Good job :)
Once I figured the boat was pretty safe when in shallow water near an island, the game wasn't quite challenging enough for me personally - I think having a stronger overall objective to aim at might have boosted the fun factor, but overall a solid lil game!
If I were to suggest a specific tweak, it'd be to have to press a button to unload materials at an island - a few times I accidentally dropped people off at a location without meaning to