Structural midship section of the America's Cup challenger Shamrock IV, designed and built in 1914 by Camper & Nicholson for Sir Thomas Lipton and the smallest of his racers at 110 feet overall. Other dimensions were 75 feet waterline length, 22 feet 4 inches beam, 13 feet 8 inches draft; sail area was 9,860 square feet, rigged first as a sloop with a single headsail, but soon changed to the conventional cutter rig.

This section drawing illustrates its peculiar form, showing the sides heavily tumbled-in to cheat the deck measurement rule and the splaying of her ballast keel to place weight as low as possible. The construction was interesting: spruce longitudinal were supported by transverses, the web plates of which were made from the seawater-resistant alloy Navaltum. Side and lower planking consisted of three skins, two laid diagonally and the outer longitudinally; the inner skin was of cedar, the center one spruce and the outer mahogany. Bottom planking was single-skin mahogany. The sheerstrake, deck stringers and lower frames were steel. The deck was plywood covered with canvas.

Shamrock IV was the first British yacht designed according to the American Universal Rule of Measurement.