A ship weighing millions of pounds might have a skin an inch thick. This is, relative to the mass, a thin film. If it hits a reef, or an iceberg, it will rip open.
A sailboat weighing thousands of pounds will have a skin that is 4 or 5mm thick. Compared to the mass, this is MUCH tougher than an oil tanker or a cruise ship. Steel sailboats slam into reef and get dents, they don't tear open.
