Question: Which built by HM Dockyard has September 1830 as the laid down?
SQL: SELECT "Built by HM Dockyard" FROM "2-15421158-4" WHERE "Laid down" = 'September 1830';

Question: What is the name that has July 1823 as the Laid down, and Portsmouth as the built by hm dockyard?
SQL: SELECT "Name" FROM "2-15421158-4" WHERE "Laid down" = 'July 1823' AND "Built by HM Dockyard" = 'Portsmouth';

Question: What ordered has Helena as the name?
SQL: SELECT "Ordered" FROM "2-15421158-4" WHERE "Name" = 'Helena';

Question: What ordered has Algerine (2nd of name) as the name?
SQL: SELECT "Ordered" FROM "2-15421158-4" WHERE "Name" = 'Algerine (2nd of name)';

Question: What name has Pembroke as the built by hm dockyard, and May 1825 as the laid down?
SQL: SELECT "Name" FROM "2-15421158-4" WHERE "Built by HM Dockyard" = 'Pembroke' AND "Laid down" = 'May 1825';