Fins are often provided on the undersides of small watercraft, such as surfboards, sailboards, waveski's, etc., to alter the fluid-dynamic properties of the watercraft, to limit lateral movement of the watercraft through water, to assist in directing the watercraft, etc.
Fins can be fixedly joined to the underside of the watercraft, but such fins significantly increase the overall dimensions of the watercraft and increase the space required when transporting the watercraft. These fins are also vulnerable to damage when the watercraft is handled, transported, or the like, and hold the further disadvantage that they are not adjustable to vary the fluid-dynamic properties which they impart on the watercraft.
Fins can be removably mounted to the underside of the watercraft, e.g. by removably mounting the fin in a box embedded within the watercraft, and retaining the fin in the box, e.g. by way of screws abutting a lower part of the fin. A fin can be mounted in a slot defined within the box, and the slot can have an elongate shape, allowing the fin to be adjusted longitudinally within the box, but other than this adjustment, this type of fin mounting does not make provision for changing the hydrodynamic properties of the watercraft, e.g. by adjusting the toe-in or the splay of the fin.
The “toe-in” of the fin is the orientation of a planar part of the fin in relation to a longitudinal axis of the watercraft, while the “splay” of the fin is the angular orientation of the planar part in relation to the undersurface of the watercraft.