I live on the Gulf Of Mexico and can tell you that Mermaids were NOT considered a good thing by sailors of old.
In in sailors lore....They were considered Sirens (one who mesmerizes and tricks) and harbingers of doom to a sailing ship.
The Freeform channels drama show "Sirens" comes closest in pop culture to how old time sailors really felt about Mermaids.
Here's a trailer. ........
https://www.youtube.com/watch?v=82NusegO1mQ