site.btaInner Workings of Bulgarian Military Research Vessel's Anchoring Mechanism

Like any other ship, the military research vessel Sv. Sv. Kiril i Metodii (NAVAL RSV 421) can be moored in a bay or harbour, drop an anchor or attach itself with ropes to a pier. The vessel is on a voyage to Livingstone Island to assist the 31st Bulgarian Antarctic Expedition. The voyage to the Bulgarian Antarctic base on the island will take about 40 days. 

The anchoring gear of NAVAL RSV 421 consists of several main components - two anchors, each with an anchor chain, devices for their lowering and retraction - a windlass, as well as spars for mooring lines.

The ship's anchors are located on each of the bow sides - one on port and one on starboard. The windlass, which moves the anchors, is attached to the bow deck. It is composed of a drive mechanism, two mooring drums and two anchor stars. The mooring drums girth or release the ropes that are used to tie the ship to the pier. The links (rings) of the chain "lie" in the anchor star, which lowers or pulls them to an anchor chest where the chain is collected, officer candidate Andrei Petrov, NAVAL RSV 421's watch officer, explained to BTA.

The windlass on the military research vessel is electrohydraulic, he said. Powered by an electric motor, a hydraulic pump creates pressure, which is converted into torque by a hydraulic motor. The torque created is used to lower or retract the anchor. The pressure is adjusted according to how fast the crew wants to lower or retract the anchor. The windlass also features a band brake and a screw stop for each of the two chains.

The two spars of the St. Cyril and Methodius" are located aft and serve for lowering or retracting the mooring lines. The spire may also have an anchor star and mooring drum. The difference between the windlass and the capstan is the axis of rotation - the axis of rotation of the windlass is horizontal and that of the capstan is vertical. The spars on the ship do not have band brakes because they only take mooring lines and not anchor chains. If the spike has an anchor star and also serves as a chain, then a screw stop is also needed, explained Officer Candidate Petrov.

The ship's anchor chain is made up of docked links that form individual parts - switches, each 27.5-metres long. 

In order to moor, the vessel must stand with the bow into the wind and spread a chain along the seabed at least 2,5 times the depth of the anchorage point. For example, if the ship is above a depth of 30 m, it will have to spread at least 75 m of chain on the seabed. After lowering, the anchor is spread in reverse - initially with the help of the engine, and then with the remaining momentum backwards. It is the contact of the part of the chain that lies on the seabed that holds the ship. Most of the force that holds the ship comes from the anchor chain, not the anchor itself, watch officer Petrov stressed.

Each of the ship's anchor chains is about 300 meters long. However, if it is necessary to lower the anchor more than 70 meters, it is not released by gravity, but is released gradually by the broach, as otherwise it would gain a great speed to the bottom, which would exceed the capabilities of the band brake, could ignite it and break the chain.

If in an emergency the ship has to be freed from the anchor if it is stuck on the seabed and cannot be reversed, for example, then a buoy should be placed at the end of the chain by the crew to indicate to other vessels that there is an anchor left at that location. It is appropriate, if possible, to notify an auxiliary vessel to remove the anchor with the assistance of divers. In such a situation, the vessel should purchase a new anchor as otherwise it will not be allowed to pass through any slough or channel where two anchors are required.

It is not advisable for the vessel to drop a second anchor due to the risk of chains becoming entangled, but in more complicated weather or other extreme situation, it would be appropriate to drop two anchors, said Petrov.

BTA's Daily News editor Konstantin Karagyozov is the only member of the media who is travelling on the ship to Livingston Island and back, and will cover the Bulgarian expedition on site throughout their stay in Antarctica. 

All media outlets can use the Bulgaria-Antarctica BTA's Log for free.