My question concerns a double concave bottom contour and how the performance is altered by whether the concave is taken out through the tail or made flat at the rear fin area. Also, if you take that same bottom contour how is it changed by a tri-fin setup vs. a quad set up? If a quad setup is used, does the concave run to the outside of the back fin (inside the forward fin), inside the rear fin, or does the concave get split by the rear fin, or is it typical for the double concave to flatten out before the fins? Just wondering about the performance differences and if there is a “typical” way to shape this contour.
You could write a book about these bottoms and I gotta get back to work,
but here’s a quick synopsis:
FOR MODERN BOARDS, the double concave was born in Santa Barbara/Ventura,
although some Aussie will come on here and talk up Terry Fitz, and I’ll bet RB did
a few in his explorations. The Campbell Bros. Bonzer was designed in the ridiculous
beachbreaks(no names please) of Ventura, where holding power and drive are
necessary for survival on some days. Hence the deep concaves off the tail.
Up the road a ways, the mellower point breaks of SB inspired a different type of
double concave designed more for lift and speed. These concaves flattened through
the tail. Michael Cundith or George Greenough are usually mentioned as originators,
but Al Merrick popularized it(to say the least).
Which version you choose should be determined by the waves you ride.
I have shaped several(many?) thousand of the “SB” style. I guess I kinda believe in it.
I don’t shape the bottom any different for a tri or quad, and the fin bases all go on
the little flat panel out by the rail, i.e., the concaves are inside the fins. It’s almost
always inside a little panel V also. Some call this a “hollow V”
back to work,
Mike
unless it’s a bonzer bottom, your concaves should fade out about 2" from the tail. if you carry it all the way out the back, your board will likely have a tendency to get hung up when you come back down off of a top turn. that 2" of flatness after the concave allows for better release.
Where do you maximise the concave in the vee? Towards the stringer or towards the fin?
I guess you’re saying to put vee panels at the rails so the rails remain above the high point of the concave?
I’ve just started putting a 2" flat accross the stringer, before initiating the vee and concave. The jury’s still out. Got any opinions?
Quote:
You could write a book about these bottoms and I gotta get back to work,
but here’s a quick synopsis:
FOR MODERN BOARDS, the double concave was born in Santa Barbara/Ventura,
although some Aussie will come on here and talk up Terry Fitz, and I’ll bet RB did
a few in his explorations. The Campbell Bros. Bonzer was designed in the ridiculous
beachbreaks(no names please) of Ventura, where holding power and drive are
necessary for survival on some days. Hence the deep concaves off the tail.
Up the road a ways, the mellower point breaks of SB inspired a different type of
double concave designed more for lift and speed. These concaves flattened through
the tail. Michael Cundith or George Greenough are usually mentioned as originators,
but Al Merrick popularized it(to say the least).
Which version you choose should be determined by the waves you ride.
I have shaped several(many?) thousand of the “SB” style. I guess I kinda believe in it.
I don’t shape the bottom any different for a tri or quad, and the fin bases all go on
the little flat panel out by the rail, i.e., the concaves are inside the fins. It’s almost
always inside a little panel V also. Some call this a “hollow V”
back to work,
Mike
Hello Mike
Thats was a nice explanation and it makes a lot of sense.
Question - What about the deep concaves that come of the tail that not only the Campbell Bros have done but thier insperatin on Eaton (Later Ace) on the Bonzers/Zingers that where roduced under the Eaton label that work in “Mellower” conditions then the orginal Bonzers.
Bottom line question is…
Does the extream double work ok in softer conditions.
Granted I have a couple of the Campbell Bro. boards and of course they work better in a steeper wave however what doesn’t ??? I think most boards on going to pierod. (Espicially since the ones I’m riding are on the racier side).
I plan on doing a 8’ (Cheetah, Mini LB, Egg, Call it what you will) that would be used in more or less not so good stuff (I have plenty of boards for when its working well). I have been torn with the decsion of going mellow out or really dished out through the tail.
Your thoughts on the above.
Thanks
-B~
On an 8’ board, the need for lift and speed is not as pronounced.
Planing surface and volume and all that. Either one will work fine.
Do two and see what the difference is!!
Have fun and enjoy the ride.
Mike
1969 Channin Diffenderfers all had double concave tails.
I rode a single to double concave downrail board at rincon winter of 70-71
Hull bottoms were what wilderness made then.
Merrick made variations of these until he got Shaun Thomson on his twins in 1980.
Thanks for the edification.
It figures Diff had a hand in this. The first I saw of their boards was 72-73,
Dick and Shagg Catri’s shop, these drop-dead perfect missiles that we all
drooled over but couldn’t afford. These were racy round pins, straight panel V.
Wonder why they got off the double? Back then you had to keep movin’,
things were hectic…
The list of Santa Barbara (or Montecito and Carp) guys who contributed to
this design is too long to start on. Wilderness deserves that mention on the
hull thing too. Those were the days…
Mike
Wilderness seemed to be a great influence on Al Merrick.
I think he moved to Santa Barbera in 1969 when they were the cult heros of the area.
He made Hull boards for 10 years after that.
John Bradbury was really strong there with his Creative Freedom label in the early 70’s.
The 1969 Channin Diffenderfers had a multi plane bottom of tri plane front with a slight center concave to vee going into double concave with slightly up turned rails forward going to down in the rear. Brewer used this bottom on his downrail boards in the 70’s but mostly without the double concaves in the tail.
Quote:
Where do you maximise the concave in the vee? Towards the stringer or towards the fin?
I guess you’re saying to put vee panels at the rails so the rails remain above the high point of the concave?
I’ve just started putting a 2" flat accross the stringer, before initiating the vee and concave. The jury’s still out. Got any opinions?
My normal double starts a little behind the widepoint of the board and ends going
into the fin cluster. The V ( which I plane in first) starts at the same place but runs
off the tail on all the wide ones. The concaves don’t go all the way to the rails, leaving
a tapered “flat” that you can see under the lights. Actually the “flat” is the panel V that
is already there. Hence the term “hollow V”, the concaves are hollowed out of the existing
V botttom. My side fins sit right on the transition line.
That puts the deepest part of the double concaves right between your feet.
Don’t measure–look. It’s different on every board.
Mike
Thank you, Mike.
Sounds really similar to what I’m achieving.
I’m looking for max vee, max concave in line with the side rails midpoint (actually their max foil), running to flat in front of rocker low point to flat in last 2" of tail (over a distance of 3’6" or so) so the whole thing is pretty subtle.
I left a 1" flat along each side of the stringer in the last board. Thiis narroved the concaves. Haven’t had enough waves to feel the (any?) effect. Hanging up in tubes may be one negative but the board’s set up for smaller/fatter conditions, so it may not be a worry.
Interesting to learn the history of dual concaves (spiral vee?). I know my bottoms are AM inspired but was not aware of the extended heritage.
Red