I think instead of getting half rewards when you set sail and half when you finish instead

you get 1/10 of the total rewards for each minute you sail after you sink or finish

Also each completed sail should increase your rewards for the next sail.
SO if you complete 1 sail the next sail is wroth 10% more
if you complete 2 sails the 3rd sail is worth 20% more then the 1st.

And that's the max you can get. You coin and get 3 more sails you start over at normal for a 4th completed sail, 10% more for a 5th and 20% more for a 6th.