Any opinions by qualified designers shapers will be appreciated- with the proliferation of grovel models being blown up to any proprtions by machine, what we end up with is some very wide (21’ -22 ‘) 6’2’- 6’ 5 “shortboards( (think Sharp eye Disco to CI Spermwhale) with tons of concave. Is this counter-productive being that lift and speed are not an issue as much for these wide shapes? tHE ORIGINAL MODELS ARE DESIGNED WITH r&d BY factory pros riding 5’4”- 5’8" boards so I can see using the concave there, but when you blow up are you decreasing your quickness rail to rail? You are certainly decreasing control to some degree. If I design a 6’2"X 21 with just a bit relaxed shortboard rocker, round pin and full but somewhat pointed nose, or something like a Weidro Ripper as well, am I better off with a little concave, none at all or added v for knee to head mushy surf? (i’m 62)hHEAVY METAL HETTEL
Define "qualified!"
I make a few boards annually, and because I surf mostly shitty beachbreaks, I like 'em short and wide. Full, single concave from rail to rail works really well for me. Usually, it's a full concave fading to the back fin(s) and flat at the tail. I like 'em!
Racing stripe board is 6"2 and 23 wide. Flat with vee in the tail. Set up in a quad. Goes like a bat out of hell.
the fishy thingy is 6'4 and 21 3/4 wide
Other can attest too here, I tend to keep things simple on the bottom of boards. If you have wild transitions going on in a short board, its a lot harder to blend all that going on.....you have less space to make it transition. For instance: if you are going from a vee entry to a concave, then a double concave to flat out the tail...then you have a lot of small areas where you are trying to make it fit. Leave that to the pros, not us backyard hacks. Don't over engineer this stuff, keep it simple.
Halibuts are flat....and they swim fast. I've even seen'em jump on ocassion.
More: The flat to vee board with a quad is plenty loose, the board will do a 360 if asked. Also works well back hand
I had a 6’-1" x 20.75" x 2.75" Roberts White Diamond with a big single concave that worked really well for me, just a great board. I’m old, and at the time I was 215 lbs and liked the float. Once I lost about 15-20 lbs. that concave really worked against me. I can muscle a board around but it was just too much pushing back, like riding a beach ball. I have a similar board now that has a shallower single to double with vee off the tail that goes rail to rail much better.
The Sperm Whale isn’t a grovel board but if you look at the Lost Domestic series boards which are similar, they are super wide at around 22". They are pretty flat bottomed with a bit of double concave with vee. Depends on your wieght but with a grovel board but I think when you get too wide you need to go shallow on the concaves or just stick with a flat bottom with some vee.
A lot of those smaller boards put strain on your lower back so it’s harder for us older fellas to ride the actual dimensions that they are designed for. Also, a lot of surfers are scared of riding the board so small so they only drop down two inches but add all of that extra volume in the thickness and width which kind of defeats the purpose of having a grovel board. A grovel board is for small, cruddy waves, with very small pockets that you want to put your board into. So, really it should be ridden 4-6" shorter than you standard shortboard. That being said, those boards are blown up to larger dimensions so they can sell boards to regular dudes, no rippers. So yeah, it kind of ruins the original design. It depends on what you like and how well your rocker flows. Flat bottoms will push if the rocker is a bit off. Concaves help to fix that as well as doing many other things. Lastly, vee is always good on boards with wide tail blocks. Was that long enough? 
If the board is proportional to the rider all is good. Best thing I’ve done yet is take a template for a dumpster diver type board and super sized it to fit my 43 year old 6’1 x 210# body. The board is a game changer in crappy surf here on the east coast.
I agree with the original poster that deep concave is counterproductive on wider, shorter boards. Single concaves are supposed to provide lift and flatten the rocker in the belly and these boards you speak of are usually low rocker already and wide enough that they get plenty of lift without the need for much concave. Biolos says as much in his description of the wide, flat, short domesticated series boards (Lazy Boy, Couch Potato). Those boards are pretty flat with some double to vee out the tail. I like the idea of double to vee out the tail on these wide boards because it gives these big planks a bit more drive/control through the fins.
Maurice Cole - Metro
Dan Mann/Fire Wire - Sweet Potato/Potatonator
Jeff Alexander - Gemini
Greg Webber - Twin Fish
I agree with Jamie… flat rockered boards don’t need deep concaves. Shallow singles work well. I like slight vee in the entry with wider noses, shallow single concaves, to either flat behind the rear fin(s) or a touch of vee, depending on tail rocker.
thanks to everyone
http://www.youtube.com/watch?v=887oTdGshzM
I figure this guy knows what he's talking about. In the video he demonstrates clearly how a single concave can interact with bottom rocker to effectively create a dead flat surface where the board actually interacts with the water.
Bill ("Flat is fastest") Thrailkill should be able to appreciate this one.