Boat leaderboards can be accessed by tapping the notice board on your dock. There are two different boat leaderboards: the Friends Ranking (where you can see the rank of all the players in your friends list) and the Global Top Player Ranking (where you can see the rank of the top players in Hay Day).
Every time you complete (and send) a boat order from your own farm or complete a friend’s boat order, you will be awarded with points that accumulate on the boat leaderboards (Friends Ranking and Global Top Players rankings). The amount of points you gain per order depends on its difficulty (type of items/amount required). In addition to this, you’ll get a bonus if you complete the order faster.
You can see the number of points awarded for a particular order below the normal reward (experience points and voucher) for that order. The points will be added to your boat leaderboards score (along with the bonus) when the boat is sent away.