A modular sponson for a small boat has discrete sections disposed in a series from the bow and along both sides to the stern. Each section has an axially extending length of tubing defining a longitudinal opening and a plurality of elongate pieces of closed cell foam material secured to the outside of the tubing for the length of each section. Flotation structure outwardly disposed from and in contact with the elongate pieces is covered by a protective covering that reaches inwardly to opposite ends of each length of tubing. A bonding agent is provided on the tubing, elongate pieces, and flotation structure to hold them together in each discrete section of the modular sponson. An elongate cable extends through the longitudinal openings of the series of sections and exerts a tensile force to hold the sections adjacent one another in compression.