Part 1: Misinformation, Misnomers, and Imitation
Misinformation
Surfboards are simple vehicles. They have no moving parts, but instead use their outline as a means to interact with fluids. That stated, they interact with the same principles of fluid dynamics as any other vehicle moving through or on a fluid medium, however, due to their small size, low mass, and low velocity, the relative effects are very small compared to something like a 737 aircraft (an aerospace comparison often drawn in surf marketing), or even an ocean going ship. For example:
A winglet on a modern 737-800 may contribute to 0.5% reduction in wingtip vortex drag and result in .0025% increase in speed (speed is a square of the reduction in drag). .5% x .5% x 500mph= 1.25 mph increase in speed at the same relative thrust. If flying 3000 miles across the US, then the reduction in time= [3000mi/ 500mph]-[(3000mi/ (500mph+1.25mph)]=.015 hours x 365 days a year= 5.47 hours saved in flying per year. Which in fuel may equate to thousands of dollars (or almost a “free” flight across the country, nearly 3000 more miles of range at 500mph!).
If we apply the same principle to say, the wingtips on a Futures fin elevon quad, you can see the effect is much smaller:
An elevon quad may contribute to 0.5% reduction in fin-tip vortex drag and result in .0025% increase in speed (speed is a square of the reduction in drag). .5% x .5% x 15mph (or 440 yards per minute an average surfer average speed)= 1.1 yards per minute increase in speed at the same relative thrust. If flying across a wave 440 yards long (1/4 mile) at rincon, then the reduction in time= [440yd/ 440ypm]-[(440yd/ (440ypm+1.1ypm)]=.003 minutes saved. .003 minutes x 60 seconds per minute= .18 seconds faster you will traverse that wave. In others words, if you got 10 perfect, 440 yard waves in a session, did no turns or maneuvers, your total ride time would be 9 minutes 58.2 seconds instead of 10 minutes. If you had a session like that 365 days per year, you would be 657 seconds or 10 minutes 57 seconds faster.
This comparison can be used to describe many interactions surfboards have with fluids. Are those interactions (fluid dynamics) present? Yes! Are they going to make a big enough of a difference to notice? No!
The same principles of buoyancy, lift, fluid adhesion and delamination, solid and digital wings, displacement, etc. all apply, BUT! Some are far more affective to your surfing than others. Additionally, drawing comparisons between surfboards and aerospace, mass transit vehicles, ships, whales and dolphins, etc., is not really a comparison at all. So stop using things that are orders of magnitude bigger than you and your surfboard (and your surfboards time in the water) to make design and purchasing decisions.
Misnomers
All surfboards have a “hull”. Hulls are simply the outermost layer of a waterborne vessel that contact and interacts with surrounding liquid fluids. In other words, if it floats or submerges itself, it has a hull. Surfboards certainly fall into this category. Additionally, all surfboards are both displacement hulls and planing hulls. Both?! Yes! ALL surfboards work on displacement principles when you are paddling. ALL surfboards work on planing principles when you are up and surfing. To call any particular type of surfboard a “displacement hull” is really a misnomer. Lets look deeper:
A true displacement hull functions by effectively parting the water. As it travels in its primary direction of travel, the contours of the hull split and move the water around it. As such, the entire length of the hull of the vessel at or above the waterline is at all times in contact with the water at all times. Think of the titanic. Think of an aircraft carrier. Think of a cargo ship. The hull of all these vehicles has a fine entry, a parabolic plan at the waterline, and is in contact with the water, tip to tail, at all times. As the speed of displacement hull increases, the length of the bow wave created grows in length. When the lengths of this wave is equal to the length of the hull, the vessel has reached “hull speed”; overcoming hull speed with a displacement hull requires a larger amount of thrust and as speed increase, the draft, or depth of the hull actually increases. This means that the hull sinks deeper as speed increases. Not exactly desirable in your surfing. Think about your surfboard when paddling now: shortboards are often fully submerged, and longboards often “glide” over the surface of the water with the entirety of their shape in contact with the water. Both displacing water!
This contrasts greatly with the planing hull which we will look at next:
Planing hulls are more often associated with higher speed applications and rely instead on utilizing the relative surface tension and compression of water, to result in a balanced net force at speed to travel with the majority of the hull well above the surface of the water. Think of a speed boat, or a skipping stone. As long as the vessel is traveling in its primary direction of travel, at a high enough speed, the vessel will momentarily compress the water beneath a small water plane (significantly smaller than the plan view at the waterline), and the force exerted back by the compressed water will be enough to maintain a vertical equilibrium. Of course your surfboard has no propeller, but the principle is the same. The angle of attack of the water in a wave, relative the bottom surface of a surfboard, creates the same phenomena, no matter what the bottom contour of the surfboard is. In shortboards, this always very apparent while up and riding, as the tail of the board is the only part of the board engaged with the wave. In longboards, while it may seem like at times the board is working on displacement principles, the board is in fact relying entirely on the same planing principles the shortboard utilizes. Even the most deeply vee’d boards (often referred to as displacement hulls) cannot displace water fast enough to cancel the compression and coincident expansion of water beneath the board. If it could truly displace water that well, your mass, coupled with the acceleration of gravity, woud result in downward velocity so large, the ENTIRE board would immediately plunge to the bottom of the wave, and then continue to submerge, beneath the water until a kinetic equilibrium was reached via speed and buoyancy (hull speed).
All boards rely on planing to keep you up and riding on the face of the wave. If your speed drops, the board sinks, your forward speed slows and the wave continues on without you. Even on “displacement hulls”. Besides, a real displacement hull would broach and dive irrecoverably, in every wave, due to the unbalanced coanda effect as relative speed increases on only one side of the vessel.
Imitation
It has all been done before. 0, 1,2,3, 4, 5, 6 fins. Diamond, pin, thumb, round, squash tail. Long, short, midlengths. Chop nose, twin nose, round nose. Wings, bumps, hips. Fortunately, nobody has a patent on surfboard designs and every shaper has at least dabbled with every design feature you can think of. Some have executed it better than others. Some have gotten lucky and set a trend. Others rode the coattails and then surpassed the individuals they were following. The key as a board rider and shaper is not to get sucked into people telling you this or that imitation of someone else’s magic board is right for you. Find what works for you, find a shaper that is willing to work with you, and develop your skills together. More people have stagnated their surfing because they bought Hypto Krypto’s, than have developed their surfing and progressed because they actually talked to a shaper and asked what they would recommend. Do not try to dance to the beat of someone elses drum just because it is popular or it looks good. You might not be doing yourself any favors.
Finally, different waves need different boards. When possible, don’t compromise. Equip yourself properly. You should strive to have 4-6 dialed-in boards to cover yourself in everything from 1-15ft. you do not have to amass them all at once (in fact I would recommend against doing that), but keeping them current to your height/weight/athletic ability is important. You will find that you will surf more often, in more conditions, and progress more quickly, if you have the tools be comfortable in the water. The one board quiver is more often a roadblock than a feature.