"Mountwood" and "Woodchurch" were built at Dartmouth by Philip and Son. The "Mountwood" was launched on the 31 July 1959 and the "Woodchurch" on the 28 October of the same year. They were loosely based on designs of the "Leasowe" and "Egremont" of the Wallasey fleet, although they both weighed considerably more at 464 tonnes, compared with 311 tonnes for the earlier vessels. They are also larger than the older Wallasey pair, being approximately 19 feet longer, 6 feet broader and over a foot taller. Both vessels were externally identical in almost every way up until 1991 when the shroud protecting the aft funnel vent on the "Mountwood" was changed from square to rounded.