Rihtniemi-class

The Rihtniemi class patrol boats, designated by the Finnish Navy as the R class, were originally constructed as coastal minesweepers. The Finnish Navy ordered the first two vessels of the Rihtniemi class, Rymättylä and Rihtniemi, in July 1955 from the Rauma-Repola shipyard in Rauma, Finland. Both patrol boats were launched in 1956 and entered service in 1957. Three subsequent, slightly larger vessels—Ruissalo, Raisio, and Röyttä—were ordered from the Laivateollisuus shipyard in Turku and entered service in 1959. Due to the size difference, these three latter vessels are also referred to as the Ruissalo class. In 1971, three additional Ruissalo-class vessels were built for the Colombian Coast Guard.

In terms of design, the Rihtniemi class was propelled by two Mercedes-Benz diesel engines. For armament, the vessels were equipped with one 40 mm Bofors gun, one 20 mm Madsen gun, and one Squid anti-submarine warfare mortar. The design featured low fuel consumption and high stability, with the capability to recover to an upright position from a list of up to 115 degrees without sinking.

By the end of the 1960s, the Finnish Navy modified the minesweepers into patrol boats. The fleet was assigned to the Patrol Flotilla and later transferred to the 7th Missile Flotilla, where they performed sea patrol and anti-submarine warfare duties. The Finnish Navy decommissioned the Rihtniemi class in the 1990s. Following their service in Finland, Rymättylä and Rihtniemi were sold to the Estonian Navy in 1999, serving as EML Suurop and EML Ristna. Among the Ruissalo-subclass vessels, Ruissalo was scrapped in the early 2000s, while Raisio was sold on the private market. The patrol boat Röyttä underwent renovations in 1980 and 2000, after which the Finnish Navy transferred it to marine reserve training units in 2000. It was subsequently sold to a private adventure company and currently operates as a commercial cruise ship under the name Vartiovene 55 in Helsinki. The Colombian Coast Guard operated its three Ruissalo-class vessels—Carlos Alban, Nito Restrepo, and Jorge Soto del Corval—between 1971 and their decommissionings between 1984 and 1997.