The more important question is how strong is you boat gunnel /gunwale? I mounted 60" tracks on my Starweld boat which has 0.100" thick aluminum (not real stiff). I used 1/8" thick backing plates and wide fender washers when I ran out of plates to spread the load. The tracks are very strong, easily taking the load of rod holders for most fresh water fish especially walleye using dipsey divers or lead core line. 18" track will have 4 or maybe 6 holes for the 3/16" screws and lock nuts so it's more important to use backing plates under gunnel for shorter tracks. I've heard of shorter tracks used for triple trees! Good luck.
Lesson learned: lube srew with wd40 if using drill driver so nylon in lock nut doesn't heat up expand and jam the nut to point of stripping the head of stainless screw. Wires and cables are open under gunnel so caution for drilling.