USCGC BRISTOL BAY

WTGB 102/CGB 12001

Aid to Navigation (ATON)

One important mission of the Bristol Bay is to install, maintain, and remove aids to navigation. On this mission ship is heading for a large floating buoy in Lake St. Clair, "R22", which marks the eastern limit of the dredged shipping channel. Without this dregded and marked channel it would be impossible for large ships to navigate Lake St. Clair. Between pairs of these markers, hundreds of ships and boats pass daily. To check the buoy's condition, it will be hauled aboard and serviced, and then it will be reposition exactly on station.

The work crew assembles on the barge, while the ship manuevers into position alongside the floating navigational aid. The crane operator has already swung the boom of the large crane over the starboard side and lowered the lifting hook down to the deck.

Once alongside the buoy, a crewman snares the aid, and the lifting hook is attached. The size of the complete buoy is still not fully apparent. The deck of the barge has been designed for just this type of work. Notice the black object along the outer edge of the hull where the bulwark lowers to deck level. It is special gear for handling the anchor chains of these big buoys.

Everyone clears the decks as the crane begins to hoist the big red navigation marker aboard the barge. This is the part of the buoy most people never see. The dimension of these floating aids begin to become more impressive. Fortunately, today is a calm afternoon, and the barge is a very stable platform from which to work. The crane hauls the buoy out of the water without difficulty, as the Bosun's Mate signals to the crane operator the desired movements.

The buoy has been hauled aboard, and is now being set down on the barge deck. Large timbers serve as chocks, and additional "gripes" will secure the heavy and awkward structure temporarily to the barge deck. Notice the large chain anchor bridle rigged to the bottom of the buoy. Each buoy has a specific length of chain, calculated with regard to the depth of water it is anchored in. Once the buoy is secured, the anchor will be hauled aboard for inspection.

Up from 32 feet below comes "The Rock", thousands of pounds of cement anchor which holds the buoy on station. The chain is captured in the special fixture mentioned earlier. If the anchor does not require replacement, it remains outboard like this while the buoy is serviced. The special chain fixture features a very quick release, so that, once the ship has established the precise position, the anchor can be dropped in very quickly!

While the Bristol Bay has been encumbered in her ability to manuever as she "works" the buoy, the bridge has flown a special signal to indicate this situation to other ships. The circular and conical black shapes are called "dayshapes", and their arrangement (ball-diamond-ball) in this case signals: Vessel restricted in her ability to manuever. Among the vessels considered to be restricted in their ability to manuever are:

A vessel engaged in cable or pipelaying or working on an aid to navigation.
A vessel engaged in dredging, surveying or underwater operations, including diving.
A vessel engaged in replenishment or transferring persons, provisions or cargo while underway.
A vessel engaged in the launching or recovery of aircraft.
A vessel towing if she is severely restricted in her ability to deviate from course.

The deck crew has been busy checking the buoy. They service the lamps, check the battery and photocells, inspect for damaged, and check the anchor chain and fittings. The bridge crew has been busy, too, keeping the ship exactly in position for relocating the buoy. Modern electronic navigation equipment allows the ship to compute the precise location of the anchor using specialized computer hardware and software. The calculations account for:

the position of the ship's GPS antennas,
the offset from where the anchor will be dropped to the GPS antennas,
the heading of the ship, which affects that offset.

The real-time nature of the positioning computer allows the anchor to be dropped to within a few feet of its target!

The ship and barge are nudged into precise position, and the signal given to the deck to "let go" the anchor. This is accomplished with a swing of the sledge hammer, which releases the rock from the special fixture. Of course, prior to this the buoy has already been set back afloat. The remaining chain on deck quickly disappears over the side, and the job is done.