Surfing Waves

I've been trying to find the answer on this for some time but can't find any definitive literature of posts on this specifically.

How does the specifi depth of a concave affect the design elements or handing, tracking and what waves it's good for?
I've seen board that have deep concaves, or just shallow concaves but can't find anywhere that explains how the depth affects everything?

As I understand it concave has more ingredients than just depth!

Length , depth , direction /angle , acuteness of edge, , whether it has a Venturi feature across the concave or in change of depth>

The relationship with the boards outline and to the rails when you surf rail to rail.

Bad concave/ channels track severely, but can give extra down the line speed if you can lay the turn over.
The single to double concave with central V section to lay the turn on. Is my favourite on my longboard.
I'm going a little deeper and putting both a vertical and cross constriction in the cawing concaves to give a Venturi effect ( look up Campbell Brothers Bonzers) but the concaves are still note overly deep.

Since you are still recovering look up one of your countrymen Al Byrne and his use of channels, he was considered a master with and in making them.

Always go back to Goldilocks and the Three Bears. One was too hot, One was too cold, but one was just right. The best shapers work with the concave, rail edge, rocker, outline and blend everything together. You can not just look at one thing ( like how people choose a board solely by liter volume ).

I know you talking about concaves under foot by the fins, But coming from a Noserider perspective, sometimes to much concave under the nose of a longboard is not good. I've heard people say noseriders must have big concave, which is not true. It can be so much that it slows the board down too much or the pressure bubble it creates, bucks the rider off.

benjl wrote:I've been trying to find the answer on this for some time but can't find any definitive literature of posts on this specifically.

How does the specifi depth of a concave affect the design elements or handing, tracking and what waves it's good for?
I've seen board that have deep concaves, or just shallow concaves but can't find anywhere that explains how the depth affects everything?

The way I understood it is concave is used to generate extra speed. Boards for big powerful waves have less or no concave because they don't need the extra speed, those waves have enough energy in them to get all the speed you need.

This way you could conclude deeper concave is good to get extra speed for weak waves, but maybe this is too simple reasoning?..

Tudeo wrote: Boards for big powerful waves have less or no concave because they don't need the extra speed, those waves have enough energy in them to get all the speed you need.

I guess that reasoning is right because Brad Domke's board has No concave ......... No Rocker and No fins. It's all rail work.

Also I notice the fins makers but concave on their small wave / hotdogging fins, but keep them flat on their big wave fins.

waikikikichan wrote:Also I notice the fins makers but concave on their small wave / hotdogging fins, but keep them flat on their big wave fins.

Yes, that's the same principle, I guess. Here's a quote from the Futures fins site: "Flat foiled fins break free sooner, and are better at controlling speed. Often surfers prefer them in fast powerful surf where they do not need to create additional speed."

Ahh interesting, I know it's a complex balance with rocker and rails etc but can't find anywhere on the net that simplicitly says 'deepen the concave for more lift, better for small waves) etc.
That would make vague sense if everything else is constant.
I guess the vice versa would be for a vee, where the deeper the vee the more drag and cut it would have.

What I don't understand is why come high performance boards use deep and full single concaves ?

benjl wrote:What I don't understand is why come high performance boards use deep and full single concaves ?

I think because the need to 'control speed' becomes more important from say 2xOH and up. That's where the need for a Step up board starts.

But I'm not speaking from experience, 2xOH is about my limit in size..

From Surfscience.com:

Bottom Contour
Different Concaves for Your Waves
surfboard concaves
Double To Single Concaves Loosten The Surfboard
Knowing the different surfboard bottom contours and how they affect surfing performance will help you communicate with your shaper or local surf shop for your next board. You want to use the right equipment given your skills, the waves you ride, and how you want your surfing to progress. Two of the more important surfboard bottom contours to know and understand are the single concave and the single to double concave. Let’s dive in.

Single Concave

The road map of a surfboard with a single concave bottom will look something like this: The first 12-20 inches of entry will be either flat, have a slight roll, or have a slight vee; this is followed with a shallow single concave that will increase in depth until it reaches its max depth just in front of the outside fins; the concave then slowly decreases in depth through the center fin to the tail.

A single concave channels water from the front of the surfboard until it passes the fins and out the tail of the board. The design allows for faster surfing and works very well in large clean surf. It is not particularly versatile as it does not do well in choppy surf, but the speed makes it a very popular choice. A single concave will enable tighter turns, but it can sometimes stick to a wave face causing it to track and become less maneuverable. For this reason, many shapers will gradually introduce a double concave to their surfboards.

Single to Double Concave

In most cases, the surfboard will have a single concave leading from the nose and will gradually fade into a double concave as it nears the tail. The single concave upfront provides a good planing surface for drive and the double concave in the rear loosens up the board. The double concave will actually channel the water into two streams through the fins and out the tail.

The single to double concave is the bottom contour of choice for most modern shortboards. It utilizes the strengths of each design while muting their disadvantages. It reduces the tracking of a single concave while still allowing for a fast ride and a loose feel to the surfboard.

Here are pictures of the contours of the venturi concaves for my new kneeboard + a side view.




I am going to use a new variable fin system that will enable me to change both the toe in and the cant of the side bites, experimental or mental only a surf will tell

After reading those article posts I decided to do a bit of measuring of my boards, actually fascinating stuff.

My 5'10 which I had always assumed like a hypto and would contain a vee didn't. It had a flat nose, light single to deep single (maybe 6mm) getting deepest at the front fins and then fading to a flat exit tail. It feels like a really faint double but almost impossible to tell when looking under the ruler, maybe only a 1mm if at all. I was surprised. No wonder I found this board hard to control and turn tightly on 3ft+. I also guess it makes the design more accurate when it says ride 5-8" shorter than your short board as this would help the turning being shorter and thinner/narrower if I'd gone with a 5'8 version.

My 5'9 was a little more as I'd expected, a similar concave design as the 5'10 (similar outlines and models to start off with) featuring a flattish nose, gradual single which deepens through the fins. Maybe 1-2mm more shallow than my 5'10 which I guess would aid in speed reduction. Then in to a little vee off the tail which I asked for. Again, a very very slight possible double which can't be visually seen like the 5'10.

I didn't properly measure my 7'4 hawian board but it had a vee in the nose (hadn't seen this before), shallow single throughout the board in to a vee in the tail.

All very interesting stuff. This answers a lot of questions regarding a board for small waves which I have been searching for.
I think design-wise, if I could take that 5'10 but cut off the tail to a squash, square or diamond, deepen the concaves and significantly deepen the double concave and also add a little vee or convex in the nose then it would be a 0-4ft small wave machine that would turn easily and plane fast.

benjl wrote:All very interesting stuff. This answers a lot of questions regarding a board for small waves which I have been searching for.
I think design-wise, if I could take that 5'10 but cut off the tail to a squash, square or diamond, deepen the concaves and significantly deepen the double concave and also add a little vee or convex in the nose then it would be a 0-4ft small wave machine that would turn easily and plane fast.

If I took my corolla and put in a 350kw engine, changed the suspension, added wider tyres, a thick sway bar and a new steering set up, it would be a faster car....

Just teasing; I know what you mean but essentially you have designed a completely different board. You probably need to look at the rails and rocker a bit as well

Yeah I know, just hypothetically speaking I guess. The 5'10 is 33l and flat as. My 5'9 is 28.7l and has a lot more curve.

It was Just interesting as I always thought my 5'10 had a vee / double concave to aid with going rail to rail and explains why sometimes I've found it difficult to get release and turn in bigger faster stuff. It just gets a bit Tracky. Seeing the solid and deep single concave explains that a bit- let alone it's flat rocker and high volume.