with reference to fig1 and 2 , the boom 1 of a small sailing craft , e . g ., a sail board , is formed by a pair of bowed tubes 2 , placed side - by - side and fixed at their ends . the end 3 adjacent to the mast of the craft presents an element 5 which effects the coupling of the boom to the mast . the sail 6 is deployed between the two tubes 2 comprising the boom , and is fastened to the two ends of the mast and to the free end 7 of the boom . the boom illustrated in fig1 and 2 is of the type housing the mast internally , which bears against the internal part of the coupling element 5 . the boom is tied to the mast by means of a binding 8 which keeps the coupling element 5 pressed against the external surface of the mast . the coupling element 5 is formed by a &# 34 ; u &# 34 ; shaped coupling sleeve in plastic into whose ends are fitted the tubes 2 constituting the boom . at its apex , the coupling element 5 has a series of through holes 9 which constitute anchorages for a binding 8 . on each of the two arms 10 of the coupling element 5 , a rotating cylindrical support 11 is mounted , with its axis of rotation 12 substantially parallel to the tangent 13 of the mast 4 at the point of contact between the support itself and the mast . the external circumferential surface of the support 11 presents a flattened surface to rub against the mast 4 . in greater detail , the flattened sections 14 of the supports ensure that the contact with the mast , whatever its diameter and the position relative to the boom , will occur along the line of the mast , the two contact lines 15 being shown in fig1 . further , the fact that the contact between the supports and the mast occurs along two lines prevents the boom from turning on its own axis . where the diameter of the mast is standardized , the flattened surfaces 14 of the supports could , advantageously , be made concave to mate with the external surface of the mast . as stated above , the supports 11 , being rotating , allow the rotation of the boom in the plane of the axis of the mast , facilitating the movement of the boom from the position parallel to the mast in which the binding 8 is tied , to the working position and the tensioning in this position . in fig1 and 2 , the coupling element according to the invention is applied to a boom of the type housing the mast internally , but it is obvious that it could be applied to the type bearing against the mast externally . with reference to fig3 the boom 31 is forced with its end 32 against the mast 33 of the craft by the tension of the sail . the sail 34 , fixed to the end of the mast 33 and the free end of the boom , keeps the boom pressed against the mast . a coupling element 35 with a concave seating 36 is fixed to the end 32 of the boom for the partial housing of the mast . corresponding to the seating 36 are mounted two rotating cylindrical supports 37 with their external circumferential surfaces in contact with the surface of the mast . as in the case of the coupling element in fig1 and 2 , the external circumferential surfaces of the supports 37 present a flattened section in contact with the surface of the mast so that the contact between the boom and the mast , independent of the diameter of the mast and of the position of the boom in the plane containing the mast axis , will be along the two generatrices of the mast . fig4 and 5 show an alternative to the classic system of fixing the boom to the mast . the fixing is effected by means of a flexible belt 40 which is attached by one end 41 to a link 42 attached to the boom on one side of the mast 4 . the free end 43 of the belt ( fig4 ) is engaged in a buckle 44 on a second link 45 fixed to the boom on the other side of the mast . a rubber strip 46 or some other non - abrasive material could be fixed to the inside of the belt . another embodiment of the invention in fig5 shows the link 42 on the other side of the mast from fig4 while the other end of the belt 40 carries one or two pulleys 47 , through which runs a flexible cable 48 , one end 49 of which is fixed to the boom and the other is locked by means of the link 50 to the through - the - centre locking clamp 51 , itself fixed to the boom at 52 and fitted with a safety locking hook 53 .