Why does the Captain reward the men with drinks?

The Captain rewards the men for their hard work after the island is sighted.

"My lads," said Captain Smollett, "I've a word to say to you. This land that we have sighted is the place we have been sailing for. Mr. Trelawney, being a very open-handed gentleman, as we all know, has just asked me a word or two, and as I was able to tell him that every man on board had done his duty, alow and aloft, as I never ask to see it done better, why, he and I and the doctor are going below to the cabin to drink your health and luck, and you'll have grog served out for you to drink our health and luck. I'll tell you what I think of this: I think it handsome. And if you think as I do, you'll give a good sea-cheer for the gentleman that does it."