[Rudder]

Vikings used sundials aboard ships to navigate.

If they were used as time-keeping pieces in the navigational computations, then that might imply the Vikings assumed the earth was round.

[Tallguy]

If they were used as time-keeping pieces in the navigational computations, then that might imply the Vikings assumed the earth was round.

I think the early Viking "World Model" was that of a flat, circular earth with landmasses all the way round the edge surrounding an inner sea (the Atlantic). That said, they could have come to understand that the world was 'round' from contacts with Greeks & Arabs.

[R. Scott]

...then that might imply the Vikings assumed the earth was round.

Why wouldn’t they? They were a sea faring people, and the round earth would be obvious to them.