Enhanced Dead Weight Anchor
Clump weights (Dead Weight Anchors) used in mooring design are known to be large, heavy by design and often requiring prohibitively large vessels with cranes and A-frame to enable installation. Often on the plus side they also work Omni directionally and failure is gradual through changes of position due to overloading and sliding. In some instances this is a preferable failure scenario and can be monitored through visual inspection by divers and ROV. The process is made easier if there is a point of reference such as star picket datum’s nearby to facilitate subsea metrology in lieu of DGPS approaches.
Where additional holding capacity is required then it is necessary, sea floor conditions permitting, the clump weight designs can incorporate keying geometry to engage the sea floor either Omni directionally as per our keyed steel gravity bases or building keying into the concrete geometry and associated steel plate skeleton structures. We refer to the later as Enhanced Deadweight Anchors (EDA). The best example is the so called Pearl Harbour Anchor, or the in some texts a concrete kedge anchor.
The fundamental difference is the anchor prefers soil conditions conducive to partial embedment (or keying) to gain enhanced holding capacity. Contrary to dead weight anchor or clump weights, EDA’s are directional and require some pulling to induce engagement. Much less pulling than drag embedment anchors for example. Failure is likely to result in tumbling of the anchor and a subsequent reduced holding capability post failure similar to that of a clump weight.
In some operations such as spread moorings and temporary construction moorings, where any failures are readily dealt with, the approach allows smaller and more efficient anchors with the associated benefits such as uplift resilience. In the case of reef pontoons, tumbling or dragging of even the simplest clump weights can result in damage to the adjacent coral reef and therefore constitutes a negative outcome by any ecologically minded operator.
ONA have developed a range of tough EDA’s which are tough and well balanced and come with rated lifting and main pad eyes for instil confidence to meet stringent OHS lifting requirements. Our units come with anodes for longevity and include a structural core to allow for safe end of life removal and disposal. The capacity of our EDA’s is up to double that of conventional clump weight or dead weight anchors depending on soil conditions.
ONA can produce these anchors ex Brisbane and Perth. Please contact us for pricing.