Fibre over steel

[yarrick88]

howdy all first time in here like to say HI, HIIIII, lol
anyway i am going to be building a Pontoon, i make air-con ducts for a living so i have access to pretty much any metal i require, what i was thinking of using was .6 or .8 sheet metal round it to 500mm DI (19.6 inches) at the lenght of 4267mm, then fill the spigots with foam. after everything is sealed up then fibreglass the 3 pontoons and add gel coat to make it water proof etc etc.the decking will be all wood, all it needs to hold is max of 6 people. but my real question is will it be to heavy for water with the metal, foam and fibreglass??? will it float, sink, tip, i honestly dont know

Length: 14 ft = 4267mm
Width : 6 ft = 1828mm

thanks guys