THE BRUCE^® DENNLA (Patented)

A vertical load anchor, or VLA, is a special design of drag-embedment anchor that can be 'triggered' so that the load line through the centroid of its fluke increases to a final angle of 90º (or 'normal') to its fluke. When the VLA is triggered it provides a triggered holding capacity higher than the pull in load but further loading will cause it to pull out of the seabed, a problem that is mitigated but not solved by imposing a higher safety factor on a VLA than on a conventional drag-embedment anchor.

In the Dennla, the final centroid angle is reduced from 90º to 78º ('near normal'), a modification that enables the triggered anchor to penetrate further when overloaded and to do so when pulled at angles at the mudline as high as 45º. At the same depth as a triggered VLA of equal fluke area, the triggered Dennla has over 95% of the holding capacity of the VLA. However, on loading further the VLA will pull out whereas the Dennla will continue to embed and generate an increasingly greater holding capacity than that at which the VLA failed. Where soil conditions are imprecisely known, this is a crucial advantage of the Dennla.

The Dennla is pulled into a penetration depth of over three times the square root of its fluke area by an anchor-handling vessel (AHV) until a chosen line tension is reached at a mooring line scope giving an uplift angle of about 25º. Tension is then reduced and re-established after shortening scope to give an uplift angle of about 40º. The change in angle of loading applied to the anchor shank results in a shear pin parting to free the shank to rotate and establish the triggered centroid angle of 78º. The resulting increase in fluke inclination causes an immediate increase in holding capacity and the anchor steepens its trajectory into the seabed to provide deeper penetration than would otherwise have occurred at the original centroid angle. This enables an even higher load capacity to be achieved. If the Dennla should reach its maximum penetration depth, further loading will cause it to move horizontally in the seabed at constant load like a conventional drag-embedment anchor.

The Dennla negotiates stern rollers smoothly and is easy to handle on deck, features which decrease turnaround time and contribute to a track record, built up since 2002, for reliability in performance and decreased time and cost in anchor handling in deep and ultra deep water.