The biennial Rolex Fastnet Race has developed into a multi-faceted competition with a burgeoning double-handed class as well as fully crewed yachts.

This year the fleet numbers 390 and includes multihulls, IMOCA 60s, maxis, Class 40s and Figaro one-designs alongside the 338-strong IRC division.

For the fortnight before the race starts on 6 August, 2017 navigators will have spent countless hours watching weather forecasts develop while they fine-tune a race plan. On race day the immediate priority will be to decide the best spot to start on the Royal Yacht Squadron start line in preparation for two or three hours of inshore racing towards the Bridge Buoy and the open sea.

But in a race this long the big calls keep coming and while it’s tempting to judge process against the boats around you, how do you keep tabs on what’s happening two or more miles to windward or leeward? How do you keep your Fastnet navigation on track?

Trying too hard too early in long races can easily lead to burn-out. Will your crew take the inevitable setbacks in their stride and will you be able to spot opportunities for the big gains when they are presented?

Top navigator Mike Broughton is quick to emphasise the importance not only of making good decisions, but knowing how to make them, and when.

“It’s no good having a great first 20 hours then the navigator starts to fade and you miss that big shift off Land’s End. Plan not just the watch system, but also the decision system and how you are going to keep making good decisions,” he says. “Then update and involve the crew. It’s always better to have a Plan A and Plan B rather than no communicated plan at all. Talk through the next sail change and let the crew boss know the likely following sail change as well.”

1. Key decision points

Have a clear idea when or where you need to be making key decisions – for example, as you approach St Alban’s Head. Think about the wind stability as there are geographic windshifts, wind shadows, wind acceleration zones and predictable windshifts in the sailing wind owing to changes in the tidal streams.

View each leg as a short sprint. While the tactics are often complex, break the decisions down and make it simple.

Keep asking ‘what if’: what if the wind backs to 220°?; what if the wind increases to 18 knots?, etc. Even the long leg from the top of the Scilly Traffic Separation Schemes to the Fastnet Rock can be viewed as a huge windward/leeward race – well, sometimes!

When you think you have a strategy, keep in mind the relative risk of your plan compared with what your main opponents are doing. Do you need to take that much risk at an early stage?

Pro navigators and tacticians are patient and measured in their decision-making. They know opportunities for many small bankable gains will come, so if in doubt don’t get exposed when you don’t need to. Of course, these decisions are all tempered by how well you are doing.

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2. Beware the bays

Heading west in the English Channel in light winds, some competitors head into the bays in search of sea breezes, while at the same time trying to cheat an eastgoing tide.

Winds in the bays in an east or west wind are often lighter owing to wind shadow effects. For example, the high ground of Dartmoor reduces the wind in Lyme Bay, just as the high cliffs of Cornwall affect the winds in West Bay.

While flying Royal Navy search and rescue helicopters in the English Channel out of Portland, I used to see this quite clearly most times I went flying, particularly in a south-westerly or easterly wind.

3. AIS and trackers

Monitoring the opposition is a key part of the race these days. You can deduce a great deal about the wind direction and strength with careful analysis of other boats’ tracks, particularly if you already have a good idea of their relative speed and how well you think that boat is being sailed.

Rolex Fastnet Race YB tracker

When you are beating your rival, the tracker or AIS can help you cover their movements to ensure things stay that way. But don’t lose sight of the big picture. The fleet will be spread over a large area and it is easy to lose touch.

4. Weather updates

You need to know what information you are looking for and then prioritise. Rely purely on GRIB files at your peril; they struggle with fronts, trough lines, sea breezes, acceleration zones, wind shadows.

Synoptic charts, real-time observations, and various satellite images are all very important in building your forecast for the Rolex Fastnet Race, though their relative importance changes with the type of weather system.

If you know there is a front coming with a big shift, it is often best to track the timing by using rain radar and not a GRIB file. Sometimes bandwidth can be limited, so prioritise what you want to download before you start the race. Live weather reporting sites such as XC Weather are also useful.

5. Know your targets

It can be a waste of money to invest in new sails then unwittingly allow poor performance at night.

Don’t settle for badly calibrated instruments or you could miss a windshift or race at the wrong target angle or speed.

I recently took the drastic action of tearing an inferior set of instruments off my own boat. We then upgraded, calibrated and improved overall performance considerably in just one week.

Mike Broughton works with international sailing teams at the top level of the sport, and has competed in 17 Fastnets. He also used to be a Royal Navy search and rescue pilot.