To be effective, boom must have enough freeboard to keep contained product from washing over the boom. Wind will act on the freeboard to move and stress the boom. The skirt of a boom is the amount the boom extends below the water. The skirt acts to prevent contained product from washing under the boom. The deeper the skirt, the more effective it is.
Deeper skirts increase the water current loading on the boom.
The weight is what keeps the boom vertical in the water. Lead weights, chain in the bottom of the boom, or the mass of the floatation can all act as weight. Boom performance is based on shape and angle of placement relative to the current. Cylindrical booms remain straighter in the water and can handle stronger currents, while flat booms are easier to transport and store. Boom must be set at a sharp enough angle to handle the present current and anticipated changes.