Offshore vessels (PSV, AHTS, DP): the English of the ship
Offshore vessels serve oil, gas and wind installations: platform supply vessels carry cargo and bulk to rigs, anchor handlers move rigs, and dynamic positioning keeps them in place without an anchor. Their English is the English of the 500-metre zone, the crane and the DP alert.
An offshore vessel spends its life next to something it must not hit. A platform supply vessel (PSV) comes alongside a rig in open sea, holds position on dynamic positioning, and transfers containers, pipes, fuel, water, cement and drilling mud while the rig crane swings loads over its deck. An anchor handling tug supply vessel (AHTS) tows and moors rigs with wires that could cut a person in half. Wind farm vessels push their bows against turbines to land technicians.
The English is procedural and clipped, on the radio with the installation and on the deck between crane driver, deck crew and bridge. Permission to enter the 500-metre zone, DP status, weather windows, lifts and bulk transfers: every step is announced and confirmed. DP alert colours, green, yellow, red, tell everybody what the ship may do.
Offshore work has its own rulebook: IMCA guidance, the client's safety management system, permits to work, toolbox talks before every job and a strict stop-work authority. Tests for offshore positions ask about DP classes, the 500-metre zone, position references and the alert states.
Words you will use every day (26)
- Platform supply vessel (PSV)
- A ship with a long open cargo deck and bulk tanks that supplies offshore installations.
- Anchor handling tug supply (AHTS)
- A powerful tug with a stern roller and winches that lays and recovers rig anchors and tows rigs; can also supply.
- Dynamic positioning (DP)
- A computer system that holds the ship's position and heading with thrusters, using position reference systems.
- DP class 1, 2, 3
- Levels of redundancy: class 1 no redundancy, class 2 no single fault loses position, class 3 also survives fire or flooding in one compartment.
- DP operator (DPO)
- The bridge officer certified to operate the DP system during operations.
- Position reference system
- The inputs the DP uses: DGPS, taut wire, laser (Fanbeam) or radar (RadaScan) targets on the platform, hydroacoustics.
- 500-metre zone
- The safety zone around an offshore installation; entry only with permission and with the vessel set up for close work.
- DP alert: green, yellow, red
- Green: normal operations. Yellow: degraded, prepare to stop and move off. Red: loss of position, stop everything and leave.
- Drive-off and drift-off
- The two ways to lose position: the thrusters push the ship the wrong way, or the ship loses power and drifts.
- Cargo deck
- The open working deck aft, laid out in rows for containers, baskets and tubulars, with a cargo rail along the sides.
- Tubulars
- Drill pipe and casing carried as deck cargo; long, heavy and they roll.
- Bulk tanks
- Tanks under the deck for dry bulk (cement, barite) and liquids (fuel, water, brine, mud) pumped to the rig through hoses.
- Drilling mud
- The fluid pumped down the well; carried and returned in the vessel's liquid mud tanks.
- Bulk transfer hose
- The floating or crane-lifted hose between the vessel and the installation; connected, tested and watched throughout.
- Rig crane
- The installation's crane that lifts cargo from and to the vessel's deck; the crane driver and the deck crew talk by radio.
- Personnel transfer
- Moving people between vessel and installation by crane basket, walk-to-work gangway or, on wind farms, bow push-on.
- Walk-to-work gangway
- A motion-compensated gangway that lets technicians walk from the vessel to the installation.
- Standby vessel (ERRV)
- The emergency response and rescue vessel that waits near an installation to rescue people and fight fire.
- Shark jaws and towing pins
- The hydraulic gripper and guide pins on the stern of an anchor handler that hold the wire or chain during operations.
- Work wire and pennant
- The winch wire used to handle anchors and the short wire attached to the anchor or buoy.
- Stern roller
- The large roller at the stern of an AHTS over which anchors and chain pass.
- Weather window
- The period when wind and waves are within the limits for the operation; when it closes, work stops.
- Permit to work and toolbox talk
- The written permission for a hazardous task and the briefing before it; both standard offshore.
- Stop-work authority
- Every person's right and duty to stop a job they believe is unsafe, without penalty.
- Crew transfer vessel (CTV)
- A fast small vessel that lands wind farm technicians on turbines by pushing its bow against the boat landing.
- Offshore installation manager (OIM)
- The person in charge of the installation; the vessel works under his or her permission.
Ten things you will hear
Request permission to enter the five hundred metre zone, port side approach.
Bridge to the installation on the working channel.DP status green, we are on location, ready for cargo operations.
DPO to the crane driver and the installation.Crane driver, hook on the mud skid, taking the weight, all clear on deck.
Deck foreman to the rig crane by radio.Bulk transfer: cement, one hundred tonnes at the agreed rate, hose connected and tested.
Chief Officer to the installation before pumping.Yellow alert on DP, stop crane operations, stand by to move off.
DPO to everybody when a reference system is lost.Weather window closes at eighteen hundred; last lift at seventeen, then we go off station.
Master to the installation and the crew.Shark jaws closed, pins up, work wire on the drum, deck clear aft.
Anchor handling deck crew to the bridge.Prepare for push-on transfer, technicians to the bow, lifejackets and harnesses checked.
CTV master to the technicians before landing on a turbine.Toolbox talk at zero seven three zero on the deck, permit to work for the tank entry signed.
Chief Officer's morning plan.Man overboard from the platform, standby vessel proceeding, rescue boat launched.
ERRV to the installation and the coastguard.
Numbers are said digit by digit on board: "one decimal five", "channel one six", "zero seven three zero". Train your ear in listening practice.
Safety on offshore vessels (psv, ahts, dp)
- The 500-metre zone: enter only with permission, with the DP set up and checked, and leave at once on a red alert.
- DP alerts mean action: yellow stops the crane and the hoses, red means everybody off the deck and the ship off station; a drive-off next to a platform is a collision.
- Deck cargo and crane lifts: nobody under the load or in the snap-back zone, tag lines, a signalman only, and lifts stopped when the deck moves too much.
- Anchor handling wires and chains under tension kill instantly: the deck is cleared, the bridge controls the winch, and everyone knows where the wire will go if it parts.
- Personnel transfers by basket, gangway or push-on are weather-limited and briefed; lifejacket, harness and a count every time.
- Bulk and fuel hoses: connected, pressure-tested and watched; a burst hose of base oil or fuel next to a rig is a pollution incident.
- Permits, toolbox talks and stop-work authority are the culture, not paperwork; an offshore crew that does not use them does not stay on the contract.
What recruitment tests ask
- What DP is, the classes 1 to 3 and the position reference systems.
- The 500-metre zone and the DP alert colours.
- PSV against AHTS: what each does and its equipment (bulk tanks, stern roller, shark jaws).
- Personnel transfer methods and their limits.
- Permit to work, toolbox talk and stop-work authority.
Sit the offshore knowledge test: 30 questions for your rank
The full test mixes up to eight questions on offshore vessels (psv, ahts, dp) with the STCW areas for your rank group, under a 30-minute clock. The names of commercial tests are used on this site only to describe what our training prepares you for.
Quiz: 10 questions on offshore vessels (psv, ahts, dp)
One question at a time, feedback after every answer, score at the end. Keys 1 to 4 answer, Enter goes on.
Sources: IMO MSC.1/Circ.1580 (DP guidelines), IMCA guidance (industry), the coastal state's safety zone rules (500 m), SOLAS, STCW; the client's safety management system applies alongside the ship's ISM.