To respond to both posts,
No the cancellation policy does not mention the ship not docking. It merely read that the tour was weather dependent and, if cancelled, you could get a full refund. The sticking point was that the tour wasn't cancelled. Our group of 4 just couldn't get off the ship in port!
And yes, I won't use Viator or HW again. I have written Viator to suggest they change their cancellation policy to read, if ship doesn't dock but a tour goes ahead, a refund is not guaranteed as it is up to the tour operator.
Just disappointed that neither Viator or HW took the circumstances under consideration and offered even a partial refund.