You can't, realistically. It would have to be a glitch.
You have to have a Phoenix Warbird, and the Shipwright and Cannoneer as crewmen. He will attack you between the Pirate Outpost and the new island. Jam him up and don't let him slip away to repair. Shoot as many cannonballs as possible and don't stop firing until he's beaten and runs off.
Nothing. You can see the pirate treasure flag there, but there is nothing to do. Once you have the largest warship, and have used it to beat Captain Crawfish, go back to the governor, who will give you the directions to the buried treasure.
Nope. It's bad enough he can cheat and run to get repairs, but unless you're pounding him with the Warbird (Cannoneer aboard), he will simply cut-and-run before you beat him, and come back undamaged.
It isn't possible. The whole point of getting a big ship on Skullduggery Island is so that you can fight an even battle against Captain Crawfish. There are no magic shortcuts that work on Poptropica.
you buy bigger ships
Rather than sinking, Captain Crawfish runs away when you beat him. That is enough for the governor. Go back to see him and he gives you the treasure location and the bone shovel.
You have to beat Captain Crawfish before you can show the map to the Governor.
Once you defeat Captain Crawfish, and collect all five map pieces, you can go to the new island (Skullduggery) and dig up the buried treasure. Before you have done these two tasks, the island has no purpose. After Captain Crawfish has been chased away, the Governor will give you the treasure location and bone shovel. (In order to beat Captain Crawfish, you will need the strongest ship, the Phoenix Warbird.)
All of the ships larger than the raft have cannons, but you need the biggest ship, the Phoenix Warbird, to beat Captain Crawfish. As you can afford each larger ship, trade up to get cargo and doubloons faster.
nothing. you will come here after you've beat Captain Crawfish and found the treasure map. (the treasure chest is on the island)
That is not the end of the quest. After Captain Crawfish runs away, sail to Fort Ridley and see the governor. He will give you a bone shovel and the location of the buried treasure. Sail to the hidden island (Skullduggery) and dig it up.
It is not in Captain Crawfish's dream: the lockers contain the Stopwatch and the Turpentine. The empty sprayer for the turpentine is in Dr. Hare's dream, at the bottom of the second level of the anthill. Use the turpentine in the sprayer to beat the Black widow's dream.
Once you defeat Captain Crawfish, and collect all five map pieces, you can go to the new island (Skullduggery) and dig up the buried treasure. Before you have done these two tasks, the island has no purpose. After Captain Crawfish has been chased away, the Governor will give you the treasure location and bone shovel. (In order to beat Captain Crawfish, you will need the strongest ship, the Phoenix Warbird.)