A boat bumper is positioned between a nautical structure and a nautical vessel. A main body includes a concave portion and a convex portion. The concave portion abuts the nautical structure and the convex portion abuts the nautical vessel. A boat bumper can optionally include an auxiliary bumper having a first convex part and a second convex part. The main body and auxiliary bumper engage to form a macro bumper with the first convex part abutting the concave portion. Alternatively, a main body includes a male connector with a male shape and a female cavity complementarily shaped to the male shape such that the male connector of another bumper fits within the female cavity to connect the bumpers together. A male shape can be keyed and/or tapered in at least one direction.