NRS calls it "tube" but they use 11/4
inch schedule 40 pipe, in T6061 for straight and T6063 for the bent sections.
Their "Lo-pro" fittings fit standard sch 40 pipe, as do Holleander fittings. Another possibility (since you're building a fishing boat) is double rail fittings like these https://www.mountainbuzz.com/attachme...8_original.jpg
which can be used to mount a flat surface to walk on.
I got those a couple of years ago from a fellow "buzzard" named Zorba The Greek. I have a few extras, if you're interested.