Hi Swaylockers, I have been a long-time lurker here. I have been building boards (mostly shortboards) for around 5 years. I try and read everything I can find on shortboard design to the point that I think my head is going to explode. It is such a great community here and I have learnt so much from so many of you. But with more knowledge always comes more questions.
Recently i have been doing a lot of thinking on concaves after reading the threads with the Maurice Cole links where he explains his flat planing single concave theory (hopefully you know what I mean) the thing is that a concave is not just a concave- there are so many ways in which it can be shaped in.
I started thinking about the way a concave is blended into the board and the rail-line of the board, If a deep concave follows the rail-line right upto the nose would it start pushing water as the nose area goes through the water until the mid-point of the board? - With the other extreme being more of a channel concave through the nose which has to start further from the nose and not go completely to the rail on the widepoint.
I have tried to put some of the theory onto paper to try and help to explain some of my ramblings- Also there are so many different possible types of concaves I have put some of these into drawings as well (obviously exaggerated so you can clearly see the idea) If any of you have any input on the different types of concaves and/or you have tried any of the following it would be cool to get some feedback.
I know that some of the CIS surfboards were using (and possibly still using) a tri-plane concave- I shaped a fair few of these with good feedback but I still don’t know for sure if it could be considered ‘better’ than a ‘normal’ single concave.
I have tried to keep the drawings as simple as possible (drawings as it would take me ages to try and draw them with microsoft paint with my limited computer skills) and so far just drawings of single concaves so not to overcomplicate things just yet and please excuse my lack of drawing skills.
All of those concaves will behave similar, but different. They are from the same family but different poeple in the family.
Ive been experimenting with different bottoms and have seen some of the articles you are referencing. In my opionion, ill say it again OPINON.
I believe the water would be “compressing”, i should note water cannot be compressed physics tell us this, all the way through the board. The water will pass down the nose follow the railline to the widest point, then be redirected out the back of the board. I invision this a very wide concave very close to the nose. This depending on your foil will add direction. You will feel pointed down the line more, but not as if youre locked and loaded flying in one direction. This also being a wider concave, with more water moving around it, will slow you down. A narrow shorter concave will result in the opposite. Less of a directional feel, looser, and much faster. The deeper the concave will effect drive and direction, similar too how the width will effect the preformance.
This is all coming from a hobby shaper as ive seen with my boards and testing. More experienced people will probably drop in and prove me wrong haha
Hydrodynamics is awesome! id love to see some of your work if you dont mind sharing.
Roundthebend we seem to be one the same wavelength got 2 single “continuous” concaves in the water and they work well. Kudu’s on your research, just eat this stuff up and hope this thread reaches out to others.
In reading your blog it seems the me you are thinking the concave thru the entry rocker, Always have been the molecule of H2O in shaping and “fade in” the concave as not to push or create drag, go easy and flow. Paddling is not the most important here; the board should not bog on drop in.
Thanks for posting some replies, sharing ideas and possible theories is an important step for many of us to start learning more and to take out board building to the next level
On some of my boards a few years ago i started sneaking the concave up the nose of the board, I was able to try one of the boards as one was bought by a friend of mine that I regularly surf with, the board was good but as that particular board was a slightly lower rocker design I did expect it to be faster than it was, also it seemed to hesitate very slightly while paddling and dropping into a wave- not enough for him to notice but I noticed it (even without an offshore wind). This was what made me start thinking more about where the concave starts and type of concave. Going back to the Maurice Cole video he uses the word catamaran to describe a single concave- I know this is not to be taken too literally but to illustrate my idea you never see a catamaran with the front of the hulls pointing inwards (like the bottom of the board if a concave is continued to the nose) again I’m kind of exaggerating just to try and get my point across.
If this is the case then in theory concave could be used further towards the nose on a board with a surfboard with a wider nose (like with some noserider longboards) although you would still get the problems of the board possibly getting hung-up on windy offshore days.
I’d really be interested if anyone has tried ‘convex tri-planes’ or ‘concave tr-iplanes’. I remember doing some research on the standard tri-plane concave and from what i found it was supposed to add an element of increased stability. I still sometimes shape in a very mild tri-plane in some of my boards, for me it certainly doesn’t seem to have any negative impacts although its hard to measure the difference without going more extreme.
Going back to one of the main points, in theory with this principle the concave could be started closer to the nose if the concave around the widepoint of the board was not shaped all the way to the rails- any opinions on this? Would it drastically affect how the board would turn?
Concaves, to me, make the board turn rail to rail better than a flat bottom. Again, this is my experience, but I put concave on everything since the first time I tried it (I’m more of a constant turner than a trimmer). I run my concave almost to the rail, and then I feather it in.
Think about this. You can use a concave to change the rocker of The Board while maintaining the original rocker on the rails. In other wards a properly done full board concave can give you the benefits of a flatter rocker while still having the rail-line curve for carving the wave. Cole is correct on how a Surfboard moves across a wave. Don’t think to much about the concave in the nose You want to think more on the “sweet Spot” The area of the board That will be in contact with the wave most of the time. The second part to think about is how the water moves off the Board. The nose should pretty much take care of its self. In other words. Get the body of your concave right and just blend in the nose area so you have a nice flow.
Hi artz, yes, I’m not really interested in putting the concave back up towards the nose but just trying to work out the theory of why it doesn’t work so great, and then adapting the theory to try and understand and progress possible designs with slightly straighter concaves rather than following the the boards outline to the edge of the rail.
I’m sometimes not very good at explaining myself at whats exactly going on inside my head.
You may have confused nose concave and full board concave. Short boards and nose concave do not play well together. With full board concave you can have some concave in the nose with little to no effect on the over all performance of the Board. The benefit of the flatter planing surface is speed.
Now think about this. You Have two different rockers to deal with one on the rail line and another in the concave. The apex on the rail can be different from what you have in the body of the concave. Play with that idea
so going off what artz said, does that mean tail development is whats important here? Different tails and the back 12" are what seems to make the most out of any board. So what does tail design change about a well developed rocker and concave or vee or even a double concave with Vee for that matter, about the ride?
Yes play with it. But do it in a methodical way. Use an outline that has always worked for you give it the rails that you like a Tail That you like now take that board and ad a concave that you think will improve speed and or whatever else you want to get out of the Board. Now test , test , test have friends ride the board have enemies ride the board. Have local hot chicks ride the board. Ride the Board with a Dog on the nose Now try it with a Parrot on your shoulder.
Ride it with different fins. Get the local hot girl to ride it nude( tell her it’s for the advancement of science)
Really small time, son serves as test rider under close observation (without hot chicks taggin’ along). Really looking for any test problems, other than hang up, tracking and sticky rails.
After all it was you who said “concave is our friend” HA!
Not sure if it’s because I’m old, but I’ve never liked the single concave. The double barrel type where there’s a slight vee in the tail is fine, but the single always felt strange, like it wasn’t stable, kinda unpredictable. The double barrel felt more neutral.
How ‘bout this, me’s knows of one “big guy” that isn’t afraid AND has the riders. More on that in a minute, remember all this isn’t new, check out this Simmons, which me do believe that it was Rabbit Kekai who saw the Simmons concave jobs in Hawaii and called ‘em potato chips. And there is some conflict in reports saying they were “flying out of control” or “mushers”. So goes the Simmons, at least the shape caught fire again!
ok, here is more of what I read: the board is small fish board…he says the under side of nose , had concave, then a ‘rolled’ flat spot…then dead flat to v in front of fins…finally flat out tail. - the board Abalirra fish that won a few contests.
If you like concave bottom design, have you seen - Ryan Burch’s Pink Fish vid on YouTube?! Omg! He runs his concave (single) from nose out the tail! But he puts a roll under rails too I think? Obviously, he started shallow at nose, and deep out back. His board seemed pretty lively! But he thought his rocker was a bit off… it wasn’t that good a vid, but it was decent. He was getting into those assymetrical board’s - that I’m thinking would be going south …not my cup of tea. Overall I would give a b + bcuz I thought he could have put less flip in nose, and tail…plus the saw he used seemed too easy. But, apparently he seems to like it.
I’ve tried two board’s w singles, and the one that had a slight concave in front of fin worked the best. I haven’t tried a double, but I’ll try one. T c and + 2
