Introduction
Ballard Marine (Washougal WA) was called in to retrieve the anchor and clear the busy navigation channel. Ballard Marine Construction called Seahorse Geomatics (Portland, OR) to identify the lost anchor using multibeam bathymetry.
The vessel captain provided the approximate location of the lost anchor.
Seahorse Geomatics mobilised the S/V Shehorse vessel from Portland, OR and towed it to Cathlamet, WA where the vessel was launched. The Shehorse was ready to conduct the search less than an hour after arriving in Cathlamet.
Large and high-frequency wind chop was present on-site, making the survey challenging.
The Survey
Data collection for the first survey line was started upstream of the reported location. The captain had stated that the location was taken some time after the anchor was dropped.
Side-scan data was logged and on the first line of the search the anchor chain was visible in the side-scan to starboard of the vessel.
The anchor chain was followed, utilising the side-scan on the NORBIT iWBMS system, to its downstream end. Additional data was collected to ensure that the shipping channel was clear of obstructions, as at this time the river was closed to shipping.
The chain was clearly visible, but the anchor was not observed. It was suspected as buried.
Recovery
A grapple was laid across the chain location and dragged until it snagged the chain on the first attempt.
At this point, the chain, all 270m, was hauled aboard the barge until the anchor was recovered.
