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OOW Oral Prep
Module 19 — OOW 3000 GT Oral Preparation
Towing, Ice Navigation & Special Operations
Towing preparations · Being towed · Ice navigation · Ice accretion · Watertight doors · Loadline marks · Steering gear
Towing — Taking Another Vessel in Tow
Emergency towing is a distinct skill. The exam tests preparation and execution, not just the fact that a tow line exists.
| Step | Action |
|---|---|
| 1 — Assess | Determine type and size of casualty; nature of the problem; sea state; distance to port of refuge; salvage vs. rescue tow (Lloyd's Open Form — LOF — vs. SOLAS duty to assist) |
| 2 — Brief Master and MRCC | Confirm situation with Master. Notify MRCC of intention to tow. If commercial salvage is intended, agree LOF terms before commencing unless life is at risk |
| 3 — Prepare tow connection | Lead the tow rope forward to the anchor chain compressor/bollards. Use anchor chain as tow messenger if available — its weight acts as a spring (catenary) to absorb surge loads. Protect the tow rope at fairleads with chafing gear |
| 4 — Pass the tow line | Use heaving line to pass tow rope messenger to casualty. Confirm the casualty has the tow line made fast to their strongest forward bitts or through their anchor hawse — not a cleat |
| 5 — Check catenary | The tow line should sag in a catenary — this absorbs shock loads. In heavy swell, increase scope. In flat water, reduce scope to maintain steering control |
| 6 — Start towing | Apply power very gradually — sudden acceleration parts the tow line. Come to towing speed slowly. Set speed appropriate to sea state (typically 2–4 kn in open water, slower in confined waters) |
| 7 — Steering the tow | The casualty must have a crew member on the helm to steer astern of the towing vessel — a dead tow (no steering on the casualty) will yaw violently and part the tow line in a seaway |
Tow line parting: A parting tow line is lethal. Never allow crew to stand in the bight of a tow line or in the line of a loaded tow rope. The whiplash from a parting wire or synthetic rope can kill at 50 metres. Crew must be clear of the danger area at all times when the tow is under tension.
Being Taken in Tow — Preparing Your Vessel
- Prepare your strongest forward bitts or anchor chain for connection — fairleads and bitts must be clear and the attachment point must take the full load
- Ensure a helmsman is on the wheel throughout — steer to follow the towing vessel exactly astern, anticipating the tow
- Monitor the tow line for chafe — check chafing gear and adjust if needed
- Maintain radio contact with the towing vessel on an agreed working frequency
- Keep anchor ready for emergency — if the tow line parts in a fairway, anchor immediately to prevent running aground
- Signal the towing vessel clearly if you need to slow or stop — agree a light or radio signal code before departure
- Sound appropriate signals: under tow, vessel restricted in ability to manoeuvre (one long and two short blasts in restricted visibility)
COLREGS Lights and Shapes for Towing Vessels
| Situation | Lights / Shapes |
|---|---|
| Towing vessel (tow length ≤200m) | Two masthead lights (forward and aft); sidelights; sternlight; yellow towing light above sternlight |
| Towing vessel (tow length >200m) | Three masthead lights (forward); sidelights; sternlight; yellow towing light above sternlight. Diamond shape by day if tow >200m |
| Vessel being towed | Sidelights and sternlight only. Diamond shape by day if tow >200m |
| Tow not readily visible or partly submerged | COLREGS Rule 24(g) — all-round white light at the forward end, all-round white light at the after end or stern, diamond shape |
Navigation in the Vicinity of Ice
SOLAS V/31 requires the Master of any vessel navigating in or near ice to proceed at moderate speed or stop when ice is encountered or when the presence of ice is reported on or near the course. The exam tests the OOW's understanding of the hazard and the required actions.
| Ice Type | Hazard |
|---|---|
| Icebergs | Only 10–15% visible above water. Can extend 300–450m below the surface. Radar does not always detect small bergy bits in a rough sea state. The most serious threat to hull integrity. Greatest risk from growlers (wave-worn fragments, very low freeboard, nearly awash) |
| Pack ice | Consolidated sea ice. Compresses and opens with wind and current. Penetration without ice class is dangerous — a vessel can be beset (trapped). Speed in pack ice increases damage risk dramatically |
| Bergy bits & growlers | Small fragments of glacier ice. Often not visible on radar because they do not present a consistent reflective surface. Extremely hard — dense glacier ice. A growler strike at 10 kn can breach a steel hull |
| Fast ice | Ice attached to the shore or seabed. Stable but can calve unexpectedly when temperatures rise |
Ice reporting (SOLAS V/31): The Master must report ice, derelicts, or any other navigational hazard to ships in the vicinity and to the nearest coast radio station. The format: "ICE REPORT" — vessel name, position, time, ice description, sea/swell/weather. Transmitted on Ch 16 (urgency: PAN PAN) and to the nearest MRCC.
Actions on Approaching Ice
- Reduce speed — "moderate speed" under SOLAS V/31. Speed at which the vessel can take avoiding action in sufficient time
- Station an extra bow lookout — bridge alone is inadequate in ice
- Switch on all deck lights if navigating at night in ice
- Engage manual steering
- Notify engine room — engines to immediate standby, reduce rpm
- Plot position frequently — increase radar watch, close range scale
- Seek ice-free water around the ice field rather than penetrating it
- Call Master
Ice Accretion
- Ice builds up on deck, rigging, superstructure in freezing spray and cold air temperatures (below −2°C in a seaway)
- Raises the centre of gravity rapidly — dramatically reduces GM and stability
- Rate of accretion: can exceed 2 tonnes/hour in severe conditions on a large vessel
- Action: reduce speed to reduce spray; alter course to reduce sea angle; deploy all hands to chip and clear ice from all surfaces; check bilges for meltwater; monitor GM against stability booklet; inform Master immediately if icing rate exceeds clearing rate
- MAIB and statutory reports required if significant icing incident affects stability
Watertight Doors, Scuttles and Scuppers
| Item | Requirements |
|---|---|
| Watertight doors | Operated manually, hydraulically, or remotely. SOLAS II-1/15 — must be kept closed at sea unless operational necessity requires them open (then only with direct supervision and closed as soon as the need has passed). Opening must be logged. Tested weekly (operation and closure time recorded) |
| Scuttles (deadlights / portlights) | Those below the margin line must be kept closed and secured at sea. Those at or near the waterline: closed and secured in heavy weather. The deadlight (blind) must be closed over glass portholes when the porthole cannot be seen |
| Scuppers and freeing ports | Must be kept clear and unobstructed at all times to allow deck water to drain freely. Automatic non-return valves (flap valves) on through-hull scuppers — confirm they function and close freely. Blocked scuppers trap water on deck — free surface effect reduces stability rapidly |
| Hatch covers | Weather-tight hatches secured with wedges or clamps. Inspect gaskets regularly. Closed and secured before entering any sea state. Hatch cover opening recorded in log |
Load Line Marks
| Mark | Meaning |
|---|---|
| Plimsoll mark (Load Line Disc) | A circle with a horizontal line through it. The line must not be submerged in the zone and season for which the vessel is loaded. The international load line certificate assigns the marks based on the classification society survey |
| TF — Tropical Fresh | Highest mark. Tropical zone, fresh water. Permitted maximum freeboard reduction for low density (fresh) water in a tropical zone |
| F — Fresh | Summer zone, fresh water |
| T — Tropical | Tropical zone, salt water |
| S — Summer | Summer zone, salt water. The standard reference mark |
| W — Winter | Winter zone, salt water. Lower in the water — less cargo allowed |
| WNA — Winter North Atlantic | Lowest mark. Only applies to vessels under 100m LOA in the North Atlantic in winter — the most severe condition |
Allowance for fresh water: A vessel designed to its salt water load line mark will float higher in fresh water because fresh water is less dense (1000 kg/m³ vs 1025 kg/m³ for salt water). The Fresh Water Allowance (FWA) gives the mm by which the vessel will rise — the vessel can be loaded deeper in fresh water by the FWA so that she reaches her salt water mark on reaching the sea.
Steering Gear — Testing and Changeover
SOLAS V/26 requires steering gear to be tested not more than 12 hours before departure from any port. Testing must be recorded in the logbook.
| Test Required | Procedure |
|---|---|
| Full movement of rudder | Helm hard to port — check rudder angle indicator and physical rudder movement correspond. Hard to starboard — same check. Note: rudder must reach its full designed angle (typically 35°) |
| Remote steering from bridge | Confirm all bridge control positions work (main helm, wing stations if fitted) |
| Autopilot and hand steering | Test changeover between autopilot and hand steering from all bridge positions |
| Emergency steering | Test local steering from the steering compartment — confirm helm order communication system (telephone or sound-powered phone) to the steering compartment |
| Visual indicators | Confirm all rudder angle indicators on bridge match actual rudder position. Gyro/compass heading indicators correct |
Steering failure at sea: If steering control is lost: immediately reduce speed; post a lookout; alert all vessels in the vicinity by VHF and sound signal (a series of short blasts); switch to emergency/local steering from the steering compartment; display NUC lights and shapes (two all-round red lights). Call the Master and engineer. Do not anchor in open water in heavy traffic — manoeuvre on engines to clear danger.
Danger Messages — SOLAS V Makes Reporting a Duty
SOLAS Chapter V obliges the master to report certain dangers to navigation by all means available — to ships in the vicinity and to the competent authorities ashore. This is not good practice; it is law, and the examiner wants the list said cold:
| Report | Detail |
|---|---|
| Dangerous ice | Kind of ice, position, date-time of the sighting — a SECURITE broadcast plus the shore report |
| Dangerous derelicts / direct dangers | The drifting container, the semi-submerged wreck, the adrift mooring buoy — any direct danger to navigation |
| Tropical storm | A TRS encountered or believed forming — with the actuals: position, barometer and its change, wind force and direction |
| Storm-force winds with NO warning received | Winds of force 10 or above for which no warning has been broadcast — you ARE the warning; the forecast chain missed this one |
| Sub-freezing gales / ice accretion | Air temperature below freezing with gale-force winds causing severe ice build-up on superstructures |
The logic is the sea's oldest cooperative bargain: the chart cannot know about the berg calved last week or the container lost yesterday. The NAVTEX warning that saves the next ship exists because somebody upstream made this report properly — position, time, the actuals, by radio to all ships and to the authority. Free to send; expensive for everyone when skipped.
Additional Question
You pass a half-submerged container 30 miles off the coast. Walk me through the report.
It is a direct danger to navigation, so SOLAS V obliges the master to report it by all means available. To ships around me: a SECURITE call on VHF 16 then the working channel — nature of the danger, position, time. To the authority: the coastguard or nearest coast station, who will assess and promulgate it as a navigational warning — NAVTEX and, if warranted, a NAVAREA broadcast — so it reaches ships beyond my VHF range and eventually the emergency wreck-marking machinery if it stays afloat. My log gets position, time and description; my own track gets a wide berth around it; and if I can safely stand by to mark it while traffic is close, that's seamanship — but the REPORT is the obligation, and it goes out before anything else.
Oral Exam Practice Questions
Question 1
A sailing yacht has lost her engine and all sail power. She asks for a tow. How do you set it up?
Call the Master. Confirm the nature of the casualty and obtain position, number of persons, and sea state. Notify MRCC of our intention to assist — clarify whether this is a duty-to-assist SOLAS situation or a commercial salvage, and whether Lloyd's Open Form applies. If LOF is relevant, obtain the casualty's agreement before passing the tow — the Master handles this, not the OOW. On deck: prepare the tow rope on our foredeck, led through the anchor hawse or bow fairlead and secured to the strongest forward bollards. Pass a heaving line to the yacht to lead the tow rope. Once the tow is connected on the yacht, ensure they have made it fast to their strongest bow fitting — not a cleat. Add chafing gear at all fairleads. The yacht must have a helmsman on the wheel. Apply power very slowly — do not snatch the tow line. Set tow speed appropriate to sea state — typically 2–3 kn in moderate conditions. Maintain catenary in the tow line. Keep a watch on the tow line for chafe. The yacht's crew communicates with us by radio on an agreed channel. Log all actions and times. Maintain contact with MRCC throughout.
Question 2
You are on passage in high latitudes and icing begins to form on deck and rigging. What are the stability implications and what do you do?
Ice accretion raises the centre of gravity because the weight is high up — on the superstructure, rigging, and upper decks. This reduces GM. In severe conditions ice can accumulate at rates that overwhelm the vessel's initial stability in a matter of hours. A vessel with significant topside icing in a beam sea can become dangerously tender. Immediate actions: call the Master; inform the engineer — we may need to fill low ballast tanks to lower the centre of gravity and restore GM; alter course to reduce the angle to the sea and reduce spray generation — this is the most effective immediate measure; reduce speed for the same reason; deploy all available crew to manually chip ice from decks, rigging, and superstructure — start with the highest points first; check bilges for meltwater accumulation and pump if needed; monitor the barograph and sea temperature — if conditions are worsening, we may need to alter course significantly to exit the icing zone. If the vessel develops a persistent list, do not correct with anti-heeling ballast alone — investigate the cause. Log all observations and actions.
Question 3
What are the load line marks and what do they mean for the OOW?
The load line marks (Plimsoll marks) are permanently marked on both sides of the hull amidships. They show the maximum permitted draught in different sea areas and seasons. The main marks from top (shallowest draft permitted) to bottom are: TF — tropical fresh water; F — summer fresh water; T — tropical salt water; S — summer (the standard reference); W — winter; WNA — winter North Atlantic (for vessels under 100m only). As OOW I must know which zone we are in and which mark applies. Before departure I check the current draught against the applicable load line mark for the zone and season — the Plimsoll line must not be submerged. The Load Line Certificate (from the classification society) defines the zones and marks. Overloading is a statutory offence and a safety issue — excess draught reduces freeboard, reduces range of positive stability, and makes the vessel more vulnerable in heavy weather. The Chief Officer calculates departure stability and draught — I refer to their calculations and the certificate.