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THE STORY BEHIND THE BUILDING OF THE FIRST STENA HSS

FACTS AND INFORMATION

Contents

  1. Concept and Design
  2. Stability and Safety
  3. New Evacuation System
  4. Power Supply
  5. The Bridge and Navigation
  6. Docking and Loading

Concept and Design

In the late autumn of 1989 Dan Sten Olsson, CEO of Stena AB and chairman of the Board of Stena Line, posed the question: "High-speed ferries - could they be of any use to Stena?"

"It was a simple question but very difficult to answer," recalls Stig Bystedt, technical director of Stena Rederi AB. "When we took stock of the multitude of different ship classes, we soon realised that catamarans were the only viable solution if we were going to get the vessels into service this side of the year 2000".

Catamarans had speed, but their loading capacity, seakeeping and above all, their comfort were moderate. Quite simply passengers suffered from sea-sickness and a number of designs had been taken out of service for this very reason.

A long series of tests were initiated at the National Experimental Shipbuilding Tank (SSPA) facilities in Gothenburg, while Norske Veritas conducted various strength trials on a variety of models. The problem lay in finding a hull form which was as "kind" as possible, to both the vessel and its passengers.

The practical method proved to be designing the hull with concave sides so that they were extremely narrow at the water line, but then swelled out again into large pontoons below the water line. Meanwhile, the angle at which the bows meet the onrushing water were made as sharp as possible - the Stena HSS's stems are only a few centimetres wide.

Stig Bystedt describes the results of the design development: "There were two main motions we wanted to eliminate. One is called "heave" and is the way the boat moves when it is pushed up and down by the turbulence of the surface water. The concave design means the HSS ferry is less affected by this force. The ship's buoyancy lies in the pontoons, several metres below the surface of the water, and the waves' effect does not reach that far down. The ship's surface area at the water line, which is where the waves are, is very small".

"The second motion, which is particularly unpleasant for the passengers is "pitch" - when the bow is for example lifted by a wave at the same time as the stern sinks into a trough of a wave. A normal vessel's centre of motion is well aft and the fore sections, in particular, move in a way which generates rapid movement up and down - rapid changes of position which induce a sinking feeling in people's stomachs and hence a feeling of nausea".

"The centre of motion of the Stena HSS ferry is, thanks to the ship's buoyant aft section and sharply angled bows, shifted well to the fore. Hence the stern moves up and down instead of the bow, which means overall, fewer vertical movements and consequently, a much more comfortable motion. "The third motion which normally affects vessels - the rolling caused by beam seas - is virtually non-existent on the 40 metre wide Stena HSS - 1500."

It all makes the Stena HSS a very seaworthy vessel, able to provide passengers with a comfortable ride at full speed, even in waves as high as eight metres.

Stability and Safety

No bow doors. A car deck located eight metres above the water line. Stability several times greater than of a conventional vessel. And a new efficient evacuation system. The Stena HSS exceeds by a wide margin the stability requirements currently applicable, as well as those it is thought will apply in the future, to this type of vessel in northern European waters.

"Even if the bottom of both the hulls of the Stena HSS were to be ripped open and filled with water, the vessel would still retain sufficient buoyancy to keep the car deck approximately two metres above the surface of the water," said Stig Bystedt, technical director of Stena Rederi AB.

"That is the same height above the surface of the water as the car deck of a conventional ferry. And even if one of the two hulls were to be ripped open beneath the water line and consequently leak along its entire length, the result would be a list of no more than 15 degrees."

The Stena HSS 1500 would, however, still be able to proceed using the other hull's two engines. Two auxiliary engines would also still be intact and the electricity supply (and power) on board would therefore be assured.

Both of the Stena HSS 1500's hulls are divided into nine self-contained areas separated from one another by water-tight bulkheads. The five furthest forward are also divided horizontally by a water-tight stringer deck, as it is known, thereby forming 14 water-tight compartments.

Even if both of the hulls were to be filled with water, the risk of foundering is very small, thanks to the presence of a large, water-tight reserve area between the two hulls - under the car deck. The buoyancy generated by this area is more than sufficient to keep the HSS ferry afloat on an even keel, even when it is fully loaded.

With its massive beam of 40 metres and the buoyancy divided between the hulls at its outer edges, the stability of the HSS ferry is remarkable. Even extreme movements in the vessel's cargo would scarcely affect it. "In principle, the entire cargo could shift as far as it can go one direction, without the list being greater than a couple of degrees," said Stig Bystedt.

The ferry is fitted throughout with fire detectors and TV-cameras. In an emergency, passengers will be given instructions by the ferry's loudspeaker system, TV monitors and crew and if necessary, a newly developed guidelight system will guide passengers to the exits.

The Stena HSS 1500 ferry has a shipwide fire extinguishing system which, with the help of high pressure water mist, enables a rapid and effective fire-fighting response. The system comprises both sprinklers and fire hydrants in the accommodation areas, engine rooms and on the car deck.

New evacuation system for HSS

The Stena HSS 1500 also has a recently developed lifesaving system on board, known as MES, or Marine Evacuation System, which can evacuate everyone on board in under 18 minutes.

The evacuation system is divided into four separate stations, two on each side of the passenger deck, directly linked to the public areas. In an emergency situation, doors open in the sides of the vessel and the evacuation stations can be reached via marked escape routes from all parts of the deck.

When the MES is activated - it is handled from a control centre directly linked to the evacuation doors - an inflatable latticework beam, made of polyurethane treated webbing, is let down from the ferry. There are two chutes on each of the latticework beams, which the passengers use to slide down to two large covered life-rafts.

Each life-raft has room for 135 people. They have broad openings facing the platform, which makes them easy to board. Two more life-rafts can, if necessary be sent down from the passenger deck. The system also includes four lifeboats.

Power Supply

The new Stena HSS 1500 ferry, with a top speed of more than 40 knots, will be able to compete with the airline traffic in terms of speed on many of its routes. Which is, perhaps, not really surprising - the crucial parts of the HSS 1500's engines are taken directly from the world of aviation.

The smaller of the two different types of gas turbines are used in the Swedish Airforce's new fighter, attack and reconnaissance aircraft, the Saab Gripen, while the larger of the two types is used in the long-haul Boeing 747 aircraft.

There are several reasons why Stena's designers elected to use aircraft engine type gas turbines as the power source for the new Stena HSS 1500. They produce cleaner exhaust fumes than conventional diesel engines, require less space, weigh less, have a high level of operational reliability and are virtually vibration-free.

The General Electric manufactured gas turbines on the Stena HSS have been rebuilt for maritime use, with each of the two hulls containing two types, one large and one small. The larger develops approximately 30,000 horsepower at 3,600 RPM, while the smaller develops approximately 20,000 horsepower at 6,500 RPM. The maritime versions of the gas turbines are powered by a light diesel oil with a very low sulphur content.

The gas turbines, including the power turbines, are completely encased in fire and soundproof containers, known as turbine modules. Each of the two hulls contains two turbine modules - one large, one small.

In narrow waters the HSS 1500 can be powered by the two smaller engine packages, giving a maximum speed of 25 knots. When the larger modules are in operation, the vessel has an approximate top speed of 32 knots, and when all four modules are operating at full power, the ferry's speed can exceed 40 knots.

Stena has chosen to use water jets from the Swedish firm KaMeWa, in Kristinehamn, for the ferry's forward propulsion, instead of conventional propellers. Not only are the water jet units efficient at high speeds, they also produce benefits in the form of improved manoeuvrability and a radical reduction in the vessel's draught.

The four water jets, two in each aft section of the vessel, draw in water through inlets in the ferry's bottom. The impeller (the propeller in a water jet) is located inside the units in a space sufficiently large for a fully grown man to stand upright.

Right at the back of the water jet units lie the massive steering and reversing drives. Each steering drive can be turned 30 degrees to starboard or port and thus steer the ferry in the desired direction. The HSS 1500 reverses by dropping massive scoops aft of the nozzles through which the water jets are angled diagonally downwards and forward.

The Bridge and Navigation

Aircraft technology on the Stena HSS does not stop in the engine room - it's also an integral part of the bridge. Except the bridge usually to be found on a ship or ferry now closely resembles an aircraft cockpit.

Being on board a ferry the size of a football pitch, which travels at speeds of 40 knots, changes the way people work at sea. This was recognised at an early stage in the HSS development programme by Stena Line's engineers, who looked to the civil aviation industry, rather than conventional shipping, to design the nerve centre of the new ferry.

On the Stena HSS the cockpit/control room is situated in the furthest forward, topmost section of the vessel and is manned by three officers - the captain, his co-pilot/navigator and the chief engineer.

The ferry's state of the art electronics system is the most sophisticated ever to be found on a merchant ship. It includes differential GPS navigation, electronic sea charts onto which radar information can be copied, and a Conning Display, where all information on the vessel's manoeuvres and speed, as well as wind and current conditions, is shown.

There are a number of other tools to ease navigation and monitoring, such as light-intensifying night binoculars and an internal television system with a large number of internally and externally positioned cameras. There is even a camera mounted between the hulls to enable the crew to monitor the wave height between them.

The captain and co-pilot can select the information they want to display on three huge computer screens positioned directly in front of them. They have constant access via these screens to the electronic sea charts of ECIDS (Electronic Chart Display Information System) - which for the first time has been developed specifically for the waters in which the ferry sails.

Usually a ferry's position at sea can be shown to within 100 metres but in using a differential GPS the accuracy is improved to plus or minus 10 metres. In the ports of Holyhead and Dún Laoghaire a more finely-tuned differential GPS network is used and it can calculate the ferry's position accurately to within a distance of as little as one metre.

The chief engineer has a separate control panel with four screens displaying all the essential data on the ship's technical operation - such as the turbine engine's status and water jet units' compressive force. The chief engineer is also responsible for monitoring and activating the safety systems on board, which means the captain and navigator can concentrate fully on manoeuvring the ferry.

The HSS 1500 cockpit electronics have - just as in an aviation context - triple-layer safety built in with three separate computers able at all times to handle and process the information retrieved from the ship's operational and navigational systems.

Docking and Loading

A new docking technique to speed loading and unloading, as well as a system for storing supplies, are among other unique features of the Stena HSS. It means the ferry can be turned around, re-stored and re-fuelled in just 30 minutes and if required, this could be reduced to only 20 minutes.

The linkspan for the Stena HSS - the docking and drive-on ramp to which the ferry berths at the stern - is a completely new design, which also includes a quick coupling with fuel, fresh water and waste water pipes.

When the Stena HSS 1500 docks in Holyhead and Dún Laoghaire, she reverses in towards the linkspan. The reversing manoeuvre is made easier by the ferry being fitted with navigation equipment, which can determine the position of the ferry to within one metre, four TV cameras, a special docking radar mounted low in the ferry's stern, and bow propellers in each hull. This system guarantees safe docking.

Once the HSS ferry has made contact with the linkspan's fenders, the quick couplings are connected on either side of the ferry's stern, pulling it automatically into the correct position so that gangways, drive-on ramps and quick couplings fit. The ferry's massive beam and a specially constructed aft fender, which prevents the ship from moving sideways - mean no additional moorings, such as ropes, are required.

Once berthed, rapid loading and unloading is achieved by using the ferry's four stern doors (there are no bow doors). Thanks to the massive beam, cars, coaches and trucks turn around on board in a wide U-turn.

Three of the doors are used simultaneously during loading. Two of them lead into the ferry's main loading deck, while the third leads cars up to an extra pontoon deck situated above the main deck, via a ramp. Three doors are also used during unloading as vehicles drive through the 180-degree curve on-board.

Foot passengers go on-board and ashore along two parallel glazed passenger gangways, located on either side of the linkspan, so avoiding stairs and other barriers.

Helping to keep docking time to a minimum is a container system for supplying the on-board restaurants and duty-free shop. Two containers are loaded on to a traverser running on rails on the outer roof of the ferry. The restaurant container is lowered through an outlet in the bow roof, whilst the container with the duty-free articles has its place in the stern. Both of the containers stay on board until stocks need replenishing.