These instructions are from Mika Skogström, who in turn has learned the fine art of the dolphin making from his father.
1. Eat some canned food, for instance pea soup is fine, the food is irrelevant, we just need the can
2. Cut the bottom of the can, making a metal tube
3. Attach a strong string to the can, so that it doesn’t slip sideways (see pic). Attach the other end to the boat. At speeds over 5-6 knots the dolphin pulls quite hard so it is better not to have your hands on the rope.
4. you can adjust how much the dolphin dives/jumps, by changing the place of the knot in respect of the long axis of the can: the nearer it is to the middle of the can, the more the dolphin will stay on the surface. You’ll want a nice combination of dives, jumps and fast direction changes. A good example of the correct position of the knot is in this picture
and here is the dolphin in action: