I am going to be shaping a board (my first) My dimensions are going to be 6’3", 19.75, 2.5, flat rocker. Should I go single to double concave or keep the bottom flat. I am looking for speed. Current short board is 6’5", 19.25, 2.5 with a single to double concave (very subtle). I am 6’0" 190. New to shaping 25+ years surfing.
Hey Concaves are shaped to produce lift, so you can ride small boards. I would think added lift is not conducive to speed, unless the waves are weak or slow. Also, shaping your first board, there’s plenty to worry about, without having to try to get any concaves even and straight. So my vote is no, no concaves. Just keep it flat nosed to accelerating V off the tail.
If you are just standing in trim and placing yourself in position on the wave for speed; use the flat bottom. If you pump your board to get speed; concaves will give you the bite to push off from… Just general suggestions. If you go the concaves, then single is great high lift and small waves, double is good when waves get bigger. For the huge stuff, the latest tow boards I’ve seen have single con but they are a different bird; estimated/tested surface speeds up to 70mph in bursts!
Is there any basis in any other planing hull for Vee accelerating off the tail? Most boat hulls made for planing flatten in the rear (although Vee up front may be substantially greater). Same for jetskis, I just wonder what aspect of accelerating tail Vee makes it desireable in a surfboard, but not in other planing watercraft. Generally, accelerating vee will break up planing forces and reduce lift in the rear - sink the tail and slow you down. Adding drag in the rear doesn’t do wonders for turning either - increased drag behind the center of mass will work to keep you straight (in the extreme think of dragging an anchor). Now, for nose-riding, I can see it. http://www.blakestah.com/fins/
possibly the reason for v or accelerating v in the tail of surfboards but not other planing hulls is their need to go rail-to-rail, often and quickly - a need that is not as predominant in boat hulls, etc.
Slalom waterskis either have straight concaves through the rear or increasing concaves, but not increasing vee. And they need to roll side to side a lot and a lot harder than a surfboard. Cigarette boats also decrease Vee towards the rear, as do jetskis and virtually all powered planing watercraft. http://www.blakestah.com/fins/
right – but waterskis are very narrow compared to surfboards, thus there is little resistance to going rail-to-rail on them. I’m just speculating here – one of the better longboarders I know has taken to putting v in the very tail of his boards and he says it makes them turn better on big waves – I’m taking him at his word as to the results (I haven’t ridden his boards). There may be better explanations. Perhaps it’s due to the fact that surfboards are externally powered, not internally…power boats and jetskis can initiate turning forces by rudder or steering, while surfboards have fixed fins (for the most part, your system being an exception). Thus a flat bottom boat can change direction by changing the angle of attack on the rudder (or turning its prop on an outboard drive), and a jet ski can change direction by redirecting its water output – they don’t need hull shape to assist quite as much…
I think the power aspect has something to do with it. Vee in powercraft allow a more consistent, effective power transmission. I’ve been in a skimming type boat that was going way too fast for its’ hull shape and when the operator turned, the boat “spun out” and got sideways before grabbing again; OUCH! When it is done right vee in a surfboard goes INSANE, power considerations make the surfboard very sensitive to getting the shape perfect. Displacement hulls, like one of Skip Frye’s Gliders are a good example of a perfect flowing shape. On the water vs. through the water. It all depends upon where you want to be… I can’t imagine one of Skip’s 12 foot Glider models dashing/skipping/bouncing because it was shaped with a shortboard bottom and rails.
Wow! Good discussion going here. Remember the “DickKeating Speed Bead”? That one actually sorta worked, separating the flow of water across the bottom of your board, so you decrease water drag. V in the tail almost does the same thing, while loosening the board as you go faster and faster. With that, comes an automatic lowering of the tail…a good thing actually, as any lift in the tail at higher speeds just seems to cause the front rails to dig, pitching the rider forwards. Now I can truly believe concaves, when applied correctly CAN be faster than flat to accelerating V, but only for that designed boat speed that is ideal for the design. NO, I didn’t bet that either. Surfboards have to work pretty well from paddling speeds all the way up to 20mph, and for bigger waves, even more. The RANGE is lacking in concave bottom designs, that plane and do not allow for constant power. Funny aside here… I find concaves are fast, but they also increase surface area drag when banked over, so they slow down really fast when turning, making the board appear faster than it really is. Gotcha on that one, I can’t understand it either!
One of the things that prompted this from me were recent personal observations. I had a board made that came with rolled tail Vee (and my rotating single fin), and I hated the feel in the tail compared to other rotating single fin boards. Then, I looked at my favorite guns. I have an 8’6" and a 9’10" gun (OB SF and Mavs) both made by David Craig in SD. I never specified bottom contours to him, but both have very slight Vee in the rear hull that flattens towards the tail, hard rails in back, and a thruster setup, glassed on, with slightly smaller side fins than center fin. I’ve ridden both extensively in appropriately sized waves, and now cannot stand tail Vee. In riding these and other big wave boards, I am convinced this general class of hulls (Vee to a flat tail) works best for big wave riding, paddle-in style. I really appreciate the feeling of lift under my back foot for keeping speed through turns. The rolled vee gives more of a sinking squishy feeling. So, that led me to wonder when tail Vee is desireable, other than noseriders (to reduce tail lift) and rigid single fins (to provide a hull directional element). The modern competition shortboards seem to lean towards mild single to double concaves that flatten through the tail. From a hydrodynamic point of view, a flat tail should be fastest, but should also provide the most lift. High performance longboards are also coming with hard rails and flat tails. http://www.blakestah.com/fins/
Hey Excellent observation there, Blakstah. Now when can I find 4-5’ glassy uncrowded surf at OB? When shaping the boards, with all that tail kick needed nowadays, it’s actually impossible to sustain the V behind your back foot, much less out past the tail. Where the most tail kick comes into play, a true V out the back would be like a hook in the rails, causing real slowdown, and a roostertail. I think terminology needs to be applied here. On a surfboard, the max V is between the riders legs, under his mass. Behind that, the way outline template and rocker curve works, you cannot maintain the same apparent amount of V. For sure, some V is needed to help the rider bank the board over in a carving turn. My terminology “flat to accelerating V” actually targets the way a shaper has to tie the ideas together. I guess I should really say…"flat to accelerating V …and then back to decellerating V, if there is such a word.
I may be right, I may be wrong but it seems I remember the “Speed Bead” as one of Tom Morey’s brainstorms? He wrote an article about using various techniques to deflect water flow resulting in less wetted area which, in theory, resulted in more speed. He proposed using silicone sealant, wire beads inside folded tape, etc as methods to build speed beads. A sharp edged strake or even vee apex might accomplish the same thing but I’m not sure the original premise (less wetted area = more speed)is even valid. My recent experience with bigger boards would lead me to believe that MORE planing surface might increase speed. Proper rocker and contours are important. For what it’s worth, both of my 10’ Skip Frye gliders have nice speed and glide in smooth conditions but are so flat in rocker that in bigger waves with any kind of chunk, they can get squirrely and slap happy. A 9’6" Eaton with frontal belly, moderate nose rocker and exaggerated tail vee right through to the tailblock has not had those problems even in bigger waves. When being pushed through a bottom turn, the Eaton seems to utilize the tail rocker and exaggerated vee to rock back and bank. Shortening the length of board in water (for maneuverability) but allowing enough rail to penetrate and maintain control seems to be the result. That’s just my take. Here’s a pic of the Eaton Vee - it measures out at about 1/2" right at the tailblock. 
Hey John - what’s the fin set up on that Eaton? One thing you can say about him, he’s not afraid to push the envelope. Does some wild Zingers w/ huge double concaves in them (glasser’s nightmares…) I’ve ridden some Eatons that I liked, and others that I couldn’t get comfortable on… I think that on a wide (and or big/heavy) board, a bit of tail v is going to allow easier initiation of turns – whereas shallow V further up on the board has the opposite effect, more of a control feature (thus good on guns)…make the board track a bit. Same feature can have the opposite (instability vs. stability) effect depending on placement…
The lift from planing is strongly dependent on bottom contour. Even with cars, we know this - flat bald tires will hydroplane, whereas rounded tires require much much higher speeds. Bicycles never hydroplane because their tires are rounded. A half inch of Vee will decrease lift in that portion of the board by a lot, and distribute weight more in the middle, and less concentrated on the rails. My impression is that overall lift dominates resistance to motion on a surfboard - another way to think about it is minimizing the water you displace as you flow through it. Longboards increase wetted area but usually decrease resistance - they have more lift. I doubt there is much speed increase at all in moving away from a flat bottom (not that I dispute benefits to various Vee or concave shapes - just that lift and speed are not among them). http://www.blakestah.com/fins/
Hey Speedbeads could well have been invented by Morey. The first samples I saw in '68 were on the bottoms of Dick Keating’s boards. Front wheel of my road bike planes right up around 45mph, with weight back. Front wheel of my RM125 planed at 3rd gear middle of powerband, weight back. Mainly, we need to clarify what we mean by “SPEED”. It could be to make a slog board go faster in knee high waves. It could be to make a gun board go faster at Mavs TOH. More important, it could be to make a gun board DROP IN EARLIER at Mavs TOH. Kinda hard to measure. Assuming both surfers take off at exactly the same spot and kick out exactly the same spot, who is going faster…the guy who trims across the middle of the wave, or the guy who bottom turns into off the lip combos, with a roundhouse thrown in for good measure? I say the second guy, but most surfers say the guy who covers the least distance for the time goes faster. The first guy. See, gotta quantify.
the first tow boards were designed with concave taken from the skurfer with the guy working with brewer at the time.cancave works at high speed!
blakesta, the reason rounded tires hydroplane less is because they have a higher psi on the smaller contact patch. Not because they are round. wide flat tires will hydroplane more because they have a lower psi.
Keith - In photo, 3 3/4" O’fishl sidebites trailing edge 14 1/2" up with a 4 3/4" trailer in a standard long box 6" up. Also has worked well at head high+ Stables in Ventura with a single 7 1/2" cutaway and in double overhead+ with same cutaway + sidebites at Morro Rock. The board has seen better days but IMO, a great utility board and still a decent rider. Other dimensions: 16 3/4" nose, 13 1/2" tail, 23" wide. 
makes sense, some tail v on a 23" wide board, w/ a fairly narrow tail…
Erik, Your 25+ years of surfing experience should tell you more than anyone else can about what works best for you. Its oversimplifying things to think there’s one right answer for bottom contours, rockers, etc.(I make this mistake all the time). I vote for the flat bottom because its your first board and keeping things simple may work best. I think that as the volume of a board decreases relative to the riders size you can add concave to give it “lift” or conversely as the volume of a board increases relative to the riders size you can go into vee(s) to help control the extra volume. The waves you’ll be riding will dictate whether you need concaves for “lift” or vee(s) for control as well. If you go with “flat rocker” than you may not need concave (or much concave) which is in effect lowering the stringer rocker even more. Some people put salt on every meal and some people put pepper. Find out what tastes best for you. Good luck and have fun.