Tolbi-bound Ship

The Tolbi-bound Ship is the vessel that conveys Isaac and party across the Karagol Sea to Tolbi. A Boat Ticket can be purchased at the Kalay Docks, and at the docks is where the ship is anchored. However, the ships that have been sailing across the Karagol have been plagued by sea monsters as of late. Because of this, the captain will not set sail without his Anchor Charm. One of the crew men stole it and hid it atop the mast because he was scared to set sail, but Isaac and his friends recover this charm. After that, they, along with Sean and Ouranos volunteer to help fight off the monsters, much to the relief of the captain, his first mate Kaja, and the rest of the crew and passengers. The journey on the ship is fraught with monster attacks, with monsters taking out four of the ship's oarsmen. Isaac is tasked with selecting replacements from among the passengers, and the right combination can land the ship on Crossbone Isle. The battles on the ship culminate with a showdown with the Kraken. Sadly, the ship arrives too late for the Colosso hopefuls on board to enter the tournament. Once the ship reaches the Tolbi Docks and you disembark, it is not possible to get back onto the ship. It is possible to find a hidden item inside a barrel in the captain's cabin. This should be picked up before leaving the ship.

Route to Crossbone Isle
There is a special way to make the ship go off course, however. After the first encounter with the sea monsters, Kaja will make you pick an oarsman to replace the one who has fallen to the the Man o' Wars. Talk with the man in the Green Threads (He says: "Hey! You're not thinking of making me an oarsman, are you?"). Then after Kaja makes you pick another oarsman. After that, pick the chef (He says: "You... You must be joking. You want me to row?"). Then pick the bald man, Lastly, after finishing with the Kraken, pick the old man (He says: "Out of all these people, you're asking a frail old man like me to row?"). You'll know you did it right when the boat visibly goes northwest instead of just west after the Kraken battle. Kaja then says says he doesn't think the ship has been heading to Tolbi. They send you out to land on the uncharted area.

The above is actually one of several available configurations of rowing passengers; another is to first use the bald man, then the blonde lady, then the purple merchant/tour guide, and finally the senile old man. Essentially, as Camelot Software Planning explained on their official Golden Sun website, the idea is to choose stronger passengers to be the oarsmen on the left side and the weaker passengers to be the oarsmen on the right, to achieve enough of the imbalance that the ship veers off course.

On the world map, there is a large rock with an opening in the middle. You want to go in that opening. You'll be greeted by a puzzle. Welcome to Crossbone Isle, even though you can't come back here until you get Cloak, you can get some always-appreciated experience for Colosso. You also get some nice stat-boosting items and an as-of-now great weapon called the Mystery Blade. After clearing the first three floors and beating the fourth floor's battle with the Gryphons, you can't go in any farther, so head back to the (now) Tolbi-Bound Ship, luckily with nothing but smooth sailing to Tolbi.

Collectibles
Since the Tolbi-bound Ship cannot be reentered after completing the crossing across Karagol Sea, the items below can be permanently missed:

23 Coins: In a barrel right in front of you as soon as you enter the passenger room. Anchor Charm: After you see the blue-capped crew member taking this item away from the captain's bridge, it will end up on top of the mast. Climb up it, get the charm, and give it to the boat captain following the necessary cutscenes to progress. Lucky Medal: In the lower right barrel of the storage room belowdecks. Nut: In the captain's bridge, this is in a white jar.