Simple GPS Navigation for Cowes Week

Once the starting line is known, enter its position as the first waypoint in your ‘Route’. Unless you have a committee boat start you can do this motoring out of the river in Cowes Week. If you are starting out in the middle on laid line, use the ‘Mark’ function when you are near the committee boat to load the position of the start line automatically.

As soon as your course is read out, write it down. I am so paranoid about missing a mark, the radio going wrong and a host of other errors, I insist that at least one other crew member duplicates this, listening to another radio on the stand-by frequency. Once you have checked that both the written-down courses agree, enter the first mark as the second waypoint in your ‘Route’ list. The GPS should immediately produce a bearing and distance to the first mark. Give this information and the name of the mark to the tactician (on a big boat) or helmsman (on a small boat). If you are sailing on a small boat you now have enough information to get most of the way up the first leg and can get on with helping to sail the boat.

Once more time becomes available (and hopefully on a boat with more than three crew this should be before the start) enter the remainder of the waypoints. Don't forget to put in the finish line. It makes good sense to draw the course on a racing chart at this stage. Not only is it then easy for the entire crew to see where they are going, but you can check that the bearings and distances between the marks roughly agree with the figures produced by the GPS. It is also as well to check for obstructions (like the Bramble Bank) which might lie on the direct track. I write the bearing and distance between each mark in my notebook at this stage for easy future reference. Cross off the marks as you go round so as to prevent the 'how many times have we been round?' problem.

Sailing to a windward mark.

Calling the laylines in the Solent with lots of tide is always a hard job. Amazingly, your GPS can make it easy or at least easier. Set the unit up to show Bearing to Mark (BTW) and Course over Ground (COG).

Let’s say you are going to make a starboard tack approach to the mark. On the last couple of starboard tack legs before the mark, make a note of COG and magnetic wind direction from your instruments if you have it.

With no wind direction information simply make a note of ‘headed’ or ‘lifted’ with an indication of by how much if you can. A record of compass heading on both tacks makes the job easier and will come in handy later on.

Assuming the wind and tide is steady, as you come across on your final port tack leg it is simply a matter of waiting until the mark bears one or two degrees below your last recorded COG on Starboard tack. You can check this either with the GPS (if the mark is a long way away) or with a hand bearing compass if the mark is close. Of course if you have been lifted five degrees on the way in on port you will need to go seven degrees (the five degrees you have been lifted plus a couple of degrees for safety) beyond your last COG to make sure you lay. A header on port means you can tack correspondingly earlier. Similarly you can make judgmental allowances for building or slackening tide.

For a port tack approach the safety angle is obviously minus two degrees rather than plus.

If the final approach is from a long way out and there are no good transits (rare in the Solent), the GPS gives a perfect indication of whether you are laying the mark or not. If BTW is a bigger number than COG on starboard tack, (and vice versa on port) you are not going to lay the mark. Converse readings however mean you have overstood and the sooner you can crack off the better.

Spinnaker or not?

Those carefully noted wind readings or compass headings on the upwind leg make a great tool to help with sail selection for the downwind leg. If you only have compass headings then split the difference between them to get a pretty good stab at magnetic wind direction.

Compare the wind direction with the course to the next mark. If the difference is more than about 100 degrees (in light winds) and around 120 to 130 degrees in plenty of breeze you can carry the kite. Those fortunate enough to have polar curves and sail selection charts will have all the information they need to make an educated decision.

Again you will have to make a manual allowance for tide but even if this is a bit out, the answer is likely to be much more accurate than a simple ‘suck it and see’. Similarly if the wind direction and course to sail are close to 180 degrees apart then the difference should allow you to work out which gybe will be favoured.

Time to the mark.

Except in rapidly-changing tide and when close the laylines (upwind and down) the Time to Waypoint (TTW) function is more accurate than any guess at the time to run to the mark. Especially on bigger boats the foredeck crew will very much appreciate a count down on the way in.

Reaching

Races in the Solent are often won and lost on the reaching legs. They key more often than not is to take the direct track across the tide and avoid sailing the ‘big banana’. Grinding up to the mark at the end of a leg or soaking off deep when your rivals are powering in is always slow.

Before the beginning of any reaching leg it pays to make a traditional tidal offset calculation and aim ‘up’ or ‘down’ by an appropriate amount. Once round the mark, and on a reach, the GPS gives a perfect ‘transit’ to the mark even if you cannot see it. The trick is simply to get COG and BTW to read the same and keep reading the same and a straight line approach to the mark is guaranteed.

Where are we?

Provided it can give you latitude and longitude the GPS is a very good tool for determining where you are. Unfortunately, transferring this information to the chart can be difficult or impossible, especially if the chart has been folded and the borders are not readable.

Fortunately for us, the solution is simple. Don’t use Latitude and Longitude. Most of the time when racing our GPS is set to give us BTW and DTW. With your marked-up protractor it is a simple matter to put the little hole in the middle over the mark and rotate the protractor round to the required bearing. A mental interpolation between the half-mile rings on the protractor gives a pretty good indication of position. With just a little practice this is much easier than fiddling about with dividers or a complex plotter.

Don’t rely on the GPS

There is much more to navigating a fast and effective route around the race course than just going straight from one mark to the next. The GPS is just one of many tools available to help you.

More often than not the best tool you have is your eyes. Keep them up and out of the boat. Look for the wind shifts and changes in pressure. The position and heading of other boats is often your best clue as to what is going on.

The tide is vital too. Knowing the depth and rate of flow is second nature to anyone racing regularly in the Solent.

Perhaps most important of all is communication between the crew. It is simply no good any one person having useful information if that information is not shared.

Happy sailing, watch out for the rocks and see you out there.