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T91. Motor Coastal Patrol Vessel built by the Royal Thai Dockyard at Bangkok and commissioned in 1971. It has a displacement of 871/2 tons on dimensions of 104.3ft x 17.5ft x 5.5ft and a crew complement of 21.
A twin-screw vessel, it is driven by two diesel engines of 1,600 bhp for a speed of 25 knots.
Armament consists of one Bofors 40mm gun and one Bofors 20mm gun.
Log Book April 1987
Thailand 1979 6b SG1005.

HTMS T 91

12 July 1967 keel laid down at the Naval Dockyard.
09 May 1968 launched, christened by the Queen of Thailand.
Tonnage 100 tons full load.
12 August 1967 commissioned.

So far I can find, she is still in service in 2015.