This is also
sunstone erasure!
The sunstone is honestly pretty cool and also feels practically lifted from a cultivation setting already given it uses cool crystals with extraordinary properties. Although given they were made of Icelandic Spar, and Iceland still has a magic forcefield around it (I think?) perhaps it's not commonly known as yet.
Regardless, the Norse were honestly amazing navigators, second only to the Polynesians before we get into the age of European exploration starting in the 15th century. So this characterisation is a bit weird in general. It would be quite accurate if we were talking about say, Greek sailors, who did tend to stick very close to coastlines and treated even voyages over the relatively calm Mediterranean as a dangerous undertaking.