Fins are a technical subject often overlooked by many windsurfers. On the other hand, their influence on the windsurfing board's behavior is significant. The topic is wide, and relatively complicated. In this article, we try to face the argument, illustrating the most important concepts.

Windsurfing, technique: fins, characteristics and possible configurations

The argument is a little tricky. So, we thought to give you all a hand, entering this world an trying to understand something. We would like to help you make the most of your boards, having more fun in your sessions.

Before starting to describe the characteristics of the fins, let's pause for a moment to understand how the fins work, that is, how the forces that act on them (and which are then transmitted to the board) are generated.

The fin is nothing but a small wing, and we can, therefore, use the same terminology used in aerodynamics. The forces created are called lift and drag. Since the fin is positioned vertically and not horizontally like a wing, lift becomes a lateral force (roughly horizontal). The fin lift is created because of the fin blade tilting in the water flow, with a specific angle of attack. The flow around the fin, therefore, is not symmetrical. Note, in this regard, that the fin due to the effect of the wind thrust on the sail and therefore on the board, will impact the water with its face facing the leeward side of the board (which will correspond to the lower side of the wing of an airplane). On the opposite fin side (the one facing the windward side of the board), the flow must take a longer path than the leeward side. Consequently, the flow must be faster on the "windward" part. This means that the energy related to the proper pressure of the water decreases on this side to convert into kinetic energy (to run, at the same time, a longer path). Therefore, a lower pressure is determined on this side than the opposite part of the fin. The difference in pressure between the two sides produces lift. Lift is always combined with the resistance that depends on the friction of the water molecules on the fin surface, and therefore on the geometry of the fin. The figures below taken from the Maui Ultra Fins website illustrate these concepts.

Let's now describe the shape and structural characteristics of the fins, which also influence the intensity of these forces. Let's start, first of all, with the way the fins connect to the board.

Connection types

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