BMT SeaTech studies re-design of Portsmouth Harbour channel

BMT SeaTech Ltd has recently completed a comprehensive study for Defence Estates South West. Forming part of the Portsmouth Harbour Regeneration Project, the study looks at the re-design of the deep water channel for Portsmouth Harbour in the light of its use by large future warships for the Royal Navy. When a large ship enters a port or harbour, it frequently has to do so along a comparatively shallow and often winding approach channel. BMT has extensive experience of approach channel design and was commissioned by Defence Estates to review the suitability of the present channel for large warships proposed for the future. In addition, an alternative "straight in" channel design, remote from the present channel, was to be reviewed.

At Portsmouth, channel design is constrained by a number of elements. One is the historic harbour entrance, bounded on both sides by structures dating back to Henry VIII which understandably must not be touched. Similarly, the Spit Sand Fort must be avoided, as should other sites of historical interest such as that occupied by the remains of the Mary Rose.

From a navigational point of view, the present approach to the harbour entrance involves a number of course changes in, or near, the entrance which puts a large ship at risk. Therefore, the elimination of these changes was seen as an important part of any new channel design.

Portsmouth, however, possesses a significant natural advantage. There is a natural channel, underlying the present approach channel, which has been formed as the tide moves water in and out of the harbour. By making use of this channel, BMT, using its PCSS fast time manoeuvring simulation model, was able to produce a design which both eliminated the awkward course changes at the harbour entrance and made the fullest use of the available, natural, deep water. This so-called "Blue 2" channel led to significantly reduced dredging costs compared with the alternative "straight in" channel and avoided both the Spit Sand Fort and the Mary Rose site.

Dr Ian Dand of BMT Seatech Ltd, who is responsible for the design study, said: "Using sophisticated computer simulation, we have been able to show that the existing, natural, channel, with some dredging, can be used for the large warships proposed for the future. This will minimise environmental disruption as well as reducing marine risk."