Materials in action

analysis of a surfboard

Fig 1. Surfboard from below [surfboard wallpapers]

please scroll

components and their materials

we are all familiar with the historic surfboard made entirely of wood.
but how are modern designs composed?

Fig 2. Board components [Estudio (2012)]

the board

The modern surf board is made in a layered construction: a blank made of rigid polyurethane foam is covered with fibreglass cloth, which is laminated onto the board using polyester resin. The stringer is a narrow strip of wood, which lies either on the outside of the board or in a vertical line down the centre.[7 facts about surfboard materials.2015]

The board can be divided into 5 regions, each controlling some aspects of the board's performance (All about surfboard parts.2015).
- Nose (front tip): entering a wave, paddling and turning
- Tail (back end): riding the wave
- Rails (outer edges): speed, turning and catching waves
- Deck (top side): buoyancy, strength, paddling power
- Stringer: strength and flex

.

Fig 3. Fins [The Thruster Setup(2015)]

the fins

The fins are placed at on the bottom side of that tail of the board, usually in a triangular configuration. They give a lateral lift to the board which opposes the water and stabilises the trajectory of the board. In other words, the fins are mostly responsible for steering the board. The standard fin is made of plastic composites [Bijarimi et al. 2010]. Several material alternatives are in use, such as bamboo or wood.

Fig 4. Leash [Matos (2013)]

the leash

The leash serves to keep the board close or attached to the body when the surfer has fallen off. It is made of an elastic cord, plastic (composite) tubing or surgical rubber tubing. It attaches to the tail of the board with a knot, and to the ankle with a velcro strap.

material properties

and how they influence the functionality of the board

polyurethane foam

Polyurethane (PU) foam is the most common choice of board material because it has a low density, and is therefore lightweight and buoyant. It is also easily shapeable. It is fine and brittle, enabling the shaper to sand off material without tearing into it. One of the downsides of polyurethane is its toxic nature. [Know your foam. (2015)]

Fig 5. Rigid polyurethane foam [come insonorizzare una parete (2008)]

fibreglass cloth

The foam blank alone is too porous and weak to use in the water. The stronger, more dense layer of fibreglass enables the board to sustain a larger load and resist more of the surrounding water. The “glass schedule” ,which refers to the number of coatings of fiberglass used, dictates the final strength and weight of the board. [Kinstle & James. (1975)]

Fig 6. Fibreglass cloth [Fibreglass cloth]

polyester resin

Polyester resin has strong adhesive properties and is used as a glue between the PU foam and the fibreglass layers. It is chemically stable in salt water, water resistant and it creates a relatively smooth surface when dried.

Fig 7. Pouring of polyester resin [Resins]

wood

The purpose of the stringer is to strengthen the otherwise soft polyurethane foam. Wood is suitable for this because it is relatively lightweight at the desired strength properties and is also buoyant. A stringer should be lightweight but this usually comes at the cost of stiffness. A stringer should not be too flexible so as to cut into the surrounding fibreglass. The type of wood used is chosen accordingly. [Types of wood used for stringers. (2015)]

Fig 8. Wooden stringer. [sbro_cali (2010)]

plastic composites

Plastic composite fins have high flexibility (i.e. low stiffness), which makes them safer in the impact of the water. They are generally used for beginners, who do not have specific requirements for performance. Fin materials are chemically stable in salt, alkali or acidic solutions that are conditions prevalent in the ocean [Bijarimi et al. 2010].

Fig 9. Pellets to make plastic composites. [Technavio (2014)]

plastic/rubber
tubing

These materials are chosen or combined in such a way that they exhibit good rebound resilience, elasticity, tensile strength and tear strength. [Bessette. 2015]. Consequently, they do not crack or snap when the board drifts away and the ocean presses against the surface area of the board, creating a large force on the leash. The resilience and elasticity also pull the board back towards the surfer so that it does not get lost.

Fig 10. Plastic tube leash.[Recycled PVC Customized SUP Leash Surfboard Leash Surf Leash (2015)]

manufacturing

how and why the materials are manufactured into the finished product

Fig 11. Refining the shape of the board using a plane. Photo credit: Bobby Hundreds

Step 1: Shaping

The manufacturing process starts with a rigid polyurethane foam blank. The blank is first cut roughly into the correct shape and dimensions using a handsaw. Expensive tools are not needed, because the polyurethane foam is easy to cut through and shape (as mentioned above). Rough edges that were sawed are smoothed out with sandpaper.

Then, the board's shape is refined to the exact shape desired using a plane - a hand tool that is used to flatten and reduce the thickness of the board. This process is unique for each board, since each board has a different shape and thickness profile along the length of the board. Lastly, a power sander is used to smoothen the surface.

Fig 12. Preparing surfboard for fibreglass layer using cure resin. [Dick Brewer Balsa Surfboard Lamination. (2014)]

Step 2: Laminating

In the next step, the board is first prepared for its layer of fibreglass. UV cure polyester resin is spread over the board to fill any cracks or voids that may have occurred during shaping so that the wood grains are sealed and do not absorb the resin during lamination. It is then and left to harden (cure) in the sun or under a UV light.

Subsequently, the board is covered in a layer of fibreglass at the bottom, and two layers at the top. This is covered in a layer of polyester resin, tinted to the customer's desired base colour. Due to the resin's strong adhesive properties, this process glues the fibreglass to the foam. It creates a smooth surface when dried.

Fig 13. Cutting fin boxes with a router. [weird. (2008)]

Step 3: Cutting

Next, the board is prepared for the fin box. Holes for the fin boxes are cut using a router and template. These tools are stronger than the hand saw used before, since the laminated surface is considerably stronger and harder than the foam blank. The holes are filled with black resin, which holds the fin boxes in place, into which the fins are inserted later.

In a similar manner, the plugs to attach the leash to the board are inserted into holes drilled into the board.

Fig 14. Artist decorating a board with acrylic pens. [John Clarke. (2013)]

Step 4: Painting

The board first receives its final sanding with a power sander to prepare the surface for painting - the sanded surface will absorb the paint better and has a flatter, more even surface than the laminated one.

Masking tape and acrylic pens are used to decorate the surface of the deck. The board is then air brushed with the desired colour of water resistant and durable paint. Air brushing is used to ensure that the board surface stays even and smooth.

Fig 15. A board being polished [surfysurfy. (2006)]

Step 5: Polishing

In the final step, the board is first coated with another layer of polyester resin. Then, the board is lightly sanded down, and polished with a polishing finish.

This gives the surface a high quality, smooth finish, which means less resistance in the water and thus higher speeds. The polish will also protect the paint so that the board will retain its colour.

Suggested improvements

and how they influence the functionality of the board

reinforcing the fin

The performance of fins is characterised by their weight and their stiffness. The most desirable fins are those which are light and have a high stiffness, i.e. an almost immediate response.

Plastic fins have more flexibility, making them less responsive but safer in the impact of the water. They are also cost efficient in comparison to other fin materials.

When a faster response is required by the surfer, plastic fins can be reinforced with fibreglass. Fibreglass is stronger and stiffer than the plastic, so the board will change direction faster. It is also shock and wear resistant and can resist the impact of waves and sand during surfing. [Bijarimi et al. 2010]

Fig 16. A fin being reinforced with fibreglass [Munkybritches again, (2007)]

replacing the resin

Epoxy resins are superior to polyester resins for the following reasons:
- Better adhesive properties
- Superior mechanical properties (particularly strength and stiffness)
- Improved resistance to fatigue and cracking - Better resistance to osmosis (surface degradation due to water permeability)
-less toxic emissions
However polyester resin remains the industry standard because it is inexpensive. [The Advantages of Epoxy Resin versus Polyester in Marine Composite Structures. 2015]

An environmentally friendly alternative is Bio-resin epoxy resin. It is less toxic and performs similarly to petroleum-based epoxy resins. Epoxy resins have dramatically less toxic emissions than polyester resin. [Guide to “ECOBOARD” surfboards. 2015]

Fig 17. Bio resin [Kevin. (2012)]

replacing the blank materials

The data from Life-Cycle Analysis (LCA) studies on surfboards estimates that a typical surfboard for example, a 183 cm short board which weighs about 2.5 kg, causes over 270 kg of CO2 to be emitted during its lifecycle.

The blank of the surfboard can be made more environmentally friendly by using recycled content. Recycle contents available are EPS (Expanded Polystyrene with 60% recycled content) and PU (40% recycled content). The EPS and the PU recycled content blanks are similar to the surfboard blanks made from virgin petroleum. They have a comparable feel for shaping, they’re visually identical, and most importantly, ride identical. [Guide to “ECOBOARD” surfboards. (2015)]

Fig 18. Recycled PU foam blanks [Vosti. (2012)]

group 33

Materials in action

components and their materials

the board

the fins

the leash

material properties

polyurethane foam

fibreglass cloth

polyester resin

wood

plastic composites

plastic/rubber
tubing

manufacturing

Step 1: Shaping

Step 2: Laminating

Step 3: Cutting

Step 4: Painting

Step 5: Polishing

Suggested improvements

reinforcing the fin

replacing the resin

replacing the blank materials

text references (in alphabetical order)

image references (in order of appearance)

group 33

Materials in action

components and their materials

the board

the fins

the leash

material properties

polyurethane foam

fibreglass cloth

polyester resin

wood

plastic composites

plastic/rubber tubing

manufacturing

Step 1: Shaping

Step 2: Laminating

Step 3: Cutting

Step 4: Painting

Step 5: Polishing

Suggested improvements

reinforcing the fin

replacing the resin

replacing the blank materials

text references (in alphabetical order)

image references (in order of appearance)

plastic/rubber
tubing