Infrared signatures are controlled by a combination of measures. The hull provides good thermal insulation, and engine and air conditioning exhaust vents are designed to reduce heat emissions. An external sprinkler system is fitted to cool the hull, and special low infrared paint is used. Acoustic signatures are controlled by the use of water jets, locating noisy equipment above the waterline under acoustic hoods, double resilient mountings for machinery and an optional underwater-above water engine exhaust. The hull has a minimal magnetic signature, and key systems are located as high as possible. A degaussing system is fitted, and the electrical systems are designed to eliminate conductive loops.
Underwater electric potential effect is minimized by the choice of a nonmagnetic hull material and the choice of water jets. Pressure signature is also low because of the lightweight hull structure and the fine hull form.
A combined diesel or gas turbine arrangement was chosen. Four Allied Signal TF50A gas turbines, developing 16,000 kiloWatts (kW) and driving two carbon fiber shafts, will provide medium and high speed. Two MTU diesels developing a total of 2,600 kW will drive the ship at cruising and low speed. The propulsors are KaMeWa 125 SII water jets.
The Visby is the first of four Series I ships, all to be configured for mine countermeasures and ASW. For mine countermeasures missions, the ships will have remotely-operated vehicles (ROVs). One, designated ROV-S, will carry a high-frequency sonar and television camera for detection and classification of mines. The others, designated ROV-ES, will be expendable robots for final identification and destruction. For ASW missions the ships will have a hull mounted medium frequency sonar and a variable-depth towed sonar array. Weapons include 400mm lightweight torpedoes and grenade-launchers.
It is worth noting that the Defense Material Command's contract with Karlskronavarvet is for the hulls only. Procurement decisions on a number of systems have not yet been made, and detailed design work on some is still in progress; The Command's design team emphasizes that the main parameters of weight and dimensions for all specified systems are known, which should help avoid potential problems in installation. The Visby is scheduled to be delivered in the spring of 2000, and two years of intensive trials will follow.
Series II of the design will be optimized for surface warfare, with the RBS 15 Mk 2 anti-ship missiles, but will in other respects be identical to series I. No date has been announced for the Series II order, but work is unlikely to start until the last of the Visby class is in the water, around 2004-2005, with the ships entering service in 2007-2008.