Board Design: The battle of balance

[Garry]

Board Design:
The battle of balance
by: Marc Lefebvre

When designing a board there are design features that are in constant battle and must be balanced to make a good design. Balancing these contradictory features are what a board designer faces on a daily basis. It is important to note however that balance does not mean equal. The balance you achieve is based on what kind of design you are going for. For example a wave board has vastly different goals than a slalom race board. A wave boards design goals are looseness, turnability, and durability; a slalom race boards design goals are top end speed, control at high speeds, and upwind ability; a recreational slaloms design goals are early planing, easy turning, and control.

Some of the design parameters you fight with are "vee", "tuck", "outline curve", "wetted surface area", and "rocker", forget volume at the moment.

Vee
Vee causes the water to stick to the board more and when taken to the extreme can make a board hard to plane, but at the right amount will help with control in the top end. A flat bottom board although fast will be hard to control and will bounce a lot.

Tuck
Tuck on the rails controls how easily the board will release water when in a turn. Hard rails will be fast in the straight aways but when it comes time to jibe they will skip and bounce rather than bite. Hard rails also help with upwind ability of a board, hence they track better. Soft rails will not release water as easily as hard rails and thus will stick to the water better in tight jibes.
Outline
Rail outline decides the turning radius of your board. A real curvy outline will turn on a dime and accelerate quickly but not track as well upwind. A straight outline will track upwind like a yacht but won't turn as well or in such a small radius as a board with a curvy outline. Outline also has to do with where you put the wide point of your board. A wide point forward will help stabilize the board in the low end and top end of the boards speed but you loose early planing. If you move the wide point back you start to gain in early planing and jibing but may be hard to control at high speeds. If you notice most boards keep their wide points near the middle because this is usually a good happy medium.

Wetted Surface Area
Wetted surface area determines the speed characteristics of the board. Maximum surface area aids in early planing but at the sacrifice of top end speed. Minimum surface area gives you maximum top end speed. This is why speed boards are hard to get onto a plane but once you do they take off like a rocket. Finding that top end speed and early planing are tough factors to maximize.

Rocker
Rocker works with the outline curve to determine how turny your board may be but the final goal of rocker is to provide speed in rough conditions. Although a flat bottom board would be fast, it would only be fast on flat water. Introduce a few bumps and this board is no longer fast. Add some rocker in the tail and you'll get the speed back. Too much rocker will cause the board to be slow but for wave boards this is what you want. Wave boards use the waves power to propel itself while slalom boards rely on sail power and need less rocker. Nose rocker helps you when you are in steep chop and you don't want to spear any incoming waves. Extreme nose rocker is usually found on waves boards and moderate nose rocker on bump and jump boards but not usually on slalom or course boards. I have always felt that a little more nose scoop on Slalom board would help with their down wind ability and it the least give you more security of not going over the handle bars when you are submarining. Just my opinion of course.

With these often conflicting variables you have decide what the design goals of the board you want are. Once you have that down it is just a matter of finding that right balance. If you can't find what you are looking for you can always make your own. Many board makers today started that in the business because they were unhappy with what was available to them. Apparently many agreed and thats why they are in business. Good luck and may balance be with you.

[windego]

Hey Guys
Can you give me a basic rocker, profile and quad fin , strap location that is more or less good to go for 60cm wide?

I assume rocker is flat till front foot and then about 6in to nose on a 6footer.

I really appreciate your help in advance.

Cheers
Stan
http://windego.ca

[Garry]

Hey Stan,

Ok here is a very basic, but successful setup.

Outline
With at nose- 7"
With at 50%- 60cm
With at tail- 18"

Rocker
Tail to 27" off- Flat
From 27" off Tail Gradual rocker to Nose -6.5"

Profile
3.5" Thickness from tail to 50% of board length, from there taper to 1"
Top and bottom can be flat

Fin boxes Measured to rear of box
Rear 3" off tail
Front 20" off Tail

Fin Boxes Measured off Rail Apex to Outer edge of box (center of box)
Front and Rear 2"

Footstraps
Rear insert about 4.5" off tail and about 5.5" off rail apex (6.5" spread)
Front strap screw off rail 3". About a 45 degree and angle for front straps. Total stance width between rear screw of front strap and front screw of rear strap (the stance) about 20"

This is an average if you were to measure boards from several brands. My 2 cents, go for a tri instead. If so move front fin box back one inch.

Ok I have given away enough now. Enjoy building! Take a look at the Tech section for basic step by step directions.
http://kiteracing.com/Shaping_Room.html

Garry

[windego]

Hey Gary

Very generous of you to share the details....thanks.

I have a rocker table setup so I think I will bag on some corecell top and bottom.

On your building notes you do not discuss that or what layup. Without the corecell I would think at least on the deck there would be strength problems. Another option would be wood veneer which I did for a surfboard and tuned out surprising stiff for such a thing adddition.

Are you guys coming to CORK in Kingston this summer?

Cheers
Stan

[Garry]

I left the layup similar to a surfboard. 2 layers of 5 oz glass top and bottom with additional in the standing and footstrap area. Additionally, reinforcement around the fin boxes. This is the easiest for someone to build without a rocker table and vacuum. For you, 1/8 HD foam is a great idea top and bottom with a layer of 2 oz glass in between the core and HD foam. Even a thin veneer over the footstrap/standing area would really help! Keep us posted!

Garry

[windego]

http://windego.files.wordpress.com/2011/04/frontenac-islands-20110430-00075.jpg?w=614&h=460

Progress.

[Garry]

Looking great! I took the liberty of posting your pics.

[windego]

[Mike Pacey]

Nice Work thank's for showing it
http://forum.bestkiteboarding.com/viewtopic.php?f=9&t=10796

some kitespeed board info
http://forum.bestkiteboarding.com/viewtopic.php?f=9&t=10796

[windego]

Mike
That is one thick beast you are working on. Over the years here have been  a lot of problems using that pink extruded foam on surfboards and windsurf hulls. Even though it looks and feels stronger then the expanded bead crap like I am using it actually has a tendency to delam from the skins. So under your feet areas make it really stiff so it cannot be compressed. I suggest some carbon as a last layer in that area. Also do not leave it in a hot car as the blowing gas will want to get out.

Good luck and show off your progress.

Cheers
Stan

[Mike Pacey]

Me to Stan had problems with extruded foams please post some photos of her on the water next
Here is one of my new speed boards that’s sorted




Do I make a race board next ??

[windego]

That speed board looks really sweet man. Respect!

[Garry]

Really nice carbon work! It looks similar to Paul Menta's original Speed Taco that was built by Dereck Camacho.

More info about it here:
http://dcboardz.com/speed.html

[windego]

Hi Gary
What is the pro and con of fin cant on the front fins?
Stan

[Garry]

The way it has been explained to me is that CANT is similar to the upward angle on a large airplane wing. Dihedral Stability. It allows the airplane to "settle" and not want to roll as much. So if you have a narrow board and you are running big fins, the cant will help keep the board from rolling upwind and throwing you off. The downside is that allot of cant is "drag" (non ideal flow angle to create lift) and not ideal for maximum performance. So when a board gets to 69 cm, you can hold 42 cm fins vertically without too much difficulty. But a 59 cm board would be all over the place, especially without a good bit of cant, adding to drag which equals stability.

Garry