The Merman's Children.
The stolen ship has a cabin on the starboard and larboard sides. During the storm, merpeople who cannot fit onto the ship hang onto lines but some are lost as is the accompanying orca.
Vanimen had intended to cross the Atlantic but the storm drives the ship south to the Gates of Hercules where dolphins advise him that Dalmatia beyond Italy in the Mediterranean might welcome Faerie creatures - whereas the now damaged ship will never cross the ocean. We remember a Time Patrol mission to "Gibraltar Falls."
We have ordered Island In The Sea Of Time by SM Stirling in order both to appreciate a post-Anderson time travel/alternative history series and to compare it with Anderson's works on these themes. In previous posts, the conclusions drawn were:
Anderson comprehensively covered every aspect of sf, including alternative histories;
Stirling, specializing in alternative histories, has developed this concept further than Anderson.
However, although the past cannot change, our interpretation of it can so we will continue to read and reread without preconceptions.