The Scotch Lass

The Scotch Lass was a floating kettle ( Robert Onedin's expression).

The steamer had three different names in the story of The Onedin Line.
1. The Golden Nugget
2. The Anne Onedin
3. The Scotch Lass

Actually it was the steam ship, James asked Albert Frazier to design
for The Onedin Steamship Company in series two firstly called The
Golden Nugget

The series three begins with the launching of this steamer and it
was named The Anne Onedin as a memory of the first Mrs. Onedin, who
died in childbirth.

In the series three when James has difficulties rising the money to
pay costs of The Anne Onedin to Frazier's shipyards, Albert's father
took the steamer to his own ownership and renamed the steamer as The
Scotch Lass.

In a reality The Scotch Lass was Carlotte Rhodes.
Alison McLeay writes in her book "The world of the Onedin Line":

Charlotte Rhodes is no means James Onedin's only vessel (although
with a quick change of name-plate she has been several of them –
Scotch Lass, Caledonia, Oberon, Cardiff).

I hope this information will answer your question about The Scotch
Lass.

Best wishes Maija