Porpoising is the tendency of some boats to flail upward and downward due to the actions of waves. You may find yourself in a porpoising boat, and you will be facing more problems than simply an unpleasant ride. A porpoising boat is harder to steer and has a greater tendency to capsize than one that is not porpoising, and it may therefore place you in need of rescue. Fortunately, however, you can adopt certain measures to at least reduce this problem.
Suggestions:
Lengthen the centerboard, the fin-like extension at the bottom of the boat. The centerboard does present the boat with at least some downward drag, pulling it into the water, and so this force will drag the boat down to the water's surface during a skip, thus shortening the duration of that skip and reducing porpoising. Of course, you may reach certain practical limits to the length of your centerboard. Certainly it cannot extend beyond the distance to the earth beneath your boat, and you can't take into waters as shallow as you could before.
Place a lateral wing upside-down at the bottom of your centerboard. A wing with gas or liquid flowing over both of its upper and lower surfaces pulls itself in the direction lateral to its longer surface, and so the wing will draw your boat further into the water and will do so more strongly with every increase in speed. Though probably more expensive than simply lengthening your centerboard, using a wing can spare you from the problems of lengthening your centerboard and thus may leave you free to continue navigating shallower waters.
Increase the amount of weight in the very bottom of your boat, called the keel, or concentrate the weight present more completely. Sailors normally put such ballast in this location to prevent lateral rolling, but the increased weight will require more lift force to raise the boat out of the water and so will decrease leaps due to uneven water pressure across the hull, such as in meeting a wave. Furthermore, by lowering the boat more completely and evenly into the water, that weight will increase and stabilize water pressure across the hull, thus stabilizing the boat more overall and decreasing the cause of porpoising.
Lengthen the hull of your boat. This will increase the area in contact with the water during porpoising and so will increase the water pressure on it. That pressure will then serve to stabilize the boat.
Narrow the hull of your boat and give it straight sides, as nearly vertical as practical. A boat of a given weight will displace water of a weight equal to itself, and so this design will permit more of your ship's overall height to be below the water line, lowering its center of gravity and stabilizing it.
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