Instructor Modules / Short Passages
IYT Module 17 · DOK Working
Instructor self-study

Short Passages — Heavy Weather, Restricted Visibility & Harbour Entrances

This is the judgement module: the weather turns, the fog rolls in, the harbour mouth is breaking — what do you do, and in what order? Full IYT Module 17 syllabus at Working depth: heavy-weather preparation and tactics, lee shores, line squalls, sea anchors and drogues, ice accretion, fog procedure, harbour entrances, short-passage planning, anchorage selection and crew delegation — with an interactive prep checklist and a "conditions worsening" decision drill.

Heavy weather prepLee shoreLine squallsHeaving to Sea anchor vs drogueIce accretionFog procedure Harbour entrancesPassage planningAnchoragesCrew delegation
Why it matters afloat: none of this is advanced seamanship — it is ordinary decisions made early. The core message is to act while you still have options, because heavy weather removes them one by one.
Lesson 1 · Interactive

Preparing for Heavy Weather

Preparation happens well in advance of the system's arrival — by the time the wind is up, half of this list has become dangerous foredeck acrobatics. Work through the boat as a drill (tick each item as you'd brief it):

The last line of the list is the most important: if heavy weather is going to persist, head for a safe haven — early, while the entrance is still safe to use.
Lesson 2

Lee Shores & Line Squalls

The lee shore
The shore the wind is blowing onto, with the seas breaking against it. Everything about rough weather gets worse there — and a boat is safer offshore in deep water than fighting for a harbour at the surf line. Watch for this: the "safe harbour" itself often lies on the lee shore, with big rolling waves at the entrance that can send a boat surfing out of control. Sometimes the seamanlike call is to stand off until it eases, or run for an alternative refuge.
Line squalls
By day: a darkening line across the sky, bringing bursts of intense rain and a sudden, dramatic jump in wind. Usually short-lived, occasionally severe, always startling. Prepare exactly as for heavy weather, and err on the side of caution — at night they hide against a dark sky and arrive unannounced.
Lesson 3

Heavy-Weather Tactics — Heaving To, Sea Anchors, Drogues & Ice

First tactic is always the same: if a safe haven is reachable in time, go there. Caught out, a sailboat's most comfortable option is to heave to:

Heaving to — reef down, then tack leaving the headsail cleated. It backs against the new wind; bring the helm to leeward and lash it, and trim the main to balance. Backed headsail cancels the main's drive: the boat parks, nearly stationary with little leeway, riding steadily — a genuine rest mid-gale. (Your sailing instructor demonstrates this on the water.)
Sea anchor — off the BOW
A parachute-shaped canvas/webbing bag streamed on the anchor rode to hold the bow into the swell — the safest attitude, since a heavy beam sea can capsize a small boat. Rode length matters: pay out enough to reach the crest of the oncoming wave. Works for power and sail alike.
Drogue — off the STERN
In strong following seas the waves slew the stern side-to-side (yaw). A drogue dragged astern acts as a brake: course steadier, ride more stable and comfortable — at the cost of speed.
Bow or stern — the one-line memory hook: sea anchor holds the nose to the weather; drogue holds the tail straight downwind.
Ice accretion: freezing rain, spray or supercooled fog can layer ice onto the vessel. The weight builds fast and high — remove it as soon as it forms, because a top-heavy boat in a beam sea is a capsize waiting to happen. In spring, melting ice flowing down rivers becomes a genuine navigation hazard.
Lesson 4 · Interactive

Conditions Worsening — What Do You Do First?

Three linked scenarios, each with one best call, one defensible one, and one that makes the day worse. Choose, read the why, carry on:

Lesson 5

Action in Restricted Visibility

Fog is air cooled below its dew point — typically land cooling overnight, the saturated air drifting miles out over coastal water, burning off as the sun lifts the temperature. Inside it, visibility can drop to a few boat-lengths and disorientation is fast. The drill, the moment it closes in:

Navigate deliberately
  • Fix your position immediately; keep the logbook running with positions and courses
  • Steer to clear hazards, shipping channels and traffic schemes — and avoid constant course changes that wreck your dead reckoning
  • Radar and every electronic aid ON; radar reflector as high as possible
  • Near a marked channel: stay just outside it, close to the buoys
Be seen, be heard, be ready
  • Slow down — to a speed you can stop or turn from instantly
  • Lookout posted to watch and listen; keep the boat silent
  • Sound the fog signal on the horn — one long blast every two minutes
  • Monitor VHF; in a shipping lane broadcast a Sécurité with your position
  • Lifejackets on; white flares to hand; know where the raft is
Related material: the four fog types are covered in Module 16 · Lesson 9, and the formal Rule 19 obligations in Module 22 (Collision Regulations).
Lesson 6

Negotiating a Harbour Entrance

Entrances concentrate everything: traffic, shoal water, current, and — on the wrong day — breaking seas. The standing rules: work out your pilotage plan in advance (pilotage = finding your way by eye off landmarks, buoys and depths in close waters, rather than by chart plotting), watch every vessel entering and leaving (big ships may be restricted in their ability to manoeuvre or constrained by draught — recognise the lights, shapes and sound signals), check astern for overtakers, and keep to the starboard side of the channel.

Ready on deck
  • Ample crew up and briefed
  • VHF on and within reach
  • Dock lines and fenders rigged
  • Anchor ready to let go — your emergency brake if the engine quits in the channel
  • At night: navigation lights on and checked; radar reflector high
The rough-weather entrance
A lee-shore entrance in a blow means large rolling waves funnelling through the gap — prime surfing conditions with rock on either side. In extreme cases (including crossing a sandbar), stream a sea anchor astern to slow the boat and kill the surf tendency — or stand off and wait. An entrance that will be safe in six hours is not a failure; it's seamanship.
Collision regs on passage: keep a proper lookout at all times, give crew the basics and a standing order — in doubt, call the skipper. Avoidance action comes early and large — big, obvious alterations that another vessel can read by eye or radar, never a string of small nibbles, and never a turn into someone else's path.
Lesson 7

The Short Passage Plan, Anchorages & Crew

A passage plan starts with an appraisal: charts with real detail for every leg, a current-year almanac (lights, tides, traffic schemes, radio), a cruising guide (fuel, water, pump-out, medical), and — beyond 5 NM offshore — the proper minimum of publications and manuals aboard.

Plan headings that earn their keep
  • Date & weather — tropical season? forecast access?
  • Distance / boat speed / passage time per leg
  • Tides — flow, restrictions, HW/LW at both ends; headlands with overfalls may dictate when you pass
  • Ports & harbours of refuge — with their own entry restrictions noted
  • Marks & lights, waypoints double-checked (transcription errors are epidemic), traffic schemes crossed properly
  • Documents, watch schedule (needed beyond ~15–16 hours), provisioning, fuel with real reserve
Selecting an anchorage
  • Wind speed/direction — and the swell it sends in
  • Tide & current — too much flow is a no
  • Access — usable in traffic and in worse weather?
  • Depth — enough under the keel at low water, enough rode for the depth
  • Holding — sand, mud, shale, rock, turtle grass → anchor choice
  • Room — swing circle clear of the neighbours
  • Arrive in daylight whenever you can
Tactics filter: crew numbers and experience, equipment reliability, tidal gates, fog-prone areas, day-vs-night at the danger points, traffic. If any of it adds an unacceptable hazard — change the plan or don't go. And stay flexible on the day: forcing a passage against conditions is how holidays (and boats) get broken.

Delegation: boating is teamwork. Every crew member knows the location and use of the safety kit — lifejackets, raft, extinguishers, flares, ditch bag, VHF, horseshoe buoy, throw ring, lifesling — knows their own duties and is genuinely able to do them, and knows the safe operation of heads, stove, heater, engine and generator before departure.

Knowledge Check

Short Passages — Knowledge Check

10 questions at IYT exam standard (75% to pass), drawn from the IYT Module 17 knowledge review.

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