DUKC® methodology can be used to optimise channel dredging through determination of minimum UKC and dredging requirements for specified design vessels, taking into account a range of environmental conditions. In analysing UKC requirements, international guidelines relating to minimum bottom clearance and manoeuvrability requirements during the transit of large vessels in shallow waterways have been applied. This information can be used to create a channel depth profile which matches the UKC requirements.

The intended aim of increasing allowable sailing drafts and tidal windows is delivered at a greatly reduced cost and with minimal environmental effects. The port can be confident that the maximum benefit will be derived from every dollar spent on dredging.

Vessel under-keel clearance (UKC) has two purposes:

1. Bottom Clearance (BC) - Prevent the vessel from touching the channel bottom.
2. Manoeuvrability Margin (MM) – Provide sufficient water flow under the hull and past the keel for the vessel to be manoeuvred.

UKC for MM differs from that for BC in that vessel wave response does not affect UKC for MM and the channel depth for UKC for MM is not necessarily the shallowest depth.

DUKC® analysis involves individually calculating each of the factors (wave response, squat, heel, etc…) that contribute to reducing UKC at all points of a transit through a restricted waterway. UKC for MM and for BC are separately calculated for each point in the channel. Consideration is given to the actual environmental conditions (waves, tides, currents, etc…), vessel dimensions, stability characteristics and speeds and actual channel configuration. The result of this analysis is a net UKC profile for each vessel transit. The critical points for UKC in the channel are identified.

Figure 1. Typical vessel transit UKC profile generated by DUKC.

Figure 1 illustrates a typical UKC profile for a vessel transit as generated by DUKC® analysis. UKC for MM and for BC are shown together with their limiting values. The critical points in the channel occur where either UKC for MM or for BC are reduced to their respective limits.

In this scenario there are three locations where UKC for MM is reduced to its limit due to vessel heel on bends and one location where UKC for BC is reduced to its limit by wave induced vessel roll. It can be seen that to achieve a greater sailing draft the depth in these four locations must be increased. A depth increase of 0.2m in these areas alone would result in a 0.2m draft increase.

In a dredge optimisation study using DUKC® methodology the UKC profile is produced based upon statistical analysis of environmental conditions as well as the range of possible vessel types and speeds. The profile created allows for the full range of conditions under which a vessel may be required to transit the channel. Optimisation with DUKC® can significantly reduce the financial cost of dredging as well as its environmental effects. Continued use of a DUKC® system in real-time will ensure the most efficient use is made of the channel whilst maintaining a high level of safety against vessel groundings.