the preferred embodiment will be described with reference to the drawing figures where like numerals represent like elements throughout . referring to fig1 a , there is shown a windsurfer 10 which is composed generally of a sailboard 12 , a mast 14 , and a sail body 16 . the mast 14 has a leading or luff edge 18 . the upper end of the mast may terminate in a bulbous portion which is referred to as a head cap 20 . connected with the cap 20 is an adjustable line or strap 22 . the adjustable line or strap engages with an eyelet 17 mounted within the sail body 16 . included with the sail body 16 at the leech edge is an eyelet 28 . eyelet 28 is located directly adjacent the boom 30 which is to be handled by the operator and is to be used to effect steering of the windsurfer as it moves across the water . an outhaul line 26 connects eyelet 28 to boom 30 . connecting the eyelet 29 to the mast 14 is downhaul line 25 . the sail body 16 includes a pair of windows 34 which are located directly adjacent the boom 30 . positioned generally in the center of the sail body 16 is a closable flap 50 with the flap 50 hinged at one end and releasable around the remaining of its perimeter . a flexible hinge 52 connects the flap 50 to the sail 16 as a zipper 54 surrounds the releasable perimeter of flap 50 . the flap 50 is released by grasping the zipper handle 51 and successively unzipping around the perimeter of flap 50 . unzipping allows for increased air flow through the sail body 16 , relieving pressure on the rider . opening the flap 50 creates extra air flow through the sail body 16 . the extra air flow through the sail body 16 enables the sail body 16 to function like a sail of smaller size . the opening allows more air to flow through the sail body 16 thus preventing the overpowering of the user . if wind speeds lower or a new rider with greater skill or of heavier weight takes over , the opening can be closed using the flap 50 so as to have the original characteristics of the sail . in addition , when the sail is placed in the water , the opening left by the flap 50 creates an area to facilitate flow of water which has collected on the sail body 16 . this flow of water aids the windsurfer operator in lifting the sail body 16 out of the water in order to begin sailing . as shown in fig1 b , the opening in the sail 16 is filled with a porous mesh 70 . the mesh 70 protects the integrity of sail 16 . by bonding the edges of the opening created in the sail 16 , the mesh provides structural support for the sail 16 . the mesh 70 also provides for controlled flow of air or water through the opening . rather than having streams of wind or water flow directly through the opening , the flow is diffused and thus more regulated with the mesh 70 . the mesh 70 is preferably a non - porous material to prevent collection and retention of fluid in the mesh . the mesh may be constructed of similar material as the sail body 16 . referring to fig2 - 3 , there is shown positioned around the general perimeter of both sides of flaps 50 velcro ® fastener material 56 . upon unzipping the flaps 50 completely , the flaps 50 are folded about the hinge 52 and placed against the velcro ® fastener material 58 secured on the sail body 16 . interaction of the velcro ® hook members 56 with the velcro ® loop members 58 secure the flaps 50 to the sail body 16 . the interaction of the velcro ® fastener members 56 and 58 prevents unwanted movement of the flaps 50 about the sail body 16 . securing tabs 59 further hold the flaps 50 against the sail body 16 . the inside surface of securing tabs 59 are further provided with velcro ® fastener material to interact with fastener material disposed on the edges of flaps 50 . an alternate embodiment of the invention is shown in fig4 . the sail 16 uses completely removable panels 60 to cover the opening in the sail 16 . preferably , two opposing panels 60 are used on both sides of the sail 16 . flap members 68 secure panels 60 to the sail 16 . velcro ® fastener material lines the inner portion of the flap members 68 . as shown in fig5 - 6 , velcro ® fastener loop members 65 protrude from the inside portion of the flaps 68 . the velcro ® loop members 65 interact with velcro ® hook members 67 displaced along the ends of the panels 60 . the flaps 68 reinforce the connection between the flap 50 and the sail body 16 and prevent unwanted release of the flap 50 . as discussed earlier herein , the opening in sail 16 is reinforced with mesh 70 . while the preferred embodiment of the sail body 16 utilizes a single closable opening , an alternative embodiment of the invention employs a plurality of closable openings disposed on the sail body 16 . as shown in fig7 the sail body 16 includes sealable openings 80 . the openings 80 may all be left closed , all opened or selectively opened and closed depending on the varying wind conditions and relative skill of the operator . the openings 80 may use hinged flaps or removable panels as discussed herein . while the present invention has been described in terms of the preferred embodiment , other variations which are within the scope of the invention as outlined in the claims will be apparent to those skilled in the art .