Surfboard ~ Single Concave Location ?

Hey Sways,

The configuration picture for surfboards is inexhaustable and trying to discuss a particular aspect of design is more that a little bit difficult because of the way one change in configuration affects another but I’m hoping for some perspective that will shed some light on this question.

All things being fairly equal on say a 8’0" board, if you put a single very mild concave in the nose section, or the mid section, or the tail section of the board how will each variation change how the board trims and turns?

Gone Surfin’, Rich

Mild you say, so swing weight, balance, or center of gravity should not be affected too much?

Nose, mostly out of the water when you turn, but trimmed can give lift, paddling gives lift so you can paddle from forwards maybe catching waves early. Won’t talk about stringer less weight, first sentence.

Mid, should help wave catching and initial response when starting to plane, but really clear of water when turned hard off the tail. Might cause some bounce action in bumpy, tide, and backwashed waves, but quicker feel might offset this and the board should be able to be turned from slightly forwards.

Tail, don’t see it very often, as it limits your banking ability and loosenss when moving fast. Most effect, as tail is always in the water, can bog on hard turns, bog when turned hard, but feels fast with light pressure surfing. Suspect if might be like hard rails on a fast wall, rides high with hold until it suddenly releases. Might be great for slow moving waves, horrid for fast moving.

We made a few boards with full single concaves, but they seemed very limited as to what waves it works in, how much pressure to turn, and converse affect after it turns…like it slows waaay down, then speeds waay up, causing no gain.

Of course, much more testing needs to be done before any real conclusions.

Just our 4 single concave thru tail boards.

Aloha Rich

this one has all three so I don’t know how to explain the difference.

All I know it is very, very fast yet very sticky but very backfoot driven.

Don’t know if it’s the concaves, weird shape, quad fins, or a combination of the three.

Too many things going on with this design it’s hard to say whats doing what…

Be interest to see what this bottom would do on a normal shape.

1/4-1/2 deep nose concave between the noses which both are vee’d to flat at the concave

blends to 1/8 full mid concave

The opens up again in the tail to anothe 1/4 3/8 tail concave

Here’s the rocker profile and thickness (2 7/8")

And here’s the quad fin setup

Oneula…thats one wicked board…what conditions does it work best on? Does that cut thru chop well?

Rich, the least obvious benefit of single concave is how it reduces rocker (assuming flat tips). That alone makes a faster board. For shortboard speed and drive I like it centered between the feet…which not coincidentally, is also the area of the board where pressure drag is most significant to riding characteristics. This transitional area (between entry and exit rocker) is the best place to place a concave for ease of speed, IMO. A perfect example is the CI Flyer…this design is relatively flat down the centerline but rail rocker is medium/heavy. Anyway thats my two cents…

Rich…you’ve been holdin’ out on me. Funky quad. I am interested in a speed machine…but like the trailer quads about half that size.

Chris

P.S. - Not real keen on the nose but if it works i’m all for it!

Seems like the deep concave in front and the twin noses would make the board plane extremely early, making it faster… Getting flatter in the middle reduces drag and the quad fin and single off the tail would help maintain control. The outline and early planning of the board would make it naturally back foot driven. Is it a very tracky board or isit decently loose? what size are those fins and what conditions do you ride it in? I’m planning on a quad fin soon but a little differnt that that…It looks sweet though.

Looking at it again…The tail shape and location of the fins, they’re pretty far up the tail, the wings and narrower tail…It looks like an awesome setup im sure it works amazing jsut looking at it. Alot of thinking and good ideas incorporated into that board, it’s cool to see something newer and refreshing…

My intent here wasn’t to hijack Rich’s thread as he has a very good outstanding question that still needs answering…

Anyway to end the ongoing curiosity…

The board is called a Gemini and it’s made by Jeff Alexander.

You can read his whole crazy story here:

http://www.alexandersurfboards.com/

People have been bashing the design since day one but I sat back and studied it for a year or so before I made the commitment to order one. The board is gaining some popularity here in the islands primarily because REX has his own version called the picklefork by Surfing Mag and Steve Morgan has his Converter design which all pay homage to Jeff’s original design.

They are very expensive $700-$800 for a 6’4"-6’6" and you can buy them off the shelf right now at Hawaiian Island Creations at the Ala Moana Shopping Center where as Jeff had me waiting 6 months for mine all because I decided to “custom” order it from him. Just like Manuel made me wait 6 months for my “custom” order quad fish…

Performance wise they seem to ride just about anything if you keep popping the tail down like you would “tacking” a skateboard. Anyone here remember what “tacking a skateboard” is? Every tack generates a burst of speed and if you link them smoothly, you and those down the line trying to drop in on you will experience some eye opening acceleration of this double nose beast.

The speed increases exponentially with the juice of the wave. Interesting part is that it also is gets very sticky. It will even hook back 180 degrees on itself at full speed if you want it to, do throwing the associated spray. Is it a better board than a top of the line “custom” performance board? I don’t know but I do know I’m not letting another shaper make me wait 6 months to find out. I dearly love both the Gemini and my new Mandala Quad but I believe the Gemini is both faster and more versatile. The Mandala flies and carves forehand but definitely catches its inside nose rail backside coming off the top more than the Gemini and unlike a regular board. The Gemini will catch a nose rail front side if you put any weight on the front foot completely opposite of the Mandala.

The concaves are much more severe than anything I’ve seen and the tail is pretty narrow. The board I have is the Gemini-1 which is the stubbiest of the design. Probably be interesting to build a Bert Burger contour mat of the bottom and press it into a 1lb EPS shape to see how the bottom translates.

I really believe that Jeff just should ship a a set of Gemini’s down to Rasta and let him put them through the ringer. I think the footage would be unbelievable and get Jeff more exposure good or bad. Rasta seems open minded enough to give it a try and his style seems to fit the board. I made a clunkier version for my brother as a christmas present using Surfgear’s balsa lam technique and he seems to like his just as much. Same comments… very fast very loose.

Everything has it’s purpose, even my Dave Parmenters StubbVectors suck performance wise in certain parts of the wave… There’s no magic solution for everything, but I guess that’s what “quivers” are for anyway.

Yea…good point didn’t mean to run off on a tangent but that board…I want to know what part of it is patented, does that mean I can’t use the double nose thing?

Single concaves- Usually on my boards i like to go double, I’ll start after the nose rocker. listen to what the other guys have said it’s all good advice…I like to have plenty of concave under my front foot also…not so much under the back, alot of times I’ll use a mild v off the tail, I like to be able to go rail to rail quickly.

Back to the Gemini, look at those pics on the website…you can see how much lift the board produces…nutz