Hello,
What I told was probably not clear enough: There are no "Foghorns" aboard ships.
Bells and whistles are used in low visibility situations, and the foghorns that you listen to in the mist, are those coming from The Needles, Nab Tower (both 2 sounds every 30 sec) or other Calshot (1 each 20s) lights, to stay in Shingles or the Solent.
So that there is no need of an F key, the default H is more than enough. But of course you can also ask for an orchestra on board, and use an O key for that.
Also, an example of diaphone (http://homepages.manx.net/fredd/diaphone.html), kind of foghorn too. And Portland Bill (http://fr.youtube.com/watch?v=bdi7t475F0s&feature=related)...
Regards,
Luc