Extended Operational and Trade Vocabulary

Tug Operations and Harbour Towage glossary

The towage operations vocabulary: the alongside and indirect towing methods, aft spring lines, all-fast reporting, and the class rules for tug hulls and reduced-manning operation. Grounds each term in the harbor-towage maneuver or the escort assignment it belongs to.

181 defined terms.

A

ABS Guide for Building and Classing Steel Vessels Under 90 Metres: American Bureau of Shipping rules covering most harbor and escort tug hulls.
ABS Guide for Vessels Operating with Reduced Manning: ABS notation relevant to small-crew tug operations.
Aft Spring: Mooring line leading aft from a forward part of the vessel to restrict forward movement.
All fast: Report that all mooring lines are secured.
Alongside Method: Tug working pressed against the ship's side, transmitting force through bow and stern fenders.
Anchor Handling Tug Supply (AHTS): Offshore vessel designed for towing, anchor handling, and supply duties.
Antwerp Tug Services (ATS): Belgian harbor towage operator serving the Port of Antwerp.
Articulated Tug Barge (ATB): Tug rigidly connected to a barge.
ASD (Azimuth Stern Drive): Tug configuration with two azimuth thrusters at the stern and the towing point forward.
ASD-Tug 2810 (Damen): 28.67 m by 10.43 m Damen azimuth stern drive harbor tug with bollard pull around 60 to 80 tonnes.
ASD-Tug 2913 (Damen): 29 m by 13 m Damen ASD design oriented to escort duty with raised bollard pull.
ASD-Tug 3212 (Damen): 32 m by 12 m Damen ASD harbor and terminal tug with bollard pull around 80 to 85 tonnes.
ASD-Tug 3213 (Damen): 32 m by 13 m Damen ASD tug, escort-capable variant.
ASD-Tug 3413 (Robert Allan): 34 m by 13 m Robert Allan ASD design used by several global operators.
Astern Drive (RA ASD-Tug Series): Robert Allan Ltd family of conventional twin azimuth stern drive tug designs.
ATD (Azimuth Tractor Drive): Tractor configuration using azimuth thrusters located under the forward hull.
Auro: Damen RSD-E Tug 2513 fully electric harbor tug delivered to Ports of Auckland in 2022.
Autonomous Tug Trials, Singapore: Svitzer remote operation trials conducted in Singapore from 2023.
Azimuth Thruster: Propulsion unit rotating 360 degrees about a vertical axis to direct thrust in any horizontal direction.

B

Backing Down: Reducing speed by reversing propulsion, used by escort tugs to control the assisted ship.
Bay-Houston Towing: US Gulf Coast harbor towage operator based in Houston, Texas.
Bee (Towing Bee): Vertical post on a tug deck for guiding the towline.
Berthing Tug: Harbor tug employed for the final approach, mooring, and unmooring of ships at a berth.
BIMCO: Baltic and International Maritime Council, drafter of standard maritime contracts.
BIMCO Standard Tug and Tow Conditions for Coastal Areas: Standard short-form conditions for coastal towage.
Bitt: Vertical post on deck for securing lines.
Bogacay Series: Sanmar Shipyards range of compact ASD harbor tugs built in Turkey.
Bogacay XLI: Variant within the Sanmar Bogacay series, an enlarged ASD design.
Bollard Pull (BP): Static pulling force a tug can exert on a stationary load, measured in tonnes.
Boluda Methanol Tug 2024: Boluda methanol-fueled harbor tug introduction announced for 2024 operations.
Boluda Towage: International towage group based in Valencia, Spain, active in Europe, West Africa, the Americas, and the Middle East.
Bow Fender: Heavy fender mounted on the tug's bow for pushing and pulling contact with the ship's hull.
Brake Holding Load (BHL): Maximum static load a winch brake can hold without slip.
Breast line: Mooring line led at right angles to the keel to hold the ship against the berth.
Bridle: Two-leg rope or chain attached to a single point.
Bridle Pull: Towing connection via a bridle ahead of or astern of the assisted ship.
Bullnose: Towing notch at the AHTS stern aiding wire alignment.

C

Capstan: Vertical-axis rotating drum used for heaving on ropes or cable.
Carrousel Tug: Novatug concept with a winch mounted on a rotating ring around the superstructure, allowing 360 degree towline lead.
Cheoy Lee Shipyards: Hong Kong shipbuilder constructing Robert Allan and other tug designs.
Chock: Mooring fitting that guides a line outboard.
Code of Safety for High-Speed Craft (HSC Code): IMO Resolution A.534(13) and successor MSC resolutions; relevant to fast-response harbor craft.
Cone Fender: Conical rubber fender used on tug bows and ship-side contact areas.
Conventional Tug: Tug with fixed propellers and rudders at the stern, towing point forward.
Crowley Maritime: US ocean towage, harbor towage, and logistics operator headquartered in Jacksonville, Florida.
CT (Carrousel Tug) Rotor: Rotating winch platform central to the Novatug Carrousel concept.

D

Damen ATD Tug: Damen azimuth tractor drive family with thrusters under the forward hull.
Damen RSD Tug 2513: 25 m Reverse Stern Drive Damen design symmetrical fore and aft, with twin azimuth thrusters forward.
Damen Shipyards Group: Dutch shipbuilder, major supplier of ASD, RSD, ATD, and Stan Tug series.
Damen Stan Tug: Long-running Damen series of small to medium conventional and ASD workboats and tugs.
Direct Mode: Escort tug operation pulling along the line of the towline, generating force primarily from propeller thrust.
Dolphin: Isolated marine structure.
Dynamic Brake Holding: Winch brake performance under dynamic loading rather than static.

E

Eddy Loss: Hydrodynamic energy lost to vortices around the escort tug hull in indirect mode.
Emergency Release System: System enabling rapid release of the tug's working line under load.
Escort Tug: High-performance tug providing braking/steering escort to laden tankers.
Escort Winch: Render-recovery winch specified for escort duty with high dynamic performance.

F

Fairlead: Fitting that leads a rope in the desired direction without chafe.
Fender: Energy absorbing system at berth, designed per PIANC WG211 (formerly WG33).
FiFi-1: IMO/class fire-fighting notation requiring at least 2,400 cubic meters per hour total monitor capacity.
FiFi-2: Notation requiring at least 7,200 cubic meters per hour total monitor capacity.
FiFi-3: Notation requiring at least 9,600 cubic meters per hour total monitor capacity.
Fire-Fighting Capability: Onboard pumps, monitors, and water spray meeting recognized notations.
Fixed Pitch Propeller (FPP): Propeller with non-adjustable blades, used on many conventional tugs.
Fore spring: Mooring line led forward from the after part of the ship.
Foss Maritime: US Pacific Northwest tug and barge operator founded in 1889 in Tacoma, Washington.

G

Gob Eye: Hard point on the after deck through which the gob rope is led.
Gob Rope: Restraint line that holds the towline down toward the stern of a conventional tug to prevent girting.
Gripe: Tendency of a tug to swing toward the towline; controlled by gob rope and towing point geometry.

H

Hai Hua: Chinese tug operator active in coastal and harbor towage.
Harbor Tug: Tug for berthing and port maneuvers.
Hawser: Heavy rope or cable for mooring or towing.
Head line: Mooring line led forward from the bow.
HVS Hydrogen Tug (Voith / Linde 2024): Voith and Linde hydrogen fuel cell tug initiative announced in 2024.
Hybrid Tug: Tug with combined diesel-mechanical and battery-electric propulsion.

I

IMCA M101: International Marine Contractors Association guidance document for marine contractors, applied in offshore towage.
IMO MSC.1/Circ.1175: Guidelines for shipboard towing and mooring equipment, supplementing SOLAS II-1/3-8.
IMO MSC.1/Circ.1318: Guidelines for the fitting and use of fixed carbon dioxide and other fire-fighting systems, including FiFi notations.
Indirect Mode: Escort technique in which the tug presents its hull at an angle to the flow, generating hydrodynamic lift on a towline ahead of the assisted ship, typically at 6 to 12 knots.
INTERTUG: Mexican and Latin American towage operator.
ITC Holland: Dutch towage and salvage operator.
ITS Convention: International Tug, Salvage and OSV Convention, the principal biennial industry conference.
ITTC: International Towing Tank Conference, the worldwide hydrodynamic research body.

J

Jacobs Ladder: Rope or wire ladder used for boarding pilots and others.
Jaw (Shark Jaw): Hydraulic chain stopper on AHTS vessels used for anchor handling.

K

Keppel Smit Towage: Singapore-based joint venture providing harbor towage in Southeast Asia.
KORT nozzle: Accelerating ducted-propeller nozzle.
KOTUG International: Dutch towage group operating in Europe and other regions.

L

Lead (of Line): Direction in which a line is rigged from the tug to the assisted vessel.
Let go: Order to release an anchor or mooring line.
Let-Go Pilot: Stage at which the pilot leaves the assisted ship.
Letzer Towage: European tug operator.
Line-Up Service: Tug service positioning a ship onto the berth.
Lloyd's Open Form (LOF 2020): Standard no-cure-no-pay salvage contract.
Lloyd's Register Rules for Ships: Class rules used for many tug designs.
LNG Tug: Tug fueled by liquefied natural gas; Sembcorp Marine introduced an LNG harbor tug in 2022.

M

McAllister Towing: US East Coast harbor towage operator.
Med Marine: Turkish shipyard and tug operator based in Istanbul.
Mediterranean Shipping Towage (MST): Towage group operating Mediterranean harbor services.
Methanol Tug: Tug burning methanol fuel; Boluda announced such a tug for 2024.
Mooring boat: launch handling lines to buoys or dolphins.
Moran Towing: US East Coast towage operator founded in 1860 in New York City.
MultiCat 1908 (Damen): 19.45 m by 8.0 m Damen Modular Multi Cat workboat suited to light towage and dredging support.
Multraship: Netherlands-based towage and salvage operator.

N

NK Class (ClassNK): Nippon Kaiji Kyokai, classification society used on Japanese-built tugs.
Notation: Class society descriptor such as Tug, Escort Tug, Fire Fighting Ship 1, or Salvage Tug.
Novatug: Dutch developer of the Carrousel Rave Tug concept with Voith Schneider propulsion.

O

Ocean-Going Tug: Tug certified for ocean towage of large barges, rigs, or disabled ships.
Overhanging Stern: Stern shape providing clear water at the tug's working end.

P

Padeye: Welded eye fitting for securing rigging on deck.
Pendant: Short rope with an eye at one end and a thimble at the other.
Pilot Cutter: Pilot transfer launch, distinct from harbor tugs but often colocated.
Pin (Towing Pin): Retractable pin guiding the towline on the working deck.
Pinning Tug: Tug pressed against the ship's side to hold it onto the berth.
Plumb Mode: Escort condition in which the tug is positioned perpendicular to the ship's track.
PSA Marine: Singapore-based subsidiary of PSA International providing harbor towage and pilotage.
Push Knee: Reinforced vertical pad on the forward end of a push boat for engaging the barge.
Push Tug: Tug designed to push barges, particularly on inland waterways.
Pusher Towboat: Common US inland river vessel pushing strings of barges.

Q

Quay: Solid berthing structure parallel to the shore.
Quick Release Towing Hook: Deck-mounted hook with remote and local release; Mampaey Towhook 4000 is a widely used model.

R

RAhuza: Robert Allan small-tug design.
RAmparts 2200: 22 m Robert Allan ASD ship-handling tug class.
RAmparts 2400: 24 m Robert Allan ASD ship-handling tug class.
RAmparts 3000: 30 m Robert Allan ASD ship-handling tug class.
RApport: Robert Allan ASD tug design.
RAstar 3200: 32 m Robert Allan escort tug design with hard chine sponson hull.
RAstar 3500: 35 m Robert Allan escort tug design.
RAstar 4000: 40 m Robert Allan escort tug design with high escort steering forces.
RAVE Tug: Robert Allan and Voith joint design using Voith Schneider propulsion for both bow and stern units in a Carrousel arrangement.
Render-Recovery Winch: Towing winch that pays out under overload and recovers automatically as load eases.
Reverse Stern Drive (RSD): Damen-developed double-ended tug concept allowing efficient operation in either direction.
Robert Allan Ltd: Canadian naval architecture firm in Vancouver specializing in tug design.
RotorTug (ART): Three-azimuth-thruster tug with two thrusters forward and one aft, developed by KOTUG.
RSD-E Tug 2513: Fully electric variant of the Damen RSD Tug 2513.

S

Salvage Tug: High-powered tug for casualty response.
Sanmar Shipyards: Turkish shipyard building Robert Allan licensed designs.
Schuyler Block Fender: High-density rubber block fender used on tug bows and sides.
Sembcorp LNG Tug 2022: Sembcorp Marine LNG-fueled harbor tug introduced in 2022.
Shark Jaw: Hydraulic chain stopper on AHTS vessels.
Ship-Handling Tug: General term for tugs assigned to assist ships in confined waters.
Single Up: Order to reduce mooring lines to a single line of each type before letting go.
Skeg: Fixed longitudinal fin on the underside of an escort tug used to generate side force in indirect mode.
Smit Lamnalco: Joint venture between Boskalis (Smit) and the Lamnalco group providing terminal and harbor services.
Smit Rotterdam: Long-established Dutch salvage and towage brand originating in the mid-19th century.
Springs: Mooring lines leading fore and aft to prevent longitudinal movement at the berth.
Standard Towing Antwerp: Belgian harbor towage operator.
Stern line: Mooring line led aft from the stern.
Stretcher: Synthetic rope inserted into a towing system to absorb shock loads.
Suderman & Young Towing: Historical US harbor towage company on the Gulf Coast.
SUPPLYTIME 2017: BIMCO standard offshore time charter party.
Svitzer: Towage operator and subsidiary of A.P. Moller-Maersk, headquartered in Copenhagen.

T

Terminal Tug: Dedicated tug assigned to a single oil, LNG, or container terminal.
Tow Bridle: Two-leg towing connection to the tow.
Towboat: US term for an inland vessel pushing barges.
TOWCON 2008: BIMCO international ocean towage agreement, lump sum.
TOWCON 2021: Updated BIMCO international ocean towage agreement, lump sum.
TOWHIRE 2008: BIMCO international ocean towage agreement, daily hire.
TOWHIRE 2021: Revised BIMCO daily hire towage agreement.
Towhook 4000: Mampaey quick-release towing hook commonly used on modern tugs.
Towing Hook: Deck fitting securing the working end of the towline on a conventional tug.
Towing Pin: Retractable pin used to guide the towline on stern-drive tugs.
Towing Staple: Closed fairlead at the tow point through which the line is led.
Tractor Tug: High-maneuver tug using Voith Schneider or ASD propulsion.
Twin-Screw Stern Drive Conventional: Older arrangement of two propellers and rudders aft with no azimuth capability.

U

Uzmar: Turkish shipyard building tugs to its own and licensed designs.

V

VLCC Berthing Plan: Procedure assigning typically three to four tugs of 60 to 80 tonnes bollard pull each to a Very Large Crude Carrier.
Voith Water Tractor (VWT): Tractor tug with two VSP units forward and a skeg aft.
Voith-Schneider propeller (VSP): Cycloidal vertical-axis propeller.

W

Wijsmuller: Historical Dutch towage and salvage company, absorbed into the Svitzer and Boskalis groups.
Winch Brake: Mechanism holding the towline against load.
Working line: stevedore line of containers being moved.
World Maritime Technology Conference: International gathering of naval architects and marine engineers covering tug technology.

X

X-Bow Influence: Reference to inverted bow forms occasionally explored in tug research, distinct from production tug bows.

Y

Y-Bridle: Two-leg connection from a single towline to two pad eyes on a barge.
Yokohama Pneumatic Fender: Inflatable pneumatic fender used as ship-to-ship and tug-to-ship cushion.

Z

Z-Drive: Azimuthing propulsion unit common on tugs.
Z-Tech 30 Series: Robert Allan family of 30 m class Z-Tech tugs designed in cooperation with PSA Marine.
Z-Tech 4500: Smaller Robert Allan Z-Tech harbor tug design.
Z-Tech 6500: Mid-range Robert Allan Z-Tech ASD tug design.
Z-Tech 7500: 30 m class Robert Allan Z-Tech ASD harbor and terminal tug design.