SH Cap. 3 — Use of Tugs (Shiphandling for the Mariner)

1. Overview: Tugs in Port Shiphandling

Fig. 3-1 oil painting — tugs alongside, arriving Baltimore Harbor

Tugs are the most versatile external tool available to a shiphandler during port approach, docking, and undocking. Their primary role is to generate controlled lateral force that supplements — but does not replace — the ship's own engine, rudder, bow thruster, anchors, and mooring lines. MacElrevey's first rule is pointed: do not use the tug unless the other tools are insufficient. A shiphandler who relies on tugs instead of developing independent skill never acquires the feel for a vessel, and loses the tugs as a safety reserve precisely when that reserve would be most valuable.

Port tug fleets include two broad families. The conventional single-screw tug — still operating in some ports — demands the greatest skill from both tug master and shiphandler: it needs two or three lines to work effectively and its maneuverability is limited. Because mastering the conventional tug's limitations builds the sharpest intuition, it serves as the conceptual baseline for this chapter. The second family covers tractor-type tugs and similar azimuthing stern-drive (ASD) tugs with patented drives (Voith-Schneider, Schottel, and similar systems), which can vector thrust in any direction and typically require only a single hawser to the ship.

A tug working alongside resolves its thrust into two components: a lateral component that translates the ship sideways, and a longitudinal component that either accelerates or decelerates the ship. The proportion of each depends on the tug's angle to the ship's centerline and the position along the hull where force is applied — a lever about the ship's pivot point. Understanding this force resolution is the key to directing tugs efficiently and avoiding unintended heading changes.

Tug family	Drive type	Lines typically required	Ability to push at right angles with headway
Conventional single-screw	Fixed propeller & rudder	Backing line + come-ahead line (+ optional stern line)	Limited — loses thrust angle as speed increases
Twin-screw harbor tug	Two fixed propellers	Backing line only (can maneuver to push without come-ahead)	Moderate
Tractor / ASD (Voith-Schneider, Schottel)	Azimuthing / cycloidal	Single hawser; winch-controlled	Full — thrust direction independent of ship speed

2. Making Fast a Tug

Once the docking master is aboard and the berth is in sight, tugs come alongside and make fast. For a conventional single-screw tug placed on the bow or quarter, the standard arrangement uses two lines sent up from the tug's foredeck.

Fig. 3-2 making fast a single-screw tug — come-ahead/backing/stern lines diagram

2.1 Backing Line

The backing line is the first line sent aboard. It runs from a bitt on the tug's foredeck, up to the ship, and is led forward and secured on a bitt — never on a small cleat or bulwark fitting. When the tug later backs hard, the strain on this line rises geometrically with ship speed; a cleat or unsuitable fitting can be torn away and become a lethal projectile on either vessel. The line must remain in sight of the tug master so he can monitor the load.

2.2 Come-Ahead Line

The come-ahead line — also originating at the tug's foredeck, led to the tug's bow and then up to the ship — is led aft on the ship's deck. The tug works against this line to position itself and begin pushing. Two ship's crew must remain standing by both lines throughout the maneuver, ready to let go instantly on signal and to slack the line down to the tug using a messenger. Failing to use the messenger when slacking the stern line risks putting the line into the tug's propeller.

2.3 Stern Line (when required)

If the ship will be backing into or out of a slip, a stern line is added so the tug does not swing around (fall away) as the ship gathers sternway. Ship speed must be kept to a minimum while the tug is at nearly right angles to the centerline; the full length of the tug acts as a drag and the backing line strain mounts sharply with any increase in speed.

2.4 Tractor-Type Tugs: Single Hawser

Tractor and ASD tugs carry their working line on a powered winch whose position is optimized relative to the tug's pivot point for safe hawser work. A single hawser is all that is sent to the ship; the tug shortens or pays out the hawser while under load, changing position without losing effectiveness. Unlike conventional harbor tugs, tractor tugs can work safely on a hawser while the ship has headway, directing thrust at right angles to the ship regardless of relative speed. Conventional US harbor tugs, by contrast, risk being rolled over ("tripped") if placed ahead of a ship on a hawser when significant headway exists.

3. How a Tug's Force Acts on the Ship

Fig. 3-3 a tug's force affects the ship's lateral motion and her headway

A tug working alongside never exerts a purely lateral force. Its thrust is a vector that splits into a lateral component (moving the ship sideways) and a longitudinal component (accelerating or decelerating the ship ahead). MacElrevey notes that computing exact percentages via vector diagram is possible but impractical in real time; what matters is knowing that both effects always exist and that the shiphandler can exploit or counteract them.

3.1 Lateral Motion vs. Headway

When a tug backs against its backing line, it both pulls the bow (or stern) sideways and creates drag that slows the ship's forward speed. When the same tug comes ahead, it pushes the bow sideways but simultaneously adds to the ship's headway — the tug is, in effect, accelerating the vessel. The closer the tug is to a right angle to the ship's centerline, the greater the fraction of its thrust that goes into lateral motion and the smaller the longitudinal penalty. This is why maximum tug effect requires minimum ship speed: as ship speed rises, more of the tug's limited power is consumed just keeping up, leaving less available for maneuvering.

3.2 Lever About the Pivot Point

Force applied near the bow or stern acts at the longest lever arm from the ship's pivot point, producing maximum rotational effect — useful for turning the ship. Force applied closer to amidships has a shorter lever arm and less turning moment but applies more of its energy to translating the ship bodily. Understanding this geometry guides where to position a tug depending on whether rotation or pure sideways translation is needed.

3.3 Tug as Steering Aid When Backing

A bow tug can also work stem-to-stem, trailing the ship as it goes astern and pushing on either bow to steer. Pushing on the port bow swings the stem to starboard and thus turns the ship to port; pushing on the starboard bow has the opposite effect. This technique extends the shiphandler's directional control while the ship gathers sternway without its rudder being effective.

4. Tug Positions and Their Effects

Tug position	Primary effect	Key limitation / caution
On the bow (or shoulder)	Moves bow laterally; holds ship alongside after arrival	Coming ahead adds headway to the ship
On each bow (two tugs)	Both backing simultaneously: reduces headway while maintaining heading; either tug alone: turns the bow	Requires coordination; two tug fees
On the quarter (after tug)	Moves stern laterally in same manner as bow tug	Acts as drag on rudder effectiveness; tends to set stern toward pier
Astern (made fast on stern)	Backs to slow ship; comes ahead port/stbd to steer like an active rudder	Officer + two crew must stand by lines; lines risk falling into propeller if not tended

4.1 Tug on the Quarter

Fig. 3-4 effect of a tug made fast on the quarter

The quarter tug is made fast with the same backing-line / come-ahead-line arrangement as a bow tug and backs or pushes with the same mechanics. Two important differences set it apart. First, it acts as a drag, reducing rudder effectiveness at the slow speeds when the shiphandler most needs to move the stern laterally without building headway. Second, and more critically, a stern tug tends to set the stern away from the side on which it is made fast — toward the pier in a docking situation — because the tug's underwater profile acts like a large rudder. This tendency intensifies as the angle between tug and ship increases. For these reasons, the stern tug should stand off until actually needed and be dismissed at the earliest practical time after undocking.

4.2 Tug on Each Bow

When two tugs are secured on each bow — for example, approaching a berth, lock, or holding position in a channel — the shiphandler gains a powerful deceleration option: both tugs backed simultaneously reduce the ship's headway while maintaining heading, since their opposed lateral forces cancel out. Either tug can also be used alone to swing the bow. The ship's engine is available in conjunction, giving maximum control over speed and heading simultaneously.

4.3 Tug on the Stern

A tug placed astern and made fast with one or two lines acts as an active supplemental rudder: backing decelerates the ship; coming ahead to port or starboard moves the stern in the corresponding direction. The tug can steer the ship without the ship's engine running, preventing excessive headway. Despite claims in some texts, a tug on the stern is not inherently hazardous — tugs have safely assisted thousands of transits through the Gaillard Cut at 6–8 knots. The real hazard is inattentive line handling: an officer and two crew must remain at the tug lines at all times, particularly when lines pass through quarter chocks, so the tug can be released instantly if needed. Lines left unattended in the water risk fouling the ship's propeller.

Caution — tug on a hawser ahead: Some texts recommend a conventional harbor tug on a hawser ahead of the ship to assist steering. This arrangement is both less effective and more hazardous. A conventional US harbor tug working ahead of a ship with significant headway is always at risk of being tripped or rolled over by the hawser tension. Tractor/ASD tugs are specifically designed for hawser-ahead work; conventional tugs are not.

5. Tug on a Hawser

Working a tug on a hawser — more common in European ports than in the United States — becomes increasingly relevant as Schottel and Voith-Schneider tugs enter US fleets. These tugs are engineered for hawser work: their winches are positioned relative to the tug's pivot point to allow safe, sustained pulls without risk of the tug being tripped. The winch allows the tug to shorten or lengthen the hawser under load, changing position around the bow or stern without losing pull.

5.1 When Conventional Tugs May Use a Hawser

Conventional harbor tugs can be placed on a hawser in limited circumstances: handling a dead ship (no engine, no rudder), or a vessel with such a light draft that making up alongside is impractical. In these cases, the ship's engines must be kept to a minimum and any headway strictly controlled, because a conventional tug in irons — caught abeam its own hawser — can be rolled over. Radio communication is used to give the tug a speed and direction to pull; otherwise the shiphandler directs the hawser tug in the same way as a tug alongside.

5.2 Tugs on Hawsers in Opposition

Two tugs on hawsers can be deployed in opposition — one pulling ahead, one astern — to increase or reduce the ship's way, or to hold a vessel at a precise position in a current or at berth. Chapter 4 covers additional uses of hawser tugs when approaching a berth.

6. Lashing Up a Tug ("On the Hip")

Fig. 3-7 cartoon — "the pilot wants a tight lash-up, Harry..."

A lashed-up tug — also called a hip tug or tug "on the hip" — lies alongside the ship and makes fast with a head line, stern line, and an aft-leading spring line. The head and stern lines are rigged as close to breast lines as geometry allows and heaved up very tight. Tightness is not optional: if the lash-up is slack, the tug and ship cannot act as a single unit and the arrangement becomes more hindrance than help. If a tight lash-up is impossible due to the ship's draft, hull configuration, or bitt/chock layout, the ship must not be moved under this arrangement.

6.1 Tug Lashed on the Stern — Twin-Screw Equivalent

One or two tugs lashed on the quarter replace the ship's engine and rudder, or supplement them. With a tug on each quarter, the ship handles like a twin-screw vessel, and twin-screw helm and engine orders are appropriate. A single lashed-up stern tug produces an off-center thrust that initially tends to move the ship laterally away from the tug before headway develops. To turn the ship toward the tug's side, back the tug: for example, backing a tug lashed to the port quarter swings the stern to starboard, turning the ship to port (bow to port, stern to starboard).

6.2 Tug Lashed on the Bow, Heading Aft — Undocking Stern-First

The second common lash-up places the tug on the ship's bow, heading aft. This is used to back a ship from a berth, especially when another ship is docked astern or when handling a dead ship. The tug backs to move the ship's stern off the dock; once sufficient angle is achieved, the tug comes ahead to steer the ship clear. Helm orders follow the same convention as undocking under the ship's own power — with one critical caveat: when leaving stern-first, left rudder of the tug moves the ship's bow to port and thus pushes the stern to starboard. This can be initially confusing. MacElrevey's practical fix: face aft, in the direction the ship is moving, then give helm orders to the tug — the correct direction becomes immediately obvious. Once clear of the berth, the tug master steers the vessel like a helmsman on a given heading.

6.3 Stopping and Propeller Effect with a Lashed-Up Tug

A ship under lash-up is stopped by backing the tug. The off-center position introduces a twisting tendency: a tug lashed on the starboard quarter moving ahead (or on the port bow moving stern-first) causes the ship to handle like a single-screw vessel with a right-handed propeller — a predictable and manageable behavior once the shiphandler recognizes it.

7. Tugs in Opposition — Pure Lateral Translation

Fig. 3-9 working with tug and ship in opposition to move the ship laterally

One of the most powerful uses of a lashed-up tug is in deliberate opposition with the ship's engine to move the ship purely sideways without developing headway or sternway. The technique requires close cooperation between the shiphandler and tug master, and a tight lash-up.

7.1 Mechanics of Lateral Translation

The tug is lashed at the ship's bow, heading aft. The tug comes ahead with rudder hard over toward the pier while the ship simultaneously applies engine ahead and rudder hard over, also toward the berth. The tug's ahead force and the ship's ahead force are oriented so their longitudinal components cancel — neither headway nor sternway builds — while their lateral components add together, moving both bow and stern simultaneously away from the dock. The result is a controlled, parallel lateral movement of the entire ship, equivalent to the effect of two separate tugs, achievable with a single lashed-up tug and the ship's own engine.

Best practice: A single lashed-up tug used in opposition with the ship's engine can do the work of two independent tugs for lateral movement, provided (1) the lash-up is tight, (2) both tug and ship apply their forces simultaneously on command, and (3) rudders on both are hard over in the same direction.