LÉ Róisín (P51) is the lead ship of her class of offshore patrol vessel in the Irish Naval Service. Róisín was built by Appledore Shipbuilders in Devon,entered service with the Irish Naval Service in September 1999 and is based at the Haulbowline Island, Cork Harbour Headquarters and Dockyard.
The ship was designed by STX Canada Marine (formerly Kvaerner Masa Marine) and has an all-steel hull based on the Mauritian Vigilant patrol vessel launched in 1995, but without the helicopter deck and hangar facilities. The high level of automation incorporated into the ship's systems allows the ship to be operated with just 47 crew including eight officers. The crew is provided with comfortable accommodation. The vessel is designed for winter North Atlantic operations.
The ship is armed with an OTO Melara 76 mm gun dual purpose gun installed on the bow gun deck. The gun fires 6 kg shells and is capable of firing up to 85 rounds per minute to a range of over 15 km. There are also two 12.7 mm machine guns and two 20mm Rheinmetall Rh202 cannon for anti-aircraft defence.
The main gun is controlled by an Ultra Electronics Command and Control Systems, Radamec 1500 optronic director with a daylight TV camera, thermal imaging camera and eyesafe laser rangefinder. System 1500 functions in automatic or manual mode. The system provides fire control for surface engagement with spotting corrections in both line and range and has an effective secondary self-defence anti-air capability. System 1500 can detect a small patrol boat at ranges in excess of 12 km, night or day. The ship's Kelvin Hughes surface search radar, operating at E, F and I bands, is installed high on the main mast over the bridge. The Kelvin Hughes navigation radar operates at I-band.
The communications package includes VHF, HF, Inmarsat Global Maritime Distress Safety System (GMDSS) and Differential Global Positioning System (DFPS) and secure communications. Three inflatable boats are deployed from each ship; two 6.5 m Delta rigid inflatable boats (RIB) launched with Caley davits, and a single Avon 5.4 m RIB.
The ship is powered by two Wärtsilä 16V26 diesel engines each developing 5,000 kW continuous power. The engines drive two shafts with Lips inboard turning controllable pitch propellers via single reduction gearboxes. Each propeller is 2,500 mm in diameter and functions at 300 rpm.
The engines provide a maximum speed of 22 knots (41 km/h) with a range of 6,000 nautical miles (11,100 km) at a cruising speed of 15 knots (28 km/h).
A Brunvoll FU45 CPP bow thrusters, rated at 340 kW with 5.6 tonnes-force (55 kN) thrust, is fitted for precision manoeuvring and station keeping. A pair of non-retractable anti-roll fin stabilisers is also fitted.
Three Caterpillar 3412D1-T generators each deliver 405 kWe at 1,500 rpm. One Caterpillar 3406D1-T emergency generator delivers 205 kWe at 1,500 rpm.