question, did anyone catch this?

Save me from waiting for the reruns someone, please. On the cliffs, as they are going looking for the backpack, James Perez (Paterson) estimates the distance of something-- the height of the waves I think, and the woman ask how he knows that figure. He says a sailor who didn't know that figure wouldn't have the sense to head for shore or not to go on the water at all, or something like that. I heard the figure as 17.5 meters but no idea-- despite reading Wikipedia on this. Was he referring to the distance they had to walk or what?
It's annoying when they sort of give us a fact, but mumble or speed past it too fast.
The show makes me want to move to the Shetlands, though like the murder mysteries set in Oxford, the homicide rate in fiction is awfully high ;-).