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 Post subject: Re: Some boards I made
PostPosted: Sat Feb 11, 2012 12:45 pm 
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BWD,
speaking of P,SD, L graph I can say that turbulence or "soft bubbles" created by dimpled bottom can effect a very limited thickness layer of the water under the board.
Maybe only 1/2 inch. On the ohter hand kiteboard front bounces +- 3 inches therefore pressure stabilisation would be limited. And I would say better feeling instead of more efficiency.

In order to shift high pressure area, as you talk, you must move the board at least in comparable velosity to the pressure wave velosity which is ~1300 ft/s in the air bubble and >5000 ft/s in the water.
Which is not true.

Less rocker boards tend to have "more efficiency" less drag on the flat water but you loose control on the choppy waters. So its not all about less drag and we can keep experimenting!
I will also make some experiments with bottom surface and post commets on summer.


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 Post subject: Re: Some boards I made
PostPosted: Sat Feb 11, 2012 8:31 pm 
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Sorry if the pictures don't get the point across clearly.

The question is, how does a slightly thicker boundary layer affect the response of the board to flex and vibrations, i.e., could it be better to have a thicker boundary layer, even though in conventional hydrodynamic terms it might make more drag?

The thing about kiteboards, is that they are constantly changing their foil shape anyway, which may not be the best thing for hydrodynamics.
If the way forces are applied to the board is altered, the way the board responds will be different also.
Perhaps the thicker boundary layer affects the "jerk" or "surge" (meters/second^3) experienced by the board, resulting in a different response and better energy recovery.
It is a question of conjecture, and best answered empirically.
It might remain hard to evaluate objectively.
Analogous questions might be what is the best material for your violin's bridge, or for your guitar pick? Answers will vary....


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 Post subject: Re: Some boards I made
PostPosted: Wed Feb 15, 2012 1:26 am 
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new to the forum so hey to everyone.
Not refuting the comments before as they seem to be in another league in the tech area. For those people.... Lindsey Lord's book Architecture of Naval Planing Hulls is a good theory read.

I have alot of experience in other areas with respect to the drag question.
I have surfed my whole life and make surfboards. With respect to surfboards the best "texture" for speed is 220 sanded finish. More gloss creates surface tension, rougher creates drag. Always tip tail direction for sanding. I had a discussion with terry martin (one of the most respected shapers in the industry) about using dimples like golf balls a few years ago. we came to the conclusion that the dimples work for golf balls because they have no right direction and spin like crazy which creates a gyro effect and also make a thin wind barrier in front of the ball which reduces the effect of the oncoming air, like drafting in car or bike racing. but surfboards and kiteboards dont spin or interact in an atmosphere of air. More like an air/water space which complicates things. I wonder if the dimples might also create a bad flow over the board. I know i go to great lengths to make my rockers smooth and the dimples would defiantly disrupt the flow and create turbulence. Turbulence could reduce the planing ability of the board because it could lower the density of the water. Like using bubblers on water ramps for skis ect... to soften the impact.

I know for sailboats sanded finish is always faster. For skis and snowboards a fine texture is fastest. both of these are to break the surface tension of the water on the surface. like picking up glass off a wet surface is hard because of the surface tension, try the same with a mat finish glass.

the exception i can think of is skimboards. they are fastest polished and waxed with a bowling alley wax. i guess the type of wax allows the water to bead off and that reduces surface tension. More of a slippery kind of ride. also ment for going on wet sand too so that might be the reason.
im just a kite noob but i thought id throw my 2c in.

If all else fails try it and see. Its the fastest and cheapest way to test the theory. Maybe it will be the best board ever. Please tell me if it is. I'm in the middle of a couple boards


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 Post subject: Re: Some boards I made
PostPosted: Fri Mar 30, 2012 1:43 pm 
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Hi guys

Glad my dimpled surface experiment has generated such interest!

All I can tell you is that my dimpled surface boards "feel" much nicer than a factory smooth finish when riding. Now we did conduct a "base line test" if you want to call it that, when several of us at my local beach rode my board back to back with a real Spleene Door. we switched off many times and even the owner of the real Spleene liked how my board "felt" on the water.
Subjective yes, conclusive...well.....bottom line was that we had a blast riding something I had made myself that was at least on par with an expensive production board! Benefits (if any) of the dimpled surface could measured scientifically of course, but we had more fun riding them! Plus it makes for a great conversation on the beach when we are waiting for the wind to show up!

One


Last edited by ONE on Mon Apr 02, 2012 12:14 pm, edited 1 time in total.

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 Post subject: Re: Some boards I made
PostPosted: Sat Mar 31, 2012 4:59 am 
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Location: Mauritius, waterman since 1960
This is an age old discussion that still keeps everyone guessing , which is best.
I remember the 'Phasers' that were put in wake boards, a replica of the golf ball theory.
I also recall windsurfers on the world tour using jelly like paints to get better speeds (the idea was to copy fish I think). The flexible surface would permit a "soft" boundary layer that could move back and forth with the angle of the boards on the surface.
Anyway, a passionating subject.
Your boards look sweet One.
Nico


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 Post subject: Re: Some boards I made
PostPosted: Sat Mar 31, 2012 8:54 pm 
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ONE wrote:
Hi guys
...
Subjective yes, conclusive...well.....bottom line
...

One

Here is a test Ya can do :

Several different weight riders; with a few different boards of the same size
as yours.

Ya need a fishing scale to determine amount of force exerted here :
Hook the scale to a tow-rope behind a boat and go wake-boarding
with Your board and switch off to the other brands.

Should be a difference in force exerted to Tow each rider of different
weight ; along with a difference for force exerted on each rider when boards
have bin changed ?? --------------------------------------------(i think)

Bille


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 Post subject: Re: Some boards I made
PostPosted: Sat Mar 31, 2012 9:24 pm 
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Location: rhode island
Bille wrote:
ONE wrote:
Hi guys
...
Subjective yes, conclusive...well.....bottom line
...

One

Here is a test Ya can do :

Several different weight riders; with a few different boards of the same size
as yours.

Ya need a fishing scale to determine amount of force exerted here :
Hook the scale to a tow-rope behind a boat and go wake-boarding
with Your board and switch off to the other brands.

Should be a difference in force exerted to Tow each rider of different
weight ; along with a difference for force exerted on each rider when boards
have bin changed ?? --------------------------------------------(i think)

Bille


i dunno billie,
a fish scale may not do it.

ONE was only willing to speculate on the "feel" of his board.
I dont know what units would apply, but its doubtful that LBS would be the definitive answer.

perhaps a "feeler gage" ?

-bill


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 Post subject: Re: Some boards I made
PostPosted: Sat Mar 31, 2012 10:22 pm 
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zfennell wrote:
...

ONE was only willing to speculate on the "feel" of his board.
...

perhaps a "feeler gage" ?

-bill


HA !! :D :D

Feel Vs Drag through water ; like i was thinking.

YEA -- A "feeler gage" would do it !! :thumb:
That' one's gonna be Harder to design.

Bille


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 Post subject: Re: Some boards I made
PostPosted: Mon Apr 02, 2012 9:19 pm 
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Guess why the rocker line is so deep on wakeboards? Its not all about the drag here.
Also you can take an old thick foam core rigid twintip and compare it against the same shape soft wood core twintip.
Any differences in drag? - minor. Any differences in "feeling"? - huge...

Human body is a part of the system. It can't be excluded from the model.


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 Post subject: Re: Some boards I made
PostPosted: Wed Apr 04, 2012 1:16 pm 
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Hi Guys

Hollow brings up a great point here, the "human factor" involved in riding a board. One thing I've noticed is that no two riders use a board in the same way! This became very clear to me when I let people try my home made boards. I would "brief" them on how to ride a particular board and they would go out and just do their own thing! Follow me on this......I ride my home made Doors and I also ride a Mako which require a totally different riding style. Now at my beach we have lots of guys riding Makos and Doors but we all ride them differently! Some guys ride their Doors in more wind than others, some ride their Makos in lighter winds, but we all ride the same boards! Some guys ride with more rail in the water, some guys ride them flatter and use the fins more, weight distribution between front and rear legs is always different as well. Thing is......we all have a different "feel" for each of the boards that we ride, so trying to gauge which board is "better" than another is going to be totally up to the individual rider. Now board efficiency (drag) could be measured by several simple methods, but it all comes down to personal preference really.

One


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