Nowadays bulbous bows of considerable dimensions have become quite common in use for low speed ships of large block coefficients, such as mammoth oil tankers and bulk carriers. Author who has concerned himself with bulbous bow design for such ships last three years presented his conjecture over how bulbs would work to reduce the residuary resistance : in the full load condition the improvement of streamline pattern due to bulbs brings reduction uniformly for a entire speed range, while in the ballast condition the wave cancellation due to bulbs is the primary cause of a predominant reduction at the characteristic Froude number of about 0.2. The conjecture is well founded on the author's streamline observations with models as well as other experimental and theoretical evidences. Design features and feasibility of large bulbs were discussed and some important problems were pointed out pertaining to model-ship correlation of the full ships fitted with the bulbs.