Like I said yesterday, I'll have to try things out, to see how I can get away with only one monkey trip. I suspect you have to visit Johnny Rolle and Blue Hole first, but maybe you don't.
Anyway, when you ARE done with the monkeys, go back to Johnny for the metal detector. You can then go sailing out to the sunken ship and play underwater Sudoku for the astrolabe and dial.
Here, I'll test if you can get the sea urchin, without talking to the monkeys on the cliff first. I hope you can, otherwise I have to schedule a cliff trip earlier in the route.
Here is a good time to get Johnny's beacon. You have to get it for the bat battery. If you do it at this point, you can do the "set up the astrolabe puzzle" and "go through the bat caves" puzzle on the same trip. Alternately, you can put off the bat caves for later, and do the "get Johnny's beacon" task at the same time you visit Half Moon Reef. I'll have to time it and see which variation is faster.
The astrolabe lets you translate various passages in El Toro's journal, which relate to puzzles. I'll have to test, to see if you have to do this. Maybe it's possible to solve the pulley puzzle, without translating the entry about pulleys. I know Nancy mentions Coucou's perch, after you translate the journal. It's possible I have to translate the whole thing, just to get Coucou's perch.