Navigation briefing Tips for navigating close to rocks
MIKE BROUGHTON on NAVIGATING CLOSE To ROCKS
Many sailors are sensible enough to stay as far away from rocks as they can.
But it’s certainly a useful skill for a cruiser to be able to explore Atlantic coves, to cheat a four-knot foul tide on a rocky shoreline, or to find a secluded anchorage. For the racer, cutting a corner or benefitting from a tidal eddy inshore can gain significant places. But confidence to pilot your vessel close to rocks is a skill that takes practice, knowledge, spatial awareness and the ability to think on your feet.
Preparation is key. A great deal of this is covered in RYA Navigation courses: the ability to properly interpret a chart and understand hazards. When I did my RYA Examiner’s Course with Bill Anderson many moons ago, he insisted that candidates be familiar with and not shy away from the ‘green’ parts of the chart (areas of shoreline that cover and uncover with the changing height of tide).
Symbols for hazards on chartplotters change from system to system and can fool the unwary. Spend time getting to know the features of your chartplotter so it’s easy to use in a moment of stress. New features, such as easy tidal height information, have been added in recent years, not just to charting apps, but to basic chartplotters too.
Time and tide
First a little due diligence. Knowing the quality of the chart you are using is essential. How accurate is it? What was the date of survey? Charts surveyed since the advent of side-scan sonar (mid-1970s) are generally reliable, but there are still many areas of charts in use today that utilised soundings by hand leadline. Even some harbour charts were created using this method, where a line was thrown roughly every 60m along a track – not taking into account any rocks or wrecks in between! This technique was used till 1935. Paper charts show the survey date in a small chartlet, usually close to the edge.
Most areas are covered by more modern surveys that afford us much greater confidence in the paper and electronic charts we have today. UK Admiralty has over 15,000 Electronic Navigational Charts and 3,500 paper charts, while Navionics says it carries out around
2,000 chart updates a day.
Once we know we have an up to date chart, we should ensure we have any relevant Admiralty Notices to Mariners. For example, we can’t rock-hop along the east Dorset cliffs if the Lulworth firing ranges are in use. Fortunately, the ranges close for the month of August, when the Rolex Fastnet Race rolls past.
The final due diligence check for charting is the horizontal datum in use. GPS usually outputs its position in a datum called WGS 84. There are over 50 different datums used on charts around the globe. Some require an offset to be entered into your position fixing system (GPS or equivalent). A good example of this is for yachts taking part in the RORC Caribbean 600 offshore. The last rounding mark is the small island of Redonda, which you can visually see move 300m as you zoom in close. After rounding the island, if you look at your track, it clearly takes you over the top of the cliffs!
A good quick check for your GPS and datums is to see exactly where you are when next to something fixed, such as a nearby breakwater, before you set sail. Remember not all GPS sets are equal and knowing the normal accuracy of the set you are using is important.
Inaccuracies
In some places the charts are just plain wrong. A good example is in the beautiful Maddalena Islands of north-east Sardinia, which host many top regattas. Each year prior to the major events you’ll see navigators and tacticians doing visual survey work on the key corners. I’ve now done over 20 days of surveying in the area, usually in a fast RIB, utilising depth sounders, handheld sounders, diving masks and aerial photos. Stan Honey, navigator on Comanche, even did his own sonar survey. Just outside Porto Cervo harbour in 2018 two superyachts hit an ‘unmapped’ rock, causing considerable damage.
Once you have the information you need to be able to translate it into practical pilotage. You need to be able to explain the distance to that rock in easy terms, such as boatlengths or time. Throughout, keep an eye on the depth sounder.
Visual pilotage should be aided by regular use of a handbearing compass. You can keep a hazard boxed by clearing bearings. For this simply use a recognisable landmark on the chart. Work out the closest point you can safely go and check this bearing, then make note that you must keep the bearing, say, no more than 125°, so in a stressful moment you can easily look it up.
If you are lucky enough to be sailing in areas of clear water, the water colour can be a great help. Usually brown or green coloured water is very shallow and differing levels of light blue and dark blue give good clues to the depth. A sandy bottom will often give a bright light blue, even at depths over six metres. It helps to calibrate your eye to a shade of colour and cross-reference with your depth sounder.
Even in the wintery brown water of the North Sea, some clues don’t change: a swirling sea or breaking white water is never a good sign. Nor are wading seabirds! Mike Broughton is a pro race navigator who has won many titles including World and European championships. He is a qualified MCA Master to captain superyachts and previously had a successful career in the Fleet Air Arm flying Sea King and Lynx helicopters.