Friday, 27 September 2013

Dynamic Under Keel Clearance

When ships are underway, a safety margin - the under keel clearance - is applied as a buffer. A static under keel clearance, or UKC, is typically 10% of the ships draft. In addition to the allowing for the imperfections in the sea bed and squat, it also makes the ship maneuverable. If the UKC is too small, Bernoulli's Principle creates localised low pressure zones under ship causing her to shear, or veer off course, and to be generally uncontrollable.

Commercially, deeper draft equals more cargo which equals more freight - depending on where you stand in the supply chain. Using predictive algorithms, shipping is dipping into the 10% static under keel clearance rule of thumb. This technology is called 'Dynamic Under Keel Clearance', and was pioneered by an Australian company, OMC International. Data from wave-rider buoys is combined with historic tide date, prevailing weather and barometric pressure. The algorithm calculates what the tide should be and then compares the predicted tide height with the actual water depth from the tidal meters. DUKC is being used in four of our ports to maximise cargo loading, and gives the Master an individualised target draft to load to.

What's this got to do with the photo below? Earlier this week, four bulk carriers were waiting for the DUKC-predicted tide to transit the Prince of Wales Channel in North Queensland.

The four deep draft vessels here had a 30 minute window to transit Varzin Passage from west to east. The line up (left to right) are our 'RTM Dias' (Captain Gupta), 'Noble Halo', 'Solin' and our 'RTM Twarra' (Captain Loveland). My thanks to Captain Wal Cray, Pilot of the westbound 'Jubilant Success' and 'Australian Reef Pilots' for this photo.

The Antipodean Mariner


  1. Very interesting! Shipping is very much about saving on transit costs. I'm not surprised to hear about this new twist.

    On a related topic, the venturi effect may have been the cause of the submarine USS Newport News hitting the Japanese VLCC Mogamigawa in the Straits of Hormuz. This blogger saw it happen elsewhere, and thinks it quite possible for a submarine to be sucked to the surface by large vessels.

  2. Awe inspiring pictures.
    Just a short note to say that the first of two sections of the accommodation block of the Rena is approaching Tauranga Harbour Entrance on the RMG 1000 barge, towed by the Resolve Monarch. Vessels are being returned to port, to avoid the tale of Cyclone Lusi, due here at the wekend.