Fin Shape

[Nando]

When I took my boat to storage, I looked around at a few others and considered how much tracking fin and rudder shapes have evolved over the last several years. Conversely, the shape of the fins on our skis has changed very little. In the 80s, I tested a bunch of different shaped fins for EP and we never really found an improvement over their standard "modified D" shape. Around that time, Connelly shipped their skis with the "tournament fin". After my first set on a new Connelly, I always replaced that thing with a standard fin, with great improvement in performance (and they sent me a stock of the "regular" fins and metal, rather than plastic, wings that were a significantly different shape). Others have come up with fin designs over the years (remember EP's tubular wing? cutouts on the trailing edge? the flat-bottomed Maha and Saucier fins way back when, and, of course, carbon fins, but we're talking shape, not materials here), but nothing seems to be an improvement that gets adopted.

 

Anyway, my question is, is there performance to be unlocked with new fin shapes? Maybe something really radical like the keels of America's Cup boats? We spend so much time tweaking our existing fins to .001s of an inch, is there a more fundamental change that could be a significant improvement?

[Than_Bogan]

Adam Caldwell has a massive pile of Crazy Ass Fin Shapes that he has tried. I'll leave it to him if he wants to comment on whether any of them are any good.

[Horton]

@Than_Bogan just another hoax

[Nando]

The question was mainly intended to get Adam (or one of the other techies on the site) to weigh in. Wonder if he has anything as weird as my short fin with a 0.75" tube in place of a wing that I had a bike mechanic weld up. I was young and stupid and had no idea if it would work- I just wanted to try something different. At least I didn't hurt myself...

[A_B]

I cut a bunch of differing shapes from sheet aluminum years ago. Tried to find the right amount of straight edge in the back and curve on the leading edge. Seemed to always gravitate back to a standard fin shape. About the weirdest fin I used was a thing we called the Whale Tail. Had an extension behind the normalish looking fin that was a just an added square section with a wing way back on it. Held a ton of angle. Think I have it laying around somewhere. Gold color.

 

My thought is that Kris Lapoint has probably tried about everything under the sun, and if he ain't using it, no one else would either.

[Adam Caldwell]

My personal favorite was one that I never actually never rode....surprisingly, it was a wise decisions to only witness it in action from the rear-view. I think @AdamCord is still suffering the consequences of that one.

 

[Bruce_Butterfield]

Yes, there is a lot to be learned from fin shapes. Its actually very surprising that we notice a few thousands of movement, but when making very significant changes in shape, the results can be subtle.

 

I've tried many different shapes and its all trial and error to get something to work, and it can take a long time to really figured it out. One of the better examples is that I used a slot fin for half a season a number of years ago. I loved the way it made the ski turn like it was on rails, but it took several months before I realized that I just wasn't as consistent on it as a regular fin.

 

Probably one of the better "alternate" fins is known as the AMF. Its more triangular with a straight back and more holes in the leading edge. It is typically run forward, short and deep. It helps keep the tip down and the completion of the turn on both sides.

 

The thing to keep in mind is that a particular fin shape may work better on a particular ski or for a particular skier.

[DW]

Another reason for potential lack of optimization is that trial and error is the methodology used to develop the shape and is not only dependent on ski design but also influenced by the skier. Engineering tools to aid in the development process are not only costly but also not mature or very available. Examples would be CFD analysis and for the marine or multi medium environment (water and air) are not really very well refined yet and available water tunnels are not really that available and most would require scaled down versions for analysis.

 

Interestingly, many times a first or early attempt at optimization hits the 95% mark early in the cycle and then the other 5% ends up being a litany of small trail and error attempts. Humans are very good at coming up with good solutions for mechanical things very quickly.

 

In other words, keep trying and have fun doing it.

[Horton]

I have made over a thousand fins.... a few hundred by hand. Interesting thing about the standard shapes - they are sort of organic. The curves are compound but simple. They are easy to recreate freehand. I have always assumed that they originally evolved from a shape that was just easy to make.

[eleeski]

There have been many wild fins. Some specific fin mods have worked quite well on specific skis. It's like tuning the ski by fin selection (more effective than .001 movements). But not every wild fin works with every ski. The stock fin is a good starting point. Enjoy the experiment.

 

One interesting aspect of fins is the flex. @Horton 's carbon fins were fairly conventional in shape but very different in flex (at least the one I liked best). I carried that to an extreme and made a nearly floppy fin. Felt great but didn't make buoys well. Again, fin flex is something to tune with consideration to the ski and the skier.

 

There is the "exotic fin du jour" popularity trend. Schnitz fins, backwards fins, Pac Man fins, Donatt's big hole fin (the current fave around socal) and many others have gotten their 15 minutes of fame. Valid small improvements but still "it's the skier, not the ski".

 

The only fin mod that has stood the test of time is the wing.

 

Eric

[Adam Caldwell]

It all depends on the system as a whole and how the setup is configured.

 

It is possible to take a fin setup that doesn't work at all as a standard shaped fin, then lock in the length/depth/dft and only change the fin area and or leading edge beveling to get it working pretty well. Same could also be true if instead you didn't touch the fin at all, but only played with bevels on the ski.

 

The tricky part about ski design is there are no requirements/constraints that we have to follow so there is really a very wide range of options and configurations for the fin & ski setup.

 

One thing is for sure fin tuning & fin shape can make a good ski better, but will never make a bad ski "good".

 

[Horton]

@eleeski you should flex a Pac-Man super. soft flex

[BRY]

@nando There is this Schnitz guy who knows a little about fins http://www.schnitzskis.com/finswings.html Pretty sure he was working with various wings long before Australia II in 1983. He has various shapes and multiple wings for sale.

Chet Raley has also played with fins/wings http://www.goode.com/wsRALEYVENTRAL.html I have seen Chet put some really whack wing configurations on his ski and still go deep 39 or run it.

I bring these guys up as you can go buy their stuff currently. Too many to name for so many years have tested shapes and appendages (wings, tubes, ect) yet seem to come back to the standard shape. Additional fins like anti-drift fins and side force enhancers never seemed to catch on. Schnitz and Chet are in Palm Beach County, and KLP a couple hours up the road in Orlando. Hop a plane, take a lesson from each and they can give you all kinds of fin info.

[Jordan]

The funny thing about fins is that so many skis are essentially built/designed with a conventional fin.

 

If you take an existing ski, start filing bevels and adding and shaping bondo etc. until it skis great, then make a mold from that. It's no surprise that the new ski works best with a conventional fin.

 

There might be some crazy fin design that could go with a crazy ski design and together they are better than anything previously thought of....but how do you get there?

[ToddL]

Let's say that Brand "X" comes out with the new Schnizzle Ski with the new Fizzizle Fin that is radically differently shaped but somehow optimized/balanced for that new ski design. Their stock numbers would be for that fin on that ski only. OK, so no biggie.

 

But if the sport ended up with the Fizzizle as a second universally-accepted fin shape that is different from the traditional fin shape, then I'd assume ski stock numbers would not apply to that fin. If this new universally-accepted fin grew in popularity, then ski manufacturers might have to publish two sets of "stock" numbers. "Are those the standard fin stock numbers or the Fizzizle fin stock numbers?"

 

Heck @SkiJay might even have to write a new edition to his book because likely the fin tuning actions might not apply in the same way to a different fin shape.

[SkiJay]

Actually, @ToddL, when a different shaped fin is used, the numbers change, but same principles still apply. Creative shapes can often work quite well, but they're usually less versatile. I have a drawer full of different fins, and for what it's worth, I think the "standard" fin is as popular as it is because it's seemingly dated design is actually a stroke of genius.

 

Not only does it allow us to adjust it in any conceivable combination of longer, shorter, deeper, shallower, forward, and back—it can do all of this without changing its basic shape. It's ability to retain its basic shape is what allows us to adjust one fin-related behavior without affecting the others at the same time. The current fin is sheer brilliance in its simplicity, predictability, and versatility.

[Drago]

None of these changed my life ('cept for that black one on the left when the magnet changed its leading edge shape , and the stainless one that fell out of the fin box as I went through the wake (re-entered the world on the shoreline after my rag doll gingerbread man impersonation). Never tried the Klem fin.

*always video testing of new fin shapes

[The_MS]

I think someone should start up a new fin company, maybe introduce some carbon into them.

[Nando]

MS, that sounds like a money-making opportunity for the right individual...

[mmosley899]

@Drago I think I have all those shapes too!

[MattP]

@MS are you trying to send @Horton into a psychotic flashback?

[thager]

@MattP It could only help!!

 

[Adam Caldwell]

Years ago I pulled @AdamCord into 38 on this fine specimen.

 

 

@Drago, Not sure about you, but my consensus on multiple stainless steel fin shapes and thicknesses = horrible.

[CsSkis]

@adamcaldwell I think that I am guilty for putting that thought into @AdamCord's head. I had cautioned him that the edge change might be a little "aggressive" and the drag might be a little higher. However, I had been hoping that after some R&D that the fin could be reduced in total area (relative to current fins) and that by rotating the tip of the fin foreward or aftward would allow for tuning tip/tail. Basically, you wouldn't have DFT, depth and length adjustments, only fin rotation angle.

 

In this case, as shown in the picture, I would imagine that the ski preferred to go straight. However, I never heard the rest of the story. Only that he "survived" the experience. Any more to the story/experience?

[AdamCord]

@CsSkis I think that fin actually ripped the fin block off of the ski, and possibly also cracked the ski. Not for the faint of heart :#

[CsSkis]

@AdamCord Yikes! I guess that I am glad that you are still speaking to me!!

[Drago]

I thought it was all about total surface area? @adamhcaldwell , the Mapple shape on my Stiletto/ schnitz very-stiletto-like shape worked decently.not so much on anything after that.

[KRoundy]

I think the reason things have stayed the same for so long is inferred in the story above. Hydrodynamic forces can be incredibly powerful. The current shape is essentially the most surface area that humans and our equipment can handle. Anything larger would just tear stuff apart and anything smaller will turn the slalom ski into a weird-looking trick ski. SkiJay makes a great comment too about the adaptability of the design. (Still hopeful that my book comes soon, I can't wait for it to appear in my mailbox!)

[Adam Caldwell]

@DRAGO, Im going to apologize now for the massive tangent....

 

Fin Area is interesting. several years ago measured a lot of the HO ski fins from the mid-late 90s when boats were a little less powerful, skis were heavier & softer etc. The fins were all much closer to 2.300-2.400 and 6.300 - 6.500 and quite a bit further forward if I remember correctly. Very small sample size, so don't quote me on that. Especially considering that I wasn't a tournament skier prior to 2004. But, the findings were interesting.

 

Would be cool if anyone who actually was skiing tournaments and short-line could chime in here. I am interested in having more of that information.

 

In my mind, the "fin area' goes full circle. Today we are running much large fins compared to 2 decades ago. It is related to much more then just the ski itself. In addition to the properties/characteristics of a ski, it is also a function of the boats power and ability to accelerate and to provide the skier with an ample source of energy prior to crossing center-line. Since boats have so much power, and we are swinging to the buoy line with much more speed.

 

Very broadly speaking, my general understanding is softer boats (lower HP) would govern a smaller overall fin area as opposed to the 400hp motors we have today. Similarly, softer skis work better with a smaller fin, stiffer ones require a larger. Another factor being the speed control systems. This one is a bit counter-intuitive I think as once you start having the discussion of speed control and the functionality, total system response time, and how that has impacted hull and prop changes. PerfectPass seems to have functioned best with props that slip less, but run in a lower RPM range, and thus lower power output. The less prop slip (or more grip) at a slightly lower overall power, may govern a slightly different overall fin area to function appropriately with the engine,prop,gear and speed control response time characteristics.

 

From what I can gather, in order to tune the boat to work better with the reactive type of response with ZO, we are running boats with a higher peak torque/hp output, at a higher RPM range, although combined with props & gear ration that "slip" more in order to balance out the higher power capacity of the system overall. I might be wrong on this, but, being that ZO is a speed control (not rpm), theres a bit more delay then PP before the prop actually turns faster to accelerate the boat at the instant the skier loads up. So that system needs to have a bit more power available to catch up (react) fast enough (to signal coming from the accelerator upon the skiers load), to accelerate the skier - (before they sink into a hole going into the first wake.)

 

One of the ways to get the engine to respond quickly, and get to a higher RPM fast in response to the skiers load, is to allow the engine speed to ramp at a faster rate. The only way to do that is with prop geometry that has more "slip" and or, run at a specific RPM range where there is more available power (higher, earlier peak power curve).

 

The thing to remember is this, even though a boat has a rated HP output of 450hp at 5500rpm , when its running at 3700rpm on a fixed gear, the actual power output going into the water is more in the ballpark of 130 -150hp. Prop it at to 4000rpm and you'll be working with 150-170 hp. I couldn't find a good plot for a 450Hp motor, but the charts below should work as an example. An engine rated at 250hp @6000rpm motor is only putting 65hp to the water (green line) between 3700-3800rpm with the appropriately matched propeller. (one that allows the engine to reach its full Rated engine speed of 6000rpm)

 

The ability for a boat to acclerate/respond has as much to do with how its propped as it does maximum power output. The higher the peak power band of the engine for a given RPM, above the prop curve power output, means the faster the engine can acclerate/respond. See immage below. On the second image, you can see that props with more blades, cupping, less pitch or larger diameter (blue & purple lines),require more power to turn at a given RPM and can reduce the boats ability to accelerate quickly, as there is less available power to turn the engine with. The converse is also true. The game is finding the best balance for what is going on at 36 & 34mph.

 

Finding that formula for Hull-drag, prop geometry, engine rpm (power), response time etc, is not an easy task. And I have tremendous respect for anyone involved with working on these systems.

 

 

 

 

 

 

 

But back to the fin setup. The way the boats are configured, and the way the speed control systems function, and how much power then engine / propeller can deliver.... I believe, has significant impact on "fin area" that we can run.

 

More available power = more speed generated before centerline = more fin area required for stability & control through the turns.

 

Less available power = less speed generated before center = smaller fin area in order to sustain speed in the turn long enough and not sink before hooking back up with the rope.

 

Its no surprise to me that at some of the big tournaments, all the featherweight skiers put up huge performances, and all the big guys suffer. Its almost always a case were the prop was changed/tuned to lower engine rpm, starving the big boys of the power they need to have to run short line. Give CP a 485hp@6000rpm rated 6L engine running at 4100rpm and I bet he will never miss 41 off. And he knows it. Put him behind a 350hp @ 5500 rated 5.7L Ilmore running at 3700rpm, and Ill be surprised to see him run through 39off, while the Howley's/Smiths/Mclintocks have a much better chance to survive it. The difference in available power of those two setups is massive, and a real issue when you consider hardly any of these guys are making "fin area" adjustments to their skis (depending upon what they practice behind) when the show up at a tournament with either an under-powered or overpowered boats.

 

Again, sorry for the massive tangent, however I do feel this is a pretty big issue in our sport. The top skiers need to be more way involved in the ZO development and prop tuning then they are. Things are progressing slowly, but need to start to work better for EVERYONE, everywhere. Speaking bluntly, the "Plus" setting on ZO was a bad attempt at correcting, or trying to provide a method of accommodation to "smaller" or "bigger" skiers. It changed way too much about the dynamics of the timing, rather then just being a multiplier for total power output into the first wake. No one I have ever talked to uses it. I know there are a million parameters within ZO, however, we need to have a better method to adjust the "gains" for skier weight SOMEHOW.

 

While "body weight" may not be the appropriate parameter, but something simple like that, that the average Joe can understand should be used to create a gain/offset that will give both the big 200+ guys and the featherweight guys the appropriate power levels they need to successfully ski the slalom course. If we had that, I think the scores we see from skiers would be FAR more consistent across the board for the top Pros and the more novice level skiers.

 

I would love to work on this side of our sport, as I believe its a more important issue then ski & fin design.

[Drago]

@adamhcaldwell I'm glad I sparked that tangent.great stuff.

Every heard a big guy say their should just be one setting?

To digress, I recall a certain boat, that has since been completely redesigned: everyone though it was a "beast", super powerful, so they tried to detune it with a softer ZO setting. I always felt that they were going the wrong direction , because the prop was slipping something awful, especially when the owners also tried to detune it with a (non-approved) "softer " prop.

Also explains why that stainless fin worked on my Stealth and Stilettos.

[thager]

In 80s I bought a Mastercraft Pro without a fin. Found a normal shaped aluminum fin that I cut the back 1 1/2 inches off squaring it off to imitate the original. Fin was short and deep. Ski was one of the most consistent turning skis I ever owned. Many PB's on it.

[Adam Caldwell]

Quick story on boats I recall hearing from Cord in 2012 about CP when he was training for a tournament a few days early at the tournament site. Shows up for practice, runs 39 & 41 easily, and is pumped for the weekend. Several other 34mph & 36mph guys ski the same day, and the tournament team decides RPMs are too high on the boat, so they swap props, and go back out the next day. CP says he can hardly run 39 and it feel like a dog. You think hes frustrated? I think he and Cord talked about some fin tweaks, but long story short, it made for an unsuccessful weekend for Chris. Not only does a boat that is not performing for the "big guys" make it harder for them, it also makes it harder for the driver, further worsening the situation for the skier. The driver is faced trying to control a extremely strong, highly leveraged skier, as they end up deep in a hole on back of the turns once they get out of rhythm.

 

Like I stated before, I think ZO is an amazing tool, and I admire the hard work and commitment of everyone involved, but there is more that can be done to improve upon situations described above.

 

@Drago,

Yeah, we have a few of them at trophy who all say that. I think it is possible we could have one setting, however something would need inform the ZO more about how big the skier is, or how heavy the load. I cant speak very technically about ZO, but from what I can come to gather the accelerator gains need to be used more, somehow, as its the only way the boat has any "feel" for whats happening behind it in an instant. What sucks is there are a lot of things going into the sensitivity of the accel unit mounted up under the dash. Rope length, rope type (stretch rate), pylon stiffness (material, lenght, how its mounted...loose pylon create timing issues with ZO response. Check your pylons regularly.)

 

I am personally super anal about rope used in tournaments. This is one reason why. As a hard puller, overly stretchy ropes kill me in the opening passes as I am more likely to make an error at 32 or 35 off an miss a pass.

 

The issue behind rope length is real, and one of the few reasons behind why I use A2 at longer line passes warming up, and move to A1 at 38, 39, 41. I need the faster/peakier response time at the longer line to make sure I'm getting enough "energy" from the boat before crossing center-line. Otherwise, I am sinking in the turn, a sensation I absolutely despise. However, for me personally and the philosophy and technique I live by, as the rope shortens, if I have overloaded at all, the quicker on/off and higher peak in power tends to take me off the line earlier then I want. The A1 will allow me to move slower/steadier through the edge change/preturn without feeling "dropped" by the boat.

 

Cord and I talked a lot about using a special rope what would have the same "strectch" no matter what the line length. This would just be a method to reduce the variability and number of parameters that are changing as you shorten up the rope.

 

IE. Currently, the rough tolerance on a full 75' rope under 50# of load is +/- 9 inches. I while back extrapolated a quick table based on the acceptable data from the AWSA rulebook with a rough number for an estimated elongation rate of 16 strand polyPro rope. Its not completely accurate, but a close representation on the extremely conservative side. After getting ripped out of my bindings at the edge change into 2 ball on my opening pass a few years back, I took a come-along to another "backup" rope identical to what was used in the tournament. I easily stretched it over 4' in additional length, not just 20". And doubtful it was much over 1000lb of load if even that. I threw it in the trash, and never get on the water at another site without checking what the quality of the ropes are.

 

 

 

Its easy to see that the variability between rope-stretch under different loads and rope lengths is significant. This is important because during the moments the rope stretching as the skier is loading, it is dampening the response of ZOs system enough to cause a delay to allow the skier to have moved closer to CL, OR, deeper into a hole in the water, before getting any "real" throttle from the boat. The more stretch in the rope or flex in the pylon, the longer it will take ZO to respond. This is bad for the skier all around, as they have less linear distance to accelerate into CL once the boat does throttle, but also, they will probably face a tremendous amount more load as the boat accelerates because of their ski now being deeper in the water, likely with more angle, driving the drag on the ski up very high.

 

I hear so many skiers talk about how a ski comes alive at shorter lines. I've often wondered how much of that had to do with the fact that at 35off and up, that rope is well stretched and used, thus being more responsive. Conversely, maybe the 22/28/32off sections not used as often, or as hard, are stretching just long enough that they are digging a hole before getting throttle out of the boat.

 

Some rope stretch is good. Some pylon flex is good. Too much is just plain BAD. It causes a tremendous amount of recoil when the skier unloads and can pull the skier well out of balance, and even make life much harder for the driver.

[Bruce_Butterfield]

Adam, great analysis (I love massive tangents) and theory on what affects ZO and the pull for the skier. However, I think you are giving too much credit to the thought that went into the development of ZO. Outside of Andy and a handful of other skiers, the guys doing the algorithms for ZO were non-skiers simply designing a control system and didn’t get that far into what affects the quality of pull for the skier. The goal was simply to get to a speed based control system that minimizes the human input. It was the classic push to meet the minimum requirements and be done. When the first version came out and no one could ski behind it, it was full duct tape and bailing wire to tweak the settings. Hence all the very real issues you pointed out and why so many of us struggle with ZO.

 

I really hope someone can prove me wrong and there really was a lot of thought an analysis put into the ZO algorithms. I’m not holding my breath.

 

PS – you should have been around in the 80’s and 90’s when we had the 12 strand ropes that were all over the map with elasticity. Talk about exciting 22 off passes and wasted tournaments!

 

[Adam Caldwell]

@Bruce_Butterfield Yeah, I cant even begin to imagine. What a nightmare. Whomever thought a stretchy rope is a good thing should be shot. I stopped going to tournaments at a few sites specifically because the organizer believed in using brand new, off the shelf ropes....and even worse, not a top quality rope either. The sad thing is 80% of the people walk away thinking they just had a bad day not having a clue it was almost a guarantee the rope was the issue! But, I guess what you don't know wont kill ya.

 

Agree, and am aware of some of the behind the sceenes of ZO. I sat with one of the programmers years ago at the Masters event and picked his brain. Despite not being a skier, he did have a damn good grip on understanding some of the dynamics at least. This sport is small, despite what was or wasn't done with ZO I am still impressed with what they pulled together, irregardless of who did it. Like anything, haste makes waste....

 

[Razorskier1]

Great thread!

[Drago]

@adamhcaldwell dang man,you're hitting some serious nerves here. I'm not going to get started on stretchey ropes.I just returned from finding a Christmas tree with the family and don't want to ruin the mood.

I hung out a bit with a certain very successful big pro skier : he was sponsored by a rope company that made very stiff, beafy ropes, and his results were going down in pro tours. Part of it was his ski, but I tried to get him to look at the rope sponsor of the pro tour, and the choice of the lower-strand rope another (light,influential) pro convinced organizers to use.

When I skied open, I would bring 2 measured ropes to local tournaments and tell the CJ that all the open skiers (1) voted to use them. Noticed in the guide "all but open" started popping up. Had to stop caring.

[Adam Caldwell]

@ Drago, I do the same. I have even walked away from a tournament on a couple occasions when I saw the types of ropes being used and the tournament director didn't want to use anything different.

 

If anyone is interested in supporting me on a small independent study I would be happy to put together a fairly detailed investigation of ropes. I just setup a strain gage type load cell to get some pylon data, and could use the same setup to get some actual test data on some of the different ropes on the market. Basically just need to get "new" ropes from all the manufacturers claiming to sell a "tournament rope".

 

Something like this... but obviously something capable of a 75'rope.

 

I'm thinking: Accuracy in length & sections, elongation during load range 44-1200lbs, Peak load at failure, maybe even some fatigue cycle data.

 

What are the top lines being used today by high level skiers? In-tow, Masterline-Pro, ???? Is that it? Would also be good to get data on "other" ropes being sold to compare to. I was thinking I might contact these companies directly, but Im not sure they would want to be subject to the results.

 

Not that it would be a good "control", but would also be good to use some "old ropes" as well, to how much of the performance & life is lost out of the line over time.

 

Again, Im under the impression that somewhere along the line "someone" looked into rope quality from a technical perspective and how it impacts performance. But maybe not. Especially with the "reactive" control of ZO, I think there is absolutely some benefit to learning more about elongation of the rope and the impact on the timing of the boats response.

 

Anyone know of a good contact who may have more info on this subject who I could contact?

 

PM me if anyone has any interest to get behind something like this.

 

 

[DW]

@AdamCaldwell: great analysis and I think you are correct on the reactive nature of ZO (P4,5 of first commentary) & I will add what I think may be a significant element. GPS based systems have a lag time of ~.2 seconds between signal sent and received. I discovered that the hard way several years ago (in the tech shed at a car race event) when we were using a data acquisition system when plotting GPS speed, engine RPM and then went back and added wheel speed sensor speed. What that all means relative to your thread tangent, is the feeling of falling in the hole basically after you put some tension load on the rope is the reaction delay of the ZO system. Not sure how much "anticipation" software is written in to the program, perhaps enough after the initial release issues to satisfy the complaints, perhaps the ZO calibrator commented on that.

 

You can get some good power curves right from the GM Performance Parts website, the marine engines are pretty much one of the crate engines with their own (relatively conservative) calibration and ancillaries hung on them. Power curves will be close to what is published. Also, something to note, the prop curves are dependent on the hull configuration and basic drag characteristics of that particular hull, and with the current crop of boats having more weight and wetted area, the drag levels are much higher than previous. On the flip side of low power, one also has to be careful not to overspin the prop as then it will cavitate although the latest CNC props are pretty immune to that & really only an issue at WOT & low speed acceleration.

 

Cool project on ropes, I would assume a good contact would be one of the actual rope suppliers (not the completed rope but the material manufacturer).

 

Another tangent, if weight equalization ideas are being discussed, as a member of the not able to dunk a basketball crowd, distance from pylon to bottom of foot should also be equalized! LOL.

[Than_Bogan]

Hey now -- having a reach of about 8'2" is pretty much my only "athletic" advantage, so no taking that away!!

[Adam Caldwell]

@DW makes perfect sense. The thing about "props" is that the ZO settings are a tuned algorithm which is dialed into the specific boat configuration its going into. Correct me if I'm wrong, but, once that algorithm is set, or tuned for specific boat/gear/prop/hull/ after it has been "accepted" by ASWA then when you change a prop to drop the RPM for example, you might make a boat 'better" for a specific class of skier, but likely make it far worse for another.

 

Its not that the lower RPM or lower power isn't still enough juice for ALL skiers to run the course, its that the ZO tuning was not "optimized" for that prop when attached to the rest of the powertrain & electronics. Go ahead and keep the lower RPM prop, and crank the gains up, and you have a boat that can pull the big boys again. I believe we are seeing that iteration process happening pretty regularly with the manufactures as new props come out for a given boat hull with updated ZO tuning. However, even a well tuned ZO & Boat configuration, there is still the issue of its ability to cover the full range of skiers in a way that could be possible could if there was another input or two specific to the skier.

 

On the time delay issue, as I understand it, the acclerometer mounted under the dash is used to account for the delay times in signal processing, so that shouldn't be a huge issue.

[DW]

@adamhcaldwell: are you referring to the time delay from when the leaves the puck travels to the satellite then returns, that is the .2 I am referring to, not any internal unit processing. That one caught us by surprise, but should not have once you think about it.

[Adam Caldwell]

@DW ...the way it was explained to me by the ZO "programmer" (nerdy computer guy, not the marketing folks, this was at the 2011 masters event , and my memory is horrible so don't quote me on this...). There is a significant amount of data processing and calculation going on within the unit looking at both GPS position and acceleration etc. This data is being used to create "estimates" on position that is being fed through a feedback loop with the GPS data. So in essence, the system still "knows" what its estimated position and velocity vector are while the unit is waiting on the 0.2sec to pass for the feedback signal to return from the satellites.

 

The ZO accelerometer is mounted on the back of the kick plate up under the dash on Mastercraft boats. Not sure where it is on Malibu/Nautique. Anyone who has removed that kick plate on a Mastercraft, and accidentally set it aside to where the ZO accelerometer is no longer situated facing North/South but rather East/West, and then tried to drive the boat through the course will know how much the accelerometer impacts the ZO functionality. With the accel positioned sideways, the boat doesnt know its accelerating, or running in a forward direction (therefore its error correction for speed and position will not be representative to whats really going on). The boat will constantly surge the throttle up and down and tremendously overshoot and undershoot the targeted speed set-point. This is the result of having no error correction during the 0.2sec delay on the speed/position signals coming back from the satellite.

 

So, that 0.2sec delay is not necessarily whats causing you to "sink" in a hole before the boat picks you up. Those accelerometers are very fast to respond. But, if your pylon is loose, or you are using an overly stretchy rope, that could be one component to that issue.

[dchristman]

@DW No signal travels from the puck to the satellite. GPS is receive only with location based on measuring time differences received from the atomic clocks in the satellites.

[dchristman]

I wanted to post this picture back in December when this thread started, but I couldn't find it. I was just perusing eBay and came across it again - some interesting looking fin shapes:

 

 

all these can be yours for the low price of $2999.99 eBay link

 

Does this collection belong to anyone here?

[oldjeep]

Wow, doesn't hurt to dream but skis like that go for $10 a piece at garage sales to use as wall art or lawn chair parts.

[dchristman]

@oldjeep but I believe those are titanium clad carbon fins, and the bundle looks to include some protective cases. Isn't the value obvious from the care taken in the presentation?

[thager]

Are those fins or battle axes?

[dchristman]

They're "Huge Skags"... (maybe that's a Viking battle axe?)

[Bruce_Butterfield]

That pic is from KLP's toybox when he was 12.

 

Might actually be worth bidding on:)

[Horton]

I recognize a few of those fins. The cases are HO and Taperflex. 3 grand? Haaa NO!