Those are either really good camels or slow ships.
My estiamtion is, that ships overland have about twice walking speed. Riding does not make you faster on a long run, except, that a beast of burden can carry your stuff and enough food that you can travel longer a day and don't need to make extra detours to shop for food at every village or even spend time hunting. ... But even with that, you only walk/ride about 8 to 10 hours a day, while a ship sails 24 hours a day, so one ship day equals about 5 land days. ... I admit, camels might probably be more efficient for long distance travel than horses, so this might be more like 4 times as fast only. Bu to get to the situation on the map where water speed is only twice the land speed, that has got to be some bad wind and/or good camels (not that it's impossible, just unlikely).