Wake attenuation systems

[lpskier]

I am running a tournament on natural water this summer. The banks of the lake are more vertical than horizontal, and I expect that we will have some wake bounce off the shore back into the lake. I am looking to improve the conditions by constructing some system to absorb wake energy. I will snow fence portions of the shoreline, but I am at the mercy of the shore owners and if they refuse permission to fence their shoreline, I can't fence it. I want to float something in the water to absorb energy that can be floated far enough from shore so that I don't need the shore owner's permission. Using phone poles or used tires will not be feasible due to cost, perceived environmental impact, and the time it would take to install them. I am contemplating 4" corrugated pipe, filled with water and floated with swimming noodles inside the pipe. I'll string the noodle lengthwise on a rope running parallel with the slalom course and slide the pipe over the noodle. The weight of the water within the pipe will absorb some wake energy (theoretically), yet the pipe is reasonably priced and can be easily installed, removed and stored, and even resold when we are finished with it.

 

Does anyone have any experience with such matters, and if so, any recommendations? Any engineers out there with better ideas? My priorities are effectiveness, cost and ease of use.

 

Thanks!

 

John Wilkins

[Joeprunc]

Sounds like a good idea. The floating noodles were what actually came to mind first. I like the corrugated pipe as well, reminds me a lot of swim lanes. I'm not sure how much backwash would be created from the pipe/floaties.

 

I would think the best solution would be to devise something that would let the wake spill over, but not come back. If you could have some sort of floating triangle with say a 30 deg to 20 degree slope. This would act as a shoreline and allow for limited backwash. The wakes with more energy will spill over the side loosing significant energy and dissipate between the shore and the floating triangle.

 

Make a few items and take them to the lake, see what works best.

[uflbret]

Using corrugated pipe can get expensive quickly. I assume you are referring to something like this: http://www.ads-pipe.com/en/product.asp?page=N-12_Plain_End_Pipe

Not sure that will work in your application in only 4" diameter. You may need to go larger to achieve your desired results.

[ktm300]

I have wondered how well the tires at Baurech work. They use them to divide the lake in two. Anybody ever ski there?

[Wish]

We park our boat on the tires at Cypress Gardens (now Lego Land) and watch the ski show from the lake side. While it does cut the wakes down, the tires go up and down with the waves so the waves do come out on the other side. Just not as steep or sharp. I think anything you float will just go up and down and the wakes will transfer though.

[lpskier]

@uflbret That's the stuff. $6.60 per 10 foot section at Lowes. But I only need about 5000 feet... If the idea works, I'll look to get a wholesale account with the manufacturer. Incidentally, you can also get it in 100 foot rolls, but then you have a bend and twist to deal with, a storage challenge, and the price per foot is the same as 10' sections.

 

@wish I expect that nothing will eat the wakes entirely. I am just trying to make them smaller by using the wake energy to do something different, like lift the weight of the tires, or in my case, the "something else." The something else will also have two bites at the apple, one going away and one coming back. I wont be able to make my site Trophy Lakes, I just want to make it better than it is.

[Laz]

Reviving and old thread....

 

I ski at a lake that has two parallel courses. Only one can be used at a time and the decision is based on the wind direction.

 

We would like to separate the lake with some sort of barrier so the courses can be run at the same time. Any suggestions?

 

I think the tire barrier at the Orlando Watersports Complex seems to work well. Does anyone have enough experience to let us know if it would be robust enough to run two boats at the same time?

[Edbrazil]

@lpskier Wonder how well things worked out in 2014? Presumably for the Easterns.

Likely, I will see you at some late-season Florida tournaments. If you can make waves

break, that will absorb a lot of energy. I have some ideas.

For the Collegiate Nationals at ASU, back in 2001, I had some ideas of how to deal with

backwash from vertical walls, but they couldn't be used. They had plastic barrels w/holes,

which helped a bit, but not a lot. Situation was vertical walls, but with a horizontal

walkway sticking out maybe 4', and under water by maybe 9 inches. In retrospect,

sandbags on the leading edge of the walkway might have worked.

[Edbrazil]

@laz Would it be possible to construct a land berm in between the lakes? Also note my

post above.

[mwetskier]

first off if you use swim noodles to float any thing be aware that they will get saturated within 2 seasons and lose at least 80% of their buoyancy. within 4 years they will actually sink on their own.

 

also if you like ed brazils idea of building a land berm you don't actually have to penetrate the surface. a smooth hump within a foot or less of the surface will cause boat wakes to become ' surf ' just like at the beach and by the time they get to the other side of the berm they will lose most or all of their energy. you still have to mark the underwater berm with some kind of floating line of fishing net buoys to prevent a boat from getting high center but those can be small and cheap.

http://www.hiseamarine.com/eva-fishing-net-float-5831.html

[lpskier]

I used 6" diameter perforated perimeter drain pipe in 100 ' rolls floated with swim noodles. I'd say it helped but didn't make a natural lake ski like a dug lake. If anyone needs swim noodles cheap, I have about 4000' of them. Only in the water five days. One year, 360 days of use left in 'em.

 

@Edbrazil I'll be at LaPoints for both days of slalom (chief judge) and at McCormick's for the jump.

[BraceMaker]

Be neat to set up a trial. My wager is it would perform best under lots of tension.

 

Maybe set it up like a volleyball net with end posts/guide wires - stretched on poly pro cable across with occasional support posts.

I would think that the real goal is to change the wave form from and modify the energy of the wave to reduce rebound. Since you don't want to be building something expensive/heavy/permanent I would think tension could be substituted for mass to have more impact on the wave.

 

Light weight objects "bobbing" over the wave should do relatively little to modify the energy. A heavier object should pick up more energy.

 

I would wonder - if you took the same snow fence and simply strung it up along the waterline if it might not be more effective - make it like a "diffusion" grid.

 

 

[gsm_peter]

Gravon in France use barriers with old car tyres.

Approx 20 tyres wide and full coarse lon

Absorbs the wakes and small wind waves OK.

 

They use 20 000 tyers....

- A lot of rope....

- A lot of work....

- Do not know about the environment impacts?

- Tyets sinks during the winter. Boat waves inject air when driving.

 

We also need a solution. Especially for strong wind. Suggestions appreciated.

 

[lpskier]

By using the perforated perimeter drain pipe with floating noodles inside, the pipe filled with water creating its own mass.

 

Our installation was temporary. If it was a permenant installation and absent the impossible environmental regulations, I would have considered phone poles, tires either hanging off tensioned cables or foam filled and floating, or 55 gal drums, half filled with closed cell foam half filled with water.

[waterskicorey]

We use tires to separate our site from a cable park and they work pretty good. Cost is low, tires are free, but takes a lot of labor to put them together and some maintenance.

[wtrskior]

Im no engineer, but in order to actually remove the waves force you need to stop the water from moving. This can't be accomplished with a floating type system, unless perhaps it is designed like an iceberg where most of the structure is actually below the waters surface..

 

The water will still be moving below the tires, barrels, etc.

 

To separate a lake so you can run 2 boats at once, the lake will act more and more like a bathtub IMO. Id think it would be helpful for low wake applications such as spearing a cable park where it's just wake from the boards, no boat and from the boat lae to the cable park. My 2

 

 

[Edbrazil]

Wave energy needs to be expended by making them break, turning them into some

turbulent water. I have an idea of something to experiment with, on a small scale for

starters.

Here is what I'm thinking of. Possible experiment here in Florida during the off-season.

Essentially creating an artificial reef. The blue line is the water line. The round item might be

a length of PVC pipe, sealed off, pulled down by anchors to even or a bit below the waterline.

Wakes would be forced to break over it.

 

 

 

[Fehlindra]

Remove chunks of "quagmire" from the shore (if you have in your lake) and anchor them there they do there job best to remove waves that is unwanted cos of wrong wind direction

 

[mwetskier]

@Wtrskior -respectfully disagree with your assessment that you "have" to stop the water from moving to '

remove the waves force ' - which is virtually impossible to do. wake attenuation is all about *redirecting* or transforming the waves force so that it can no longer move in the same direction. correctly shaped shorelines do this by forcing the waves to crest and then break which transforms the horizontal force into a vertical force -making gravity your friend. the action of washing upward on a sloping shoreline ' uses up ' the waves energy until it can no longer move toward the shore -after which it can only flow gently and harmlessly back down the shore into the lake.

 

floating obstacles that allow a boat wake to wash smoothly over them accomplish the same thing by transforming the horizontal force into a vertical force required for the wave to wash over the obstacle and down the other side. boat wakes carry a limited amount of energy with them -redirect this energy and you reduce or eliminate the traveling wave that we refer to as ' rollers '.

[OldboyII]

There are few things that we have to keep in mind dealing with waves:

- wave is not a movement of water in horizontal direction, it is just vertical oscillation of water particles. In fact each gram of water stay in its place.

- in horizontal direction wave is not a mass transfer, but spreading of energy.

Wave can interfere only with objects which have similar to wave or bigger size.

These objects must apply to wave similar or bigger energy which wave carry.

From this logic theoretically the ultimate wave stopper is concrete wall which is higher than wave with unlimited strength.

@mwetskier correctly noticed that the most efficient and working approach to this problem is to make wave working against itself - either redirecting wave or let it go via labirint constructions.

Simple floating objects with modest sizes may remove some water chop but they hardly can help with rollers. IMO... it is just a waste of time and money.

 

 

[Laz]

I think anything that floats would only be a partial solution.

 

Would this work:

 

Create a wall of tires, say about 5 feet deep and a few feet wide with about about one foot above the surface of the water. Then, have this wall anchored to the bottom of the lake and with flotation to keep the tension on the anchor lines.

 

This would act like a non-floating barrier and the tires would work to diffuse the waves allowing for the peak and trough to cancel out.

 

I tried find out what the risk is of having hundreds or thousands of tires in a lake but could not find any clear answer. It seems that particulate matter from tire wear is the bigger issue and likely having tires in the water is reasonable but I would have to find an expert.

 

https://goo.gl/FGJo0m

 

The scrap tires might be free and the installation would be very labour intensive.

 

 

[BraceMaker]

Waves change nature in shallow water, that energy flowing into shallow water causes the deeper water to sit and the wave to break

 

I think defining the issue the wave energy is the top foot of water, you need a slopped surface just sub surface to penetrating or just at the surface that causes the wake to break over and reduces rebound.

 

Artificial shore line as it were

 

[wtrskior]

@mwetskier you don't disagree then. It's impossible to stop a wave, to a certain point you cannot have enough horizontal plane to make for perfect wave entenuation. It would requiem too much land and not enough depth. A concrete wall as @OldboyII suggests stops the wave entirely but that won't work in this application because you'll get the bounce back bathtub effect.

 

The waves force is below the surface, hence why shorelines have a certain ratio of height to length. At a certain point the height doesn't matter due to the size of the waves ski boats create. The more water is displaced by a boat the deeper the attenuation device has to be.

 

This is why I do not believe a tire wall will work that well. You will stop some of the wave but you will also have more backwash into the body the wave was created in.

[gsm_peter]

What I did experience at Gravon.

 

A tire Wall of standing tyers eliminate almost all needed energy.

The tyers should be barley floating.

20 rows wide and needed lenght.

Each row a half tyer out of sync.

The boat waves 'inject' sufficient air to keep them badly floating.

 

I would guess it is very bad to the environment.

[OldboyII]

@wtrskior i did not suggest to build a wall )) Certainly it is not a solution for this situation. It was example of force that unlimited times more than wave energy.

Speaking practically I saw only one floating construction that was solving similar problem: it separated ski area from wakeboarding/surf boats.

It looked as very big and expensive something - about 1.5m wide pier-like construction with walking desk on the top, few meters deep and inside it was a kind of moving mechanics made of rocking tubes of different diameters.

Unfortunately do not know more details.

But for sure I would not dump thousand of old tires in ski waters.

 

[Dacon62]

There is a need out there obviously. Surprised someone has not made a system available commercially yet.

I am on the same wave length as @Edbrazil but rather than round pipe make a triangularly shaped half submerged 'wedge' that would simulate a gently sloping shoreline that the waves would break over. Would need 2 cables likely. 1 running through the front and the other through the rear of the connected low pitch triangles to keep them from flopping over from the waves.

[OldboyII]

del

 

 

[OldboyII]

It will be just jumping with waves with no serious effect.

There are solutions, but almost always custom made and expensive.

Probably because Sir Isaak Newton does not allow cheap inexpensive stuff :D

 

[mwetskier]

@OldboyII -I don't think waves will affect your floating obstacle the way you have drawn it. a wave will want to run up the surface of the slope and that will tilt the triangle away from the wave. your drawing asks the shape to surrender its buoyancy and sink -but remain level -as it slides sideways against the force of the wave but i think it will simply tilt and allow the wave to wash over it. not saying it won't diminish the magnitude of the wave but i am quite sure it won't behave as you've pictured it.

[OldboyII]

@wtrskior You are correct in both aspects:

- it will tilt according to level of buoyancy (the higher flotation, the less tilt and vice versa)

- it will not produce effect which we want: diminishing rollers magnitude because it will travel up and down with water line.

[PatM]

what if the triangle was shaped more like a ski jump ramp? Mimicking a shoreline.

[ToddL]

Expanding upon the above... Top, Centered Float. Angled pseudo shoreline flat surface. Anchored to bottom. Stretched plastic construction fence netting between anchor lines and attached to the bottom edge of the pseudo surface. I have no idea if this would work or what it would cost. Just adding to the brainstorming above.

Hypotheses -

Center-floated pseudo shoreline surface would work like real shoreline.

Construction fence would aid in suppression below surface.

 

 

Also, whatever solution, could be built as a one-way or half solution for preventing waves from reaching and bouncing off bulkhead shorelines, too.

[OldboyII]

Hmm... interesting task...

5 cents to piggy bank:

Starting from 2 things

1st - the main part of wave energy concentrated below waterline.

2nd - wave is a transfer of energy, not mass.

Very similar to heat transfer. In fact it is almost the same, the only difference it wavelength.

 

It might be interesting to use "thermos flask" effect.

In our case it may be two parallel walls of vertical anchored floating elements about 2 meters high, 2/3 in the water, 1/3 above.

Second wall on the distance 1.5 meters form first.

The space between walls is analog of space in "thermos flask" (the low quality one :) )

 

 

 

 

[gsm_peter]

Gravon used approx 20 000 tyers for a full course lenght.

 

Stiff objects like a concrete wall will bounce waves.

Tyers gradually absorbs the energy.

Needed solution is something heavy and should move slowely in the the water.

[Bdecker]

I've often wondered about whether these would be effective for breaking up backwash. It seems they absorb the energy by rotating the components. Probably too small for the application but it would be interesting to try. No idea about cost per foot. http://www.antiwave.com/products/antiwave-maximum-6-inch-racing-lanes

[h2onhk]

If the water depth by the shoreline was conducive, would a couple layers of snow fence attached to T-posts driven into the bottom work? 2-rows say 4-5' apart? The fence would extend from the bottom to above the water level thus helping dissipate the entire wave and backwash. I realize this wouldn't work for dividing a lake but may help in some trouble spots on the shoreline as long it didn't pose a risk to the skier.

[lpskier]

@h2o.nhk Tried it. Waste of time and my energy. No wave energy wasted though!

[Edbrazil]

I've seen snow fence used. Maybe knocks the backwash down by 10%, at most.

[Dacon62]

Think @Bdecker is on the right track. Just have to produce them in a larger size.

 

[lpskier]

@Edbrazil Do you mean the old style on a roll with wood slats or the light weight plastic web material that is available today? I used the web material and it was useless, not to mention very difficult to install in glacial till soils.

[DefectiveDave]

How about something asymmetric which just floats without the need for a tight anchor? This is just a sketch, but this design should allow waves to efficiently head towards the shore (while redirecting a little bit of the energy downwards with it's own weight) and minimize any reflecting waves. It would then prevent the waves from readily traveling back towards the course by forcing them up the ramp. It would have to be weighted correctly and I'm sure the proportions are wrong, but seems like a reasonable idea.

 

Other designs already mentioned would probably be better at dissipating energy, but this one wouldn't need to be adjusted if the water levels changed significantly.

 

 

[Edbrazil]

@lpskier Old style snow fence w/wood slats. Seen it installed just laying flat on the water.

Multi-rows of it standing up help, but it's a lot of work.

[escmanaze]

@scotchipman Those three brands you show look great, but you are right, they are very expensive and it seems like they are also kind of overkill for the purposes we would be wanting for our club. It seems like we need a nice middle ground between the huge expensive ones you are showing and the tiny swimming ones that @Bdecker is showing.

 

Looking at that Wahoo option, I wonder if we could get the price to come down significantly to buy just one 24" tube for maybe $100 per foot instead of the 3 24" tubes for $225 per foot. It seems like one tube would still do pretty well, certainly better than nothing, and we could start just buying a 20 foot length here and there and placing it strategically around course #4 and #3.

 

Otherwise, if we can get the ranger to approve it, I have an in to get us some tires for free - it would just be a lot of work to start putting together something like that.

[Bdecker]

@scotchipman and @escmanaze - Agree completely. I wonder if having multiple 6" systems would have the same effect as a larger one? I assume our market is not large enough nor do we have deep enough pockets to justify manufacturing something not otherwise commercially available. At one of the sites I ski I think this might work to dampen reflected chop, but I can't see it allowing someone to run -38 with a loaded surf boat running on the other side of the barrier though.

[Dacon62]

Yup. Larger size would be the ticket. Judging from the swim lane set up it would be important to have the length of the line stay in tension. Might have to set up a few 'poles' or solid attachment points along the length of the line to accomplish the task.

[lpskier]

@scotchipman Tried that. Contacted the company that makes it. HUGELY expensive and they weren't interested in working with us at all. It would have cost around $100,000 for what we needed.

[gcam4]

@lpskier you are correct, lane lines are very expensive. Back when I used to swim, we had to put the lane lines in ourselves by swimming them down the pool. You also had to get them very tight, but I think that was more so the lanes themselves stayed the same width down the length of the pool. Potentially an olympic length pool, 50meters, would let you borrow their lines, but I highly doubt that.

[lpskier]

@gcam4 I needed about 5000 feet-almost a mile- of the stuff.

[OldboyII]

The main shortcoming of wake fighting constructions which I met was that their sizes, which did not correspond to lenth of wave. IMO the width of construction does more matter than depth.

Looks like full lenth of wake from the boat is some 1.5 meters. If floating construction will be wider than that it may work... Wave has to pass through this two times - from boat and back. It may significantly reduce it sharpness.

[gcam4]

@lpskier yeah, you are only going to get about 1100 ft from a pool. I don't think they would ever let you borrow them either...