River-class batch 2 Offshore Patrol Vessel (OPV) is a new U.K. design that is being exported to a number of countries already. It is 90 meters (297 ft) long, has a top speed of 25 knots, and a flight deck that can accommodate a Merlin helicopter (with the BAE Systems upgrades).
The Royal Navy version has many upgrades as compared to its foreign sales versions such as a reinforced flight deck able to handle a Merlin helicopter. Better fire control and built to tougher military specs (costing almost 50% more, bring each vessels cost to $200 million).
The River-class has a displacement of 2,000 tons and uses 2 MAN 16V28/33D diesel engines with 2 pitched propellers
Armaments for UK vessels are 1 Bushmaster 30mm cannon and 2 machine guns. However, the Brazilian vessels use a 30mm DS30M cannon, 2x 25 mm guns and 2x 12.7mm (50cal) machine guns. While the Thailand vessels use one Oto Melara 76 mm main gun and two MSI 30mm secondary guns, 2 machine guns as well as 4 Harpoon block 2 (speed 525mph, range 125 kilometers) anti ship missiles.
As you can see this OPV can be configured as a coast guard vessel or as a naval corvette with teeth.
Thailand is in a dangerous neighbourhood with China testing how far it can push into others territorial waters, so it may need a 76mm gun on its vessels.
The Bofors 40mm Mk4 or the BAE 57mm MK3 Naval Gun would make more sense for most other navies.
I do think the British have under gunned their vessels, even if their intended purpose is constabulary. Being able to defend itself against other patrol vessels should have been in the mix. Considering these vessels are serving in foreign waters and often in disputed waters. The British vessels should upgrade to prevent getting swarmed with fast attack speed boats. The addition of 2x25mm gun stations could solve this problem. This upgrade would be a one time cost of $1 million per vessel vs $1 million per Harpoon missile.
image sources
- 800px-HMS_Medway_sea_trials: Royal Navy | CGL