as best shown in fig2 fig5 and fig6 lower outer tumblehome edges 46 and 48 are not only approximately parallel to each other but are also approximately even horizontally with substantially flat under surface 44 and with each other that is substantially flat under surface 44 or at least the portion thereof in back section 16 generally defines a horizontal plane and lower outer tumblehome edges 46 and 48 and lower transom edge 54 are approximately coplanar in this horizontal plane some inventive embodiments provide for lower outer tumblehome edges 46 and 48 which though horizontally coplanar with each other are situated in a vertically different horizontal level from that in which lower transom edge 54 is situated or from that which is described by a substantially flat under surface 44 as shown in fig7 substantially curved under surface 44 is connected to transom 42 such that lower transom edge 54 approximately is horizontally coplanar with lower outer tumblehome edges 46 and 48 while under surface 44 curves below this level forward of transom 42 regardless of whether under surface 44 is substantially flat or substantially curved in inventive practice lower outer tumblehome edges 46 and 48 will themselves preferably lie in parallel fashion in approximately the same horizontal plane however the disposition of such horizontal plane in relation to lower transom edge 54 or under surface 44 can be coincident or noncoincident depending on the inventive embodiment side stabilizers 70 and 72 which are each generally characterized by an upwardly inward slope according.