The boat is entered by the stairwell (really a ramp) near the helicopter. The boat is probably the easiest way to get a lot of points in the game because the ball frequently just sits there bouncing around like crazy.
A multiplier is used on the scores for hitting the pop bumpers in the boat if you light up all three slots. You can control which slots are lit by using the flippers. When the ball gets stuck bouncing around (usually on the left slot and bumper) you can wait for the slot to line up, hit the flipper, wait for it to light up again, hit the flipper, and all three lights will light up, upgrading your bumpers. They start out blue, then aqua, then bright green, then gold, and finally red.
You get 3,000 points for entering the boat. The pop bumpers are worth 1,500 points each, but the multipliers increase that.
Blue: 1,500 points