ASD tug simulator — harbour towage, azimuth drives and the towline, in the browser

A tug is a small ship that does a big ship's work, and most of what goes wrong on her happens in the line: a jerk that parts it, a lead abeam that pulls her over, a tanker's steering failure with your bow line on her stern. Nobody learns that safely on the job. Our browser-based marine simulator puts a 28 m ASD harbour tug under your hand, with towlines that behave like rope, tows that behave like dead ships and six scored towage exercises a demo tug master sails for you first. You can sail her now in the browser, on your phone too.

The boat

The ASD TUG is a harbour and coastal tug of our own design: 28.0 × 11.2 m, 5.0 m at her drives, some 520 t. Two azimuth stern drives — fixed-pitch screws in nozzles, about 2 × 2,000 kW — turn all the way round at 20°/s. She pulls 58 t bollard ahead and about 53 t astern, and makes 12.4 kn ahead, 11.5 kn astern. Aft a towing winch works over the stern staple, forward a bow winch over the bow staple; both drums carry 44 mm HMPE line (breaking load 132 t), and the exercises also hand her a 64 mm nylon towline and a 52 mm steel wire. Fenders all round, a heavy cylindrical one at the bow.

She is stable but not unsinkable: GM 2.1 m, deck edge under at 13°, lost at 32° — figures that matter the moment a line leads abeam.

Her handling is an ASD's: hard over at full ahead she turns in about 2.7 lengths; with the units opposed she spins on the spot at about 8°/s; full sideways on the joystick she walks at 2.3 kn. In the 3-D view — charcoal hull, red bottom, white deckhouse with an orange band, a mast with the Rule 24 lights and a black diamond — her drives turn under her as you order them, the winch drums turn, and the towline is drawn: its sag, and its snap when it parts.

What you learn on her

• Three ways to drive an ASD tug (key V, or AZIMUTHS · ASD in the helm panel). TANDEM: the lever is both drives' power, the wheel turns both up to 45°; astern the units swing outboard to 180°, holding their power down while they swing, and the wheel is where her stern goes. JOYSTICK: ahead and astern, turn, sideways on Z / C; her heading is held while no turn is asked. INDEPENDENT: each drive on its own dial — point it where it is to push her, pull it out from the middle for power.
• Passing a towline. The TOW panel calls a tow ahead of you: + YACHT, + COASTER or + SHIP 5 kn. Within 30 m of her bow and under 2 kn apart, PASS LINE (T) sends a heaving line, then the towline hauled across and made fast — hold station 10 s. ALONGSIDE (Y) makes her fast on the hip instead, and you con the pair.
• Working the winch. HEAVE (I), HOLD (J), PAY OUT (K); BRAKE − / + sets the load at which the drum renders. G lets the line go, only with little weight on it; R is the QUICK RELEASE.
• Reading the line. Lines are real ropes: a line hangs in a catenary, then stretches — nylon a lot, HMPE little, wire hardly — and parts at its breaking load, or at the weakest fitting on the tow (a yacht's bow cleat goes long before your line). The gauge shows the load, the SWL and the brake. Take up slack at dead slow; a jerk parts lines, and a parting line snaps back. In a seaway pay out more: a long, deep line rides the waves, best a whole number of wave lengths.
• Girting. A line leading abeam, high on her staple, pulls a tug over. The HEEL gauge marks her deck edge in red; the docking plan draws the safe sector within about 45° of right astern. Take the power off, turn under the line, RELEASE (R) before she goes — past about 32° she floods and is lost.
• The lights of towing. Rule 24 as she shows it: the yellow towing light over the sternlight when towing astern, three masthead lights and a black diamond when the tow is over 200 m, no towing light alongside or pushing; in restricted visibility one prolonged and two short blasts (Rule 35(c)).
• The six exercises (⛓ TOWING, beside ⚓ DOCK), each with a briefing, live steps and a score out of 100: 1 pass the tow to a disabled yacht and tow her under 6 kn; 2 a dead coaster on 300 m of wire — the catenary in step with the sea, a 60° alteration without girting; 3 a hip tow to a berth of four dolphins; 4 escort — a 183 m tanker down a 400 m channel on your bow line to her stern; when her steering fails, check her swing and brake her; 5 push-pull at the berth with a second tug; 6 flanking, on the PUSH TUG. Fails are honest: a parted line, a girting, a collision, a hard landing, out of time.
• The debrief and the guide. Every step with what it cost and why; ┄ GUIDE (Shift+G) draws the recommended track on the water — the turn that lays your stern staple 20 m off the yacht's bow.

The sea is real

Free Mode starts in the Gulf of Riga off the Daugava mouth, and the whole Baltic is yours — Gotland, Bornholm, the Estonian islands, the Swedish and Finnish archipelagos, the Danish straits. AREA opens a harbour picker with 107 real harbours round the Baltic; the loads the detailed chart as she sails.

The sky is real — sun, moon and stars where they stand over you now — and the weather is MET Norway's real forecast: cloud, rain, snow, fog and the visibility they leave, day and night. The wind is today's wind; the exercises set their own wind and sea state, and in Free Mode the line rides whatever sea the forecast gives. 〰 CURRENT runs the rivers by their monthly discharge for today's date — the Daugava at 1–1.5 kn in the April flood — and stopped, you and your tow drift with it.

The radar PPI and AIS overlay give every target CPA and TCPA; the chart is OpenSeaMap with your track and the plotter's CPA graphic. The traffic — always a 183 m tanker and a 260 m cruise ship among it — gives way as COLREG says, and leaves your tow alone.

Shared sea — other real people on the water

Logged in, SHARED SEA is on by default — one live sea for everyone at ×1 — and you can switch it off. The boats you meet are other skippers' boats, sailed by real people now; a sailing vessel converging on your tow expects you to act as the rules say, and sees your Rule 24 lights.

Classroom and the scenario builder — for schools, clubs and instructors

✎ SCENARIO BUILDER opens over the simulator: an instructor names the exercise, writes the brief, picks the place (any harbour of the Gulf of Riga or the Baltic), the own vessel — the ASD TUG, under way or made fast — and TIME & WEATHER: dawn to night on any date, wind with gusts, visibility down to thick fog, the sea state. ⊕ VESSEL places ships and their routes; triggers make the fog close in or a vessel start. ⇗ MAKE A LINK packs the whole scenario into the link, ready to ▶ RUN.

🎓 CLASSROOM → TEACH opens a private class: free sailing, a scenario, a docking lesson or a DRILL — towage among them. OPEN THE CLASS gives a code and a link; up to 30 students at a time, from any browser. The INSTRUCTOR VIEW shows every boat with her track and CPA ring and injects 🌫 FOG, 🌬 WIND or ⚙ ENGINE FAILURE. TEACH is for the subscriber or instructor; students run shared scenarios for free, in the class's own private sea.

Where she fits

The ASD tug lives in ⛓ TOWING, beside ⚓ DOCK, with five of its six exercises; ⚓ DOCK shows the whole tow from above with the line's load and the girting sectors. ▶ DEMO in every exercise is the demo tug master sailing it: each order goes through the real control and rings it orange — the lever, the wheel, TANDEM / JOYSTICK / INDEP, PASS LINE, PAY OUT, HOLD, BRAKE −, ALONGSIDE — while the camera moves out to a chase view; the score is shown, never kept, and ▶ YOUR TURN hands you the same exercise. A game controller steers her too. On the tanker and the cruise ship the TUGS button (key T) calls two tugs to push or pull — on the ASD tug you are that tug.

Who it is for

Professional and leisure alike. The cadet before the first watch, the deck officer, the pilot, the tug, offshore or survey crew, the training centre that wants a situation every student can repeat — and, on the same sea, the leisure skipper who is curious how the working boats are handled and what the ship on the horizon can and cannot do. The vessel, the sea and the rules are the same for everyone; only the exercises are the professional's.

How to start

Free Mode is open to everyone — no account needed — with the 15 m motor yacht and the 50 ft cruiser LATEKO at up to TIME ×10; every other vessel — the ASD tug among them — the docking, sailing and ECDIS units, the scenario builder and Classroom TEACH come with the simulator subscription; students join shared scenarios free. SHARED SEA and the regatta need a free SkipperCheck login. Our main product is the VHF course (€199) at /vhf-course: the certificate comes from the course, the practice from the simulator.

FAQ

Does it run on a Mac or a phone?

Yes — it is a web page: Mac, Windows, Chromebook, iPad or phone, nothing to install.

Is the wind real?

Yes — MET Norway's live forecast where your boat is. The towage exercises set their own wind and sea so a score means the same for everyone.

Can I tow with friends?

In the shared sea you meet other skippers on one sea at ×1 time; a class puts your group on its own private sea.

Can a school use it?

Yes. The CLASSROOM takes up to 30 students per class with a code and a link; towage is one of the drills, students join free.

Do I get a certificate?

The simulator gives practice and a scored debrief; the certificate comes from the VHF course at /vhf-course.

Take the ASD tug's helm now at /colreg-simulator?scenario=familiarization&area=gulf-of-riga&vessel=asdtug — and get your VHF certificate at /vhf-course.

Related reading

• Tug simulator — towing, escort and push-pull with real towlines, in the browser
• Ship bridge simulator — handle a 183 m tanker and a 260 m cruise ship from a live bridge, in the browser
• Push tug simulator — flanking rudders, backing down a narrow cut, in the browser
• Tanker simulator — ship handling on a 183 m product tanker, in the browser
• Cruise ship simulator — azipods, the joystick and berthing a 260 m ship, in the browser
• All articles · Open the simulator

Boat types are described generically; SkipperCheck is not affiliated with any boat builder or class association.