An aide-memoire to using a handbearing compass, transits and bearings for quick and easy coastal pilotage
1: Leading Lines
In many harbour entrances you don’t need the buoys – you can use the leading lines instead. Here, two posts with topmarks keep your vessel in safe water. Many topmarks are also lit. If the posts are not in line, head towards the front marker, which will bring you back on course.
2: Compass Bearings
Sometimes you can plan your passage to take advantage of a prominent local landmark, keeping it on a steady bearing to make sure you stay in deep water. Taking regular bearings of this church tower on 290° will keep the boat in safe water irrespective of any cross-currents.
3: Open Transits
Where there are two landmarks almost in line, you can use them to help keep you clear of dangers. In this case, keeping the island superimposed on the headland will keep the yacht clear of the shoal. If the island becomes separately visible, or ‘open’ to the left of the headland, you are too close to the shoal (see red line) and should head to port. A clearing bearing ensuring the headland was on a bearing greater than 045° would also keep you clear.
4: Clearing bearings and sectored lights:
In narrow, unmarked channels it can help to work out clearing bearings from a prominent landmark. In this example, keeping the boat between bearings of 235° and 250° will keep her in safe water. This is especially useful if beating towards your destination, when it’s impractical to stay on a single leading line that lies dead to windward. At night, staying within the white sector of the light range achieves the same result.
In the absence of a leading mark, staying on a constant back-bearing of a mark behind you can keep you clear of danger. Back-bearings are especially useful if there is a strong crosswind or tide. Keep the helmsman looking forward and nominate a crewman to keep checking the hand-bearing compass. Here, keeping the green pile on a constant bearing of 060° will keep this boat clear of underwater obstructions.