The patterns for a ship's rib-head ventilator, instead of being set out by the method of triangulation, as just explained, can often be more conveniently developed by treating each segment of the ventilator as part of a cone. Before describing how this can be done, however, it will be necessary to first explain how a cone and a cylindrical pipe can be made so as to fit together exactly. To do this it will perhaps be the best plan to go over the striking out of the patterns for a simple cowl made up in the way of a