Perhaps the author has not read about Titanic!
There are plenty of GRP boats up in the arctic waters, some even stay the winter frozen in the ice. The more impotant may be the design of the boat. The risk of hitting small submerged ice bergs/blocks are rather high and a fin keel would not be my first choice of design. I think the real reason for using steel boats have more to do with repair
facilities and economy than the material itself. A bit tricky to do glassfber jobs in