Hi Cap’n,
Wow, really good questions. First I’ll get you the basic answers, then I’ll throw something out there that
Maurice did with me, kind of a “board designer’s boot camp.”
First, yes the concave may seem to spread as you progress aft, then flare out around the trailing fin.
7’5" would probably be hitting close to 1 inch at the max spot, though MC has gone well over to about
1-1/8" after that they start to become harder to paddle, though the primary function is still there.
“Is there a performance trade off?” Yes, if they are not shaped exactly “spot on” they can be a real
bogger. Certain elements need to be there if you want it to work. I’ll try to get back here to delineate
those things, but first you’ll need to get your head around something very important…
…STOP LOOKING AT THE CONCAVE. Look at the various rockers, the easiest to look at is down
the stringer. The next rocker is along the “rail line” (along the tucked edge.) Let’s stop there, (it
took me a long while to get my head around what Maurice was talking about, thinking back I see that
looking at these two things will help get the right perspective/reference frame.)
When you look down one of his boards, there is minimal rocker down the stringer, I’d say ZERO off
the tail of some models. BUT, along the rail, there is a MASSIVE amount of rocker… …the by-product
is concave. But never mind the concave/channeling/lift ideas for the moment, let it go.
When you surf the board, running “flat” down-the-line the board is mainly riding on the center rocker, BUT
as you turn, and make a demand on the rail/outer edge zone, the board has a BUNCH of rocker, and it
gets really loose.
Now, admittedly there is a lot more going on and I can detail that if there is any desire for it. I’ve made a ton
of these, done the programming for them, hand shaped some, done SUPs even, and they concept does work,
and quite well as I am very picky.
Another thing to consider is the blank. This was the biggest headache as we ramped up production, one of
Maurice’s Metros may be almost 3 inches thick, but with the concave, you’ll need a blank close to 4 inches
or even more if you are milling. To further the challenge, the concave (rail rocker) is maximum AFT of the
center of the board, and most conventional (P/U) blanks are not designed for that kind of use, so think THICK
when you go shopping, ha ha.
Lastly for now, are the edges, which are sharp nose to tail, which don’t catch and make paddling easier, actually
“cancel out” some of the drag they present when paddling (imagine the rails dipping down deep because
of all their rocker, like Hobie Cat hulls) and they slice through the water quite well when they have a sharp edge.
Anyways, if there is more interest, I’ll try to enlighten (or confuse,) if I can…
regards,
George