From Law wiki, the wiki for law research

It is interesting to compare this case (Hartley v Ponsonby [1857] 7 EB 872) to Stilk v myrick (1809). In both cases a crew of sailors refused to complete a voyage because their conditions had been worsened by desertions; in both cases the captains offered extra money if the crew carried on working; in both cases the captains refused to pay at the end of the voyage; in both cases the sailors sued for the additional wages. The difference is that in this case there were substantial desertions: only five were left of the orgininal complement of 36. In Stilk two deserted out of eleven.

The sailors won their case in Hartley, where they had failed in Stilk. Why? In both cases the sailors had a contractual obligation to work the ship back to port, so in neither case was there any fresh consideration. The difference can be accounted for like this. In Stilk the change in the sailors' conditions was not dire: the crew should have been able to cope with two desertions. There being no fresh consideration, the captain's agreement to increase wages was not binding. In Hartley, there were so many desertions that the contracted parties were no longer working in the same circumstances as when the contract was formed. Hence there were entitled to consider it discharged. This makes the captain's offer of increased wages, and acceptance by the sailors, an entirely new contract.