Quote:
DeadShaper,
How does this all apply to single fin boards (short board)? Does this single to double approach still apply without having the side fins? Are these bottom contours as beneficial or more beneficial without side fins?
Gary
As a generality, most people would feel that the concave combos’ benefit is more pronounced with side fins. But that’s open to argument as tris and singles are different animals altogether.
A single fin can very definitely reap benefits from single to double concaves in the sense that the concaves direct water flow differently than flat bottom or vee’d boards. A single fin tri hull has ‘pumpability’ that is notcieably different than a flat bottom.
I’ve always felt as though concaves provide what I call an ‘implied edge’. By this I mean it can give you some traction to push against. If you envision a board with a softer rail and a flat bottom, and then you envision the same board with a soft rail but a concave underneath, I would venture to say the board with the concave will allow you a push point and edge effect giving you more speed through the same turn than it’s counterpart.
Concaves serve to straighten centerline rocker (or off-centerline rocker) opposed to a flat bottom board. A true flat bottomed board will have the same rockerline at center as it does to the rail rockerline. Vee’s lift rail rocker line, concaves lower rocker line wherever they are placed.
Concaves provide a straighter run for the water, bring the feel of the water closer to your feet on deck, redirect the flow of water (to some degree) and provide lift. The whole originalattraction to concaves was to provide lift in the quest for the faster surfboard. They can also accept chop smoother than a flat bottom but different than belly (round bottom).
To get back to your question directly…even though we are comparing aples to oranges in a sense, both designs have potential benefit from single and double concaves…IF that is the effect you desire. You also have to take into account what outline (planshape) you are putting on the board(s) as there are so many variables.
I will tell you this, I shaped myself a contemporary 7’6" round pin for Rincon one winter, and I made it a single fin. This was a day and age when everyone was riding tri fins. I recall people looking at me like ‘what?.now what is he doing with a SINGLE fin?’
Hey, I’m a boardbuilder, I can test and experiment all I like…I had a whole quiver of tris and more at the factory.
Anyway, what I did find as a chief difference was that my thrusters paddled TO the wave faster than my single fin, but the single fin DROPPED IN faster than the tri fins. Both designs had good early entry points: (1/2" @24" on the shorter tri’s, and 5/8"@30" on the 7’6" single). Just figure there was more water loading on three fins with more tail area than one slighter larger fin with less tail area.
A lot has been done with concaves over the years, in the 70’s I think it was Col Smith that was riding some boards that looked like wavy potato chips or corrugated plastic roofing they install over patios. The whole board had them. We made them here in CA, and they did their thing like any other design does it’s thing. During the 80’s I shaped many different types of concaves on a daily basis (for sailboards I’ll have you, but imagine tri caves, quad caves, concaves with planing rails, single concave speed boards, hook rails, on ad on). Even little concave slots called Opi’i’s.
Anyone remember Opi’i’s???
