To get the Northeastern Sea Chart, you need to reach a new area of the Temple of the Ocean King by putting the crystals into the pedestals in a specific order.
Getting the Northwestern Sea Chart
If you don't have the Northeastern Sea Chart, you have to go back to the Temple of the Ocean King. If you warp using the golden light, you will start on B6 with the amount of time that was left when you warped out of there before.
Temple of The Ocean King, B6
Go north and down the stairs.
Temple of the Ocean King B7
Step on the moving block, then when it goes left, step on the block above you. Face the left side so that you can block the arrows with your shield. When the block stops, walk onto the block on the left. From here, you can walk onto the safe area and use your boomerang to hit the gold pot to the right, giving you 30 more seconds.
Then wait for the moving block to reappear, and walk across it to the left, onto the blue floor. Remember to go slowly so you don't alert the Phantoms. Go to the safe area in the northwest corner. From there, go south to the stairs in the southwest corner, and go down.
Temple of the Ocean King B8
You can go to the northwest corner of the area to find a gold pot to add 30 seconds to the hourglass.
Then cross the invisible bridge and go up the stairs in the southeast part of the room.
Temple of the Ocean King B7, part 2
Shoot the southeast Phantom in the back with an arrow, then run to the crystal switch and hit it to lower the flames. Be sure to time it correctly so the moving platform will be there when you go to where the flames were, and the Swift Phantom won't be coming toward you. From the moving platform, go to the safe area. From there, go west, and open the chest to get the round crystal.
Take the crystal east to the safe area, then go southeast, and make your way back to the stairs in the southeast corner of the area. While holding the crystal, you will always walk too slowly to make a sound on the blue floors, so go at top speed while carrying the crystal. If a Phantom takes the round crystal, shoot the Phantom in the back to make it drop the crystal.
Go down the stairs with the crystal.
Temple of the Ocean King B8, part 2
Go west across the invisible bridge, and carefully take the round crystal to the pedestal in the northwest part of the room.
The spikes will lower. Step on the switch to make an air vent turn on. Go down to the air vent and step in it to reach a gold pot to add 30 seconds to the hourglass. Then go down the stairs near the switch that you stepped on.
Temple of the Ocean King B9
Open the nearby chest to get the triangle crystal. You can't go any farther, so take the crystal upstairs.
Temple of the Ocean King B8, part 3
Take the crystal east across the invisible bridge. Stand in the safe area below the southeast stairs, then send a Bombchu through the hole in the wall to the north and make it hit the crystal switch on the right. Then you can take the triangle crystal northeast and down the stairs. (If you don't have any Bombchus, make your way to the northeast corner of the room and drop the triangle in the safe area there. Then go to the west and bomb the blocks to reveal the triangle pedestal. There is a safe zone under the block that you bombed, so stand there when the Phantom comes back. After that, go east to get the triangle crystal and take it west to the pedestal. The spikes down below will disappear, so go there when it is safe to do so. Hit the crystal switch to open the door that was blocking the stairs. Then take the triangle crystal northeast and down the stairs.)
Temple of the Ocean King B9, part 2
Use the boomerang to kill the invisible Wizzrobe in the northeast corner.
Take the triangle crystal to the pedestals in the middle of the northern part of the room. For now, put the triangle crystal on the ground.
Go to the southeast corner of the area and kill the invisible Wizzrobe there, then go to the left and hit the arrow shooter with the boomerang, then shoot an arrow at it. The spikes will lower in the southwest area.
Go to the safe area near the middle of the room and bomb the barrier that is blocking the way. From the safe area, wait for the Phantom to walk by, then shoot it in the back and take the crystal that it was holding. When you have the crystal, put it in a safe area.
The switch in the middle of the southern area makes a trap door open, so get rid of the Phantom that way. (You have to hit the eye switch to the right to lower the spikes blocking the path to the floor switch there).
Now put the square crystal in the pedestal in the northwest part of the room (not the central part where there are three pedestals) to remove the flames. Go up the northwest stairs.
Temple of the Ocean King B8, part 4
Take the round crystal, then go south and walk onto the air vent to go up onto the wall. Walk north on the wall to reach the stairs that you just came up. Take the round crystal down there.
Temple of the Ocean King B9, part 3
Now put the three crystals into place, starting by putting the square crystal into the square pedestal, then putting the round crystal into the round pedestal, then finally putting the triangle crystal into the triangle pedestal. Then go north and you will feel a tremor. Go south again and you will be in a new area.
Temple of the Ocean King B10
Send a Bombchu through the hole in the nearby wall to hit the crystal switch near there. This lowers the spikes in the northwest corner of the area. Go to the northwest corner, and stand in the safe area with the boulder. Wait for the Phantom to be in the path of the boulder, then stand behind the boulder and tap it to push it downward. When the boulder hits the Phantom, the Phantom will die and drop its key. Go south from there, picking up the key on the way, and go to the southwest corner. Send a Bombchu through the nearby hole to hit the crystal switch near there. This lowers the spikes in the eastern part of the area.
Now go clockwise to make your way to the southeast corner of the room. Go past the spikes, then stand in the nearby safe area. Hit the crystal switch there to stop the spikes. You can use your boomerang from here to hit the gold pot in the southeast corner and add 15 seconds to the hourglass.
Go southwest until you see a part of the wall that is lighter in color than the rest. Bomb that wall to break it open. Go north through the wall and go northeast to the safe area beyond the spikes that you lowered earlier. Use the boomerang to stun the Phantom Eye when it comes close, then kill it with your sword.
For now, go southwest to the locked door and open it using the key that you got from rolling the boulder onto the Phantom in the southwest part of this room. Go down the stairs.
Temple of the Ocean King B11
Go around this room killing the Phantom Eyes. A chest will appear in the safe area in the northeast corner when they are all gone. It contains a random loot item.
Pull the switch in the northwest corner of the area, and the northeast corner of the area, to make bridges appear. There is a pile of sand near the northeast corner of the room that will let you float up to one of the upper-right ledges. Try shooting the nearby Phantom in the back before you dig up the sand and float up in the air vent. After you float up, go across the bridges and step on the switches. The nearby signs say that you have to step on all four switches on the ledges near the corners of this room.
Use the air vent in the southern area to reach the ledges there. Go east across the bridge and step on the switch there. Then, while standing here, use a Bombchu to hit the crystal switch in the southeast corner of the room. Before the Bombchu hits the switch, start running to the left so you can be near the bridge when it comes out. Cross the bridge and step on the switch. The nearby door will open. Go there and go down the stairs.
Temple of the Ocean King B12
Use the boomerang to break the nearby golden pot to get more seconds added to the hourglass. Then pull the nearby switch to lower the spikes.
Go south past the spikes, then use the boomerang on the Phantom Eye and kill it. Then go to the safe area in the west side of the room.
There is a safe area to the north with a treasure chest in it. The chest contains a Force Gem. When you open the chest, a Phantom will appear to the south. The Phantom stays where it is, but turns around counterclockwise. You might want to shoot it in the back while you take the Force Gem east to the pedestals.
After putting the first Force Gem in place, an invisible Wizzrobe appears in the southwest part of the room, indicated by a skull on the map. The Wizzrobe will approach you if you turn away from it while not standing in a safe area. Kill it with the boomerang if possible.
Go to the southwest corner of the area where the large Phantom is walking around, and step on the switch to lower the spikes. Then shoot that Phantom from behind and take the Force Gem that it drops, and put it into a pedestal.
Then go to the southeast part of the room. Kill the Phantom Eye in this area. If you killed all the Phantom Eyes in this room, a chest appears in the safe area on the west side.
Go to the northeast area and open the chest there to get another Force Gem. A Swift Phantom will appear and start walking counterclockwise around this area.
Because of the spikes southwest of where you got the third Force Gem, you will have to go east and south to take the Force Gem to the pedestals.
After you have taken the final Force Gem to the pedestals, the door will open. Go through and down the stairs.
Temple of the Ocean King B13
Go southwest from the stairs and jump down the ledge. Dig up the sand so you can quickly go back up there. Go southeast from the air vent and open the chest to get the Northeastern Sea Chart. Step into the blue light that appears in the northwest corner to return to the entrance of the temple. Then you can go to your ship and sail to the Northeastern Sea.