Hello ALL,
- Who can tell me where the drag on the single to double concave high performance (h.p.) shortboards is LEAST desirable, but still existing ?
- What do top shapers do to diminish this drag on these h.p. boards ?
- What is the definition of drag? What elements are involved in creating drag?
Answers to any of these questions are niiiiice…
I know Bert Burger has talked about it, making comparisons to speedboats,
Any links to good discussion are welcome too.
Wouter OOSTING
I read a piece by Simmons, he said the hotcurls in tank testing dispayed too much drag, if surfboards had no drag, they wouldn’t work at all, drag is caused by water flowing over a course surface or around a very curved surface. Single to double concaves reduce the curves through them, thusly reducing drag
The drag exists mainly in your choice of board size (surface area) to the given wave size and power.
Too big, or too small, is draggy.
Bottom shape only makes a diff if you miss the choice.
Theory is good talk, but you can’t always be wrong, and you are hardly ever right every time you choose a board to paddle out.
In other words, don’t worry too much about it, get quiver and pick the right board for the conditions.
Hey Wouter,
Generally, I try to avoid double concaves because they seem to be too draggy (many customers complaints). I think the very pronounced stringer is the reason. All re-shaped boards (i.e. a clone with a single concave) proved to have a better performance than its previous version.
- What do top shapers do to diminish this drag on these h.p. boards ?
carefull and appropriate use of rocker and bottom contour comes to mind…
lotsa rocker = lotsa drag
and dont be a kook like many guys i see on the beach with wax and scratches and all kinds of shite on the bottom of their boards
search/archive is loaded…
Always found for less powerful/speedy waves, the less concave depth you want until you are at the barely perceptible range.
As the waves get stronger, you can use more/deeper concaves, but most rider’s just choose belly to V for control.
So…point of diminishing returns?
but on the other hand we also increase our surface area without increasing planeing area , so we now have more viscous drag without anything to offset it , unless we go narrower but that then changes things again …
like jim quoted …
if surfboards had no drag at all they wouldnt work…
drag is a control feature , and leedd alluded to the fact that it needs to be balanced against the speed range we are operating at …
all contours have an element of drag and an element of control …
all contours need to be balanced against each other …
redirecting water takes energy , if you can afford to waste the energy because you have an excess of power thats fine …
if you have very little power then you looking for very little drag …
turbulent drag …
pressure drag …
viscous drag …
balance the three …
you will always find shapers will most favour the curves that function best in the waves they surf and build boards for …
so forget the hype and brands and check out the boards that work well in whatever condidtions your trying to shape for …
regards
BERT
Who can tell me where the drag on the single to double concave high performance (h.p.) shortboards is LEAST desirable, but still existing ?What do top shapers do todiminish this drag on these h.p. boards ?
What is the definition of drag? What elements are involved in creating drag?
Drag is usually thought of as a force proportional to velocity and opposite the direction of movement.
Concaves INCREASE drag in movement. All concaves make motion is a straight line slower. However, there is a benefit.
Surfboards re-direct water as you flow through it. They push water down, and they part the water to the side.
If you go in a straight line, concaves push more water down and less to the sides. This causes greater drag for all surfboards operating in the under triple overhead range (meaning 99.9% of them, but tow-boards may be different).
The benefit is the surfboard sits higher in the water. So, you can apply torque to the board and turn it more easily. And, this effect is especially pronounced in turns. Boards with concaves carry speed through turns dramatically better than boards without concaves. The board is sitting higher in the water, and the force of the fin operates against a much smaller water displacement.
Keep in mind, surfers are supported by a force from water displacement, and a force from planing. Over all speeds up to double overhead, both forces (planing and displacement) are significant and relevant. The concaves bias the equations towards planing and away from displacement. Easier to turn, and lower drag in turns, but slower when not turning.
The fastest boards when not turning are those that create the most lift from displacement, and least from planing, or boards with rounded hulls in the middle, and flat tails.
Flat tails are always the least draggy. Add a concave under the front foot and you get a good turning board, add belly vee and you get a board that coasts through flat spots well…
Fins also cause substantial drag…
HTH
Men,
These are all very informative answers (I was hoping for)…
The reason I ask is because I had this wild idea in my head (always wanting to do something new/different/creative bla bla bla):
“Introducing air into the waterflow underneath the surfboard, thus reduce drag, thus increase planing speed and manoeuvrability of the surfboard”
Hence the question on which place drag underneath a h.p. board is least desirable…(no specific replies)
Imagine drilling holes in the back 1/2 of surfboard, from top to bottom, (somewhat in the direction of waterflow). This air introduction to the waterflow underneath the board should stop water from sticking to the surfboard.
Some questions pertain though:
If drag is desired, what does this drag do then? Steer the board, give hold, direction? How should I think about positive drag/control in a High Performance surfboard (NOT longboards, fishes etc…)
What is pressure drag?
Is viscous drag, drag resulting from friction between the liquid and the surfboard shell?
Is Turbulent drag, drag resulting from water turbulence, which sort of results in viscous drag???
Have a nice day folks,
Wouter
air induction as you described has been done and is covered in the archives…
pressure drag?
next time youre driving your car, stick your hand out the window…point your hand/fingers in the direction of travel…nice…then turn your hand and face the palm in the direction of travel…max pressure drag…somewhere in between is the rockered out relationship…its a function of area and fluid velocity…squared somewhere if i remember correctly…its been a while…
too much rocker increases p drag particularly in the entry
wrt the archives, there more about skin friction than any other subject…friction is such a drag 
Surfboard drag is often more a question of 'when" then “where” – a flatter board creates less drag when going straight than one with more bottom contour. When turning, bottom contour may create relatively less drag. A good example is the behavior of V in the tail area. Overall, most high performance, competition boards are fairly flat (other than rocker) or the contour is very subtle modification of flat. Making it complicated often does not make it better. Precision in simple, proven design produces reliable results.
Wouter, you can just copy the F-2 Formula board with all the air holes…
But you’ll find increased drag catching waves and paddling, plus plenty more spots for the board to leak when it gets flexed punching thru waves.
The increase in speed might be noticeable, but the increase in fragility and bad paddling even more so…
You don’t need more speed surfing. Instead, more skill is the best thing to apply.
So,
everybody says it is simple proven designs and more skill that is needed, any good instruction books or videos?
Wouter
heres one of the early ones …
i ran a brand back in 91 called air factor , built quite a few of these , the design changed several times , the pic below was taken in 91 on this board , in fact this was the first one …it survived a major clean out because someone else had it stashed in there rafters for the last 15 years and gave it back recently …
once we had the brand up and running , poto got a result on one in a contest in margaret river , some footage turned up in a surf vid of him surfing the box on one …
in the end i gave up on the concept , not because it didnt work , we still had a few bugs to iron out , but they were costly to build and being busy , it was easier to build what was most profitable …
a blast from the past , i think this concept still has merit , maybe it will get resurected again one day ???
regards
BERT
Wow
That is nice to see Bert, motivational !
Costly huh? Same story as for channeled boards?
Thank you