As I understand it "Top-line" is a reference to being of top class or high class, but is now used to describe how well someone is. I think it comes from early passenger ship travel, where richer people travelled in the highest cabins
A mis-quoted saying that annoys me and also comes from our sea-faring history is "bog-standard". It should be "bulk-standard", which was always used to describe a lesser quality of goods shipped in high numbers for extra profit.
A very high number of old sayings can be traced back to either shipping or farming, which is probably because they were our main employment categories and where people used to develop their own language.