TYPE XVII BOATS

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TYPE XVII BOATS

Berichtdoor Tandorini » 05 jan 2009, 21:56

Afbeelding

The Type XVII boats had both conventional diesel engines and a single Walter closed-cycle engine. They were designed for coastal operations. Few in numbers but rich in variants, the Type XVII U-boat was not a success, trying to press the Walter turbine into service before its time. Planned to run to a dozen boats (U- 1081/1092), the ‘G’variant was halted before any were complete. It was designed for an ultimate submerged speed of 25 kts.

Afbeelding

One of the nearly complete TypeXVII Walter turbine boats is transferred by a 350-ton floating crane through the shattered Kiel yard of Howaldtswerke. Advanced features include a hydrodynamically clean hull and a single propeller set in cruciform control surfaces. Note the sonar dome forward.

There was little development of the basic submarine in the inter-war period, except that the once-popular saddle-tank design, in which the buoyancy chambers were located outside the pressure hull, gave way more and more to the double hull, in which they enclosed it almost completely and were themselves contained within a light enclosure which could be shaped to improve sea-keeping and performance. In Germany, developments in the late 1930s were aimed only at increasing the size and endurance of existing types, not making any radical changes to their design. However, by 1941, experimental boats with a new type of powerplant which did not need atmospheric oxygen had been produced, and were proving to be quite remarkable. The powerplant in question was, once again, the creation of the prolific Professor Hellmuth Walter, whom we have already met.

The key to the concept was the Walter closed-cycle propulsion system that relied on the near-explosive decomposition of concentrated hydrogen peroxide in the presence of a catalyst, The reaction produced a high-temperature mix of steam and free oxygen into which fuel oil was injected and fired, resulting in high-pressure gases that were made to drive .a conventional turbine. A weakness of the principle was that almost any impurity could act as a catalyst to initiate the process at a disastrously early stage.

Walter had constructed a small experimental boat, the V30, launched on 19 January 1940, which displaced just 73.8 tonnes (75 tons) submerged. He equipped it with a steam turbine, fed by a variant of the liquid-fuel motors which were to power the VI flying bomb's launch catapult, producing their steam by the chemical reaction of hydrogen peroxide with a catalyst. Walter soon discovered that his submarine could make almost 30 knots submerged - around three times the submerged speed of any conventional submarine running on battery power - and that led him to suggest to the Kriegsmarine the construction of a fleet of similarly powered submarine warships. When asked where he proposed to store the large quantities of reagent and fuel that would be required, he produced a design for a two-decker submarine, in itself virtually two existing double hulls joined into a tigure '8', the bottom portion of which would serve exclusively as 'bunkerage'. Someone at this proposal meeting noted that it would be just as easy to fill that lower section with batteries.

More 'Walter' boats were built or at least were in the course of construction when the war ended. The two Type XVIIB boats which were successfully salvaged after having been scuttled in Hamburg harbour were later transferred to the US Navy and the Royal Navy, who operated them experimentally, but the powerplant required massive quantities of fairly exotic fuel and was most temperamental. It would perhaps become a valid solution in the fullness of time, but that was something the Kriegsmarine did not have, and it was essential to look at other suggestions.

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Two prototype boats proved the machinery feasible, and the system was pressed into service in the Type XVIIs. A drawback was the extreme thirst of the system, dictating a small boat with a single propeller. For cruise purposes, this was driven by a conventional diesel/electric combination, with the Walter coupled up only to force or decline an engagement.

Externally, the hull was cleaned-up, with no guns and a minimum of proturberances. It was of figure-eight section, formed of two overlapping circular pressure hulls of unequal diameter. In practice, the length to beam ratio was too high, resulting in an unnecessarily high drag. This meant that the Type XVIIA never realized its theoretical top speed of 25 kts possible with two turbines on a common shaft. So only four such boats were built, the modified Type XVIIB (three completed) having only one turbine. Space was available for only two torpedo tubes, with but one reload for each, a deficiency offset by the increasing lethality of the weapon. A projected Type XVIIK would have abandoned the volatile Walter for conventional diesels aspirated with pure oxygen stored aboard.

TYPE XVIIB

Type: Coastal submarine

Displacement: 317 tonnes (312 tons) surfaced; 363 tonnes (357 tons) submerged

Length: 41.50m (136.17ft)

Submerged speed: 21.5 knots

Submerged range: 210km (130 miles)

Armament: 2 x 533mm (21 in) torpedo tubes

Crew: 19
NEC JACTANTIA NEC METU ("zonder woorden, zonder vrees")

Avatar:De Siciliaanse vlag,oorspronkelijk uit 1282,de triskelion (trinacria) in het midden,is van oorsprong een oud Keltisch zonnesymbool.


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