Contact   Imprint   Advertising   Guidelines

convex or concave sidecut?

Here you can exchange your experience and datas about your home build boards
User avatar
lieutenantglorp
Medium Poster
Posts: 169
Joined: Sat Mar 01, 2008 7:19 am
Gear: Any
Brand Affiliation: None
Location: San Mateo, CA USA
Has thanked: 0
Been thanked: 0

convex or concave sidecut?

Postby lieutenantglorp » Wed Apr 23, 2008 12:09 am

Building a finless lightwind plywood board. Convex or concave sidecut? What are the advantages and disadvantages of each? Snowboards use concave, surfboards use convex. Both turn good so will either one work on water?

fluidboards
Rare Poster
Posts: 8
Joined: Wed Apr 09, 2008 12:49 pm
Local Beach: New Brighton, Christchurch
Christchurch Estuary
Style: waves and cruising
Gear: PL twinskins
Homemade kiteboards
Brand Affiliation: Fluid Kiteboards
Has thanked: 0
Been thanked: 0

Re: convex or concave sidecut?

Postby fluidboards » Wed Apr 23, 2008 1:24 am

From what I can understand, a board with convex edges will work better without fins. I'm guessing it has got something to do with less displacement in the centre and more at the tips?

On a lightwind board I'd say the absence of fins is a good thing.

aeberl
Very Frequent Poster
Posts: 659
Joined: Tue Nov 22, 2005 10:57 pm
Has thanked: 0
Been thanked: 1 time

Re: convex or concave sidecut?

Postby aeberl » Wed Apr 23, 2008 3:34 pm

lightwind boards are all about early planing and thus depend on a lot of surface area and as little drag as possible. Therefore, you need a wide board with large tips (= large area) and very little rocker (= low drag).
The outline of the board has less influence on lightwind characteristics than on upwind performance and handling.
For upwind performance you want either a lot of lift from large fins (surfboard) or as long a rail as possible in the water. That's were the concave sidecut comes into play. It allows for more rail in the water when edging and the board will generate less drift downwind.
That was the simple part.... now to more complex issues:
Flex: for lightwind board it is best not to have any. Flexible boards tend to increase rocker when subject to load. You'll have to finetune the flex to your prefference, very stiff boards are hard on your ancle and knees, very soft boards are better in chop but not so good for jumping (flex kills pop).
Concave: the main effect concaves have is to reduce rocker (concave only between pads, not all the way to the tips). Flat bottom boards glide earlier than concave boards, but tend to vibrate a lot in rippled water which causes ancle swelling if user with very tight straps.
if you wand a good lightwind performer and not sacrifice other characteristics, I would suggest to have straight (parallel) rails between centers of your pads, 2 to 2.5cm three stage rocker (flat in the center), stiff in the middle and progressively flexy towards the tips. Tips somewhat narrower than the center, hard rails close to tips, softer (about 8mm diameter) tucked rails in the center.
I would not go any wider than 44 and not longer than 140. This will give you a good lightwind board without sacrificing parformance in chop and mushy waves, decent upwind performance and some pop. Wide tips, as in concave outlines, generate a lot or unconfortable spray.

User avatar
lieutenantglorp
Medium Poster
Posts: 169
Joined: Sat Mar 01, 2008 7:19 am
Gear: Any
Brand Affiliation: None
Location: San Mateo, CA USA
Has thanked: 0
Been thanked: 0

Re: convex or concave sidecut?

Postby lieutenantglorp » Thu Apr 24, 2008 7:49 pm

Thanks for the info. I think the Spleene Door outline is the right idea. Concave sidecut, but slightly narrowed tips for less spray.

HAMLINDP
Frequent Poster
Posts: 353
Joined: Tue Feb 06, 2007 5:50 pm
Has thanked: 0
Been thanked: 0

Re: convex or concave sidecut?

Postby HAMLINDP » Fri Apr 25, 2008 6:15 pm

If a dude is a 200 pounder, would you go longer than 140 in length?

I haven't glassed my ply yet, so I still have a chance to shape it. I already have my fabric (design) laminated to surface of the ply. Can you suggest a way to create a slight underside concave between the footstrap area? I was thinking about glassing a couple rolls of glass, close to each side, before my final glassing. Would this suffice? Any suggestions?

Thanks,
David :o

scklandl
Very Frequent Poster
Posts: 1603
Joined: Mon Sep 19, 2005 12:49 am
Style: all
Brand Affiliation: None
Location: scott klandl burlington, VT
Has thanked: 0
Been thanked: 2 times

Re: convex or concave sidecut?

Postby scklandl » Tue Jun 10, 2008 1:46 pm

other things to keep in mind

performance vs. pure application

I'll agree with Aebrl entirely in theory and Practicality

but...

concave outlines provide a really crappy ride. its unforgiving in the slighest chop and all it wants to do is go upwind. they are very rough on the knees

the bigger tips are bulky, which makes them heavy and cumbersome, both in the air and when turning in the water

only skimboards equal these shapes for LW riding, so the question you gotta ask is how bad do you want to mow the lawn?

IMO the north phantom is the best way to lessen the evils of big boards


Return to “Gear Builders”

Who is online

Users browsing this forum: No registered users and 119 guests