user: Question: Tell me the sum of Gross Tonnage for isis ship on date commisioned less than 1842
Columns: ['Ship', 'Date Commissioned', 'Gross Tonnage', 'Propulsion', 'Material']
Types: ['text', 'real', 'real', 'text', 'text']
Sample row: ['Actaeon', 1842.0, 650.0, 'Paddle', 'Wood']
SQL:

assistant: SELECT SUM("Gross Tonnage") FROM "Table" WHERE "Ship" = 'isis' AND "Date Commissioned" < 1842.0;