Step hulls and horsepower back in the 40's
05-18-2011, 09:11 PM
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Step hulls and horsepower back in the 40's
In 1943, an inquiry was held by the Navy to discuss planing, hull design, and fuel consumption issues, but no major modifications were made before the end of the war. (Wooden Boat Forum) During the war, both Elco and Higgins came up with stepped hull designs which achieved significant increases in top speed,.....
All U.S. PT boats were powered by three 12-cylinder gasoline-fueled engines. These engines were built by the Packard Motor Car Company, and were a modified design of the 3A-2500 V-12 liquid-cooled aircraft engine. The 3A-2500 was an improved version of the 2A engine used on the Huff-Daland XB-1 Liberty bomber of World War I vintage. Packard modified them for marine use in PTs, hence the "M" designation instead of "A". (i.e., 3A-2500 then 3M-2500). The three successive versions of these engines were designated as 3M-2500, 4M-2500, and 5M-2500, each of which had slight improvements over the previous version. Their aircraft roots gave them many features of aircraft engines, such as superchargers, intercoolers, dual magnetos, two spark plugs per cylinder, and so on. Packard built the Rolls Royce Merlin aero engine under license alongside the 4M-2500, but with the exception of the PT-9 prototype boat brought from England for Elco to examine and copy, the Merlin was never used in PTs. The 4M-2500s initially generated 1200 hp (895 kW) each, together roughly the same power as a Boeing B-17 bomber. They were subsequently upgraded in stages to 1500-hp (1,150 kW) each, for a designed speed of 41 knots (76 km/h). The final engine version, the Packard 5M-2500, (late 1945) had a larger supercharger, aftercooler, and power output of 1850 Hp.
All U.S. PT boats were powered by three 12-cylinder gasoline-fueled engines. These engines were built by the Packard Motor Car Company, and were a modified design of the 3A-2500 V-12 liquid-cooled aircraft engine. The 3A-2500 was an improved version of the 2A engine used on the Huff-Daland XB-1 Liberty bomber of World War I vintage. Packard modified them for marine use in PTs, hence the "M" designation instead of "A". (i.e., 3A-2500 then 3M-2500). The three successive versions of these engines were designated as 3M-2500, 4M-2500, and 5M-2500, each of which had slight improvements over the previous version. Their aircraft roots gave them many features of aircraft engines, such as superchargers, intercoolers, dual magnetos, two spark plugs per cylinder, and so on. Packard built the Rolls Royce Merlin aero engine under license alongside the 4M-2500, but with the exception of the PT-9 prototype boat brought from England for Elco to examine and copy, the Merlin was never used in PTs. The 4M-2500s initially generated 1200 hp (895 kW) each, together roughly the same power as a Boeing B-17 bomber. They were subsequently upgraded in stages to 1500-hp (1,150 kW) each, for a designed speed of 41 knots (76 km/h). The final engine version, the Packard 5M-2500, (late 1945) had a larger supercharger, aftercooler, and power output of 1850 Hp.
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