Last time we had a comprehensive, well, as comprehensive as possible in the black art of board design, look at three of the fundamental aspects of board design, namely: Rocker, Outline and Bottom Shape. That trinity don’t work alone and in this issue we’ll round off the other interplaying factors that make your board go good or surf like a lump of wood.
Foil
In the kitchen its silvery stuff for wrapping food, in surfing and hydrodynamics foil is defined as essentially the relationship between the deck and bottom arcs of your board. In other words when you look at your board from the side the rocker defines the bottom curve and the foil is the shape between the bottom curve and deck curve. The term is more easily applied to fins or airplane wings, but the concept works for boards. Put simply it’s all about the distribution of foam in cross section. More foam under the chest and the volume diminishes in all directions from there. The thickness measurement on your board is the measurement of the foil at the board’s widest point.
So what does foil do? Well, if you think about it there are two options forward foil- where the volume is pushed forward towards the front half the board, good for fast powerful down the line waves and rear foil favouring a tail based style of surfing. As with most aspects of board design the shapers use a combination of both with neither dominating. Rails
A board can have the perfect outline, rocker and foil but is nothing without the rails. The development of rail shape theory exploded with the genesis of the shortboard movement in the late 60’s. Prior to that longboard shapers paid little attention to boards perimeter shape; favouring a soft egg shaped rail, not really realising how simply moving the apex in the rails cross-sectional curve could make a massive difference in board performance.
The simple act of moving the apex nearer to the bottom (known as a down rail) was a paradigm shift in board performance, allowing greater traction, control and deeper tube rides it was a real watershed moment and now rail shape is a fundamental and involved part of the board design. Most modern boards follow the same pattern, utilising different rail shapes through the length of the board as each area has a different task. The nose rail is soft and rounded so it wont catch and lets the water flow easily. Through the middle of the board an squarer edge is applied giving bite and control. Towards the tail the rails get sharper knifing through the water to help extort all possible power from a turn. If you examine a few boards you’ll see the variation. Nose and tails remain similar through most boards, the central section is another ‘depends on preference’ area, with some shapers preferring squarer ‘boxy’ rails spreading volume through the whole board others go for the thinner curvy rails and maintain volume in the board core with a more domed deck.
The shaper makes the rails but it’s down to the sander to really fine-tune them, find a good a sander, hold him to your bosom and never let him go. Fins
Are worthy of a book in themselves. The surfboard is a hydrodynamic projectile and as we’ve seen the infinite variation in possible curve combinations means it’s a complicated beast. Boats are easy to design, they go in one direction, surfboards however can go straight, perform tight turns, slide sideways or go backwards. Take this complexity of water moving over a curved surface and add three fins to the mix and the maths goes right out the window. Surfboards do not necessarily need fins, after all they slow your board down due to drag, bodyboarders stand up and surf their sub three-foot tea trays, performing tube rides and rudimentary turns. Jamie O’Brien has a whole section in his profile vid showing him tearing into a little North Shore shorebreak on a regular surfboard sans fins. He is a freak, but the clip shows how the fins are an addition, an extra device designed to turbo charge board performance. Tom Blake whacked one he nicked off a speedboat on his big wooden board back in the thirties to add some control, before that the big koa wood boards of the Dukes time were finless. The ‘skeg’ didn’t catch on until the mid-forties. The twinny surfaced in the seventies and in 1981 the familiar thruster tri-fin, which soon became standard, appeared and has dominated ever since. The thrusters set up Simon Anderson took to the world did more than control, it gave surfers drive.
The physics of how fins work is far too complicated and requires a level of geekness not to be found in the Slide office so we’ll keep it simple: Fin variables and their effect on performance, ahem.
Your fins have a number of dimensions, depth (self explanatory), base (the length of the fin where it meets the board), rake (the distance between the fin tip and trailing edge of the fin base), foil (like with boards it’s the cross sectional curve, side fins have an asymmetric aeroplane style foil, the centre fin is symmetrical) in essence bigger fins hold better but turn worse and vice versa. The placement of the fin set on the board also effects performance, the distance between the central and side fins width ways and how far the rear fin is set back from the side fins all add another layer of confusion to the design process. Tighter turning arcs, looser handling, better hold in the barrel, all depend on the size of your fins.
In the kitchen its silvery stuff for wrapping food, in surfing and hydrodynamics foil is defined as essentially the relationship between the deck and bottom arcs of your board. In other words when you look at your board from the side the rocker defines the bottom curve and the foil is the shape between the bottom curve and deck curve. The term is more easily applied to fins or airplane wings, but the concept works for boards. Put simply it’s all about the distribution of foam in cross section. More foam under the chest and the volume diminishes in all directions from there. The thickness measurement on your board is the measurement of the foil at the board’s widest point.
So what does foil do? Well, if you think about it there are two options forward foil- where the volume is pushed forward towards the front half the board, good for fast powerful down the line waves and rear foil favouring a tail based style of surfing. As with most aspects of board design the shapers use a combination of both with neither dominating. Rails
A board can have the perfect outline, rocker and foil but is nothing without the rails. The development of rail shape theory exploded with the genesis of the shortboard movement in the late 60’s. Prior to that longboard shapers paid little attention to boards perimeter shape; favouring a soft egg shaped rail, not really realising how simply moving the apex in the rails cross-sectional curve could make a massive difference in board performance.
The simple act of moving the apex nearer to the bottom (known as a down rail) was a paradigm shift in board performance, allowing greater traction, control and deeper tube rides it was a real watershed moment and now rail shape is a fundamental and involved part of the board design. Most modern boards follow the same pattern, utilising different rail shapes through the length of the board as each area has a different task. The nose rail is soft and rounded so it wont catch and lets the water flow easily. Through the middle of the board an squarer edge is applied giving bite and control. Towards the tail the rails get sharper knifing through the water to help extort all possible power from a turn. If you examine a few boards you’ll see the variation. Nose and tails remain similar through most boards, the central section is another ‘depends on preference’ area, with some shapers preferring squarer ‘boxy’ rails spreading volume through the whole board others go for the thinner curvy rails and maintain volume in the board core with a more domed deck.
The shaper makes the rails but it’s down to the sander to really fine-tune them, find a good a sander, hold him to your bosom and never let him go. Fins
Are worthy of a book in themselves. The surfboard is a hydrodynamic projectile and as we’ve seen the infinite variation in possible curve combinations means it’s a complicated beast. Boats are easy to design, they go in one direction, surfboards however can go straight, perform tight turns, slide sideways or go backwards. Take this complexity of water moving over a curved surface and add three fins to the mix and the maths goes right out the window. Surfboards do not necessarily need fins, after all they slow your board down due to drag, bodyboarders stand up and surf their sub three-foot tea trays, performing tube rides and rudimentary turns. Jamie O’Brien has a whole section in his profile vid showing him tearing into a little North Shore shorebreak on a regular surfboard sans fins. He is a freak, but the clip shows how the fins are an addition, an extra device designed to turbo charge board performance. Tom Blake whacked one he nicked off a speedboat on his big wooden board back in the thirties to add some control, before that the big koa wood boards of the Dukes time were finless. The ‘skeg’ didn’t catch on until the mid-forties. The twinny surfaced in the seventies and in 1981 the familiar thruster tri-fin, which soon became standard, appeared and has dominated ever since. The thrusters set up Simon Anderson took to the world did more than control, it gave surfers drive.
The physics of how fins work is far too complicated and requires a level of geekness not to be found in the Slide office so we’ll keep it simple: Fin variables and their effect on performance, ahem.
Your fins have a number of dimensions, depth (self explanatory), base (the length of the fin where it meets the board), rake (the distance between the fin tip and trailing edge of the fin base), foil (like with boards it’s the cross sectional curve, side fins have an asymmetric aeroplane style foil, the centre fin is symmetrical) in essence bigger fins hold better but turn worse and vice versa. The placement of the fin set on the board also effects performance, the distance between the central and side fins width ways and how far the rear fin is set back from the side fins all add another layer of confusion to the design process. Tighter turning arcs, looser handling, better hold in the barrel, all depend on the size of your fins.
It’s a wonder anyone ever figured it out really. Board design is fascinating, it can be incredibly complicated but as with most curved things if you take it in your hands and it feels good it generally means it is good. Nice curves are there for a reason. Surfing is a progression, pay attention to your boards, what works and what doesn’t, experiment with board shapes, lengths and fin set ups, changing your fins can give an old board a whole new lease of life. With the baffling array of fins now available for you to change at will it would be rude not to.
