Expert advice: boat navigation

Good seamanship starts with excellent navigation skills. Yachting Monthly experts share their top tips for a smooth passage

Boat navigation is more than just chart work, it is about having a sense of your surroundings and relating the information on the chart to what you see in the real world.

A lot of sailors now rely solely on electronic charts, but many argue that it is worth keeping traditional skills fresh, and having a paper chart on board as back up is a good idea.

However you prefer to navigate, Yachting Monthly experts share their hints and tips for a stress free voyage.

Lacy’s Law for easy navigation – Graham Lacy

 

This is not so much a novel law as an observation of the simple laws of existing trigonometry. It is nevertheless a useful rule of thumb to know when helming and you haven’t yet been given a Course To Steer (CTS).

Nevertheless I have not heard of or encountered it before. It is as follows: If you are sailing at an average of 5 to 6 knots and have a cross tide, then to maintain your intended rhumb line course; steer into the tide in degrees by 10 times the value of the tide in knots.

For a cross tide of 1 knot steer 10º into the tide. For a cross tide of 2 knots steer 20º. For a cross tide of 3 knots steer 30º. This holds remarkably accurate up to a tide of about 3 knots, at least as accurate as the course a helmsman can maintain.

Interpolation: these values can be interpolated, maintaining their accuracy, so for instance steer 15º into a tide of 1.5 knot tide.

Speed extrapolation: If you are lucky to be sailing at twice this speed (10-12 knots) then the correction values can be approximately halved. (The rule of thumb becomes inaccurate at less than 5-6 knots.)

Angle extrapolation: If you have tides at 30, 45 or 60º and you are adept at mental maths then you can use the cross tide adjustment as the starting point and further factor the adjustment by 50%, 70% and 85%.

It should be noted that a fixed transit remains the best form of navigation.

With a cross tide, steer into the tide by 10 times the value of the tide in knots to maintain your rhumb line

Satellite navigation – Thom D’Arcy

During my circumnavigation, I found satellite imagery to be a hugely valuable way of not only verifying my electronic and paper charts but also as a principal method of navigating through poorly chartered areas.

In Fiji, for example, where electronic charts were very inaccurate in some areas, satellite imagery allowed me to plot courses through the coral reefs with confidence.

There are various ways of utilising satellite images for navigation but I found the best to be through OvitalMap, a cross-platform app for phone or tablet that allows Google and/or Bing imagery in any area of interest to be saved for offline use.

The boat’s position, speed, course and track can be displayed in real time, or waypoints can be extracted in advance for plotting on your chart.

Other benefits of satellite imagery include the ability to identify the nice areas of sand to drop the anchor or for studying a harbour or marina layout before arrival.

Just remember to download the data in advance when you still have an internet connection.

OvitalMap can be downloaded from Apple or Android stores.

Finding the nearest refuge – Dag Pike

Passage plans require you to identify alternative ports that you can go to if conditions deteriorate.

As with most requirements for passage plans it makes sense but don’t forget that perhaps the most convenient alternative port might be the one that you have just left.

It’s a bit like the safety briefing on aircraft, ‘The nearest exit might be the one behind you’.

You have made all your plans and checked the forecast and as is so often the case things might be a bit marginal, but you want to keep your cruise on track.

It could be that the conditions are worse than expected because the wind is against the tide.

Turning back will not be something you will like doing, but it can be the best option in some cases.

Identify your no-go areas – Rachael Sprot

When we learn navigation there is a focus on calculating the perfect route.

We take tide, leeway, variation and deviation into account to come up with a course to the nearest degree but we rarely ever sail that exact course.

In reality, the wind shifts or the sea state is uncomfortable, we are delayed and the tide has changed or we have to deviate around a fishing fleet.

What you need to know now is not where you want to go, but where you can’t go.

Once you’ve identified hazards, take a pencil and shade out all the no-go areas to leave yourself with a safe area to navigate within.

This will highlight the dangers to crew who might be doing the navigation, and will help you build a mental map of the area so you can confidently make decisions on the hoof.

Traditional navigation has its place – Tony Curphey

I guess my kind of navigation would be described as old hat because it doesn’t depend on, or even involve chartplotters, laptops, software or hardware.

I am admittedly, and proudly, old fashioned.

I do use a GPS, a hand-held Garmin plugged into the ship’s electric system and I have an AIS transceiver which as a single hander is worth its weight in gold.

But I work on paper charts.

When on the ocean I plot one position each day, at noon, but in the all-important log, I note the position every time I have a reason to write or report anything: windshift, sail change for example, thus I always know where I was several hours ago.

When in close quarters, near a coast, an island or the English Channel, I may be using a larger scale chart and I may put a position on it as frequently as every 15 minutes, depending on conditions or circumstances.

There is not a single electronic device on Nicky which I could not do without if, for instance, a lightning strike wiped it all out.

My sextant and tables and a perpetual almanac always travel with me.

It’s 22 years since I really worked out sights when I finished my first circumnavigation around the world on Storm Petrel.

The sextant was my only means of navigation on that voyage so I think it might take me a day or two to get into it again, but I feel confident that these traditional tools would get me home.

Overcoming steering bias – Dag Pike

After you hand over the helm to one of the crew and give them the compass course to steer, it can be a good idea to check out the actual course being steered because most people at the helm will bias the course by steering to one side or the other.

This is not done on purpose but is just a natural reaction to steering.

On a yacht you will find that most people will let the heading drop down to leeward when close hauled or reaching, and then bring it back to the required heading before letting it drop away to leeward again.

Rarely will they bring the heading up to windward, so that in effect the heading being steered may be as much as 5° away from the desired course.

It is easy to assess once you watch the heading for a while, and you can build in a correction to the course to be steered once you recognise what is happening.

Identifying the problem can save you getting too far down to leeward.

Don’t always go with the tide – Helen Melton

For a long time after learning to sail we followed the generally written advice closely, timing arrivals at famous tidal headlands for slack water at the turn of the tide, then using the favourable stream to help along the ongoing journey.

After a few uncomfortable passages travelling wind over tide, we began to rethink our strategy and consider whether there were alternative options for those situations where wind and tide were against one another.

One of these was to aim to reach a headland or tide race towards the end of the favourable tide rather than the beginning.

We did this when sailing north from Camaret-sur-Mer, Brittany to L’Aber-Benoît in a strong northerly wind.

We arrived at the southern end of the Chenal du Four – its narrowest point and where the currents are the most intense – at slack water, and proceeded through on a bumpy but flattening sea, pushing increasing amounts of tide as we travelled.

As the boat sails faster on flatter seas, the journey to L’Aber-Benoît only took an hour or so longer and the crew all felt it had been a more comfortable passage in comparison to sailing earlier in the day, when the wind was kicking up a steeper swell.

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