Can someone tell me why theres a belly in the bottom of some boards ? I would think it would cause drag to have that "Keel" down there . I had a board shaped for me I am very happy with it but it has this belly in it . 8ft. fun gun type shape for an older 48 bigger surfer 190lbs I'm also in fla. so I need a board for the crummier waves here . Got the hard rails I asked for and the double concave but if you put a straight edge on the bottom it has about a 1/2 in. belly in the middle of the back . Not the one created by the double concave but even sticking out further like a Keel or something .. Everything else about the board is perfect and I just think I need to have one more made and ask for it without the belly..
slight belly done by the right shaper works good, I have never heard of it with double concave though.
One of the best longboards I've ever had was Stu Sharpe out of the Rockledge T&C factory. This board had a little belly as well which, as he explained to me later, made the board a little more difficult to get up on a plane (bad for our mushy FL surf) but made the board a touch faster in the flats. He did say that he wouldnt necessarily put that on a new board today (the board we spoke of was shaped in 1998).
Consider this: Belly, Doom, and panels on the bottom of a board are some of the ways that a bottom can be configured to allow a surfboard to ride more deeply and more quietly in the water. Bottoms that are flat and concaved ride higher in the water but are relatively unstable. Round bottoms are very quiet and blend into the water hold their line beautifully. Dooms are used for a quiet entry and in the tail section a rolled vee facilitates rail transition. Panels are used to great effect on Rhino Chasers and rough water boards because the vees they form help the board track and keep it from getting skittery in choppy conditions. By offering less wetted surface they acuatually allow the board to go faster. Panels are commonplace on tails modern boards because make for very positive rail transition. This is a very basic look at different sorts of convex bottom configurations. Obvious there is a very important place for this type of configuration in surfboard engineering. The combination of convex, concave and flat surfaces on the bottom of board are what can make come to life or be an awful slug. Try and take to time to witness an accomplished shaper at work and see how the process goes. You'd be amazed at how much is going on that you can even see. It's the same way on the bottom of your board, though you sure can feel it. An experienced shaper can tailor something that will suit you and the conditions you surf if you give him half a chance. Respect your local shaper; the good ones have to build what will work for their clients or they don't survive in their trade. It's tricky business but there are some great artisans in the craft. Mahalo, Rich
I'd have to agree with Rich, the common belly (subtle convex curve) will smooth the ride of a board. The price for smoothness is a loss of a little bit of dynamic lift (skimming) because there is some lateral (spanwise) flow as well as the main directional flow. Just visualize a flat-bottom power boat (like a punt) skimming along versus a deep vee hull (like a tugboat) splitting through the water. The belly-type bottom would be like a snow dish skimming on the water. At first, the slow speeds would allow some spanwise flow off to the sides, but then once a certain speed is attained the spanwise flow reduces and an optimum flow regime is established (a rated hull speed, if you will). On the up side, once a belly-bottom (?!) gets going, they will keep trying to maintain the flow regime which would be its' own state of dynamic equilibrium. The outward result is a sense of unstoppable momentum. If the rider knows how to pick the right line, a board with this feature can potentially be INSANE! Now, if I am reading this right, I think the bottom contour that Speed Skeg is describing is a basic vee-bottom where a ridge splits down the middle of the board between two flat, or semi-flat panels. Maybe the 1/2 inch of belly "in the middle of the back" is forward vee. Anyways, the last time I was in Oz, a friend kept raving about this funboard of his; it was small so I tried it. After my first wave, I stood in knee deep water examining the thing, completely blown away how bitchin' the board felt. It was smooth, forgiving, and once I got up to speed, it stayed at speed. It was a "loaded dome" and it was obvious the builder optimized the flow through the bottom of this example of belly/awareness/art. Like Rich says, some shapers got the stuff figured out. It's very cool when we come across this stuff from time to time...
I like how boards with roll in the bottom find their way and "settle" into the wave as they aim down the line. Flat bottom boards skim the water surface and are fast but seem a little squirrelly at times. Concave has its place but I find a slight belly in the nose of longboards adds some stability when walking the board and riding the nose.
Do any of you use convex bottom contours (in combination with concaves and flats) for shortboards that are designed for places that have more powerful surf, where control is more of an issue, while staying away from convex contours in the same shapes made for smaller, mellower places?
I made a little 6' by 22" single fin pin with a convex nose and double concave in the tail like a bonzer. I worked, but i hav'nt surfed it much. I figured that the convex belly in the nose pushes water and the concave in the tail pulls the water, probably a simple way of saying what the previous fellers where saying.
I had a 7' hull-bottomed stubbie-well, hull up front transitioning into a double concave in the back.Not too fast but a loose, turning board.Required a lot of fin to get desired drive.A friend now has it and has surfed it to death in mostly beach break waves.He's ready for another!
From what I know, Rhino Chasers (9'6"+ big wave guns) will have no concaves and only variations of belly, roll or panel to them.
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