Integrated masts:
​​​​​​​the sensor sweet spot

The FDI frigates being built for France and Greece are examples of integrated masts. Credit: Naval Group

Anaval warship’s mast that brings together all the communications, radar and electronic warfare systems means that platforms can be better controlled and coordinated with software and digital processes.

In doing so, it prevents interference with the ship’s structure while enabling performance to be optimised using specialist materials in the mast structure. The equipment centrally located on a single mast means that powering the devices and supporting them is simplified and the electronics are better protected.

Furthermore, the physical construction of an integrated mast structure on the hull of a ship is made easier during construction and its position gives it a higher mechanical strength to withstand the harsh oceanic environment. Importantly for warfare at sea the placement of all the antennas, sensors, and detectors on a covered mast – instead of either an open mast or located where antennas and sensors are positioned all over the topside of the warship – reduces the radar cross section of the vessel, making it less detectable.

In a sea of examples available in the naval marketplace, determining trends can be difficult. However, taking two examples from European industry, a set of benefits begins to emerge. 

Swedish defence company Saab Kockums has been a leader in the development of integrated mast systems over the past two decades with the fitting of composite masts onto new-build warships as well as retrofitting them to older vessels. In Sweden these have included the Stockholm-class corvettes, Koster-class Mine Countermeasures Vessels and Gävle-class corvettes.

The company’s latest offering is the Saab Lightweight Integrated Mast (SLIM), which accommodates all of a warship’s major radars, sensors and antenna. The Pohjanmaa-class corvettes (SQ2020) under construction for the Finnish Navy will be fitted with the SLIM. 

The mast on the Finnish corvettes will include the Sea Giraffe 4A FF and Sea Giraffe 1X radar, identification-friend-or-foe (IFF), an electronic warfare suite, electro-optical systems and communications antennas. The mast also hosts fire detection and extinguishing equipment, a CBRN pre-wetting and washdown system, HVAC, navigation lights and meteorological sensors.

According to Magnus Dannemyr, product manager, composite at Saab Kockums the SLIM is approximately 50% lighter than a steel mast of the same design, whilst also being non-corroding.

Dannemyr told Global Defence Technology that because it is lightweight this “gives reduced top weight for increased ship stability, a higher mast to facilitate longer sensor range, a weight margin for more sensors and weapons and also future growth.” 

SLIM is modular and scalable and therefore can be adapted to improve its performance depending on the sensors selected by the navy customer. Saab’s intention is for the SLIM mast to be a solution optimised for smaller and less high-end naval vessels to give them the capabilities of larger warships. The design and lightweight materials used in the SLIM mean there are also lower life-cycle costs and reduced maintenance compared to steel solutions.

“A composite mast can enhance sensor performance and will reduce maintenance cost over the ships lifespan and thereby have lower life-cycle costs, but initially it can be more expensive to acquire than a similar mast made of steel,” Dannemyr said.

Saab has experience in the use of composites and carbon-fibre construction through its build of the RSwN’s Visby-class corvettes. The features of SLIM highlight the benefits of an integrated mast system over earlier antenna and sensor arrangements and over steel structures.  

French shipbuilder Naval Group has its own mast products known as the Panoramic Sensors and Intelligence Module (PSIM), which was originally developed for its Gowind ship programme.

PSIM combines several functional chains of the combat system from sensors to computing capabilities and operator consoles. This allows them to be integrated and commissioned in parallel with the assembly of the hull during the construction of the host ship reducing ship lead times and providing more reliable testing. Because PSIM is a modular part of the ship it can be built separately, activated, tested, and used for training ashore prior to integration on the hull. 

A spokesperson from Naval Group told Global Defence Technology that in addition to the need for 360° coverage “strong transmitters and sensitive receivers are positioned on the same vertical, so that they don't pollute each other from an electromagnetic compatibility point of view. Some antennas need zenithal coverage, which means no obstacles at maximum elevation.”

The spokesperson added: “Given the chosen arrangement of antennas, sensors and detectors, there are no incompatibilities between them, nor any restrictions on their use.”

The mast integrates the sensors with the ship’s Combat Management System and the ship’s Combat Information Centre through the data processing centre.

PSIM is made of different types of metallic materials including aluminium and steel, composites, and specialist absorbent materials. However, it is also designed so that functional chains can be tested in an onshore integration centre making PSIM predominantly a software product. PSIM weighs about 150-tonnes and is 42m high.

It is fitted to the Gowind corvettes and FDI frigates of the French Navy as well as the Gowind corvettes of the Egyptian and UAE navies. PSIM has also been integrated on Amiral Ronarc’h, the first of the FDI frigates for France and HS Kimon, the first FDI frigate for the Hellenic Nay.

On both the French and Greek ships, the PSIMs will host the Thales Seafire 4D AESA multi-function radar and Thales Bluegate TSA 6000 e-scan IFF,  which both employ flat panel antennas. It is also fitted with low probability of intercept radars, two Safran PASEO-XLR electro-optic and fire-control systems, short-range day and night cameras, the Thales Sentinel R-ESM and ALTESSE-H communications ESM and Communications Intelligence systems, as well as standard datalinks and satellite communications.

Meanwhile the demands on integrated mast systems are growing with an increasing need for communications systems.

“Communications requirements are increasing, with other ships, aircraft, and drones. The ship's topside, including the PSIM, must therefore be further exploited to increase the number of possible communications,” the Naval Group spokesperson said.

“The need to combat asymmetrical threats and better identify naval and airborne motives is already taken into account in PSIMs. We need to continue adapting to changing threats, or rather anticipating them to stay one step ahead.” 

The US Navy is the most obvious outlier of services that have eschewed the use of integrated masts, using the more traditional span design seen on the Arleigh Burke-class guided missile destroyers, as well as the future Constellation-class guided missile frigates.

China’s People’s Liberation Army Navy, also known as the PLAN, as a rapidly evolving fleet, also makes use of traditional ship’s masts, but is gradually moving towards integrated designs. 

A combination of costs, capability, and form factor will drive the development of ship’s mast, with the clear trend in Europe for integrated designs for both future warships, but also the potential addition during mid-life upgrades of existing surface combatants.

Climate is also likely to be a factor, with maintenance requirements also a consideration as navies seek to balance sensor effect with costs, as well as the requirement cooling for radars and other systems housed inside an integrated structure. 

Australia could be one of the main beneficiaries of this dramatic increase in demand, where private companies and local governments alike are eager to expand the country’s nascent rare earths production. In 2021, Australia produced the fourth-most rare earths in the world. It’s total annual production of 19,958 tonnes remains significantly less than the mammoth 152,407 tonnes produced by China, but a dramatic improvement over the 1,995 tonnes produced domestically in 2011.

The dominance of China in the rare earths space has also encouraged other countries, notably the US, to look further afield for rare earth deposits to diversify their supply of the increasingly vital minerals. With the US eager to ringfence rare earth production within its allies as part of the Inflation Reduction Act, including potentially allowing the Department of Defense to invest in Australian rare earths, there could be an unexpected windfall for Australian rare earths producers.