Abstract: This invention relates to a rotary cutter comprising a central member (11) adapted to be mounted to a shaft for rotation therewith and supporting a plurality of teeth (14a, 14b) located at intervals around a circular path, each tooth having at least one cutting edge (15, 16), a second member (12, 13) adapted to be mounted in association with the first member for rotation therewith and being capable of selective angular displacement in relation to the first member, said second member supporting a set of guides (18, 19) located at intervals around a circular path such that each guide is associated with one tooth of the plurality of teeth and is located ahead of said tooth.

Abstract: A boat hull having at least one extending hull (10), an intermediate hull portion (13), a flexible plenum chamber (14) to raise and lower the intermediate hull portion (13), and a flexible skirt (17) formed integrally with the intermediate hull (13) to entrain air beneath it so that its lower extremities are clear of the ground or water.

Abstract: A boat hull having water engaging parallel hull portion separated by a bridge portion and an intermediate water-engaging hull portion disposed between adjacent parallel hull positions and underneath each bridge portion. An expandable and compressible plenum is disposed between each intermediate hull portion and bridge portion so that each intermediate hull portion will be lowered and raised respectively as the plenum is expanded and contracted.

Abstract: A boat hull having a pair of water engaging parallel hull sections separated by a bridge portion, an intermediate water-engaging hull section being disposed between the parallel hull sections and underneath the bridge portion. An expandable bag being disposed between the intermediate hull section and the bridge portion such that the intermediate hull portion will be lowered and raised respectively as air is blown into and out of the bag.