<XMP><BODY></xmp>SSS Warships


Added 7-1-02
Updated 2-11-12
SWATH Warships



        When considering the design of large ships it is worth considering for a moment what large surface ships are for. There is a concept currently popular in Naval circles that a ship can do its job out of sight of the shore, beyond the horizon, striking with long range guided weapons. Part of the ship's role is a psychological/symbolic one. It is both ambassador and cop walking a beat, the sight of which should hearten friends and deter foes.

        History clearly shows that for an amphibious landing to be successful a naval bombardment is an important element. Aircraft and guided missiles cannot produce a sufficient volume of fire to do this. If they could armies would have scrapped their howitzers and MBRLs for cruise missiles decades ago.
        I've even heard it said that the Navy does not expect to have to make landings against defended beaches. If this is the case, this begs the question why the ship has to hide over the horizon and why bother with long range landing craft and AAAVs?

        There are many conventional and not so conventional designs for large ships, but one that is not so well know is the Semi-Submerged Ship (SSS, SWATH or S3) configuration. S3 ships such as the Mitsui Seagull and US Navy SSP Kaimalino have been in use for many years and ships as large as more than 20,000t are already in use. S3 ships are characterized by good seagoing characteristics, low drag and good fuel economy.
        S3 ships are rather like engined versions of the free floating oil rigs used in the north sea. (In fact one SWATH vessel is a converted oil rig!) Underwater are two torpedo shaped hulls. For large ships these might be built in submarine shipyards or adapted from obsolete subs. A rectangular platform stands above the water supported by four legs that are attached to the hulls.
        The rectangular shape of the platform allows for very space efficient organization of structures. For some ship types the upper part of the ship will look like a multistory building on legs.
        The underwater hulls can be used for the carrying of cargo, fuel and munitions. They are also the logical place to position ASW systems such as AS torpedo tubes. Underwater they are less vulnerable to bombs and missiles. The S3 ship is also harder to torpedo than a conventional ship. Many types of torpedoes will pass over the hulls or between them. The legs of the ship contribute little to the buoyancy of the ship, and could be constructed that they can absorb the blast of torpedo or bomb strikes with little loss of structural integrity.

        I can see four main types of large S3 ship.

        Amphibious landing ship or Assault Carrier. This has an extensive complement of helicopters. Between the legs of the ship are lift platforms that lower landing craft, LC-AC (hovercraft) and AAAVs onto the water. This type is equipped with medium and short range SAMs and both standard and large calibre CIWS. It may also mount shore battery systems such as MLRS.

        Hospital ship. Like the amphibious ship but with no or just short ranged defensive armament. This will mainly be equipped with SAR and Casevac helicopters.

        Aircraft carrier -mainly carrying Helicopters and VSTOL, but can also handle aircraft such as A-10 Seahogs, carrier medium bombers, CAScopters.

        Battleship or Cruiser. This mounts a variety of weapons suitable for use against other ships, aircraft and submarines but would also provide naval bombardment acting as a sort of floating fire base.
        Armament would include a large number of Mk 41 launching tubes capable of firing a variety of anti-ship, anti-submarine, surface to air and land attack missiles, including Tomahawk cruise missiles, Harpoon, Standard SAMs, SeaSparrow, ASROC, LASM and SLAM-ER. Unlike the proposed Arsenal ships these vessels would have ample defensive armament and be capable of operating close to shore
        Gun armament should include several 8” guns, which could be used both for interdiction and for close support of friendly forces.

        “The MK-71 8-inch gun can deliver the firepower of three 5-inch guns, and much longer ranges are possible by procuring the MK-63 8-inch projectile. This was an upgraded German “Arrow” projectile from WWII, with a long, pointed nose and a sabot sleeve which achieved a range of 41 miles when fired during the Vietnam conflict. However, an improved aerodynamic shape called “base bleed” later developed by Dr. Gerald Bull for 175mm projectiles can add another 10 miles by reducing drag. The MK-63 projectile weighed 115 pounds (the average 8-inch HE round weighs 260 pounds) and was used against Viet Cong base camps deep in the interior of the country with good success. Unfortunately, the Navy did not fully develop the round combination (projectile and powder) and the resulting range error was about 250 yards, which is outside the lethal effect of the round. By simply determining a better powder match to the projectile, the Navy could have cut that range error down to around 80 yards, which would be close to a GPS guided munition. Multiple rounds will reduce this error considerably to meet engagement requirements”.
G2mil

        The 8” guns would be supplemented with 5” Secondary guns, which would be mainly used in a defensive role. With the correct ammunition and fire control these would also prove effective against airborne targets. It might in fact be more prudent to develop a 155mm naval gun to utilize projectiles developed for land-service weapons.

Naval Weapons of the World

         The platform of the ship may include room for a two or more forward firing 16” guns, which would mainly be used for long range interdiction, being too powerful to be safely used to support friendly troops. To use these weapons the ship would have to point towards the shore presenting less of a target to enemy weapons and sensors. Stern mounted 5” and 8” guns can still be used to fire at the target if capable of being fired at a high trajectory.
        With the currently used forms of ammo 16” guns have a range of under 23 miles, although this seems to have been long enough for many Iraqi units. Innovations such as Rocket assistance, Sabots, Basebleed and Athodyd (ramjet) assistance can all increase the range of 16” shells. There is also ample capacity for guidance systems. All of these systems were tried with the World War 2 German K5 28cm (11”) railway guns.

Range for a conventional shell 36.6miles/ 62km
Rocket Assisted shell 53.7miles/ 86.5km
Peenemünder arrow shell(PPG) 93.8miles/ 151km
Athodyd Shell (estimated) 250miles/ 400km

        The calibre of the K5 was 11”, so these figures give some idea what could be achieved with the 16” guns.

        The MLRS is a particularly attractive weapon system to mount on a ship. Automated reloading and ammo handling systems will allow a much higher rate of fire than is possible with land based MLRS.
        MLRS has other potential uses as a naval system. Many Navies use multiple rocket systems for anti-submarine warfare. Some of the best know weapons of this type are systems such as RBU-1000 or RBU-6000. These systems also have capability against torpedoes, frogmen, midget subs etc. MLRS rockets could be adapted to this role by the addition of depth-sensitive fuses, a larger warhead or more sub-munitions and a smaller rocket motor since a range of only a few kilometers is usual for these weapons.
        In the 1980s several Italian warships mounted 51mm and 105mm multiple rocket systems which were intended for bombardment missions but also to launch illumination rockets and decoys such as chaff and flares as a defence against Anti-Shipping Missiles (ASM). Rockets carrying airbursting submunitions could also be used to destroy ASMs or against both land and sea surface targets.

        The ship is also likely to mount other systems such as CIWS, Railguns and close range ASW and air-defence systems.

        Defense of this Battlegroup includes a screen of patroling Pocket Corvettes and their motherships and Manta Flarecraft.
        Glider-like AWACS-RPVs are also used and are launched and recovered by a medium-sized vessel.

FEEDBACK
Ed Sackett comments:
        "Seems to me the chief advantage of semi-submerged design is low visual/IR/radar signature: you can put a lot of the hot & reflective gear below the waterline. That won't do anything to lessen your sonar signature, of course -- but then nothing will, unless somebody clever has patented a sound-absorbing paint.
         For all I know, you could build a Swath ship with a fully expendable top hamper, i.e., no crew at all, with the submerged hulls functioning as a submarines (together or separately) after the payload is delivered."

Brady Hauth writes:
         Ed Sackett says ".........unless somebody clever has patented a sound-absorbing paint."

http://physicsweb.org/article/news/4/9/5

UPDATE
        China is apparently planning a SWATH carrier.



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