. The historical reality must be considered over a strict reading of an arbitrary rule. And the rule allows(ed) .5 mph swings so chasing zero deviation is not necessary or right.

 

Eric

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@scoke don't confuse RPM swings with speed swings. I suspect those first official ZO versions had a very low Kp factor so when the hardware felt the skier pull it gave a few revs for as long as it took to catch up. The result was that if you were heavy on the line the boat was always making up ground after the skier past centerline and it felt like shit.

 

Trick Mode or now Plus Mode gives more revs in less time so after you pass centerline the revs are back to baseline. I think the result is actually less speed swing.

 

Interesting note: there was at least one preproduction version of ZO that was fantastic. I took one ride the fall before it was released and loved it. The next year when I got it at tournaments it SUCKED!

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I’ve reread my post three times. Don’t put words in my mouth, in my posts or let your reading comprehension to try and change my post.

 

My post was speaking in fact and we have evidence when I used the word “swing” regarding rpms and my experiences. I wasn’t and am not hung up on rpm/speed swings nor did I post that.

 

Sorry you got confused reading my post.

 

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@scoke this was a friendly conversation.

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This summer there was suspicion surrounding a specific tournament. Maybe was related to hydro-mechanical variation that present metrics fail to quantify. Maybe swing variations are far far more important than we realize. Water/ prop/ hull drag/ power/ skier drag, all players. Constant speed is at one end of Bell Curve
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Jumpers have a switch seams like a simple solution to me. With pp we had a switch not sure why We slalom skier don’t have one it would react quicker and get off you when not pulling it would be more fair to big guys now that I have lost 25 lbs and I’m at180lbs zo does effect me as much
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Disclaimer, I'm not a tournament skier and am new to the sport. That out of the way. Maybe integration of a strain gauge into the pylon would be beneficial. That would let the software know the rope load and allow adjustments specific to the skier's style. It would allow faster reaction to the load so the boat wouldn't need as much power. Speed variation would be programmed into the system.

 

On a side note, increasing prop size isn't necessary going to give what you want for application of the torque. Prop design is really complex, I had to learn just the basics for a project years ago. Large diameter props are generally for slower rotational speeds and high torque so cavitation can be controlled. That isn't always best for a high input flow rate. I'm no expert though, I'll stick with structural design and shock.

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This is an interesting topic but the current state of ZO is pretty good. I would vote to not mess with the basic system. Each manufacturer does tweak the settings to deliver what they think is best. Sometimes they get it right and sometimes not.

 

There is no question in my mind that the transition from Perfect Pass to ZO had an apocalyptic impact on tournament participation but that was 10 years ago and it is long since time to stop crying about it.

 

It is also my opinion that any better pull is going to be achieved ( mostly *) with software. The sensors in ZO are good enough and all the current boats have enough horsepower. The 5.7 200 was the only modern boat I know of that theoretically was really underpowered for the amount of drag designed into the hull. Oddly many of the 5.7 200s are strong enough but others were not. I have always wondered if more aggressive software settings would have fixed the "soft" boats.

 

(* Props, power curves, revs and such should not be understated)

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@T_C the core of the system is locked down but the factories have parameters the can tweak for each engine or hull

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@ms nobody hated zero off in the beginning more than I did. It's been 10 years what is your malfunction?

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I don’t hate it. I hate the company and the people that except it on our behalf. Tolarances need to be set to reflect ZO or ZO needs to set system for a 16.98. If I get a bad 1 ball, I don’t need to have the boat react to get any speed reduction back by 2 ball.

I would also not like to piss away my early passes at tournaments trying to figure out what letter to use.

I think am done with tournys anyway so who cares what I think

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@ms does that happen? Slow one ball times and perfect times?

 

Use B2 and don't worry about it.

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The post about parameter tweaking has possibilities for skier customization.

 

Have a USB port or Bluetooth interface to allow a skier to supply their own adjustments to the algorithm. Then, the boat is customized to their preference. Set ZO to accept the override.

 

If a skier wants the default pull, no problem. Just don’t supply anything and don’t use the override.

 

If their supplied customization results in an out of tolerance pull, too bad, no reride.

 

Those working with Zero Off today could have a small side business creating “designer pulls”. It’s about the same as instructing your favorite driver how to deliver a great pass just driving by hand (while still meeting the tolerance).

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@MISkier we now have 18 standard settings. Do we really need mores tweaks? I think we would all be pretty happy if we could show up at a tournament and be confident that the pull would be a lot like our practice boat. I would rather the boat factories work toward a standard pull. There is actually an agreement to do this but there is still a fair amount of variance.

 

Realistically driver steering input is often a bigger impact than one letter or number change. This fall my regular driver changed his driving methodology. The result is that my boat "felt" softer and more forgiving.

 

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ZO is a small side business for e-controls managed by a somewhat passionate but way too distracted group. There's not enough money or volume to justify more. I'm impressed by the quality of their product and that they are upgrading it.

 

Sometimes they can be slow and unresponsive to issues. Eventually they took care of my ZO problems so I'm happy with them. But I understand some of the complaints about ZO.

 

@MS makes an interesting point. Just changing the tolerance time won't help. Allowing deviations for unusual pulls will improve the feel. With the horsepower and responsiveness of modern boats with ZO, an overpull can be hit hard enough to avoid any deviation - but that makes the pull feel harsh. Using the tolerance to soften the response to a massive accelerometer input would make the feel much friendlier.

 

Go C3 and the pull always feels harsh so you get used to it. Or choose A1 and ski smoothly always and you are OK. B2 will show the most variation between boats and rough style - plus it sucks.

 

Eric

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@Horton, it may be that there are skiers who do not like any of the 18 settings on any boat and might not like them even if they were 100% identical on every boat, engine, prop combination. These are are the target demographic for a customizable option. I would expect it to be a small number. And, like I said, the default pull is still there. Nobody is required to do any tweaking and, more importantly, they do it at their assumed risk.

 

For me, boat settings are not my biggest issue. I do notice differences, but not enough to quit skiing. However, some have reached that point.

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@eleeski

"B2 will show the most variation between boats and rough style"

 

http://media.tumblr.com/fe497dd337d9af8479bb6398b9565d16/tumblr_inline_mg6n5ltl6X1rxe4lt.gif

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