Looking at the above ratio of core to rails 18:1.7, it seems to me that the question of rail volume should be reclassified as one of rail diameter/flow (because the volume of rails (at a factor of 10) is almost immaterial relative to the core). Sure the rails want to bob out of the water, but this is likely to result from its size and shape rather than bouyancy because we're operating at speed and the water flow is generating lift (or not) (depending on rail shape)
Red_boards' comment is along the lines of what I've been thinking lately: People talk about rails in terms of displacement and buoyancy, but shouldn't we be talking about the effect on water flow? Are thin rails not easier to "sink" because they have less surface area? Isn't that the main reason why rail geometry is so important - because it changes the downward facing wetted surface area? I expect that, because we're talking about flow rather than displacement, water flowing over the deck assists in sinking the rail, rather than causing the board to want to cork-up. Actually, I think that we're really talking about a mix between displacement and flow effects - a pivot turn on a long board is almost exclusively about buoyancy, and I expect that a carve on a tow-in board on a huge wave is almost exclusively about planing surfaces.
That's what I'm talking about when I say you have to keep both factors in mind... volume and shape... because they have, to a great degree, independent effects. Add to that the FLOW of water... and not only that, the SPEED of that flow. For example, a low volume rail that's knifey will release water like a hard edged modern rail, but only at certain speeds.
Here's something I wrote about water flow...
Monmouth County Vocational School District
Water flows in almost all
directions along a surfboard’s rail. First and foremost, water flows along the
rail from nose to tail as the board slices through the water’s surface while in
trim or during a turn. In fact, while water may flow along only a small portion
of the rail at any given time, namely the back half or third of rail leading
into the tail, this lateral flow makes up the primary movement of water along
the rail/water interface. Water may flow only under this portion of the rail,
or may wrap part way, or in some cases, fully around the rail and onto the
deck, depending upon the rail’s shape and volume. Still, the flow of water
along the rail from where the rail first engages the wave face, until it
releases from under the board out the tail area, must be designed so that
turbulence, drag, and release are all controlled and manipulated to attain the
Water also flows upward under
the bottom of the rail as water molecules rise up the face of the wave, which
creates a lifting force under the rail. This water interacts with the rail at
varying vector angles, depending upon the speed of the board and wave. In
sailing, the angle of the wind interacting with the sail is changed by the
speed of the moving boat. This combination of relative motions produces what is
referred to as “apparent wind,” and may be very different from the “true wind”
if the boat is traveling fast enough. A similar condition exists between water
flowing along the rail, and the speed of the board and wave. If, for the sake
of illustration, we hold the speed of the wave constant, we can see how at
higher board speeds, the net vector
angle of the upward flow into the rail’s bottom is tilted at a greater angle
toward the tail, and becomes closer to parallel with the plane of the rail. At
lower board speeds, the net flow is closer to vertical, or more perpendicular
to the plane of the rail. However, if we hold board speed constant, we will see
an opposite effect when we look at wave speed. At higher wave speeds, the net flow vector upward into the bottom of the rail
is more vertical and perpendicular to the plane of the rail – faster wave
speeds require water to rise up the face more rapidly. But at lower wave
speeds, the net flow is more horizontal along the rail while the board trims,
as slower waves require water molecules in the face of the wave to rise more
Water also flows into the
rail, from apex toward the stringer. If the path of a single water molecule is
followed as it first interacts with the rail apex, it leads from that point to
some other point on the deckside of the rail if it rises, or some other point
below the rail apex if it sinks, until it is released. Again, the water flows
at some angle along the rail, but still moves inward from the rail apex. Here,
the shape of the rail, particularly on the deck side, helps determine the path
water will follow as it travels at some angle inward and back along the rail.
Water also travels inward from the rail apex as a board moves laterally, or
slides, particularly ahead of the widepoint as the tail is pushed ahead of the
nose, and the nose is forced to slide into the wave face laterally as the board
pivots under the rider’s front foot. During these types of snaps or tail
slides, the nose rail is abruptly forced into the wave face, and both the shape
and volume of the rail determines, at least to some degree, what happens next –
rail shape may force the nose to rise or drop as it slips into the wave face,
while rail volume determines the amount of resistance the nose will incur, as a
larger volume rail along the nose will not allow the nose to sink as deeply as
a thinly foiled nose rail. Similarly, a thicker nose rail will tend to pop back
out of the face easier than a thinly foiled nose rail, as the added volume translates
into added buoyant force.
The flow of water along,
into, and up under the rail, combined with the varying speeds of the wave and
board, creates a complicated and dynamic condition that is for all practical
purposes in constant flux. Still, among all of this seeming chaos, there can be
order. The challenge of the designer-shaper is to create a sense of
“equilibrium within the chaos” for the rider, where water flowing in a
multitude of directions around the rail can be used deliberately to achieve a
desired result… to make the board rise, fall, trim, change speed, release,
slide, or even fly. Therefore, when designing a rail for a given board, the
shaper must keep in mind the type of wave – is it a thick, ledgy peak, or a
thin, peeling wall? Is it a slow, mushy sandbar wave, or firing pointbreak? The
shaper also needs to consider the goals of the rider - does the rider want a
board that is stable and catches waves easily, or one that is more loose, and
suited more for vertical, aerial-oriented surfing? Does the rider want to set a
line and walk to the tip, or do hard, driving turns out on the open face?
You are correct, I just did the standard thing and clicked the quote button. I read the article three times, it was thought provoking. As far as content, I agreed with most of it, but not all of it.
But If you were expecting the conversation to go a certain direction you need to be more involved in it. The reality is, this is Swaylocks and it rarely does - its the ugly side affect of international free speech.
Good article. Thanks for taking the time to type it and post it here.
Crafty No harm, no foul. But you are right about the thought provoking. While the article may have points of disagreeement for some, the discussion of those points is lively and a good thing. My thought was along the lines of focus on Bills statemnts about rail volume as opposed to rail shape. Seems to me that the focus was on rail volume and had little to do with rail shape. But it is interesting that the discussion of the article by others immediatly turned to rail shape and replicating various rail shapes as opposed to rail volume and its relationship to center thickness. I would say the reason being that there are a number of people who frequent this site that are hobbyists or beginning shapers. By that I mean that an aesthetic or pretty and consistent rail is one of the first things our "Bros" look at when we take our early shapes down to the beach for critique. A good looking, consistent rail is also one of the hardest things for a begiining shaper to replicate and often the most critisized part of a shape by others. Hence the concern and grafitation towards that part of the process by novices. That is evidenced by the many threads that are started on this site by beginners requesting help in cutting a nice consistent rail. For my part though I was more interested in the relationship that Bill placed on center thickness and how it related to rail volume. I have never heard or seen anything written that laid that relationship out so plainly. Just my two cents. I'm really not a person that get too technical when it comes to displacement quotients, calculations etc. If fact when I shape I take minimal measurements and those are only done to keep me within the boundaries of the desired shape. My design ideas are based on things I have seen and surfed over the years that I know work. You would think that would put me in the "copy cat" camp. But my boards always come out with their own expressive quirks. Bill's way more technical than I could ever be and a great teacher. The thought he puts into the whole process is amazing to me. Lowel
Maybe the conversation would have gone in the "right" direction if it was titled differently.
"Barnfield on Deck/Rail Contour" or "Volume Distribution" or something like that.
If provoking thought was the goal, the one thing that sticks out in my mind is the part about rail volume being more important than rail shape. The provoking thought I got was that of disagreement. I believe this is partly/mostly due to the fact that he's on the North Shore and myself and most others here are not. North Shore board rails are generally are rounder, softer and less edgy for foregiveness and control in really fast conditions. Much of the rest of the world is seeking more speed in average conditions, so the bottom half of the rail shape means more, IMO. If was surfing the North Shore and ordering or making boards, I probably wouldnt want too much variety in rail shape. I would want more consistency and foregiveness - KISS on the rail shape.
I liked the article! thanks bill.
crafty wrote: the one thing that sticks out in my mind is the part about rail volume being more important than rail shape... the bottom half of the rail shape means more, IMO.
I am in agreement with Crafty(though I think Bill is saying the same thing also), but I'll put it in my own words.Rail volume is a meaningless parameter without considering the shape of the rail...and here's why: The only volume that matters is the volume that is touching water. This applies to the whole board, not just rails. I stuck a sealed 5 liter Tupperware container on the nose top of my board. I dunked it in a displacement tank and sure enough my board went from 30 liters to 35 liters. So following Spicoli logic, I figured that the board is going to paddle so much better now. I tried it and the strangest thing happened, the board road the exact same way! and the paddling was the same! Since the tupperware container was only displacing air, it had no effect on the board.The shape of the rail (especially the bottom half) WILL determine how much of the rail is in contact with water. Precisely two things: 1)the radius of curvature throughout the rail 2)the angle created by the discontinuity of curvature at an edged rail (the angle created by the upper and lower tangent lines at the discontinuity in curvature--the edge)As the radius of curvature gets smaller and/or the angle of the edge gets sharper, the water will break off the rail at a lower point, and everything above the water breaking point is totally meaningless from a fluids stand point (yes, structurally the upper volume matters). So if you have a fat 2.5" rail and a 2" rail, but because of rail geometry, the water is breaking off at only 1/2" from the bottom in both boards, the boards will feel the same (if everything else about the board is identical).
While I agree with your post, I think that you omit the use of rails on edge. When a rail is buried for 80% of its length, then a considerable portion of the "unused" top half of the rail is in play. The entire rail shape and volume come in to play - and rail foiling (or the flow of volume/shape fore to aft).
Love your thoughts. Your post makes it obvious that people who surf slow (and sure?) need fat rails and waves that are slow need fat (oops! high volume) rails.
Rails are obviously very personal. After a year of surfing my ultra thin rails in everything from competing in mush mush to free surfing big and hollow waves I think there is something special there, but another surfer may not like the ready "on rail" response.
I think the reason rail shape gets so much more attention is because its the one design element of the board we can truly feel with our hands when we hold a board. Most people cant feel rocker, deck dome, fin set etc with their hands. When I hold a new board, right away the feel in my hands takes over all senses, at least for a few seconds. We can feel volume too, but geometry is more visceral.
Btw, my approach to shaping is like yours. Its part science and part art. Mostly science when I design, mostly art when I shape.
For the average working person, how often do we get to produce functional art? Not very often and I cherish it when I do. Its the best thing about shaping. And shaping the rails is the best part about shaping. By far.
I've had guys ask me just to shape their rails. I'm like, "sure!" Plouging out all that foam foiling it out is a drag. Rails are fun!