What do you think would happen if.........

[Dr. Jet]

Just to state for the record, I'm not suggesting anyone actually attempt to build what I am suggesting here, as the complexity would no doubt negate any possible improvements; this is purely a "What if?" thought experiment :

I was watching a water skier on 2 skis and was impressed how he could carve corners. What if a rigger had a fixed fin at the rear and the sponsons could lean from side-to-side like that water skier?



You probably wouldn't need a turn fin any more...

[Panther6834]

I know it's not the same, but you should check out the Yamaha Niken.


~ More peace, love, and kindness would make the world a much better place

[Dr. Jet]

I know it's not the same, but you should check out the Yamaha Niken.


~ More peace, love, and kindness would make the world a much better place

That kinda got me thinking of this idea too....

[NativePaul]

It sounds a bit like a wetbike, wetbikes work, but I guess there are disadvantages as they got overtaken by jetskis and eventually disappeared.

I recall in the early 90s there was a team that traveled the model show scene doing synchronised displays with Robbe wetbikes in the temporary pools doing PR work for the Ripmax (the big RC distributor in the UK), they were unsurprisingly a fair bit slower than what we were racing at the time, but they looked like a LOT of fun.

Technically I don't see what you say as an advantage, if it has a fin at the rear you are not getting rid of the drag of the fin, just making it less effective as it is further away from the CoG and nearer the rudder.

With the angled sponsons I suspect that they would act like turn fins to some extent and I doubt that you would need a fin at the rear, but you would also lose a lot of lift up front and you may need a lifting surface on the front of the tub to act like stumble blocks on a poorly designed cat to stop the front end digging in too far and hooking.

[Dr. Jet]

Just thinking aloud here...... No scientific testing to reference, no empirical data to compute; just wondering "What if..."

Ski2.jpg

He still seems to have plenty of lift. Turn fin? Probably not. Rear fin? I don't know; would propwalk require a fin on the back? Would you need something to keep it from swapping ends? Whatever, a fixed fin would be less drag than a fin that moves (a rudder).

Maybe for minimized steering drag in SAW applications (too much rudder at 100mph is probably a bad thing....)?

[Panther6834]

Just thinking aloud here......

Ski2.jpg

There's two things it looks like you've possibly failed to think about:
1) The reason "why" skis are angled to turn.
2) Why such won't work with a boat.

Skis are, in essence, completely flat left-to-right...plus, front-to-treat, they curve down...and then back up. Their front-to-rear has a lot in common with, say, the wrong of a plane. A boat's hull, on the other hand, is curved/angled left-to-right. Also, boats use a rudder for steering...a ski has no "built-in" steering device. There are numerous other reasons why your idea, while "interesting", just can't be done...at least, not without a complete redesign of the entire hull, not to mention a whole lot of mechanics (including something that would allow the weight to be shifted).

Now, of you want to plow thousands of dollars into designing, producing, and testing models...by all means, no one here is going to stop you. But, you should ask yourself, "Is it really worth it?"


~ More peace, love, and kindness would make the world a much better place

[Dr. Jet]

Now, of you want to plow thousands of dollars into designing, producing, and testing models...by all means, no one here is going to stop you. But, you should ask yourself, "Is it really worth it?"

That's not my intent.

Just to state for the record, I'm not suggesting anyone actually attempt to build what I am suggesting here, as the complexity would no doubt negate any possible improvements; this is purely a "What if?" thought experiment.

[boredom.is.me]

One thing I haven't seen mentioned, which happens to be the entire way "leaning" works, hasn't been mentioned. Leaning doesn't result in turning. Try leaning while riding a bike. YOU WILL FALL! Leaning allows you to counter the centripetal (path of inertia) force. You still have to turn. The only situation where you don't have to turn in the traditional sense would be at speed on motorcycle where gyroscopic forces are strong enough to require you to counter steer.

[Nachtschatten]

good morning lads+gents,
am i supposed to mention the aqua skip here?
am new to the forum and just looking around

[NativePaul]

It is a very interesting thought experiment.

I hadn't considered having no rudder, but I don't know why. The Robbe wetbikes had tightly spaced contra contra rotating props geared together to eliminate prop walk and minimise torque roll, and had no rudder or fin at the rear.

The front ski did steer though and was shaped kind of like a shallow upside down u section so had a fin on each side.

I have no real idea how a waterskier turns, I believe that their weight being on the centre of the ski will curve the ski, and when tilted over those long urged blades would be a pretty effective rudder, but I don't know how the turn is initiated, my guess is that there is some rotation of the skis done first to avoid falling over as mentioned above.

I was assuming that the more upwardly curved front of the ski was in the water in the turn doing the grunt work of the curved ski acting like a long rudder, but in your photo that section of the ski is well out of the water due to the high angle of attack.

Is that your photo, if so do you have another of the skier going straight? I suspect that he is running the ski at a higher angle of attack in the corner to compensate for the loss of lift from the planing surfaces being angled over.

If I am right it would be possible to recreate the effect on a rigger and if controlled very well could have some hydrodynamic advantages over the typical sponson setup, but while possible it would be a hell of a comple arrangement and I doubt it would be worth the weight in performance terms (though it would be a splendid puzzle to overcome).

If I am wrong about needing to increase AoA in turns to overcome loss of lift, or if that could be negated reasonably well by the use of ride pads on the skis, while keeping the necessary flex (if it is indeed necessary) through clever material engineering. That would simplify the mechanism a lot, as a double wishbone/A arm with the top arm on servo controlled sliders would be all that was needed.


Everything in my post above is guesswork and may be total BS. If I was to do it (not that I am going to) I am sure that a LOT of trial and error experimentation would be needed, and my stating point would be taking some water-skiing lessons to try and ascertain what was going on first hand.

[Dr. Jet]

That skier was just a stock photo I found on the Internet to show two skis turning.

All the above is guesswork and may be total BS.

The entire point of this discussion.

If I was to do it (not that I am going to) I am sure that a LOT of trial and error experimentation would be needed, and my stating point would be taking some water-skiing lessons to try and ascertain what was going on first hand.

I wonder if someone could do a computer simulation; that way you wouldn't have to build countless unsuccessful prototypes to see if it worked.

Just thinking aloud here, not seeking attacks on something that has never been tried (and maybe for good reason).

[NativePaul]

The entire point of this discussion.

That is what I thought, it is an interesting, intruiging and entertaining topic for thought and discussion that i had not considered before, thank you.
I felt the need to add the disclaimer that I am guessing just in case someone mistakenly thought that I was a double major doctorate mega cum louder in waterskiology from MIT and was spitting facts, rather than a bozo having a guess. I would feel bad if anyone wasted there time on something bad, or conversely skipped doing something that was amazing based on what I said.

I wonder if someone could do a computer simulation; that way you wouldn't have to build countless unsuccessful prototypes to see if it worked.

Probably, but not me. I'm a bit of a luddite, I think I could probably knock out prototypes quicker than learning the software, suspect that the materials use would be cheaper than the software, and I know I would have more fun doing it IRL. I now think that it will work, and think you could get some degree of success on the first prototype, the tub is easy and the mechanism while hard could be made with plenty of adjustment,so it would only really need CoG and skis iterating, I am sure they would be a lot of ski iterations before you got to the point that you were happy that it was in the sweet spot, and say whether it is the bees knees or the dogs poo, but skis are easy to make.

Just thinking aloud here, not seeking attacks on something that has never been tried (and maybe for good reason).

I wasn't trying to attack anything. Did you think that when I said "All the above is guesswork and may be total BS." I meant everything above my post, ie what you, Panther, Boredom and Nachtschatten said, if so nothing could be further from the truth; I apologise for any offence caused by the unfortunately ambiguous phrase I used, what I meant was that everything in my post above was guesswork and may be total BS (and I have now edited it to clarify this).

[Dr. Jet]

Did you think that when I said "All the above is guesswork and may be total BS." .......

No, not at all. I consider you one of my good friends here. I was thinking of possible future attacks saying I'm out of my mind. That's possible, but I still think it's a fun mental exercise. The mechanism to move the sponsons would be heavy and cumbersome. Perhaps if they were made of that weightless, frictionless material we used in our high school physics classes.

[Dr. Jet]

OK, here's another thought to throw into the mix: As I was looking at the photo of the skis and thinking about high school physics, I realized that as long as the force vectors remain the same (direction and magnitude), the skis would not know if the human is being pulled by a rope or pushed by a propeller.

[jkflow]

Not a bad idea, you would lose steering though if they are out of the water, which is fairly common. Like driving a 4WD with front tires up in the air.
At lower speeds it will work just fine.