I was listening to Mark Knopfler's song "Privateering" from 2012 album under the same name and and I am intrigued by lyrics line I do not understand. The song tells about a life of a privateer, a civil sailor or a pirate authorised by a government to attack foreign vessels during wartime. The chorus goes:
To lay with pretty women
To drink Madeira wine
To hear the rollers thunder
On a shore that isn't mine
I do not understand what thundering rollers are. Is it a reference to some kind of loud harbour equipment (e.g. rollers used to move heavy loads), some type of war equipment (e.g. artillery) or am I missing the reference completely?