How far does one have to travel in a boat (24 ft.) during the summer to have to say Hagomel when he returns?

Poskim disagree as how far should one travel on a sea to be required to recite Hagomel. Following the Sephardic tradition, Ohr Letzion (2: 4) maintains that if one travels on the regular depths of the sea to a distance where the shore cannot be seen anymore and it is over 72min.of travel on one direction, one may bless Hagomel. The Ashkenazy tradition is to recite only if the travel was longer than a couple of days. Minchas Yitzchok (4: 12), Betzel Hachochmo (1: 20), Kinyan Torah 1: 16) and others rule that crossing the English Channel (21 miles) does not require Hagomel.