The cabins on sailing yachts are meant to be a nice, cozy place for napping and sleeping.  So there isn't much space for standing or walking around.  On most yachts, the standard bed size is equal to a Queen sized bed.  Each cabin has windows (deck hatches), which work as skylights as well as a way to and let in sun and a nice cross breeze.
There is space for storing clothing and other personal items, however storage space in the cabins and yacht in general is limited, so remember to follow our packing guidelines and try to bring soft luggage.