The parts of a trimaran are named using old Polynesian words that described the components of their multihulled craft, which plied the worlds waters starting 4000 years ago.
The VAKA is the main, or center hull of a trimaran.
The AMA (you get a pair of ’em on a tri) are the outer hulls. You can call them outer hulls if you like, but don’t call ’em floats or pontoons, as that would make you sound like the kind of person who calls every bit of running rigging on a boat simply “rope”, thus tempting fate via impromptu keelhauling.
The AKAs, or crossbeams, are the structures that connect the three hulls together. Calling them crossbeams is acceptable, and you can even call them crosstubes if you like. Provided thay are, in fact, made of tubing. They are sometimes called ‘wings’, and if you take a look at some of Dick Newicks’ designs, you can see that they do indeed resemble wings on his boats. He designs BEAUTIFUL boats, by the way.