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Do parabolic rails really make a difference?
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littlefoot



Joined: 14 Mar 2010
Posts:
Location: NW Spain

PostPosted: Sat Aug 07, 2010 4:39 am    Post subject: Do parabolic rails really make a difference? Reply with quote

Hi,

Well what I was wondering is whether parabolic rails really do make such a great difference.
I know there's lots of stuff on it already but I haven't really found any convincing reports.

I'll soon be working on a new alaia project (promise I'll post pics) The last one was a parallel-rail shortie - 4'6" and this one's going to be a 6'6"x16" craft for trying to stand up on.
With 12mm birch plywood I bet it'll flex like a mermaid and give a joyous ride.

The thing is I've seen pics of traditional museum pieces with plain straight rails tapering down to a narrow tail. So if parabolic ones are so different, then why weren't they all shaped like that in the old days.

After all, those kids in papua New Guinea ride fat-tailed "alaias" and I can`t see any parabolic rails anywhere.

My experience in alaia riding is limited to riding prone on the 4'6" shorty so I'd appreciate opinions from the more seasoned riders.
Do you notice much more hold on the wave to make it worthwhile reducing that precious planing area?

And why didn't the Hawaians ever think of fish-tails either?

Aesthetically speaking, I prefer the straight rails & tails myself.

Thanx in advance, mates.
L.
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kid



Joined: 11 Jan 2010
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Location: Bells Beach

PostPosted: Mon Aug 09, 2010 2:02 am    Post subject: Reply with quote

I've been riding stand up and prone alaia's for nearly 4 years, and I've found that the parabolic rails make a huge performance difference. This is especially true for stand up surfing. While I can't claim to know the science behind it, it's really noticeable how much difference it makes. As for why the ancient surfers didn't use parabolic rails, I'm not sure. For fatter slower waves the straight rails work fine. But in a steeper wave they slide out easily. The parabolic rail hold in much better, but doesn't feel as fast. I guess this means it must be creating drag, or maybe it just gives the board a longer rail over the same board length. Anyway, its something worth experimenting with. I have tinkered with them extensively and in my opinion, they absolutely work!

Fish or swallow tails, again in my opinion, don't make any difference. They seem to perform exactly the same as a square tail of the same width.

Oh, one other thing....a straight railed alaia can be made to hold into the face better if you run a concave up the back third of the board. Combined with a rolled bottom, the concave increases the surface area of the board, without increasing the width. This creates pressure pockets under the board which effectively sucks the board down into the wave. There is trade off again, as anything which gives hold will also create a bit of drag. A top surfer like Rasta can ride a very traditional alaia with straight rails and a rolled bottom, but these do take a lot more skill!


Cutback on a parabolic rail alaia


Bottom Turn
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littlefoot



Joined: 14 Mar 2010
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Location: NW Spain

PostPosted: Mon Aug 09, 2010 4:08 am    Post subject: Reply with quote

Hello,
Yes, I'd read about the drag effect on a couple of sites or somewhere but I can imagine that would mean very little compared to fins.

So, about the rails, should it be a splayed out tail right at the end or rather a more evenly distributed curve coming down from, say, the middle/widest point of the board?

I've seen both kinds out there though the evenly distributed ones look better. I'm going for 15 1/2" at the tail just to get more planing surface. I reckon I'll need all I can get.

PS
Beautiful pictures! I hadn't noticed them on my e-phone this morning. Is it you on that board? Pardon my asking.
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kid



Joined: 11 Jan 2010
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Location: Bells Beach

PostPosted: Mon Aug 09, 2010 4:37 am    Post subject: Reply with quote

Yeah, thats me all right! Ha ha, it was a great day at a local pointbreak a couple of years ago. My brother is a whizz with a camera and he made me look better than I really am in these shots!

As for the rails, I find that on smaller waves you can get away with a fairly traditional shape and just flaring the tail a bit. As the waves get bigger and steeper, I run the curve more uniformly and further up the board. You're right about the drag from the concave, it's barely noticeable, and because it allows you to ride more powerful waves it really cancels itself out!

Here's a pic of the board I'm riding in these pics. It's 6'6 by 15 and 1/2 wide by 1' thick. You can clearly see the concave in the bottom.


And another water shot

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littlefoot



Joined: 14 Mar 2010
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Location: NW Spain

PostPosted: Mon Aug 09, 2010 4:54 am    Post subject: Reply with quote

A very nice looking board. Is it pine? It looks quite "unflexy".

We often get pretty good though crowded swells here in NW Spain. All kinds of beach breaks from very vertical waves to more longboard type ones (I mainly Lboard myself).
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kid



Joined: 11 Jan 2010
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Location: Bells Beach

PostPosted: Mon Aug 09, 2010 5:02 am    Post subject: Reply with quote

No, it's paulownia. It is a bit thicker than the boards I ride now (these pics are a couple of years old). It is quite flexy though!
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bgreen



Joined: 20 Feb 2004
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Location: Qld. Oz

PostPosted: Mon Aug 09, 2010 5:08 am    Post subject: Reply with quote

I've never tried parabolic rails myself and tend to ride a reasonably flat bottomed board. If wood isn't real expensive, why not make two identical boards, one with and one without parabolic rails, or make one board without parabolic rails, then after you have surfed it for a while bring out the saw and parabolise it.

regards

Bob
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littlefoot



Joined: 14 Mar 2010
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Location: NW Spain

PostPosted: Mon Aug 09, 2010 5:14 am    Post subject: Reply with quote

Ah, I can't get my hands on that kind of stuff. Plywood will float like a stone but it'll flex a lot more. Sour grapes Laughing

Also made a Hawaian Style Paipo (guitar pick) out of 9mm birch ply and it does well, albeit with flippers!


bgreen:

Yes, plywood is quite cheap in my area. With a bit of extra work I was thinking of perhaps making two with varying rail designs.

But now I think I'll do maybe two boards with concave and no concave. And really sharp rails.
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bgreen



Joined: 20 Feb 2004
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Location: Qld. Oz

PostPosted: Mon Aug 09, 2010 5:25 am    Post subject: Reply with quote

If you are working with thin sheets of ply you could still experiment. I have sent Rod some photos of sub 3' ply bellyboards which he will post up at some stage. These might be of interest as they are a different shape, again.

regards

Bob
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littlefoot



Joined: 14 Mar 2010
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Location: NW Spain

PostPosted: Mon Aug 09, 2010 5:50 am    Post subject: Reply with quote

I'll go for 12mm birch or fir ply. A 9mm sheet just bends too much under my weight and you cant get any decent concave on it. My guitar pick is 9mm with a crescent tail. I'll post some pictures of that one too when I get it all done.
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rodndtube
Dolphin Glider


Joined: 06 Jan 2004
Posts: 690
Location: USA, MD, Baltimore

PostPosted: Mon Aug 09, 2010 10:19 am    Post subject: Reply with quote

Some decent books to read on surfboard design:

Kelly, John M. Surf and Sea. New York: A.S. Barnes, 1965.

Orbelian, G. (1987). Essential surfing. San Francisco, Calif: Orbelian Arts.
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littlefoot



Joined: 14 Mar 2010
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Location: NW Spain

PostPosted: Mon Aug 09, 2010 10:44 am    Post subject: Reply with quote

I'll try and get hold of some of those books but for this one I think I'll just keep it simple and cheap. If it breaks just make another one and enjoy experimenting Very Happy

Thanks to all. As soon as I get some spare time, hopefully by tomorrow, I'll get to work and post those pictures.

happy surfing
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rodndtube
Dolphin Glider


Joined: 06 Jan 2004
Posts: 690
Location: USA, MD, Baltimore

PostPosted: Mon Aug 09, 2010 11:45 am    Post subject: Reply with quote

Littlefoot, I forgot to mention the design of the old Hot Curl surfboards. As I recall there is a discussion of the hot curls in the Kelly book. Kelly was one of the hot curl innovators along with Wally Froiseth and Tom Blake.

Also see: "Surfboards," by Guy Motil
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OG-AZN



Joined: 27 Jul 2009
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Location: Norcal

PostPosted: Mon Aug 09, 2010 3:37 pm    Post subject: Re: Do parabolic rails really make a difference? Reply with quote

littlefoot wrote:


The thing is I've seen pics of traditional museum pieces with plain straight rails tapering down to a narrow tail. So if parabolic ones are so different, then why weren't they all shaped like that in the old days.

And why didn't the Hawaians ever think of fish-tails either?

L.


Check out the photo & article towards the bottom of this page: http://driftsurfing.com/blog/?cat=94
That board had parabolic rails back in the 1800's & possibly a subtle fish tail going too. I don't have any experience with stand up alaias, but parabolic rails have worked well for me for drop knee & knee rides on my bigger (skeg less)ply paipos.
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Poobah
Dolphin Glider


Joined: 09 Jan 2004
Posts: 696
Location: California, San Diego

PostPosted: Mon Aug 09, 2010 6:06 pm    Post subject: Reply with quote

My theory... because parabolic and peanut shapes have a more sexual (Goddess) look to them, they may have been the first boards tossed on the bonfire by missionaries.

Plywood will float better if you add a 1/2 inch (12.5 mm) thick cork to the deck. I've made prone boards with cork and ply...haven't tried a standup model.
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