Every delivery between Istanbul and the Aegean passes through two of the world's busiest waterways and the Sea of Marmara between them. The route looks short; the difficulty is not distance but traffic, current and wind.
In the straits
- Traffic
- Large ships follow the traffic separation scheme; small craft keep to the starboard side for their direction, outside the traffic lanes. If a crossing is needed, it is made at right angles and quickly.
- Radio
- The relevant sector channel of the straits' vessel traffic service is monitored, and calls are answered.
- Current
- Surface current generally runs from the Black Sea into the Marmara and from the Marmara into the Aegean; it speeds up in the narrows, with counter-currents close inshore. Against it, time and fuel increase.
- Ferries and small craft
- City ferries and fishing boats cross often and fast; a daylight transit is preferred.
The Sea of Marmara
- Wind: the north-easterly poyraz and the south-westerly lodos; lodos raises a short, steep sea.
- Ship anchorages: waiting areas for large ships are allowed for when passing.
- Fishing nets: need care, especially at night.
- Shelter: ports to run to if the weather turns are chosen in advance.
Planning
- Weather window. Days when poyraz or lodos is blowing are avoided.
- Timing with the current. Strait transits are planned around current and daylight.
- Fuel. Running against the current is allowed for; fuel stops are set.
- Stops. A night in the Marmara if needed.
Current in the Bosphorus
The surface current in the Istanbul Strait generally runs from the Black Sea to the Marmara, north to south. It strengthens noticeably in the narrow, winding sections; near the shore in places, counter-currents form. For a boat heading north the current cuts speed considerably, and fuel and time are planned accordingly. Strong southerly winds can change how the current behaves.
Shipping traffic
The straits and the Marmara carry heavy large-ship traffic. A big ship may see a small boat late and cannot manoeuvre quickly. So a yacht keeps outside the traffic separation scheme at a sensible distance from shore, and when it must cross the main lane does so by the shortest route and at right angles. The VHF is kept listening on the area's traffic service channel throughout.
Rules
The rules and reporting requirements for passing the straits are updated from time to time. Before the passage, the current rules are confirmed with the traffic service or harbour master.
Marmara weather
In the Marmara, the northerly poyraz and south-westerly lodos can raise a short, steep sea. In winter the weather changes faster and knowing where the refuges are matters more. The Dardanelles call for the same care, with strong current and heavy traffic.
Watchkeeping in the strait
The passage is planned in daylight, in good visibility and at a time that works with the current. Two people keep watch throughout: one helms while the other watches traffic and the radio.
Fuel
A northbound passage against the current uses more fuel than the distance suggests. The fuel plan allows for it, with a refuelling stop before the straits if needed.
At night, ship lights, shore lights and navigation marks are hard to tell apart, so a night passage is not advised without an experienced crew and working AIS and radar. Where possible, departure is timed so the passage ends in daylight.
Before the passage, engine, fuel, cooling and steering are checked; in the straits a failure turns dangerous much faster than offshore.