Sorry, NH, I intended to respond to you, but got side-tracked by that (inappropriate omitted)
There are so many ways to leave it cliff-hanging. Meeting the next deadly intimidating island tribe, a storm rages and sails are hanging in the wind, three sheets gone. (That's where the drunk acting 'three sheets to the wind came from, by the way'.) Hell, the sun sets that way, the main characters can say "We started chasing the sun", "Yeah, let's catch it", whatever.
You have a good idea here, but only a couple producers will tackle something this expensive. I write 'sea stories' some, as a former ship's captain. I stopped because they are so expensive to produce, didn't think mine could make the cut. Now I'm rewriting two earlier novels. Who knows?
If you need some incredible music to help inspire you, check out Canadian Stan Rogers. His music and lyrics are phonomenal. He died young, but you can still get the music. He has the feel of what you are writing, if you can capture it in script form, you win. I never could.