The seakeeping characteristics of various boom geometries in irregular waves and currents are investigated. The response of a floating boom on the open sea is a function of a number of parameters, such as boom geometry, distribution of mass, buoyancy/weight ratio, and wave and current characteristics. To understand the relationship between these design parameters more clearly, a series of regular and irregular tests were conducted with 6 different 1:4 scale models for three current velocities and six different wave conditions. To simplify the problem, only rigid boom sections consisting of a buoyancy cylinder and vertical skirt were used. In parallel with this experimental program, a numerical model for the responses of two-dimensional floating booms in small-amplitude waves is also developed. The numerical results are compared with are large-scale experimental results. The boom effectiveness on the open sea is evaluated based on the concept of “effective draft” and “effective freeboard” assuming that drainage and oversplashing failures are the prime mechanisms of containment failure. Using the present results, a guideline for the optimum design/selection of future booms is developed.