I am NOT nautical, but doing some quick research, and a little math. Assuming channel was 40-50 ft deep (let's go with 45 feet) Observer claimed 3-5 knots (going with 4.5 knots = 7.6 ft/second)

Say the Anchor was ready for deployment, it has to sink 45 ft (5 seconds?) Then assuming 45 degrees for maximum drag, the ship has to travel 45 feet before the anchor catches.

So, zero reaction time + (5 sec*7.6ft/sec) for anchor to hit bottom forward travel would be 23 ft. Then 63 feet for anchor to dig in - that's 88 feet (Pythagorean theorem, solving for hypotenuse). Then Drag and deceleration of considerable mass of cargo ship - several hundred feet (I am guessing with zero experience). Assuming muddy bottom, there is a likelihood the Captain could not have avoided this in the time/distance he had to work with.