Instructions
Purchase a hammer from any General Store. This item will cost between 107 and 113 gold.
Obtain 90 nails. You can purchase nails from other players or craft them using the Smithing skill. You will need 6 steel bars to craft 90 nails.
Travel into the wilderness north of Varrok, toward the Chaos Temple. Locate the graveyard, northwest of the Chaos Temple.
Take three wood planks from the planks scattered around the ground in the graveyard.
Return to the boat in Port Sarim and get on board.
Climb down the ladder and locate the hole in the boat. Click the hole and select "Repair" three times to fix the boat.