The highly competitive duels fought between Britain and America through the Harmsworth Trophy pushed speedboat design and engineering to the edge. Gar Wood (USA), land speed hero Henry Segrave (UK), and later Kaye Don (UK), battled over the prestigious title with increasingly more powerful boats. The financial backing of the playboy pioneers enabled both teams to produce a succession of incredible machines.

Specifications

			Miss America X		Miss England II
	Length		11.6 metres		11.6 metres
	Power		4 x Packard 2500 V12 (1600 horsepower each)		2 x Rolls Royce 'R' V12 (2000 horsepower each)
	Top speed		124.9mph		120mph

Design

Speedboat design has to consider three main components – powerplant, hull and the water. The effect of water depends on how fast a vessel is travelling. Fluid and absorbing beneath a still boat, water becomes an uncompromising surface as hard as glass beneath the bottom of fast moving boat.

The design of the hull has to deal with this aggressive change in surface, and also be able to cope with the colossal power delivered by the engines. The Miss America boats were based on a large rigid hull that could handle serious knocks at speed, whilst coping with the torque of its four massive 2.5 litre engines.

The Miss England boats followed a development path that started with a smaller flexible hull and compact engines. The path led to the long and robust Miss England II, which was more along the larger American lines.

Both vessels featured stepped hydroplane hulls. This cut-away step, or spoiler, approximately halfway along the underside of the hull, breaks the flow of air under the boat as speed is increased. This reduces the effects of lift, cuts back drag and makes the boat more stable in a straight line. Both boats were relatively unstable when it came to cornering around the buoys of the Harmsworth course. A fraction of a second too early on the power out of a corner could result in rolling the boat.

Engines

The original Miss England used the same Napier Lion engine that Henry Segrave had in his land speed record car, the Golden Arrow. As the search for greater power continued, the Rolls Royce 'R' engine became the natural choice for the British team. This fantastic engine (which would develop into the RR Merlin of Spitfire fame) was supercharged. Supercharging an engine involves pumping extra air into the cylinders to burn more fuel, resulting in a big horsepower gain.

Miss America X used four of the massive 2500cc Packard V12 engines. These were also supercharged with an uncompromising eight supercharger units driving hard to keep up with the 16 carburettors. Eventually the large-scale American engineering would finish top after several years of close competition. The success of these lightweight yet powerful aeroengines resulted in Packard producing all the engines for the US Navy's high-speed motor torpedo boats in the Second World War.