Tunnel fins
Encyclopedia
Surfboard
A surfboard is an elongated platform used in the sport of surfing. Surfboards are relatively light, but are strong enough to support an individual standing on them while riding a breaking wave...
s, especially heavy longboards and longboard guns. The weight and length of these boards make it easier to control the fore and aft angle of the tunnel.
As the name suggests it is shaped like a tunnel. Tunnel fins were first used by Richard Deese and Bob Bolen (also known as the Greek) in California during the late sixties and continue to be developed by shapers today, especially Roy Stewart in New Zealand. The inspiration for Roy's tunnel fin came after playing with a flying gyroscope
Flying gyroscope
A flying gyroscope is a cylindrical item which when thrown like a football, can fly great distances. X-Zylo is one of the biggest names in flying gyroscopes. The William Mark Corporation invented their flying gyroscope in 1993. It was invented by Mark Forti, a Baylor University student, and...
.
The Tunnel fin is based on the principle of the annular wing with the lowest drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
and highest lift
Lift (soaring)
Gliding flight is heavier-than-air flight without the use of thrust. It is employed by gliding animals and by aircraft such as gliders. The most common human application of gliding flight is in sport and recreation using aircraft designed for this purpose...
fin configuration possible. It has no drag inducing fin tips, this is important as it means that rail to rail turning movements are dragfree and effortless. Tunnel fins have the ability to enhance hydrodynamics by slightly twisting the water flow into a vortex
Vortex
A vortex is a spinning, often turbulent,flow of fluid. Any spiral motion with closed streamlines is vortex flow. The motion of the fluid swirling rapidly around a center is called a vortex...
as it passes through the tunnel, preventing random turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
in its wake
Wake
A wake is the region of recirculating flow immediately behind a moving or stationary solid body, caused by the flow of surrounding fluid around the body.-Fluid dynamics:...
. The tunnel fin has a large amount of horizontal lift utilizing the hydrofoil
Hydrofoil
A hydrofoil is a foil which operates in water. They are similar in appearance and purpose to airfoils.Hydrofoils can be artificial, such as the rudder or keel on a boat, the diving planes on a submarine, a surfboard fin, or occur naturally, as with fish fins, the flippers of aquatic mammals, the...
principle providing better lift-to-drag ratio
Lift-to-drag ratio
In aerodynamics, the lift-to-drag ratio, or L/D ratio, is the amount of lift generated by a wing or vehicle, divided by the drag it creates by moving through the air...
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The horizontal area in the tunnel fin also acts as a means of transferring rider energy into forward thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
through board flex (similar to a dolphin tail). As the board pumps up and down it drives the 'fluke' at the tail. In other words, the speed of the tunnel finned board can be increased by weighting and unweighting (pumping). This is slightly different from the side to side movement used by thruster riders.
The ability of the tunnel to organize volumetric flow rate
Volumetric flow rate
The volumetric flow rate in fluid dynamics and hydrometry, is the volume of fluid which passes through a given surface per unit time...
means that (in the case where a central fin is used in front of the tunnel) any turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
coming off the trailing edge
Trailing edge
The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential control surfaces are attached here to redirect the air flow and exert a controlling force by changing its momentum...
and base of the front fin is organized into a lower drag flow pattern.