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post #21 of Old 01-20-2013
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Re: US Navy ship strikes reef because of incorrect charts

Originally Posted by Lake Superior Sailor View Post
I was taught never to rely on one piece of information , use charts, depthfinder, radar, sonar, Chart plotter, and what ever else you have. A pilot is nice!...Dale
You're right, of course, but if you look carefully at the photos showing the ship lying perpendicular to the reef you'll notice the bow on the coral and the stern in dark blue water. There could be 200-300 feet of water under the stern. My guess is the depth sounder wasn't much help -- one minute you're in hundreds of feet of water and within fifty yards or so you're stuck on the coral. One of the thing that makes reefs like this great dive spots are the reef walls -- which are often near vertical and rise hundreds of feet from the sea bed to within a foot or so of the surface. At 15 knots the ship does 100 yards in 10-12 seconds, so by the time the depth alarm goes off (even with forward looking sonar) you're already on the reef.

Radar doesn't help either -- can't see under water and many of reefs in this part of the world never dry out. The wave line / break might show up on radar, but in relatively calm conditions you might mistake the break for normal ocean swell.

Real long range sonar (not just a forward looking depth sounder)?? Don't know if minesweepers are rigged with sonar that can see something 1/4 to 1/2mile ahead.

Visual watchkeeping might have been the only way to have seen this coming, but reef breaks are very hard to see when viewed from the seaward side especially if it was a relatively calm night with little moon (waxing crescent ~ 1/4 moon on that day).

And remember 100 yards of travel every 10-12 seconds....doesn't leave much reaction time. Say you're the lookout stationed on the wing of the bridge. You're responsible for maintaining a look out in a 180 deg arc on your side of the boat. You've panned astern and you begin a pan forward -- you think you see something a couple of hundred yards ahead, but you're not sure. You take a second look, adjust the zoom on your binoculars, refocus, think about it for a few seconds and reach for the intercom. "OD, I think I see something....not sure if it's anything.....". OOD says, "OK, I'll be right out. Puts down his coffee cup and walks to the bridge wing. Could 30 or 40 seconds have elapsed and the ship traveled 300-400 yards? Sure.

A career ender? Usually that's the case, but let's see what happens at the inquest. A faulty electronic chart is possibly a big mitigating factor. My guess is that a lot will depend on how far off the chart was. If it was a few hundred yards off, the skipper is toast. If it was several miles out, and if this was a reef with nothing showing above the water....well that might be another matter althogether.
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