A composite sandwich is simply a structure made up of many different materials. A traditional surfboard is essentially a sandwich made up of foam and fibreglass held together by polyester resin. One of the most significant drawbacks of this style of design is its lack of durability. If you’ve ever owned a surf-style wakesurf board made this way, you’ll know the heel dents appear almost immediately after the first ride. A true composite sandwich of multiple density foam will now be made up of a low density EPS foam heart, a layer of lightweight fibreglass, a layer of high density foam, and a final layer of heavier weight fibreglass, all of which would be laminated together with epoxy resin. You can learn more at https://www.theepoxyresinstore.com/blogs/news/diy-wakesurf-board
The higher density foam skin avoids most heel dents and dings, among other items. Many surf style wakesurf boards use a 2 to 3 pound density foam that tends to dent under pressure, such as when they are rode, while this foam is in the 5 pound density range, which is considered structural. It also separates the fibreglass layers, as discussed below.
There are more layers of fibreglass in this composite sandwich, which is what makes a surfboard solid. One layer of fibreglass on the bottom and two on the top is the most popular lamination schedule. A minimum of two layers would be present on the top and bottom of the composite sandwich. The composite sandwich’s strength is enhanced by the additional fibreglass.
The stiffness of any composite beam is measured by the distance between the facings, without going into the math. That is to say, the thicker a wakesurf board is, the stiffer it will be. In addition, the stiffness rises in a linear fashion. By increasing by a factor of one, stiffness increases by a factor of four. The heart of our wakesurf board acts as the web of an I-beam, while the fibreglass skin acts as the facings. By sandwiching a high-density foam skin between the two layers of fibreglass on the deck, the composite sandwich improves on this. Since there is no gap between the two layers on a typical surfstyle wakesurf board, increasing the distance increases stability while also enhancing strength and dent resistance.