High def has...
a red, blue, and green input cables instead or or in addition to the video, left right cables. Can also be indicated by a "funky" looking high def socket with squair holes and different size holes in the same socket.
My bet is that if it is a high def then you would also have gotten a:
cable receiver box??? on a boat???
or a
satellite dish$$$$$???? probably would have noticed that on the stern already