i am planning on turning a 6’2" c into a 5’4" saucer type thing, wide all the way around and super flat rocker. what are the benefits of deck concave? what are the downsides?
Concave decks came (and went) a long time ago. Sank without a trace, apparently.
That said, good for you to experiment. Every design variation has a place, though few may consider a variation in proper context and realize its correct application.
Benefits: maybe more comfortable lying on them; may “hold” your back foot in place better; concave at the high-stress back foot area may put the glass in tension where it’s the strongest.
Disadvantages: minimizes overall volume thus may not paddle well; transition from concave to convex rail may chafe; requires you remove the topmost/strongest portion of the foam blank.
stu kenson does them…
Decks can be concave in a fore and aft direction, or across the board. Whichever way a deck is concaved, the result is a lower riding position, which gives the rider better control over the board.
The parallel profile which I use on all my boards uses the principle of fore and aft deck concave to achieve a relatively thin board. The results are a significant improvement over boards with tapered profiles and flat decks.
A board which has concave across the deck is a spoon. The advantages of a spoon in terms of a low riding position are the same as the advantages of a parallel profile.
Buoyancy is not an issue for boards with concave decks, it can be tailored to suit, just like with any other board.
Concave decks are alive and well over here Mr Honolulu!
From my experience .25 inches or so of “spooning”, you won’t notice a difference. If you really spoon one out though, you will lower your center of gravity enough that it will affect the performance…it will make a board a lot more stable but slow from edge to edge (you’ve lost leverage). Maybe you will like it on long carvey turns but it will feel very stiff otherwise. You can screw with rocker to overcome the stiffness but why sacrifice float for stiffness?
If you spoon it to the point where the board begins to flex a lot (roughly 1/2 inch of foam or less between your feet and the water) you might feel some of that. Depending on the shape of the spoon you might control where it flexes and when (a subject discussed at length in the Archives).
In the end I found they were very uncomfortable to paddle and somewhat pointless for a standup board unless you were experimenting with flex.
Our experiences seem to differ markedly.
In my experience, surfing a board with a lower centre of gravity, one has more leverage than on one with a high centre of gravity. A board with a high centre of gravity cannot be surfed from as close to the rail as one with a low centre of gravity. Thus a board with a low centre of gravity is looser, not stiffer. I can find no basis, theoretical or practical, for the idea that a board which is thinner is stiffer.
You also mention that a board has to be half an inch thick before it begins to flex. This is not true. The flexibility of a board depends upon its length to thickness ratio, not just its thickness. I have boards 2 inches thick which flex up to three inches, and which are very successful.
The Greenough spoon is a classic example of a concave deck. The advantages of the spoon are well known.
There is no need to ‘screw with rocker’ or ‘sacrifice float’ to achieve a good all round concave deck performer. It is simply a matter of careful design.
Please remember that I surf boards with concave decks all the time, and have been doing so for many years. My experiences go way beyond the purely experimental, and the concave deck boards which I produce are eminently practical, well tested, and user friendly.
perhaps on your longer boards concave in the deck might, in fact, be a good thing.however, we have found on boards up to 7’8" it tends to do the things lee v. mentioned-and this guy is talking about a board under 7’.
When I write something, I am fairly careful about what I say. I try and frame my response to the question and define my terms…I was discussing spooning or dishing out the deck not thinning the board or fore-to-aft “concave”. The affects of losing leverage means it is more difficult to rock the board from rail to rail. It has nothing to do with placing your feet closer to a rail. It also has nothing to do with the ability (or inablility) to put more or less weight (or force) on the rail. It’s why a thick board is “tippy” and a thin board is not. It’s why trucks and boats with high centers of gravity tip over or capsize. For all the surfers I know, not being able to go from one rail to an other quickly is called “stiff”.
The question asked was regarding a sub 6’ board. Its been my experience that about .5 inches of foam and stringer on a 6 foot board (stiffened by 2-inch thick rail pontoons) is about where you start to really feel the effects of flexing.
I have built and ridden several flexy kneeboards like Veloce and the “spoon” is a means to an end only. Those boards are about flexing rail rocker, and twisting. The pontoons or rails are there for stiffening beam effects, to give the forward rails some volume to avoid catching. For George, anyway, float was probably just a bonus. They were not designed to be stood upon nor could they function properly when stood upon.
To get a 6 foot, spoon decked standup board to go rail to rail as easily and quickly as a full decked 6 foot board you will indeed have to “screw with the rocker” (either stringer, rail or both). Oh yes, you could also narrow the buggah up to loosen it also (mea culpa).
If you put a 2- to 3-inch deep, 18-inch wide trench down the middle of one of your boards you will very likely come to the same conclusion I did.
“My experiences go way beyond the purely experimental, and the concave deck boards which I produce are eminently practical, well tested, and user friendly.” I’m sure that they are and if Gatordave built a 6’ spooned foamy it would probably be about as loose.
The Greenough spoon is a board under 7 feet, as are the 5’9" and 6" spoons which I build. Please explain the theoretical basis for your idea that a board with a concave deck is necessarily stiffer. I cannot find any such reasons, nor have I experienced anything like this on my 5’9" spoon or 7’ standup boards, in fact I find that they are definitely looser.
Thanks in advance.
PS The attached picture shows a pair of ‘loose’ concave decked single finned boards, one 7’9", and one 8"5".
With all due respect Roy, neither of those boards are anywhere near “spooned” enough to qualify as a “Greenough” anything. I think my previous post covers your question…
mot theoretical basis, but fact from expeirence. but then again, what we ride are much different than what you do, so who is to say…on a sub-six foot board i would be very cautios as to how much spoon i run through the deck(less is more…)
Thankyou for your reply.
A concave deck is a deck with concave in it, whether or not this concave is fore and aft or athwartships. The effect of a concave deck is effectively a thinner board in the riding position(s). You stated that a thicker board is more unstable, and ‘tippier’, due to a high centre of gravity. Two boards of the same width and rail section, but of differing thicknesses in the riding position, will both require the same amount of weight on the rail in order to roll on the fore and aft axis. initially, at low angles of heel, there will be very little difference between the thick board and the thin board, as the centre of gravity will not be very different in either case. When the angle of heel becomes greater, the centre of gravity of the thick board will shift outboard abruptly, resulting in a sudden increase in the angle of heel. This characteristic is not desirable as it leads to control difficulties, but is apparently the ‘looseness’ to which you are referring.
Your assertion that "to get a 6 foot spooned standup board to go rail to rail as easily and quickly as a full decked 6 foot board you will indeed have to ‘screw with the rocker’ " is misleading. Both boards will require the same input to initiate roll, and all that is needed for the thinner board to increase roll at extreme angles is to move the riders weight outboard. For a standup board this is difficult only if there are side pods in the way, as in a spoon. That is why I concave my decks fore and aft in standup boards, to keep the rail clear for the rider’s feet as he moves his weight outboard.
In practice, the thinner board is much looser at extreme angles of heel than the thicker board, because the looseness of a thick board increases so fast at extreme angles of heel that it is all but useless due to control difficulties. A thin board neither gains nor loses looseness as it increases its roll angle, and can thus be ridden at higher angles of heel due to the fact that control over the heel angle is retained.
I am sure that is why competitive shortboarders prefer relatively thin boards.
Kenson board my friend has is a Frye style fish…nothing like any of the wooden boards described above.
I didn’t say that those boards were ‘Greenough’ anything, and in the picture it is impossible to see how much concave is in the deck! Please read what I have actually said, not some ‘potted’ version of your own!
The theoretical and practical results of deck concave apply to boards of any design.
Lee – thanks, i wasnt thinking of too much concave, maybe only 1/4". i am really just interested in it because i want this board to be wierd as hell.
roy – the spooned kneeboards work well because they are kneeling. i dunno about you, but i have found the kneeling i can apply so much more pressure and really apply myself to banking the board without too much worry of instability. standing would maybe not cause too much of a problem if you were turning from the tail, but i could see how a dep concave would hinder the rail to rail performance.
anyone else interested – i will be concaving this deck, but shallow, like 1/4", hopefully it will replicate the feel of a skateboard, as this board is gonna be nutso, 5’4" x 18" n and t, and 21" w. a perfect saucer. twin fin and single.
well , i really like concaves from a performance perspective…
i tend to disagree with you lee v …
i found it made it easier to bank onto the rail,you had more leverage , because you hadnt used all your ankle movement range…closer to the bottom of your board so more sensitive…
a thicker board takes longer to respond…
i really feel part of my board when im in the concave…
loss of volume isnt an issue if its wide…
ive also found the concave makes my board flex less , because of the corrogated effect…
because it flexes less i can go thinner and more sensetive,
youd be surprised how slow you have to be moving before a loss of volume becomes noticeable…
if your in knee high surf then down to ankle high foam dribble heading straight to shore , then you will feel the effects of low volume…
but if you have enough ability to work your board for speed , then you will benifit from concave…
As always, a really nice board Herb.
Sure you’ve say it before, but, have your boards the same weight of a modern foam/poly standard board?
Nice work again! It would be nice to test one of your boards, or just see it in person. Let us know when one of your team riders come to Europe Bert!
On concave decks, i only tested one, the board paddles as a thin board, but once you’re riding the wave, it feels like a thicker board, sure, and your feet seem like integrated with the board. I felt that the concave deck give you a better response of the board, and i liked the feeling, but with the board i tested, the take off was very late due it’s low volume.
I would like one of Stu Kenson’s Mutant shapes, i think Rob Machado rides one in Shelter.
I too don’t understand the “less leverage” comment unless perhaps that is for super deep spoons where the center of effort is below much of the rail.
For shallower deck concaves, like Bert’s, you will have more leverage over the rails. I wrote this a long while back, it’s something everyone can try at home. Your bathtub is a concave deck; stand as though your surfing your tub; put your toes near near the transition to the vertical sides; stand up straight; now slowly lean forward. The pressure you feel on your toes translates into added leverage on the surfboard’s rails.
This exercise may also explain Lee’s comment about less leverage. Imagine the bathtub as an deep spoon. What effect is your leaning going to have on that bathtub? Not much, you’re too far below much of the rail. (Of course the bottom design can be changed to let the tub (er…spoon) move from rail to rail.
Does this make sense?