As soon as you start dive down and get the boat right in front of you.

Swing around to the right and you will see another boat coming out of the tunnel. Go get him and make a sharp turn left and go into the tunnel.

You will meet one boat about half way up and another at the top. Make sure to flame both of them.

Go through the arch right in front of you then go left and get the boat over there. ignore the arch on the island fir now. Instead go around the back and you should meet the 6th boat along the way

go through the arch on the other side and you should see the 7th boat through it, get him and come around to the right til you see the arch on the island.

Complete your circle through the arch and keep going around and you should see the 8th boat coming up the channel.

take him out and just go through the rest of the arches down the way the boats where coming from.

After the last arch you should see the first treasure chest on an island. Flame it and come around nearly a full circle to the right and go through the tunnel with the chests. There are 2 in the tunnel.

when you exit the tunnel up to the left and get the two chest in tunnel up there.

when you exit go down right and get the sixth chest on the ledge and go through the tunnel where the planes are coming through.

The planes do a figure '8' through the upper and lower tunnels and you want to fly against them. Also the planes alternate high and low, so if the first one is near the ceiling then the next will be near the water.

As you go though the lower tunnel you can get 3 or 4 of the planes. when you exit go up to the upper tunnel(reverse from when you got the chests), taking out any plane you meet along the way. Hopefully by the the time you exit the upper tunnel you will have all 8 planes. either way go down to the left and get the last 2 chest on the ledges then go after any planes you may have missed