The shear defines the longitudinal curve of the deck (from front to back). This line is often concave, very rarely straight. In the classic lines of a boat, the ends are raised (as in our diagram). We speak of inverted shear when the curve of the deck goes down towards the bow. This is the case of the Ofcet 32 presented in preview at the Grand Pavois de La Rochelle 2016.
If the shear is the longitudinal curve of the bridge, the move is the transverse curve of the bridge. It is the difference in height between the centre of the boat and the edge of the hull. Often this curve is convex to remove water from the deck. But we can also find situations where the movement is reversed. This is the case on some Vendée Globe yachts which "dig" the deck to position the sail furlers lower and lower the centre of gravity. An idea put forward by Michel Desjoyeaux. (Maître Coq on the next Vendée Globe is like this).
A hull is said to be frigid when it is less wide at deck level than below. The freeboard is then convex, and the main beam is not at deck level but amidships. Many motorboats of the Riva type are frigate-rigged. In sailing, the First 30 designed by André Mauric also has a frigate hull. Recently, Michel Desjoyeaux asked that his IMOCA for the 2008 Vendée Globe (Foncia) had a frigate hull. This solution was adopted to reduce the deck area and therefore reduce the weight.
Freeboard is the height of the deck above the waterline. This height is important because it shows the sea defences. The higher the freeboard, the better it will withstand the sea.
This is the height between the bottom of the hull and the waterline. It is measured at the lowest point where the hull sinks. This is a concept that you need to know when sailing to know where you can walk your keel without touching the bottom..