Austal USA has continued with the selection of Kongsberg Maritime’s Promas propulsion system for the latest vessel of the US Coast Guard’s (USCG) fleet of new Offshore Patrol Cutters (OPC), ensuring design commonality with earlier vessels built by Eastern Shipbuilding Group.

In a 10 April 2024, announcement, Kongsberg Maritime stated that it had been selected to provide its Promas system to the fifth-in-class, the US Coast Guard Cutter (USCGC) Pickering, which is the first to be built by Austal USA at their yard in Mobile, Alabama.

The US Coast Guard’s new fleet of OPCs – dubbed the Heritage-class cutters – are being fitted with the Promas propulsion system, a capability that could offer efficiency benefits for the vessels, according to Kongsberg Maritime’s own system performance analytics.

“Our Promas systems typically deliver efficiency savings of around 6%, so vessels are able to extend their range, something which can be crucial on longer missions,” said Björn ten Eicken, Kongsberg Maritime, vice president – Naval.

A computer generated image shows how the completed USCGC Pickering will look, with the OPC class replacing two older generations of cutters still in service: Credit: Austal USA

Kongsberg Maritime’s own literature on the Promas system indicates that a 6% efficiency gain for multi-screw ship would be at the top end of the spectrum, which usually falls in the 2-6% range. For single-screw vessels, the Promas system provides a 3-8% efficiency bonus.

According to Kongsberg Maritime, Promas combines rudder and controllable pitch propeller into a single propulsion system to optimise the hydrodynamic properties of the ship and delivers increased efficiency and thrust while using less energy.

For the USCG’s OPC programme, as well as twin Promas, Kongsberg Maritime is contracted to supply steering gear, rudders, fin stabilisers, and tunnel thrusters.

USCG Heritage-class cutters: troubled, but crucial

The Coast Guard’s new OPC programme represents a significant investment in maritime capability and is expected to run up to 25 ships. The Heritage-class cutters will replace the Medium Endurance Cutters of the Famous and Reliance classes, some of which have been in service for more than 50 years, and form the central element to its fleet, alongside the larger, frigate-sized, Legend-class cutters.

In terms of mission output, the OPCs are intended to provide long range patrol capability. At 360ft long, they will have a displacement of 3,700 long tons, maximum speed of 22.2 knots, and a range of 9,050 nautical miles at 14 knots.

However, the impact of Hurricane Michael along the US eastern seaboard in 2018 delayed construction by Eastern Shipbuilding of the first-in-class USCGC Argus until 2019, with the vessel only launched in October 2023 (top image). The timeline indicates a commissioning at some point in 2024, around three years behind the initial schedule.

In October 2022 the USCG issued a notice confirming that it had awarded Austal USA the deal for Stage 2 of the OPC programme, following the withdrawal of an award protest filed in July the same year with the US Government Accountability Office “by an unsuccessful Stage 2 offeror”.

The USCGC Thetis enters Guantanamo Bay in 1995. The US Coast Guard is keen to replace older vessels still in service with the new OPC ships.

The initial award, made in June 2022, would see Austal USA produced up to 11 OPCs, and was valued at $208.3m to support detail design and long lead-time material for the fifth vessel in class, the USCGC Pickering. The USCG at the time said that the overall production contract had a potential value of up to $3.33bn if all options are exercised.

In a statement, the USCG said that requirements for OPC Stage 2 detail design and production were developed to maintain commonality with earlier OPCs in areas such as the hull and propulsion systems but provide flexibility to propose and implement new design elements that benefit lifecycle cost, production and operational efficiency, and performance.

With a planned 25-ship OPC programme of record, a further ten vessels are likely to be contracted to US shipyards at a future date, on top of the 15 already confirmed (four with Eastern Shipbuilding, 11 with Austal USA).

The OPCs will be reasonably armed for USCG vessels and will feature a single BAE Systems Mk110 57mm main gun, a BAE Mk38 Mod 2 25mm gun weapons system, and M2 Browning 12.7mm machine guns.