Hydroplane Slo-mo-shun IV establishes world record on June 26, 1950.

  • By Greg Lange
  • Posted 7/06/1999
  • HistoryLink.org Essay 1465
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On June 26, 1950, in Lake Washington, the hydroplane Slo-mo-shun IV, piloted by Stan Sayres (1896-1956), shatters the world speed record on water. His speed of 160.3235 mph betters the previous record of 141 mph set in 1939 in England. The run on Lake Washington is completed about 7:10 a.m., so early that few people witness the event.

Stan Sayres's Amazing Hydroplane

The Seattle Post-Intelligencer announced the world record run with:



Slo-mo-shun IV did it!

Stan Sayres' amazing hydroplane, Seattle designed and Seattle built, Monday established a new world speed mark when it averaged 160.3235 miles per hour in two dashes over a measured mile off U. S. Naval Air Station, Sand Point, on Lake Washington.

With Sayres, Seattle automobile dealer and sportsman at the wheel, Ted Jones, Boeing supervisor and designer of the craft in the bucket seat alongside, Slo-mo-shun IV made the first run over the measured mile in 21.98 seconds or 163.785 miles per hour, the second one in 22.95 seconds or 157.2 miles per hour (Seattle P-I, June 27, 1950).

Stanley S. Sayres (1896-1956), the owner and driver of the hydroplane, moved to King County in 1932. He was in the automobile business heading the American Automobile Company, a Chrysler car dealership at 1001 Broadway in Seattle, and an auto parts store in the University District. Sayres also owned the Jen-Cel-Lite Corporation, a manufacturer of cold weather clothes.

He became interested in speedboat racing in 1926 in Oregon, and his interest continued after he moved to King County, Washington. In 1949, Sayres built a 17-room home on the east side of Hunts Point near the point's north end (4450 Hunts Point Road), along with a boathouse for his hydroplanes. Hunts Point is on the east side of Lake Washington.

Sayres had owned and raced smaller boats, but he wanted to try for a world record. With this in mind, he commissioned Ted Jones to design the Slo-mo-shun IV and Jensen Motor Boat Company, at the north end of Seattle's Lake Union, to construct it. Jensen Motor Boat Company launched the 28-foot-long, 4,750-pound hydroplane in October 1949.

A Perfect Day For Speed

From June 21 to 23, 1950, due to rough water and a broken propeller, Sayres's first attempts at world record runs failed. But in the early morning hours of June 26, lake conditions, with a light chop on the water, were perfect for speed. At 5:30 a.m. boats went out along the measured one-mile course and picked up any debris they could find. At about 6:45 the course was ready and the Slo-mo-shun IV, with Sayres and crewmember Ted Jones, headed out.

On the first attempt, the timer malfunctioned. The Slo-mo-shun IV continued to the south end of the course, and turned north. Sayres opened the throttle, and the hydroplane ate up the mile in 21.98 seconds (163.785 mph). For an official speed run, rules required the boat to make a second try within 15 minutes, going in the opposite direction. The Slo-mo-shun IV refueled in seven or eight minutes. Sayres then pointed the hydroplane south and zipped over the course at 157.2 mph. The combined times were averaged to establish a speed of 160.3235 mph.

It was 7:10 a.m. and the Slo-mo-shun IV had set a world record.

Easy Rider

Upon reaching the dock at the Sand Point Naval Air Station officers' beach, Sayres told reporters that the ride was "Just like sitting in a comfortable chair in your living room" (Seattle P-I, June 27, 1950). The ride was easy, but the roar of the 1,500-horse-power engine kept Sayres's ears ringing into the evening.

Sir Malcolm Campbell in the Bluebird II had set the previous world speed record on water in August 1939 at 141.74 mph on Lake Coniston in England. By the summer of 1950, his son Donald Campbell had just installed a more powerful engine in the Bluebird II and was about to try to beat his father's record. Upon learning of Slo-mo-shun IV's record, Donald Campbell conceded, "If this is official, then our job is defeated for the time being ... . This speed is out of the range of our present boat and is five miles an hour faster than the speed at which the Bluebird is known to stay on the water" (The Seattle Times, June 27, 1950).

Stan Sayres also shattered by 33 miles per hour the United States record established by Dan Arena and Jack Shafer on the Such Crust I in Michigan in August 1949.

After winning the world record, Sayres stated, "The boat was not extended" (The Seattle Times, June 10, 1973). He proved it in 1952 when the Slo-mo-shun IV set a new speed record traveling at 178.497 miles per hour. But Don Campbell was not to be denied. In 1956, on a new jet-driven boat, he set a new world record traveling on water at a speed of 202.32 mph.

King County Built and Maintained

The Slo-mo-shun IV was King County's own. The owner, designer, builder, mechanics, and crew were Seattle and King County residents. The only parts of the hydroplane not constructed in Seattle were a surplus World War II airplane engine and the boat's propeller. In addition to Stan Sayres, the following men were on the team that constructed and maintained the Slo-mo-shun IV:

  • Ted Jones, designer and one of the drivers, was assistant foremen at Boeing Airplane Company. He lived in McMicken Heights (4612 S 170th) just outside Seattle city limits.
  • Anchor Jensen (d. 2000), builder, managed and owned the Jensen Motor Boat Company at 1417 NE Northlake Way where the Slo-mo-shun IV was built. He lived in Seattle's Montlake neighborhood (2715 10th Avenue E).
  • Don Spencer built the gearbox. He was an employee of the Western Gear Works in Seattle (417 9th Avenue S).
  • Elmer Linenschmidt, mechanic, was a salesman who lived at 7035 Beach Drive near the Fauntleroy neighborhood of Seattle.
  • Mike Welch, mechanic, was a cableman for Pacific Telephone and Telegraph, and lived in West Seattle (4702 Beach Drive).
  • Jerry Barker, mechanic, an engineer at the Boeing Airplane Company, lived in the View Ridge neighborhood of Seattle (8046 Fairway Drive).
  • Doug Miner, a mechanic who owned Miner's Aircraft & Engine Service, lived in Arbor Heights in West Seattle (10635 Marine View Drive).
  • Bob Swanson, mechanic, a boat builder at Jensen Motor Boat Company, lived in Shoreline (1222 NE 184th).
  • Joe Schobert, a mechanic employed as a dispatcher at Interstate Freight Lines, lived at 5657 42nd Avenue SW in West Seattle.
  • Hi Johnson produced the boat's propeller outside of King County in Newport Beach, California.


"Seafair," Typescript, n.d. Seattle Public Library (Call No. 394.26979/Seafair/1961), Chapter VII, p. 2-3; The Seattle Times, June 26, 1950, p. 1, 23; Ibid., June 27, 1950, p. 29; Ibid., September 17, 1956, p. 2; Ibid., September 18, 1956, p. 28; Ibid., June 10, 1973, Ibid., Magazine section p. 4-5; Seattle Post-Intelligencer June 27, 1950, p. 1, 9-B; Ibid., September 18, 1956, p. 1.

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