Some boards I made

[plummet]

You use a lot less plywood if you use glass. Therefor alot less weight and better performance. Its about sandwiching the glass apart to gain strength.

So yes glass makes the baord better.... if you have the money carbon is even better

[alancFS13]

Carbon is not always definitively better than fiberglass. Carbon is much stiffer than glass, to the point where it will break before it bends. Glass does not have as much tensile strength but handles impacts better. Kevlar is more impact resistant an glass or carbon with tensile strength in between the two. I am planning on trying a carbon / glass hybrid. Use a layer of lighter unidirectional carbon with a layer of glass fabric over top of it. Going to use a core 1/4 inch plywood core, 2 1/8 laminations. One day after I have built enough I want to make one with the carbon kevlar hybrid fabric.

[Samb0o]

Hi Guys



The weight came out the same as a real Spleene Door (Monster) and they really fly upwind.
Nice riding board with the OR pads and straps.

What kind of plywood if weight is same? Flydoor XL weights 3,4 kg. I cant find such light weight plywood.

[mikellli]

I heard that the best poplar plywood, light weight due to less density than the others, it is also very strong. Is anyone has plans for a spleene monster door that I could use for cutting plywood?

[Peterdj]

The idea of the disturbed flow under the board is a good one.
In a way they float on air. Air gets trapped under the front edge and rolls under using the textured bottom to keep it "bubbling " along.

It's kinda why the super swim suits got banned. They are also using that technology on cargo ships, or trying to by pumping air under the ship to make it roll across the water on air ( simply put).

Flat surface on water = resistance
Rippled surface on water with air rolling underneath = less resistance and should result in a fast board

[Hollow]

Peterdj,
advanced swim suite, cargo ship bubbles and dimpled ball surface are three different things.

Swimsuite has smooth and hydrophobic surface (SCS nano coating by Yamamoto). Water drag coeficient of 0.026 compared to traditional neoprene drag coeficient of 4.0. It does not create any bubbles and works opposite, reduces turbulence + repels water in order to minimize interaction between swimsuit surface and water surface resulting less drag.

Mitsubishi cargo ships reduces drag by blowing bubbless under the keel.
The ship speed is comparable to the kiteboarder speed but the bubbles are blowed by the compressor and not by the ships dimpled undervater surface itself.
The algae on the ships undervater surface can increase its fuel comsuption by 10-20%.
The same way "textured bottom" would increase drag. I am sure that bubble blower cargo ship underwater surface is clear smooth and hydrophobic in order to create laminar flow (without turbulence) and stable bubbles under the surface maximizing the area under air. Its similar to hovercraft sitting on the pressurized air area.

Dimpled golf ball is a differt story too. It is an object traveling in the Air. Dimpled surface creates a turbulence in order to reduce drag. In this example surface drag coeficient is not a major factor. It is not a surface interacting with another surface (ship and swimsuit cases). Is all about pressures. Check out http://www.sciencebuddies.org/science-f ... p012.shtml

Liquid can not change its volume as easily as air. Golf ball comparison in the water would be a Shkval torpedo and supercavitation. The whole torpedo is "flying" in the "air" bubble and Only the tip is touching the water. All the fun works in greater than 150 mph speed underwater

The conclusion would be that kiteboard "textured" bottom does not reduces the board surface to water surface drag
but it can create a specific properties because the board has a curved outline and the board surface has some angle to the surface of water or waves.
It would obviously create some turbulence and a different ride feeling.

[BWD]

But what if the dimpled bottom's boundary layer "inefficiency" tunes the flow to the boards' shape and physical properties thereby stabilizing pressure distributions, resulting in more efficiency via less board deflection and trim change? Like this:

bumps.png (17.68 KiB) Viewed 2538 times

That is a question, to which we would like to know the answer....

[Hollow]

BWD, could you please specify more details regarding your charts. P, SD, L?

When talking about the board shape its better to paint a picture of the board and pressure distribution.
Could you point out the "bubbles" and pressure distribution on my picture or so?

[BWD]

Well they are just concept illustrations in the form of graphs, but of course...
P=pressure
L=length -as in distance from the forward waterline of the board (could draw a picture of the board on the x axis)
SD=standard deviation
And I have another picture, just to show how the waterline and high pressure area are moving constantly under the board in response to trim and waves.

My idea, which may be silly, is that the rough or dimpled surface may affect the time it takes for the high pressure area around the stagnation line (i.e., just behind the forward waterline) to shift in response to changes in water surface, board trim and flex (vice versa, etc....), and how far from the mean stagnation line it shifts, resulting in different accelerations imparted to the board and possibly more stable trim and/or less energy lost to flexing the board..

Normally we think of changing board's modulus, shape, or other physical properties to make the board react mechanically in a beneficial way.
Perhaps this different type of surface could contribute to getting the board to behave as we want it to by affecting how the forces are applied to the board in the first place.
Flex of a board is affected by sub-millimeter differences in thickness at key areas,
maybe similarly small differences in how forces are applied to a board also impact how it responds.
Whether dimples or striations of biaxial fiberglass really affect the situation in this way for better or worse, I really don't know.
Maybe someone will apply test tanks and FEA techniques to the question, as they do for aircraft and superyachts -but I don't know who would pay for that....

[highrollerkite]

One, Your boards look amazing! Nice work.