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Outline and tip shape

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lovethepirk
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Outline and tip shape

Postby lovethepirk » Fri Apr 15, 2016 1:44 pm

Hey all...I'm going to begin building my first board here soon and it will be a big lightwind board, I'm thinking 160x46. I see boards like the Spleen Door and Naish Orbit have pinched in centers on the outline. I have a SS glide and it is basically a rectangle. What is the design thought behind the pinched curve in the middle and also some of the strange angles and curves on the ends of the board? I'm trying to decided whether to just do a simple rectangle like the glide or get fancy and make her look sexy :naughty:

Below you can see a model I made with a possible outline...also, I goofed around and was thinking in the future I may try to 3D print out a foil like fin as you can see as well. I would attached it in the center(as seen) and also on each end of the foil where each fin typically is(not in current pic) for support so it doesn't snap, I know the drag might be a lot, but I was thinking maybe the lift could outweight the drag, something fun to try maybe.

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Image

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Kamikuza
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Re: Outline and tip shape

Postby Kamikuza » Sat Apr 16, 2016 4:09 am

Just to add to your misery, the Flydoor uses an asymmetric outline--the head side edge is concave (for better upwind) and the toe side edge is regular convex for toe side riding (lol!)

Pointy corners are asking for trouble, but I like the look of channels and slots.

If it's going to be big and really wide, consider a center fin...

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Re: Outline and tip shape

Postby rynhardt » Sat Apr 16, 2016 8:11 pm

I think the pinched centre has something to do with maximising the edge length vs the area. I can't remember why this would be important and I'm guessing it's got more to do with marketing than actual utility.
My opinion is you'll get more benefit from going wider, say 48cm, than using complex curves.
That being said, the curves look cooler than a plain rectangle.

nice CAD skills, bro.

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Re: Outline and tip shape

Postby plummet » Sat Apr 16, 2016 8:29 pm

If we think about the waterline the center of the board adds less planning surface area than the tips. The pinched design gives more planning surface area at the tips and thus better upwind.
But it will come at the sacrifice of carvability, Chop munching, and power holding ability

Capture1.jpg

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Re: Outline and tip shape

Postby Johnny Rotten » Sun Apr 17, 2016 12:45 am

Plummet I disagree,
Experimented with side cut a-lot. Power holding is not sacrificed. these boards hold down power like mad. As there is a ton of edge buried around the rear foot.
carve-ability is weak. Load and pop is horrible. face spray can often be bad.

Upwind and power holding are advantageous.

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downunder
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Re: Outline and tip shape

Postby downunder » Sun Apr 17, 2016 12:11 pm

Yeah Plummet,

why do you think it's not any of this? Or more? It can be really anything depending on the rider...Also, the pic is suggesting having both fins deep underwater (top and bottom fin), which is never the case (at least for me).

I am voting for a yellow line btw.

Capture1.jpg
Capture1.jpg (25.09 KiB) Viewed 474 times

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Re: Outline and tip shape

Postby TomW » Sun Apr 17, 2016 3:21 pm

I think trick to getting these boards to turn is lots of flex in tips and rocker. And you are not pinching the middle, you're adding wings to the tips...increasing surface area.
I've built a mega Mako 150x45 with 20mm concave and small constant rocker and rounded outline. Worked pretty good but prone to pearling in chop, needed flex.
Built directional strapless155x 48 swallow tail totally flat bottom and flat tail rocker with low nose rocker and quad fin. No flex in tail. Fins not positioned right and too vertical, anyway tracked in turns. But was really good mowing the lawn in lightwind.

If you are stuck on TT I would try traditional square with pinched ends like you have, to minimize splash, a 5mm concave and figure out how to make it flexy. I don't like your pointy tips, they are going to catch if you have low rocker,

Or build a copy of a shinnster strapless

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Re: Outline and tip shape

Postby rynhardt » Sun Apr 17, 2016 3:23 pm

and the waterline does not necessarily run through the centre of the board. It's all about surface area at a given speed.
if you want the board to turn better, move the fins toward the centre, but no further than your feet. The further the fins are from your feet, the bigger the leverage the fins have which you are fighting when turning.

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Re: Outline and tip shape

Postby greenkiteskier » Sun Apr 17, 2016 4:25 pm

I just built a few boards like you are proposing and I found the pinched waist to allow great upwind tracking. I also added concave 18mm , rocker moderate about 30mm,and rounded the corners. The boards are heavy and slow but great for light wind and perfect for learning on, and for teaching. Which was what they were designed for.They're around 44mm wide.

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Re: Outline and tip shape

Postby Johnny Rotten » Mon Apr 18, 2016 1:26 am

downunder wrote:Yeah Plummet,

why do you think it's not any of this? Or more? It can be really anything depending on the rider...Also, the pic is suggesting having both fins deep underwater (top and bottom fin), which is never the case (at least for me).

I am voting for a yellow line btw.

Capture1.jpg



The assumption it goes through the center of the board is also not always the case usually when on edge it's just a corner on the heels which is why the "wings" work so well upwind and for power holding. Look at some pictures Of people riding where the board bottom is facing you.
As you add flex to the tips. You will decrease the wetted area when turning hard and make it a bit more manoeuvrable but may also lose power holding for te same reason


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