Krabi Class Offshore Patrol Vessels, Thailand

The HTMS Krabi offshore patrol vessel is built by Thai naval shipbuilder Bangkok Dock under a licensing agreement with BAE Systems, to meet the specific operational requirements of the Royal Thai Navy (RTN).

Image –

The vessel is intended to conduct routine patrols, border control and fishery protection missions in Thailand’s exclusive economic zone (EEZ) and can also be deployed to perform disaster relief operations and natural resources protection in the Gulf of Thailand and the Andaman Sea.

Krabi-class vessels construction

BAE Systems signed a technology transfer agreement with Bangkok Dock to supply the 90m offshore patrol vessel design for the construction of HTMS Krabi in Thailand in June 2009.

Keel laying ceremony of HTMS Krabi (551), worth THB2.8bn (approximately $79.2m), was held in August 2010 and the vessel was launched at Mahidol Adulyadej Naval Dockyard in November 2011. It was inducted into the RTN’s service in August 2013 and has completed 1,000 days of operation at sea.


HTMS Krabi took part in the International Fleet Review 2013 organised by the Royal Australian Navy in Sydney Harbour, Australia, in October 2013.

In January 2016, BAE Systems received a contract from Bangkok Dock to provide design and engineering support for the second 90m offshore patrol vessel, which is estimated to cost THB5.5bn (approximately $155m).

Design and features of Krabi vessel

HTMS Krabi (551)

The design of HTMS Krabi vessel is based on 90m offshore patrol vessel, an evolution of the 80m River-class offshore patrol vessel (OPV), which is designed and built by BAE Systems for the UK Royal Navy.

HTMS Krabi is 90.5m-long, 13.5m-wide and 7.7m-high, and has a draft of 3.8m. With a displacement of 1,969t, the vessel can accommodate up to 39 crew members plus 50 embarked personnel.

HTMS Krabi (551)

The vessel is operated from the navigation bridge, located amidships. The marine radars and communications systems are attached at the top of the bridge.

A large 20m flight deck at the aft section supports the operation of a Super Lynx multi-purpose military helicopter. The vessel also carries a rigid hulled inflatable boat (RHIB) on both sides to perform patrol and transportation tasks.

A4013207091734758RTN Super Lynx multi-purpose military helicopter

The OPV is installed with air-conditioning and electrical systems, storage and accommodation facilities, as well as a crane to lift equipment.

RTN Super Lynx landing on HTMS Krabi

Second OPV project 552 ร.ล.ตรัง “HTMS Trang”

ShipTech3-2016-19The second 90m offshore patrol vessel

The navy will build its second offshore patrol vessel, this one to be armed with guided missiles, at an estimated cost of 5.5 billion baht.

Vice Adm Jumpol Lumpiganon, deputy chief-of-staff and spokesman for the Royal Thai Navy, said on Monday the first OPV the navy built was HTMS Krabi.

The second offshore patrol vessel would be developed from the design of the first OPV, which was based on a design by BAE Systems Ships Co of England, he said.

The navy had signed a contract to buy the vessel’s design and materials from Bangkok Dock Co, a state enterprise under the Defence Ministry. The Mahidol Naval Dockyard of the Naval Dockyard Department would build the vessel and the Naval Ordnance Department will be responsible for its weapons systems. Source Bangkok Post

Aside from the BAE Systems’ enhanced design, the ship has helipad capable to accommodate the 11.5-ton helicopter or S-70B in RTN. RGM-84 Harpoon will be installed on board the ship and most of electronic systems are from Thales. Source TAF

AIR_S-70B_Seahawk_Thai_lgSecond OPV  can accommodate 11.5 ton helicopter like the  RTN S-70B

Royal Thai Navy lays keel for second OPV: Here


The Royal Thai Navy (RTN) has laid down the keel for its second 90 m offshore patrol vessel (OPV), which it is building in collaboration with BAE Systems.

The keel laying ceremony was held on 23 June at the RTN’s Mahidol Adulyadej Naval Dockyard in Sattahip, Chonburi, a facility managed by state-owned company Bangkok Dock.

Armament to combat shore-based targets HTMS Krabi 

An Oto Melara 76mm lightweight naval gun, developed by Italian OTO Melara, is installed on the bow. With a rate of fire of 120 rounds a minute, it is designed to provide defence against shore-based targets.

The vessel is armed with 76mm lightweight naval gun. Image courtesy of Saberwyn.

Two dual-feed MSI 30mm guns, fitted on both port and starboard mounts, offer protection against light targets. The offshore patrol vessel is also armed with general-purpose machine guns.

The offshore patrol vessel is equipped with two MSI 30mm guns on port and starboard mounts. Image courtesy of Saberwyn.

The second patrol vessel in the class can be equipped with a RGM-84 Harpoon anti-ship missile.

Thales reveals weapons configuration of the RTN’s second OPV 552 ร.ล.ตรัง “HTMS Trang”

Main gun will be Oto Melara 76/62 compact stealth shield and two MSI-DSL/ATK 30 mm DS30MR Mk.44. There are also an preparation for the anti-ship missile to be installed. RTN is looking at the RGM-84D Harpoon, but if there is any export ban RTN will shift to C-802A instead. But believe that the Harpoon deal, if it is exist, will go through consider United States just approve the additional sale of RIM-162B ESSM to the RTN. The two Terma DL-12T will make this ship the first RTN ship that capable of avoiding the anti-ship attack.

Oto Melara 76/62 compact stealth shield

Oto Melara 76/62 compact stealth shield

Oto Melara 76/62 compact stealth shield . The gun’s high rate of fire and availability of specialised ammunition make it well-suited to varied roles such as short-range anti-missile point defence, anti-aircraft, anti-surface, and ground support. Specialised ammunition includes armour piercing, incendiary, directed fragmentation effects, and a guided round marketed as capable of destroying manoeuvring anti-ship missiles.

MSI-DSL/ATK 30 mm DS30MR Mk.44

Two MSI-DSL/ATK 30 mm DS30MR Mk.44.

RGM-84D Harpoon

2 x 4 Harpoon launchers096be7cca51cbfaff9d777a9b82412abRGM-84D Harpoon

The Harpoon is an all weather, subsonic, over the horizon, anti-ship missile which can be launch from surface ships, submarines and aircraft. Its guidance system consists of a 3-axis integrated digital computer/ radar altimeter for midcourse guidance, and an active radar seeker for the terminal phase of the flight.

The Harpoon flies at subsonic speeds, with a sea-skimming flight trajectory for improved survivability through reduced probability of detection by enemy defenses. It was designed to strike enemy ships in an open ocean environment.

The ship launched RGM-84 Harpoon was introduced in 1977, as well as the encapsulated submarine launched UGM-84.

Diameter: 340 millimeter
Length: 4.63 meter (15.2 foot)
Wingspan: 910 millimeter
Max Range: 124 kilometer (67 nautical mile)

Top Speed: 237 mps (853 kph)
Thrust: 660 pound
Warhead: 224 kilogram (494 pound)
Weight: 691 kilogram


Safran’s Sigma 40 integrates with Harpoon missile system: Here


Sigma 40: laser gyro technology inertial navigation system

The Sigma 40 inertial navigation system is making use on laser gyro technology. An advanced system designed by Sagem for maritime applications, the Sigma 40 meets the most demanding navigation and weapon system stabilization requirements.

Both an inertial attitude and heading reference system, the Sigma 40 offers high performance and precision for all sizes of surface vessels. Both compact and robust, the Sigma 40 delivers all data needed for navigation: heading, roll and pitch, angular velocity, position and heave, vertical/horizontal speed and acceleration.

The Sigma 40 is suited to all types of platforms, including fast patrol boats, mine-hunters, corvettes, frigates, aircraft carriers, etc. It comprises an inertial navigation unit (INU), control and display unit (CDU) and an installation bracket, for fast removal and reassembly without recalibration. Both innovative and scalable, the Sigma 40 is easy to install, maintain and operate. Source

The main features of RLG Sigma 40 are :

  • It has got high-level performance
  • It has very simple installation requirements
  • It has very convenient operation procedure.
  • It does not requires any preventive maintenance.
  • It consists both Synchro and digital interfaces. There is no need to provide any extra hardware interface.
  • It is IMO approved and military standards certified.
  • It is very reliable and rugged.

The core aim of RLG sigma 40 is :

  • To provide the target navigational data like heading, roll, itch etc in real time.
  • To regularly update the target navigational data like speed and velocity.
  • Interfacing of other navigational inputs from/to other Navigational equipments like EM Log, GPS, DGPS, Radar, Anemometer etc.

Sub-Units of RLG Sigma 40:

The RLG Sigma 40 system contains four basic sub-units. They are as follows:

Components of Ring Laser Gyro Sigma 40 – Image

Here,  INU stands for Inertial Navigation Unit

CDU stands for Control and Display Unit

DDU stands for Data distribution unit, and

UPS stands for Uninterrupted Power Supply

The Inertial Navigation Unit of basic RLG Sigma 40 unit consists of the following sub-units:

  • Inertial Sensor Block (referred as BSI)
  • Basic Synchro Module
  • EB Module
  • UTR-SP Module
  • Interface module (or RS 422 Module)
  • Power Supply Unit
  • HT/ THT Module
Composition of Inertial Navigation Unit – Image

The Inertial Sensor Block (BSI) consists of the various sensors. They are :

  1. Laser Gyros (Model GL S32) 03 in numbers : It senses Angle of Rotation and Speed of Rotation.
  2. Accelerometers (Model A-600)   : It senses the acceleration.
  3. EACC : It consists the circuitry for controlling the Pendulum of Accelerometer using servo elements. In addition to that, It also contains the EEPROMs which stores the sensor’s calibration data.

** EEPROM stands for Electrically Erasable Programmable Read Only Memory.


50 cal General-purpose machine guns

browning_m2_greypage_by_abiator-d8d24m82 x 50 cal General-purpose machine guns.

HTMS Krabi navigation and communication


HTMS Krabi is integrated with a variety of sensors developed by Thales, such as Lirod Mk2 fire control radar, Variant surveillance radar, FIT 10 Voice Terminal, Tacticos combat management system (CMS), FOCON IP communication system, MOC mk3 consoles, TSB 2520 IFF interrogator and combined interrogator transponder (CIT), and integrated communication system.

Lirod Mk2 fire control radar

Lirod Mk2 fire control radar HTMS Krabi

Variant surveillance radar

Variant surveillance radar

TACTICOS MOC Mk.3 console station

limnos tacticosTACTICOS MOC Mk.3 console station (example)

FIT 10  Voice Terminals

FIT 10 Voice Terminal
  • 1- Multifunction terminal
  • 2 – focon ruggedized terminal
  • 3 – Receptacle extension unit

IP-based voice and data communication system

Integrating all communication subsystems into ONE solution
Multi-service communication network (voice and data)
Red / Black separation with multiple security levels
100% non-blocking transport of time-critical services
Full integration of IP and non-IP (legacy) equipment and subsystemsRadio and SATCOM integration and distribution
Crypto integration and distribution
Tactical Data Link integration and distribution (L11, LY, L22 …)
Conference and point-to-point connections in various modes
Modular design to fulfil all customer needs

Focon IP Naval LAN

No single point of failure

  • Survivability
  • High level of redundancy
  • Extremely fast automatic reconfiguration
  • Flexible allocation of communication assets
  • High data rate due to fibre optic interconnections
  • Low cost and efficient ship building installation
  • A high degree of future upgrading

TSA/TSB 2520 M-Scan IFF Interrogator/CIT

  • For aircraft and surface radar
  • Qualified on Mig 29, NH90, Gripen
  • Dimensions (WxHxD): 157x193x332 mm
  • Weight: 8.8 kg
  • Available in a 19″ rack
  • 1500 W Antenna Amplifier Unit (AAU appliqué)

– Dimensions: 33x193x313 mm
– Weight: 2.7 kg


HTMS Krabi

Thales reveals sensor configuration of the RTN’s second OPV 552 ร.ล.ตรัง “HTMS Trang”

Royal Thai Navy is on the preparation process of building its new OPV, the second of the Krabi class, and they still choosing Thales Nederland as lead system and combat system integrator. The second ship will have a higher capability.

RTN second OPV

TACTICOS still a combat suite for the yet-to-be name OPV. 4 MOC Mk.3 console station will be installed along with two large collaboration wall displaying the situation picture.

TACTICOS 4 MOC Mk.3 console station

TACTICOS still a combat suite for the yet-to-be name OPV. 4 MOC Mk.3 console station @thalesgroup

The air-surface surveillance radar will be the rotating 2D dual C/X-band TWT Variant radar along with rotating 2D X-band FMCW LPI solid-state Scout surface-helicopter control radar. Mk X(A) TSB2525 and STIR 1.2 EO Mk 2 is the main fire control. R-ESM capability rely on Vigile Mk 2. L3 Wescam MX-10MS optronic surveillance system and Terma SKWS C-Guard, X-Band and S-Band Sperry Marine Vision Master radar, Furuno ARPA radar will also be installed.

2D dual C/X-band TWT Variant radar

The 3-in-one Variant radar, offers surveillance and target indication. Its principal role is as an automatic, fast reaction time radar sensor, supplying targeting data to weapon systems. Automatic target detection and tracking in 2D plus radial speed is supplied for both air and surface targets simultaneously. For surface targets, it offers 3 gunfire channels.

Variant includes a dual-band radar, utilising both the I- and G-bands (X&C-band). Fully coherent, Variant provides pulse-doppler operation for optimal clutter suppression and air target detection without disturbance by multi-path (or lobbing) effects thanks to the dual-frequency. Outstanding ECM facilities are provided by the ability to operate over two frequency bands, an octave apart, and the third part of Variant, an integral Low Probability of Intercept (LPI) radar. This LPI radar (see also entry: Scout) can be used alone, thus providing Variant the unusual ability to operate in a mode that is almost undetectable to external ESM.

Variant’s low power consumption, lightweight construction and compact design, make the system well suited for use on fast patrol boats and OPVs. For larger ships that need helicopter/UAV guidance, it’s the radar of choice, due to it’s extreme short minimum range. Source

Performance Data

Number of tracks
Air : 200
Surface : 200
FC Surface : 3

Instrumented ranges
Air targets : 120 km
Surface targets : 70 km

2D X-band FMCW LPI solid-state Scout surface-helicopter control radar

2D X-band FMCW LPI solid-state Scout surface-helicopter control radar

SCOUT Mk2 Thales Naval Nederland, a Low Probability of Intercept (LPI) short-to-medium range surface surveillance and tactical navigation radar. Scout can be operated as a stand-alone mobile system for flexible responsiveness. Additionally, the system can be operated remotely (radio or line connection). It is an all-weather fully solid-state system of high reliability operating in X-band radar featuring Frequency Modulation Continuous Wave (FMCW) and therefore has an extremely low output power which makes the system ideal for cover operations in hostile environments where radar silence is required and thus its transmissions cannot be detected by ESM systems or radar warning receivers. SCOUT Mk2 outstandingly detects targets in adverse sea clutter conditions, thanks to its very small range cell size. The system is also very suitable for coastal surveillance. The range of the radar exceeds the 44km. Source


STING-EO Mk2, Thales’s lightweight dual band (I and K) weapon control system, supports gun fire control, performs kill assessment and makes a valuable contribution to classification and identification of threats. In addition, the system can be used as a surveillance sensor, even under radar silence conditions.

The three data sources (I, K, EO) provide high redundancy, performance and ECCM resistance. STING EO Mk2 incorporates the latest solid-state I-band and K-band radars transmitters (low life cycle cost and high operational availability) and a new generation of electro-optical components (especially a third generation focal plane array infrared camera).

For operation in the littoral environment, STING EO Mk2 offers a list of benefits, such as: superior stealth target detection in strong (land) clutter, higher resistance against more stressing jamming scenarios and an extended EO capability for target identification and observation. Source THALES

Instrumented range
– I-band : 120 km
– K-band : 36 km

Thales Vigile

The Thales Vigile is a fourth generation electronic support measures (ESM) system tailored for naval applications (both surface and submarine).
The Vigile system provides wideband, high sensitivity reception (C to J bands) and pulse analysis with the ability to detect low probability of intercept (LPI) or invisible hostile radars using ultra sensitive search mode. The wide-open system architecture provides 360° coverage and 100% Probability of Intercept.
Furthermore, this ESM supports electronic intelligence (ELINT), precise de-interleaving, and specific emitter identification/platform identification using ESM tasked mode measuring signals frequency, phase and amplitude.


The system provides real, multiple, instantaneous radar acquisition and handling of up to 500 tracks. Also adaptable library generation by flexible programming and “on task” modification/updating capability to maximise the ability to cope with new tactical situations is provided.

When coupled with the Scorpion ECM system, this system provides a powerful EW suite capable of responding to any threat with very low latency.

The Vigile family consists of Vigile-400, Vigile-300, Vigile-200, Vigile-100 and Vigile-LW (Light Weight). Source

USN, USAF, Royal Thai Navy select L3 WESCAM in $90 million order: Here

Terma SKWS C-Guard

c-guard-tubes_464Terma DL-12T.

Two Terma DL-12T. Terma’s C-Guard Soft-Kill Weapon System is a decoy system for naval platforms made to defeat stream attack with multiple missiles and torpedoes from multiple directions. The system will effectively counter advanced threats like small range gate Radio Frequency (RF) missiles, imaging Infra Red (IR) seekers missiles, and advanced next generation torpedoes. These threats require fast response and utilization of advanced tactics supporting the latest in decoy technologies available. 

Sperry Marine Vision Master radar

X-Band and S-Band Sperry Marine Vision Master radar

Scanner Features 

Scanner features include advanced clutter suppression, target acquisition, AIS targets, interswitching, compatibility, dual-channel options and personalisation.

Advanced Clutter Suppression

In the presence of sea or rain clutter, our VisionMaster FT Radar scanner features advanced clutter suppression technology that automatically detects small, weak targets without the need for adjusting controls.

Target Acquisition

Rather than manually acquiring targets, the ARPA scanners automatically and safely acquire and track targets at relative speeds up to 150 knots.

AIS Targets

The VisionMaster FT Radar can display AIS targets and supports processing and display of AIS ATONS, Search & Rescue Craft, AIS SARTS, AIS Base Stations, safety messaging and AIS MKD.


An optional digital Interswitch allows the operator to display radar video from any scanner at any desired display. For improved user operation and flexibility, interswitching gives up to six transceivers and up to six displays


To reduce cost and time required for retrofit, our VisionMaster FT Radars are compatible with the BridgeMaster-E product line by partial hardware and software replacement.


Settings can be customized for different watch officers, with voyage plans and operating systems that can be saved and moved to different vessels, offering flexibility, control and safety. 


Furuno ARPA radar

1165Furuno ARPA radar console (example) – Image @Furuno

The ADS-B and AIS are also believed to be install on board.

Thales also providing the FICS integrated communication system and FOCON IP phone (see above)Network centric mission will go through Thales Link Y Mk.2 that enable the ship to share information with allied force. Thales also integrating the Link RTN developed by Avia Satcom/Rohde & Schwarz. SATCOM will be using Cobham Sailor and underwater communication will be using Ocean Technology Systems Aquacom to communicate with diver. The LRAD also be installed for law enforcement mission.

Thales Link Y Mk.2

Network centric mission Thales Link Y Mk.2 second OPV

Naval version (“shipborne”)
Link Y Mk2 is built in a compact housing compliant to military standards that meet the requirements for equipment in a naval environment. The naval version is to be integrated into any
Combat Management System, e.g. TACTICOS, for surface vessels or submarines. Alternatively, the naval version can be delivered with a local control station to act as a standalone system on board. Source

Thales Network centric  @thalesgroup.comA01157625130914110001Thales Network centric to integrate with RTN developed by Avia Satcom/Rohde & Schwarz

Cobham Sailor

SATCOM will be using Cobham Sailor (example)


LRAD also be installed for law enforcement mission  (example)

LRAD’s highly intelligible, long range voice and warning siren broadcasts establish large safety zones, determine intent, safely change behavior, resolve uncertain situations and save lives on both sides of the Long Range Acoustic Device®. Source

Imtech Marine UniMACS 3000 series integrated bridge system will handle all bridge work. TACAN will be also installed.

Example of Imtech Marine integrated bridge system for Second OPV

Servowatch platform management system selected for second Royal Thai Navy Krabi-class OPV: Here


The IPMS provides integrated monitoring and control of ship propulsion, electrical and auxiliary plant management systems. Integrating these capabilities at the platform level can optimise operational effectiveness and contribute to crewing reductions.

Functions and Features

  • Multi-level Redundant Networking
  • Remote Terminal Units
  • Integrated Propulsion Control System
  • Integrated Power Management System
  • Integrated On Board Training System
  • Condition Based Monitoring System
  • Battle Damage Control System

Krabi propulsion and performance


Two MAN 16v 28/33D diesel engines, each developing an installed power of roughly 9,700hp at 1,000rpm, allow the vessel to sail at a maximum speed of 23kt. The OPV can operate up to a range of 7,800nm, when sailing at 12kt.

Two controllable-pitch propellers are fitted aboard that provide better efficiency and high-manoeuvrability.

Main material source

Updated Jun 24, 2017

HTMS Krabi documentary 


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