On February 3, 2007, approximately 1500 Pacific standard time, a Waco UPF-7 single engine airplane, N30140, and a Boeing A75N1(PT-17) single engine airplane, N49270, collided in midair while maneuvering about 1 mile offshore west of Palos Verdes, California. Both of the airplanes were being operated by their respective owner/pilot's under the provisions of 14 CFR Part 91. The airline transport pilot in N30140, the sole occupant, sustained minor injuries, and the private pilot in N49270, the sole occupant, was not injured. N30140 sustained substantial damage and N49270 sustained minor damage. Both airplanes were on a local personal flight, which departed Zamperini Field Airport (TOA) Torrance, California. Visual meteorological conditions prevailed, and no flight plan had been filed for either airplane. According to the pilot of N30140, he and another PT-17 departed TOA to the south and established radio communication with each other. For approximately 15 minutes, the two airplanes flew independently of each other. During that time, the pilot of N30140 heard over the radio frequency two other pilots that were operating in the area, and the pilot did not see either of the two aircraft. One of those two aircraft was N49270. N30140 and the other PT-17 had then decided to return to TOA. N30140 began to regroup with the PT-17 at an altitude of 3,000 feet mean sea level (msl). Approximately 1,000 feet from the PT-17, the pilot of N30140 felt "a hard impact on my aircraft." The airplane rolled more than 90 degrees to the right in a steep descent. The pilot thought another aircraft struck his; however, he did not see another aircraft. The pilot regained partial control of the airplane and executed a forced landing to shallow water at Cabrillo Beach Park, San Pedro, California. During the landing, the airplane stalled approximately 35 feet above the terrain, impacted the terrain, and nosed over. Examination of the airplane revealed the rudder and elevator control surfaces were destroyed. According to the pilot of N49270, he departed TOA to the south and climbed to 3,000 feet msl. Approximately 20 minutes into the flight, he observed N30140 and another PT-17 coming toward him, and they were not in formation. The two airplanes were flying northwest (N49270 was flying south) and N30140 was a "few hundred feet lower." N49270 and the other PT-17 confirmed visual with each other over the radio. N49270 and the other PT-17 intended on joining in formation. About 1/2 mile separation between the two PT-17s, N30140 crossed under N49270. N49270 then joined up with the other PT-17 and "stabilized on [other PT-17] left wing in the step-up position and headed easterly." Approximately 1 minute later, N49270 felt a bump and noticed N30140 was slightly to the left and below his airplane. N49270 pulled up and the propeller struck the tail section of N30140. N49270 reported the event to air traffic control and landed uneventfully at TOA. Examination of N49270 revealed damage to the propeller blade tips and a small dent in the lower left wing.