We typically take our measurements from the back of the ship. This keeps long lines away from the engine screws while moving (very good!!!), the downside is that the ship’s wake contaminates the upper 10 meters of the measurement, as it mixes up the surface waters. For this project, we really want to get undisturbed observations near the surface of the ocean… enter the bow chain!
This is a steel wire hanging over the side of the ship, pulled straight down by a 150 lb weight attached to its end. Along its length, we attach instruments, these then get dragged horizontally through the water as the ship moves. The bow chain measures temperature and salinity over the upper 10 meters of the ocean out in front of the ship’s wake.
In addition, to record water temperature right at the sea surface, we also have a “sea-snake” on the other side of the bow. This is basically a sensor in a garden hose that floats at about 5 cm below the sea surface, dragged along a few meters next to the ship.
We only have the bow chain in the water when the ship is moving slowly, so it has been recovered and deployed a few times now. Everyone enjoys the break from their typical jobs, so we often have a lot of hands out for this type of activity. The forward davit holds the line with the instruments. We use the aft davit to raise and lower a 150 lb. weight that keeps the instrument line vertical. E.S.