Thank you for all your replies.
Yes the picture is almost spot on. Thank you flap.
Thank you prim for the information.
I have found 2 old ones in a shed of a house I just bought. I wondered what on earth they were. The house did belong to a retired naval commander, so i did think that it was something to do with aircrafts or the seas.
Just wondered if they had a particular name.
Thank you very much
Karen