They were the final Watson type boats to be built and survived in service almost to the end of the displacement hull era.

Production continued until 1963 when large displacement hull development turned to the self-righting 48 ft 6in Oakley-class and later Solent-class.

The wheelhouse was fully enclosed with sliding doors on either side and there were bulwarks above the fenders fore and aft and, from the second boat, the forward cabin was increased in size.

In this case, two 60 bhp Gardner 5LW five cylinder diesels were fitted with the exhaust being taken up the mast as on the later 46 ft 9in boats.

From 1973, the boats were modified to become self-righting by, in most cases, the fitting of an air bag on the starboard side of the rear cabin roof, adjacent to the radar.

This gave a once only self-righting ability which was successfully deployed when Salcombe's The Baltic Exchange capsized on service in 1983.

Six boats were rebuilt with larger forward and aft superstructures (akin to the 48 ft 6in Oakley and Solent classes) which made them inherently self-righting.