The Port of Portland is situated amongst some of the most treacherous waters in the UK, including the Shambles Bank and Portland Bill, where tidal races produce dangerous seas and a vessel's seakeeping is paramount.

‘Culverwell’ is fitted with twin Volvo D12 engines rated 450 hp continuous at 1,800 rpm. They give the vessel an operational speed of 24.5 knots on a lightship displacement of 15,000kg (16,500kg loaded). Stern gear was supplied by Clements Engineering and included the decision to try five blade propellers for the first time. This proved most successful, with lower vibration levels with no loss of speed. The propellers, run in tunnels to give optimum shaft angles and high tip clearances, eliminating cavitation problems. Power steering gives a light responsive helm with five turns lock to lock. Ample rudder size allows the vessel to respond well at slow speed and provide sharp high speed turns in which the vessel stays level with a slight inward heel.

Culverwell is very strongly built, featuring 150x150mm transverse frames with large, substantial knees providing exceptional strength, especially at the hull to deck join at the vessel's shoulders. This is most important on a pilot boat that undergoes multiple controlled collisions daily. Heavy 150mm D section main fendering is augmented by a lower line and multiple diagonals to provide comprehensive hull protection.

Culverwell's internal arrangement has been specially designed to suit its intended role as a pilot boat with occasional crew transfer duties. To this end, the main cabin has twin CAB 300 seats for helm and pilot with additional belted bench seating for seven passengers.

Below in the forward accommodation area there is further bench seating to provide a total capacity of 12 passengers. A central helm position provides a panoramic view all around through a high glass area. The central helm also allows the helmsman to come alongside a ship on either port or starboard depending on prevailing sea conditions with equal ease and confidence.

Culverwell has a large engine room that is 5m in length, providing a spacious area which allows for easy maintenance. There is 5' 10” of headroom which diminishes outboard, while all maintenance components have been designed to be easily and quickly accessible. An important design feature is the allowance for easy engine removal, which can be carried out in under three hours. This involves the removal of seating pedestals, all on quickly unbolted modules, removal of the roof hatch and lifting of the hinged main cabin sole hatch, allowing the engines to be quickly lifted straight off their mounts and taken vertically upwards thorough the cabin roof hatch.

As with all Safehaven’s Interceptors, Culverwell is graced by elegant lines which make for a striking appearance on the water, enhanced in this case by two red stripes on the sides of its hull.