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In 1952 Stanley Sayers increased the water speed record to 178.49mph. John Cobb was to challenge the record in his boat "Crusader". Donald considered building a boat to enter the Harmsworth trophy, this was suggested to him by Bill Coley. The Americans had held the trophy for a number of years and it could provide Donald with the challenge he desired. He asked Lewis and Ken Norris to design the new boat. Unlike the K4 the K7 was to have a metal hull, capable of withstanding more stresses than a wooden hull. The design was different to Slo-Mo-Shun, which had a wide surface with planning points each side and at the rear. (This made for a very close to unstable boat, with the front of the boat tending to rise the faster the boat went). The K7 design was similar to John Cobbs in that "outriggers" were used in conjunction with a central planning surface, which helped move the centre of pressure behind the centre of gravity (The main difference between the two boats layout was that the outriggers on K7 were at the front, whereas with "Crusader" they were at the rear. Early on the boat was designed to be fitted with a propeller, rather than the jet engine. To comply with Harmsworth trophy regulations, two seats were built into the design side by side in front of the engine. Donald still preferred the jet engine route though and also had tests done on a model by Saunders-Roe.

On 29th September John Cobb was killed whilst attempting to break the record at Loch Ness in Scotland. Donald's attentions now moved from building a boat for the Harmsworth trophy to the water speed record.

Donald sold his half share in a company he owned, and set about the task of putting the project together. The jet configuration model tests encouraged Donald to try to secure a jet engine. It would enable Donald to put the record out of reach of the propeller driven Slo-Mo-Shun. Donald approached Air Commodore F.R. Banks at the Ministry of supply. He suggested using a Metropolitan Vickers Beryl engine. This engine produced 3750lbs of thrust, which was plenty of power to obtain the record. Two of the engines were obtained from the ministry of supply and as a bonus Metropolitan Vickers agreed to overhaul them.

Saunders Roe, who were going to make the boat, decided to drop out, they were only interested in propeller driven craft. They would still provide any technical advice and tank testing facilities though. Castrol who had sponsored Sir Malcolm, decided against sponsoring Donald, this was a huge setback. After John Cobb's tragic crash persuading large sponsors to invest in a seemingly dangerous pursuit was not the easiest of tasks.

Despite these setbacks plenty of commercial interest was shown initially by companies, who offered their services or small amounts of money. Accles and Pollock offered to make the main frame, this was made of square section high tensile chrome-molybdendum. A subsidiary of the Lancashire Aircraft corporation, Samlesbury Engineering offered to construct the hull after Donald had asked the Sir Wavell Wakefield, who was a director in the company. This was only after some lengthy talks and meetings. One of the clauses of building the boat was that it was to run at Ullswater, where Sir Wavell owned the pleasure steamers. Donald did have concerns because the water narrowed at the eastern end, however on the whole was happy. Samlesbury were mainly concerned with coachbuilding at the time but they also built aircraft wings, however building an all metal hulled jet boat represented a groundbreaking challenge. The boats frame was covered in aluminium sections, which were made watertight by sealing and overlapping. After fitting out, Bluebird K7 was handed over to Donald Campbell on the 26th November 1954, after being unveiled by Lady Wakefield. The boat was not quite finished at this time as leaks were found during tests that had to be rectified after the ceremony. The boat had still personally cost Donald around £18,000 of his own money, which he could only finance by remortgaging his home.

The boat was taken to Glenridding, the teams HQ for the trials on Ullswater. The boat was "launched" by Donald's wife at the time, Dorothy. The boat was then lowered down the slipway in her cradle and eventually released onto the water. What was hoped to be an encouraging but tempered first run ended in frustration. The boat was completely new to the team and Donald, however Donald was determined to try a trial run as soon as the boat was in the water. Donald fired up the jet engine and proceeded to accelerate down the water, however as soon as the boat accelerated it dipped forwards and water sprayed into the air intakes and "flamed out" the engine. The engine fired a number of times (automatically as it happened, as a faulty solenoid meant the starter was permanently engaged!), but the same problem occurred. The boat was bought in, it appeared that the trim of the boat was out. Over the next couple of weeks various remedies were tried. The boat was fitted with buoyancy tanks which were supposed to be filled with water to weigh the boat down, however these failed to hold the water, weights were eventually added. The front sponsons were adjustable, and they were moved forward, while the engine was moved back. Things were also improved by removing part of the stern to reduce the buoyancy at the rear. Although these improved the boats trim, it still wouldn't rise up and plane. The front spars, that connected the sponsons to the hull, were found to be too low, this meant that when trying to get the boat to rise, a suction effect caused by the spars resisted the boat rising. After consulting Ken and Lewis Norris the team then fitted deflector panels in front of the intakes, between the sponsons, this helped to stop the spray of water into the intakes and also had the added effect of increasing lift. On the 14th March the newly modified boat went onto the water again, this time she lifted up onto her planing points and to the delight of the team planed properly for the first time. Donald was under instructions not to exceed 150mph as the modifications were pretty much improvised. He actually took the boat up to around 130mph. Back on shore Donald had described how it felt as no sooner had the boat come up ready to plane, than it seemed to want to dip again, before she rose up fully. This did not seem apparent to the observers and what Donald suggested next gave Leo Villa a sleepless night! Donald suggested that Leo take the boat out to see if he experienced the same effect. Leo was just as worried for the boat as himself! however he was able to confirm the same effect. The team then headed south after satisfying themselves that the boat, when up and planing was capable of very fast runs.

Whilst the boat planed comfortably at around the 150mph area, Lewis and Ken Norris decided they needed to test model to determine the effect of the improvised deflectors. Imperial college provided a wind tunnel for the model boat to be tested in. Meanwhile Donald, Leo and Maury Parfitt decide to run some tests on a model of their own. A fishing line was attached to the boat at a point designed to reflect the angle the boat would have if powered by the thrust of the jet engine. This line was then reeled in on a small motor. Donald would film the model with a cine camera; the team would then develop and review the film. They would then make modifications to the model to see if there were any improvements to be gained. All the while information was passed between Lewis and Ken Norris's wind tunnel results and the rest of the team's findings. They concluded that the baffles between the spars should not be used, as the lift they gave would cause the boat to flip at speeds of around 200mph. The solution Lewis and Ken Norris came to was to raise the front spars higher above the water. Tests carried out with the model on the water confirmed this to work.

The team set about the modifications, raising the spars 10 inches as well as other smaller modifications, including rounding the nose. Other weight saving measures were taken, the onboard starter was removed, and some special automatic water deflectors were taken off also. These modifications took around two months to complete. Once done Bluebird needed a few more minor adjustments after tests in late June and early July.

On July 23rd 1955 Donald prepared for an attempt on the record. Instead of a measured mile, Donald preferred the Kilometre (either sufficed for the official record), this was because he was worried by a narrow part of the lake he would have to pass through at speed if he was to be measured over the mile. Despite a painful back Donald eased himself into the boat, and prepared for his run.

Donald Campbell
Speed 320mph
Length 11.2mtrs
Width 2.02mtrs
Weight 150 kilos