September 20 – 21, 2009
Thunderstorms kept us at the dock until mid-afternoon Sunday, when they cleared and we headed toward North Rock for remotely operated vehicle (ROV) shakedown surveys. Our targets were some relatively shallow — 55 to 65 meter (180 to 213 feet) deep — sinkhole features discovered in the multibeam data. Since this was a shakedown, we tried several different methods for attaching a clump weight to the ROV to help it descend faster at the first sinkhole. We saw many invasive lionfish under the ledges at this feature.
The second sinkhole feature we dove on at North Rock was circular, with a complete rim all the way around. There was no outlet to the offshore edge of the bank. A tiger shark attacked the ROV here, pushing it around but not biting it. During this dive, our ROV pilot, Todd, did successfully capture a rock sample with the ROV’s claw for future analysis. An additional bonus here was catching two jacks for dinner later.
With no storms Monday morning, we confirmed "all systems go" and motored out to the southwest end to look at features on the steep slope of the platform’s edge. Some difficulty anchoring led us to look at several features to the west of our initial target that appeared to be small cave mouths with entrances approximately 1 m (3 ft) in diameter at a depth of 119 m (390 ft), based on the multibeam data. We did find the features, but each one was a dead end.
Despite having to do a small bit of on-site repair when the ROV had a minor problem with a vertical thruster, we were able to complete a total of three dives today.
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