If an oncoming wave is particularly big or a wave is about to break on top of you, then a duckdive is required.
Paddle towards the wave at speed. When you get about two metres away slide your weight forward and move your hands about 30cm down from the nose, holding tightly onto the rails. Push up into a press-up position with your head directly over the nose of your board. As your board begins to sink, shove your knee into the tail to guide it downwards. Stretch your other leg out behind you. If your timing is good, the wave should now break over you. Now lay flat against your board and look up at the whitewater as it passes over you.
When it’s passed, move your weight further back on your board and angle upwards. The whole time that you are underwater you should kick with your fins to avoid being dragged back. The bigger the wave is, the earlier you should aim to become submerged. The main hazard with duckdiving at shallow reefs is hitting the reef by going too deep. Avoid this by keeping your hands flat on the boards deck or by clutching the boards rails – don’t put them underneath.