I was thinking about concaves and compsand boards. Bert uses flat bottoms on his boards. I was thinking is this merely a production convenience, that Bert is trying to sell as a performance enhancement? Perimeter stringers are a production convenience but also definitely a performance enhancement, so he’s probably onto someting. So I thought why do thrusters have concave in the first place? The first thrusters were thick, flat rockered, wide tailed with vee – basically a development of the twinfin fish shape with the vee serving to make the board go rail to rail better and to control the width and volume. Pretty quickly people figured out that thrusters really surfed well in the pocket but all that volume and width was stil hard to control, so tails got narrower, more rockered and thinner – you didn’t need the vee any more because the volume and width was gone and narrower more rockered tails went rail to rail easier. But more rocker meant less speed though turns, so concave gets added to the package and now you’ve got more squirt through turns as water flows faster acoss the middle of the board, and you can take advantage of increased rocker to do more critical rail to rail surfing, without loss of speed. It all works nicely together and modern surfing is born(Thanks Greg)
Now I look at compsands - why don’t I need concave shaped into the board? Flex is the key, the board will hold in the pocket, because the tail rocker will increase under load so you can have a flatter tail rocker to give you drive through turns rather than the concave that a more rockered conventional board needs. Flex also means you can do a morph bottom so you can get squirt through big turns as a concave is induced as the board flexes under your front foot. The tricky part is tuning the flex in the tail so you get the right balance between drive in low load and control in high load. Too little flex and you won’t be able to surf in the pocket and the board will surf flat like a fish, too much and you lose drive.
Anyway that’s my thinking at the moment. What does the panal of experts think?
Concaves will be induced via flex…if a board is built to flex in a bottom turn, and it has a flat bottom when not turning, it will morph into a concave bottom when you turn.
Normal comp boards with deep concaves and 2 inch thickness actually reduce concavity when you turn from flex…
Concaves would also slightly effect the flex of the board. Something flat flexes much easier than something that is domed in the middle. I’m sure there are ways around it but just another variable to deal with.
Here’s what Bert said about it in the “Where is Flex important” thread
Quote:
whats the benifit of a concave on the bottom of our board ??
when do we use the concave ??
why do traditional p/u p/e boards go better with concave bottoms ??
because p/u boards have there rail line flex off in turns , a flat bottom turns into a v bottom so to speak and will lose a certain projection out of a turn , add concave to the tail and it ends up flat under load on the inside rail but still releasing water nicely on the outside rail …problem solved !!!
not entirely , you still have to deal with the concave when your not using it …
while trimming on the flat you have a bottom curve that really only wants to work best when on the rail hard …
a different form of construction allows shapes to be explored not possible with p/u p/e …
get some paper to form a concave like it was a concave deck , now bend it in the middle as if you were standing on your deck and the nose and tail was being supported …
what shape does it go into???
concave deck flat bottom surfboards …
fast when flat , then when you load into a turn and flex the board the bottom starts to concave ??
yep flat when you need it and then concaved when you need it
Ive never been that sure that concaves in the amount that most people refer (less than 1/8 inch )do a lot
Ive built identical boards one with concaves one with more flex,I gota say flex seems better for me
Flex is something that does seem to work
Think about the average wave face its ever changing in shape and steepness it can also range from smooth to very bumpy and you spend all your time on the wave trying to move all over that wave face as much as you can
Nature has a way of fairing out concaves and nature also has a way of using flex
Ive never been that sure that concaves in the amount that most people refer (less than 1/8 inch )do a lot
I’ve never found a good competition-style Pu/Pe rider that didn’t prefer concaves. Especially the guys who shape their own, then you end up with a much thinner board with a much deeper bottom concave (all center stringer boards).
I can definitely tell a 1/8" concave from a non-concave in a largely flexless board…when the boards get in the flex range the concaves need to be much deeper, but the boards don’t seem to last very long (all referring to single stringer foam/glass boards)
yah i got some, for real… the 1 15/16" 6’6" that i built i can almost bend with my hands… the rails are seriously thin (at least for what i usually ride). another factor is it was the first board i made with rr epoxy which seems to be much more bendy then the fgh 2:1 that i was using before… how does it compare to a pupee… not really sure since like i said i have never really ridden a board that thin in a long time. but the board works well, has a few strange behavior problems but i think i set the fins about 1/4" to far from the rail towards center… passed it around really fun rocky point yesterday and guys were really stoked on it. i think when push comes to shove if you could do a blind test people enjoy riding anything that is around the same dimensions that they are use to… i have really noticed a change in the air this year in attitudes towards “different” boads. people seem really intrsted in new stuff. people are buying/considering buying surftechs, talking about nev jumping on boards, tripping out that ther are $1400 Lost boards at the shops, have actually seen vents on other boards… consider this. when my turck pulled away from rockys there were four guys in it, 6 boards, 5’10" quad poope, 6’1" merric single fin poope, 5’10" surftech, 5’10" Jc poope, 6’6" balsasand, 6’8" balsasand…
oh yah, pinhead, my latest four boards all got concave decks, they will be finished up in a week or so so i’ll give my report. it is actually really easy to shape the concave into the deck (i was a bit worried)… the 6’6" that i mentioned before convinced me that it is possible to get a board bendy enough to actully take advantage of a concave deck…
oh yah, pinhead, my latest four boards all got concave decks, they will be finished up in a week or so so i'll give my report. it is actually really easy to shape the concave into the deck (i was a bit worried)... the 6'6" that i mentioned before convinced me that it is possible to get a board bendy enough to actully take advantage of a concave deck...
Jjp,
how deep are your deck concaves?
How close to the rails do you carry your concaves?
(i.e. if I use my rail tool to markoff where to start my deck concave, 3" from rail?)
yah i got some, for real… the 1 15/16" 6’6" that i built i can almost bend with my hands… the rails are seriously thin (at least for what i usually ride). another factor is it was the first board i made with rr epoxy which seems to be much more bendy then the fgh 2:1 that i was using before… how does it compare to a pupee… not really sure since like i said i have never really ridden a board that thin in a long time. but the board works well, has a few strange behavior problems but i think i set the fins about 1/4" to far from the rail towards center… passed it around really fun rocky point yesterday and guys were really stoked on it. i think when push comes to shove if you could do a blind test people enjoy riding anything that is around the same dimensions that they are use to… i have really noticed a change in the air this year in attitudes towards “different” boads. people seem really intrsted in new stuff. people are buying/considering buying surftechs, talking about nev jumping on boards, tripping out that ther are $1400 Lost boards at the shops, have actually seen vents on other boards… consider this. when my turck pulled away from rockys there were four guys in it, 6 boards, 5’10" quad poope, 6’1" merric single fin poope, 5’10" surftech, 5’10" Jc poope, 6’6" balsasand, 6’8" balsasand…
oh yah, pinhead, my latest four boards all got concave decks, they will be finished up in a week or so so i’ll give my report. it is actually really easy to shape the concave into the deck (i was a bit worried)… the 6’6" that i mentioned before convinced me that it is possible to get a board bendy enough to actully take advantage of a concave deck…
Hey jjp, Yes the RR 2000 formula is not quite as stiff as the FH aluzine but as far as flex is similar to pupee. The 1980 has a similar stiffness to the FH…call me if you got anymore questions.
basically what i did was shap the board with an almost flat deck to the point where i would normally call it ready for the top skin… then mark where the curve of the rail goes flat, you marking gague would work… next take the planer and run an 1/4" deep or so cut right down the middle of the deck, then i run an 1/8" or so deep cut down each side of the initial cut… then i put a sheet of 150grit on a really soft sanding pad and keeping my fingers in the middle of the board sand away… turning the side lights off and on one at a time really helps check for evenness… i have been ending up with about 1/4" deep concaves… we shall see how they go…good surf this week so things are on the slow track,
Not to be demeaning or anything but just for me personally…
I don’t know about all this flex flat to concave and back nonsense
But I do know that I’ve been riding a twin nose double bump bat tail Alexander PuPe gemini for the past two years and hands down it flat out blows by any other design hard soft etc etc I’ve ever test piloted…
With a 1" nose concave between the hulls blending into a 1/4 full bottom concave 24" back from nose on thru, it has the most concave I’ve ever ridden on a surfboard and still be in control at very high speeds. Probably has to do with it’s reverse profile wide nose narrow tail and the quads in the back but with a 3" thick domed/stepped deck and thin sk8 rails it’s exactly opposite of what you are talking about. But everyone who’s tried it says its a bar of soap ride on a thin film of water fast. It’s what I would envision riding a air injected Morey would be like… And yes you have to learn how to ride them…
So far especially to me this whole flex pursuit of the mutating board has been a panacea for the imaginative… i.e, not any better than what I’m already fooling around with design wise…
I’d prefer to have a defined parameter(good or bad) to structure my surfing around not something that will do something different everytime I ride it depending on how it’s fitting in the cure where my foot happens to be a 1/4 or so here or there or whether my center of gravity is forward or back of my big okole a fraction here or there. I really do not want a board making up it’s own mind how it wants to react when I least expect it. Trying to engineer flex to be adaptive to every wave and riding position seems beyond the average bear versus building a board with engineered flex for a specific purpose, specific wave…
But that’s me I just try to ride’em to the best of my ability till I figure them out. Seems like that would be a challenge if the board was smarter than you in what it wants to do in any particular part of a ride.
I don’t know about the morph bottoms and what not (although I find it interesting), but if nothing else, deck concave just feels good. I started putting them in my boards around the early eighties and never looked back…I never liked domed decks that much to begin with.
I don’t need any explanation to make me like them, but they do lower your center of gravity, and stiffen the board up a bit.
Hey Oneula it’s all about personal experience. How does the rail up front on the gemini flex? like if you layed the board on the grass put your knee on it and pulled on one of the hulls does it move?