Rethinking Surfboard Design:
The Semi‑Displacement Bow
A Hidden Weakness in Flat‑Bottom Boards —
And the Solution
Flat‑bottom surfboards perform brilliantly on the surface — but fail during high‑impact collisions. The semi‑displacement bow is engineered to penetrate water, reduce abrupt stops, and help surfers recover from dangerous pearl dives. A simple change in nose geometry can cushion impacts, prevent catapults, and improve safety without sacrificing performance.
.avif)
The red section in the diagram above may resist surface penetration with high impact, resulting in an abrupt stop.
Introduction
Most modern surfboards are built with flat bottoms. The flatness often extends from nose to tail. Many boards have slight indentations called concaves, and a few have a subtle Vee shaped into the tail. Despite these features, the dominant design in modern surfboards is the flat bottom. Flat bottoms are designed to ride on the surface because flatness maximizes planning area. The large planing area can interfere with performance. Foiling introduced a smaller wings that can generate tremendous speed, demonstrating how reduced wetted area can improve efficiency.
At lower speeds, surfboards partially submerge and must displace water to move. Flat bottoms displace water inefficiently and slowly. A flat bottom pushes water forward before moving it aside. A traditional flat bottom becomes inefficient when speed drops because it cannot manage displacement cleanly. This study introduces an alternative.
The above photo is of a partially submerged surfboard generating a wake. An arrow points to the bow wave which is creating a plume of spray. This indicates that the board is displacing water to move. The nose bend is distorted due to light refraction.
Resistance
A dangerous characteristic of a flat bottom surfboard is its tendency to stop abruptly in a free fall or during a high‑impact collision with chops, wakes, or a wave trough. In such collisions, the flat bottom may not penetrate water. Flat bottoms cannot move water out of the way quickly enough to allow displacement. Water must move in order for objects to move “in water.” During an impact with a speeding object, there is no time for water to move in multiple directions before finally moving aside.
Falling objects momentarily stop on the surface and decelerate before entering water. A low pin drop fall or dive is cushioned because the body displaces water while descending.
A fall from heights above 200 feet may cause serious injury because the diver cannot displace water fast enough. If the diver lands flat, he will momentarily stop on the surface with high impact.
Many years ago, I lost a friend in an accicent. Curt fell from a helicopter into the ocean. The helicopter was unequipped for rescues and attempted to fish Curt out with its landing skids. Exhausted, Curt could not hold on to the skids and fell. The fall impact caused severe internal injuries. Water resistance is impenetrable to fast moving people, surfboards, and objects.
When a speeding surfboard collides with water, it stops and the surfer is catapulted. The stop is due to the hydrodynamic force of water impacting the flat bottom. This stop is known to surfers as a pearl. Any board will pearl and decelerate in a high‑impact collision with water. One capable of penetrating and displacing water may keep moving and recover. A momentary stop disrupts the surfer’s balance. Impact can be cushioned by a penetrating bow that absorbs force and continues to move.
The following video is of Garrett McNamara's gallant attempt to ride one of the largest waves ever attempted. His partially inflated suit and tremendous speed prevents water penetration. He shattered his arm in a high speed impact with water.
Warning:
The following two videos are of fatal wipeouts linked to flat bottoms and nose rocker combinations. The captions provide adequate information without watching the video. This photo of Mark Foo shows him paddling on a surfboard with extreme nose rocker. The photo may be taken with a fisheye lens giving added distortion to the extreme design. The flat underside combined with high nose rocker cannot penetrate water. The board abruptly stops and causes Mark to lose his balance and fall.
Mark Foo. directly off a plane from Honolulu, paddled out to Mavericks. He was equipped with surfboards designed for tropical waters of Hawaii. His surfboard had an extreme nose rocker. This extreme design can better penetrate warm water in Hawaii, in a poke. Mark unsuspectedly met cold, cohesive, icy water in San Francisco.
Kirk Passemore hits chop visible as shadows on the wave's face. A flat bottom surfboard cannot cut through chop and penetrate water's surface. A flat bottom is blocked and pushed back by resistance or lift. A wake is visible spraying water from the nose underside of the nose over his legs as he collides with a bump. This is evidence of his surfboard pushing water. He is launched as the chop abruptly stops his surfboard. The wave breaks on him. He is last seen diving toward the ocean bottom, possibly disoriented by the violent wipeout.
Niccolo Porcella survives two violent wipeouts caused by the nose rocker catching in the wave. The nose tip is visible above water but the underside bend of the nose rocker abruptly stops the surfboard.
The Pearl
The pearl is one of surfing’s most dangerous wipeouts. It is a violent event that catapults a helpless surfer toward many hazards. In a pearl, the nose of a speeding surfboard makes a high‑impact collision with water. The collision usually occurs in a dive, sometimes called a pearl dive. The impact abruptly trips the surfer and launches him through the air.
The nose underside, or bow, usually takes the impact because of the gravitational pull in a dive. The bow should part water so the board can follow; it is the key landing area in a free fall. The bow is the bent underside section of the board known as the nose rocker. It is curved like the bases of a rocking chair. The curved nose combined with a flat underside can prevent surface penetration, resulting in an abrupt stop and wipeout.
The wipeout itself may not be injurious, but it may land the surfer in dangerous predicaments. Many hazards lurk: drowning in a turbulent underwater hold‑down, collisions with shallow rocky bottoms that can fracture bones, sharp reefs that can gash and lacerate flesh, and flying surfboards that can spear a surfer or knock him unconscious. The goal of this study is to reduce wipeouts that cause injury, concussions, and drownings.
Cohesion
Water is cohesive; it bonds to itself. Intermolecular hydrogen bonding holds water molecules together. This bonding leaves little space between molecules. Without space, water cannot be compacted or squeezed together. Water molecules push back when high force is applied.
Water can be easily parted by slowly moving a finger through it. Water cannot be parted by fast‑moving objects, especially those with flat surfaces. Movement “in water” requires moving a volume of water equal to the object’s submerged mass — a principle discovered by Archimedes. A flat, speeding vessel cannot move water out of the way fast enough. Instead, speedboats and surfboards that attain higher speed rise and move “on water.” They transition from displacement (Archimedes’ principle) to lift (Bernoulli’s principle). They move on the water’s surface. Bernoulli discovered that speed “on water” produces a force known as lift.
Red O'Shaughnessy is in a shallow pearl. The flat bottom cannot penetrate the surface. His board nose rocker is hydrodynamically blocked with the nose tip still visible. A board with less nose rocker and flattened bow may continue to move. Instead, he is catapulted and sustains serious head injuries despite wearing a helmet.
Parting Water
Surfboards must penetrate water to move "in water". Flat bottoms struggle to displace water efficiently; they push water forward before it can part to the sides. Alternative shapes can move water directly out of the rider's way. When a flat‑bottom surfboard strikes water at speed, movement often stops because the board cannot move water out of its path quickly enough. Water needs more time to move forward and out of the way. The surfer is often launched or cannot maintain his balance.
Vessels moving in high seas part water when encountering chops and swells. To successfully cross oceans, early mariners and Polynesians designed boats and ships with round or Vee‑shaped hulls and pointed bows. These features allow vessels to penetrate water and maintain forward movement “in water.”
When surfboards pearl, they must penetrate water to continue moving and possibly recover. A flat bow can stop movement and disrupt a surfer’s ride. Flat bottoms perform best in smooth, predictable water where penetration forces are minimal.
The best bottom shape for riding both "in water" and "on water" is the Semi-Displacement bottom. Semi Displacement design utilizes the best performance features from displacement and planning designs. The term "Semi" refers to the partial modification of the bottom. Only the forward 1/3 to 1/4 of the surfboard is modified with a Vee, round, or combined shape. The remainder of the board retains the popular flat planning surface.
The board planes like a flat bottom and rides "in water" in a poke or pearl. It will continue to move through a pearl to possible recovery.
Historical Proof Displacement Surfboards Worked Well
In the archival photo above, Tom Blake stands with surfboards he made and designed. Note the rounded bottoms of the surfboards on the left. Blake also built hollow round-bottom surfboards to part water and paddle faster.
Tom Blake was an inventor and surfboard designer. He is credited with developing the first surfboard fin. He was a contemporary of Duke Kahanamoku. Duke also built and developed surfboards. The following video features him riding a displacement SUP also known as a surf ski.
The photo above is of a replica of a big wave surfboard from the late 1950's to early 1960's. It has a full displacement bottom with round roll to the tail. This limits top speed but does not interfere with displacement. Boards similar to this one were ridden by the late Greg Noll. A great surfboard designer and shaper from this era. Two videos of Greg follow, demonstrating how surfboards can ride out of a pearl.
Semi‑Displacement Design
I have shaped and tested semi‑displacement surfboards. They paddle faster, cut through chop, recover from a shallow pearl, and cushion a hard impact with water. Only the bow area of the surfboard is modified with a round or Vee shape. I prefer a combination of both shapes.
The bow area of a surfboard is out of the water when the board planes hydrodynamically. It is also out of the water during turns. The forward fourth of a surfboard can be out of the water for an entire ride or many rides, due to its nose rocker. The exceptions are a nose rider and fish, which use different board shapes with less nose rocker.
Surfers have developed skills over the years and are adept at keeping the nose from catching and tripping them up. The danger arises when surfers lose control or lose contact with the wave and free‑fall. This leads to a nose‑first landing and a possible nose poke. In such a situation, a displacement bow may prevent a wipeout.
Conclusion
Surfing will always involve risk, but board design can reduce the severity of wipeouts. Flat‑bottom surfboards perform well on the surface, yet they fail to manage displacement during falls and high‑impact collisions. These failures contribute to pearls, abrupt stops, catapults, and injuries.
A semi‑displacement bow gives surfers a margin of safety. By allowing the nose to penetrate and displace water, the board can continue moving instead of stopping on the surface. This simple change can reduce dangerous wipeouts, improve recovery, and cushion impacts without compromising performance. The aim of this design is to protect surfers in the moments when control is lost and impact is unavoidable.
Contact:
Questions, comments and inquireys Donn Ito email ito808@yahoo.com