Abstract: A fluid pressure member (26 or 26' or 100) is connected between foot portion (3) and upper portion (4) of the mast (3, 20, 4) of a sailboard (1) which, in turn, are connected to the head (6) and tack (10) of the sailboard sail (7). Controls for a source of fluid under pressure (32 or 50) for the pressure member (26 or 26' or 100) are mounted on the boom (5) for convenient access by the user. While under sail, the user can cause a portion (29 or 101) of the fluid pressure member to extend and retract to adjust the overall effective height of the mast (3, 20, 4) and, consequently, the tension of the downhaul (11), i.e., the vertical tension applied to the leading upright edge of the sail (7). A similar fluid pressure member (76) can be carried in the boom (5) to adjust the tension of the outhaul (9).

Abstract: A diffuser for air or other fluids has a rigid body with a flat disc and a hollow boss defining a central opening. The perimeter of the disc is scalloped and is defined by alternating curved crests and valleys. A flexible elastomeric diaphragm overlays the top of the disc and has a rim portion with spaced recesses that receive the crests of the perimeter of the disc. The rim portion does not extend to the bottom of the valleys of the perimeter and as a result, air openings are defined between the rim portion and the bottoms of the valleys. Air under pressure admitted to the central opening will deform the diaphragm and allow air to escape through the air openings. A series of vanes may be formed on the underside of the disc radiating from the boss. The vanes, together with vane extensions formed on the underside of the diaphragm rim portion, define a compartment for each air opening so that bubbles released from one air opening do not mix or combine with bubbles from adjacent air openings.