These replacements for the Hants & Dorsets evolved over an eight year period. The first batch to enter service were 2747-2750. Mk.1A boats with wooden superstructures and triple 500HP Napier Sea Lions. Their external appearance bore a striking resemblance to the earlier BPC craft, this may have been a case of "if it works then leave well alone or possibly it was due to the influence of George Selman who assisted Vospers with propeller design after he moved there from Hythe.
These early R.T.T.L.s were heavier and slower than their predecessors, as due to the unavailability of the preferred twin Sea Griffons, the builders had to resort to a triple Napier installation. Even with a dry boat, it was impossible to match the speed of the earlier Hants & Dorsets, and when the hulls had soaked, their performance became little short of an embarrassment. The next batch were the Mk.1B, with the only difference being their aluminium superstructures giving access to the wheelhouse from the deck by means of a door on the port side. It was not until the introduction of the Mk.2 craft with the long awaited Sea griffons that the Branch had an HSL to be proud of again, with a top speed of over 40 knots.
The new boats were not without other problems. The three tank fuel system had to be replaced by a five tank system after degradation of the tanks filled the bilges with high octane fuel. Another mechanical problem was with the Plessey cartridge system used to start the engines. For years Fitters wrestled with near useless cartridges until it was discovered that the wrong type had been specified. An even more damaging problem manifested itself with cracked frames and split bottom planking down the starboard side. After completing a series of trials, the problem was diagnosed as a result of torque reaction from the left handed screws which caused the starboard chine to slam into the sea thus damaging the hull. The solution was to fit fixed trimming wedges under the transom, and a triple skin to the hull bottom. The downside to this weight increase was a decrease in top speed.
By the early 1960s, all the Mk.1A and Mk.1B boats had been converted to Rolls Royce Sea Griffons and were re-classified as Mk.2 craft. They were now the true flagships of the Post War Marine Branch and only RAF craft entitled H.M.A.F.V. status. Duties ranged from First Line Rescue Duty, Target Towing, Weapons Recivery, and 'Attack Trainers' for the RN. The high freeboard of the Vospers, made it a difficult task to get injured survivors aboard, this problem was overcome with the "Mount Batten" system, where a crew member entered the water in the 'Catwater Strop' which allowed the launch crew to place the survivor onto a stretcher prior to being lifted onto the deck.
Throughout their lives serviceability was often a problem, firstly it was the starters, later others would blame their marinised petrol aero engines which they claimed were unsuitable for such a harsh environment. They were tricky to handle at low speed, creeping as they did around 10 knots with gearboxes engaged and engines on idle.
Only one boat was lost on service, 2754 from Gibraltar, which went down in the Med in January 1976, after being holed in the Sickbay, thankfully with no loss of life. Others were written off due to wear and tear, or beyond economical repair. One such launch was 2767, written off at Bahrain in July 1971, she was towed out to sea where HMS ZULU attacked her with Seacat Missiles - they all missed, she was subsequently targeted by Rocket firing RAF Hawker Hunters, but still refused to sink, being kept afloat by her fore peak compartment. She eventually went to the bottom after divers cut a hole in her hull allowing the trapped air to escape.
Vosper Ltd were entrusted in January 1952 with the design of a 68ft launch primarily to act as a floating test bed for the first pair of Rolls Royce Sea Griffon Mk 101 engines, which were at that time being developed for marine applications from the famous aero unit by Rolls Royce Ltd, on behalf of the Ministry of Supply. In addition, the Marine Craft Research and Development Section of the same ministry agreed to an experimental hull structure being produced. Hence RTTL 2762E was a one-off. It was built entirely from aluminium, the only timber being the teak deck planking. The boat ran into troubles very soon, as even before it was launched, it was realised that the number 2762 clashed with a German D-boat in RAF service. Consequently after acceptance trials, the number was changed to 2772E.
Because of its light construction, RTTL 2772E was the fastest of all the Mk.II launches and in its early days was reputed to have achieved around 52 knots. The launch remained in service for many years, but was the subject of constant monitoring for the effects of sea water and electrolytic corrosion on the hull. Eventually, the hull deteriorated and had to be skinned with traditional double-diagonal planking. The modification, among others slowed the boat to a more or less standard Mk.II performance and it finally had its "E" designation removed.
| Back |