Most of us have a lot of electronic kit on board. Toby Heppell 
asks the experts how to make the most of all this technology

‘Last summer I took a few weeks out and went cruising with my family in Brittany and met a customer who had a lot of expensive gear on board but was not using much of the available functionality because he “had got manuals coming out of his ears and hadn’t had the time to study them all”.’ So says Matt Eeles of B&G and I’m sure it is a familiar story for many sailors.

For all the improvements sailing tech and software has made over the years, there have been times when it feels like a lot of hassle for limited reward.

It is certainly true that the amount of functionality available with even some of the most basic systems can seem overwhelming, particularly when you are faced with an incredibly dense manual.

Electronic passage planning

Winds and tide information makes for incredibly accurate auto-routing

It is also true that not all of us require every bit of functionality built into a device, but this should not stop us getting the most out of a bit of kit that you have usually paid a great deal of money for.

There is no avoiding the fact that setting up instrumentation is something of a chore, but if we want to take advantage of the kit we have on board then it is something of a necessary evil.

Many of us use our onboard electronics in the simplest way to offer boat speed, wind angles and to do some passage planning.

In truth, however, there is a vast array of useful tools you probably already own that could be making your sailing more enjoyable, interesting and safer, merely for the cost of a bit of time setting them up and understanding their functionality.

1. Polars

Polars are, in their most basic form, a dataset by which you can judge your boat’s performance. If the windspeed is x and you are sailing at y angle to the wind, then your best or target boatspeed is z.

Polars have long been seen as the preserve of racing sailors, largely as they are difficult and often hugely time consuming to draw up.

Top flight racing campaigns invest vast amounts of time and effort into getting a polar dataset that is incredibly accurate and goes well beyond that which even an enthusiastic amateur can achieve.

Polar data shown on a screen

Polar data shows boat speed at wind angles across the wind range. A polar diagram makes the data easier to decipher. This is fed into the systems calculations for things like ETA and route planning

‘If you step onto a real top-end racing 
boat the key thing they are usually thinking about is their polar or target speed,’ says Greg Wells of Raymarine. ‘Sometimes they are looking at that, almost to the exclusion 
of everything else.

‘For most of us, though, it is more a function of reassurance and to be honest, unless you want to put hours and hours of work in they are not going to be pin-point accurate anyway.

‘We’re building a list of polars into our Lighthouse 3 software and trying to cover 
off as many boats as we can, but if you take 
a Jeanneau Sun Odyssey 410, there are 17 variant factors which all have an effect on the performance numbers. What we are trying to provide is a broad guide that can give you something to aim at.’

To that end, Wells notes that you may well have polars that you can never hit but simply by having them there you get a good idea of your performance anyway. You might well always sail 1 knot slower than target speed but provided you know this, you know you are aiming for that adjusted target.

For Eeles, the key is calibration and accuracy of data. ‘It’s always surprising to 
me how many boats we step onto where the owner has not calibrated their equipment.’

It’s well understood by most sailors that an offset paddle wheel, on one side or another of a keel for example, will provide differing readings from tack-to-tack as water pressure differences change the speed readings.

‘This is the sort of thing that must be calibrated on boat and will vary from boat to boat. There are a range of similar factors that will see boat speed numbers vary too.

‘Furred up paddle wheels are well known as an issue and on my own boat just a couple of weeks in the water without the paddle wheel being cleaned, I can see anything 
up to ½ a knot of boatspeed lost,’ Eeles continues.

In built polar list

Raymarine is now supplying a built-in polar list; just find your boat or one like it and you are off

‘That might not seem huge but that has a massive effect on all the instruments and can put your feedback 
out significantly. It’s also important to make sure your wind instrumentation is properly calibrated. It’s not massively time-consuming, – for windspeed and heading calibration, you’re only looking at 30 minutes or so and cleaning a furred up paddle wheel takes very little time too.

‘In terms of actual polars, provided your numbers are realistic from calibration you really don’t need a huge amount of information, just a broad set of speeds in certain conditions at certain wind angles 
will work well enough. There are quite a few apps out there that work for developing a list of polars. We use KND Sailing Performance, which is pretty easy to use and allows you to just input your boat’s dimensions and a few other details and it will draw up a list that I think is pretty accurate.’

To some extent most of us probably already have some broad polars we use in our head anyway — if you usually achieve 
6 knots boat speed upwind in moderate conditions and you are only making 4 knots, few of us would not conclude something 
in our setup is wrong. Adding them into onboard electronics merely gives us a specific percentage of performance loss.

‘It’s fun and useful to have something telling you how close you are to optimum speed,’ says Wells, ‘but more than that it 
can give you a better understanding of your likely speeds when passage planning.’

In and of themselves polars have limited use for cruising. Where they are very important, however, is in unlocking the functionality that comes with modern electronics.

As soon as you have broadly reliable speed and direction information for specific conditions then functionality of many software packages increases significantly.

2. VMG

VMG or Velocity Made Good can be useful in a number of circumstances and is a function of heading and speed, usually towards a waypoint.

In real terms this means if your waypoint is directly upwind and you set off at a TWA of 45º making 4.5 knots then your VMG will be 2.8 knots. If you set off from the same point with a TWA of 55º and are making 5 knots your VMG will also be 2.8 knots.

In theory, 
all other factors ignored, these two different headings will arrive at the windward waypoint at the same time.

Many of us will probably have used a VMG chart at some point in our lives but having a live reading is helpful to understand how well you are sailing to a destination.

‘VMG is 100 per cent the key number when sailing for me. VMG gives you much more accurate passage planning so enables you to have a more realistic ETA but it’s also so much more useful than boat speed in terms of the actual trim and sailing angle.

‘With most systems able to incorporate current experienced tide and future tide changes within the VMG number, you quite quickly get to the point where you realise how crucial it is. You will see it all the time 
in racing; people’s instruments tell them their best VMG is achieved on a downwind by taking a tight reach into shore and then running out of the tide rather than sailing 
the straight course to the mark.’

A VMG display

It pays to spend some time setting up your instruments to get the most out of them

VMG can take a little bit of getting used to sailing with, as there can be slight lags in the data. As such it is best used to find the best course by luffing 5 degrees and seeing what VMG you get compared to your previous course after the numbers have settled down.

On this note, remember that for the VMG number to be accurate you need to have settled into your new speed for the new heading.

Just luffing 5 degrees without changing trim or letting the boat accelerate will not provide you accurate representation in terms of your VMG number. All of this combined makes steering to VMG very laggy when compared to pure angle or boat speed, which respond more directly.

While VMG alone is useful to tell us we 
are making best progress towards any given point — and makes for enjoyable experimentation in cracking the sheets and footing a bit to see if the loss in angle is compensated by the boat speed gain — there are far more practical benefits too.

It might be that in the example at the start of this section, sailing an angle of 55º is not directly into a seaway in choppy conditions and so delivers you to your destination at the same time but in greater comfort, once you know VMG is the same for both options, you can choose the most satisfactory.

3. Laylines

‘Laylines can be hugely useful to cruisers,’ say Wells. ‘I often consider myself a 
bit technologically adverse when it comes to my sailing, oddly enough given my job. But I like having an idea of whether I’m going to be able to tack to make a headland. It’s particularly useful when I’m sailing shorthanded and want to minimise tacks. There is nothing more annoying than thinking you’re okay to clear a headland and then realising you are going to have to make two more tacks to clear it.’

Beyond just using laylines as a guide, however, Wells says he likes to use them to test his own conclusions and feel for whether he is going to make a certain point when tacking.

‘Quite often I will sail with the layline software running and not look at it until I have decided it is time to tack and then use the software as confirmation.’

B&G SailSteer

B&G’s SailSteer function shows apparent and true wind, port and starboard laylines, waypoint heading, tidal vectors and more, all on one display

Though most sailors familiar with their 
own boat will be able to pick out a reasonable layline, the big boon from decent instrumentation is the ability to add tidal and predicted wind data into the mix.

Almost all the big software packages offer this and it is quite often surprising how much further you need to stand on in an adverse tide to clear a specific point or vice versa.

Again, Eeles is keen to point out that laylines are only as accurate as the data the system is offering, so if your tacking angles are incorrect then the layline can be out, but most systems are able to offer a cone of reliability.

4. Autopilot modes

‘If I’m using my autopilot and I’m not motoring, I will almost always have it set to wind not to course,’ says Eeles. ‘There are several bonuses to this, principally 
it is a safety issue for me downwind. If I want to avoid an accidental gybe then setting to wind is going to help me do that in a way that setting to compass does not. Because of potential surging down waves and increased acceleration I almost always set it to steer to true wind direction. Upwind, my autopilot usually steers a better course than I can and I usually have that set to apparent wind angle, as fluctuations in boat speed are less dramatic.

‘Again, you do need to have confidence you have the right equipment and your wind sensor is free from any masthead objects that might mess up the readings. I think having something that is motion-corrected is important too. If you think about how much a mast moves around when a boat is pitching, that has a significant effect on readings.’

Wells adds that another key to using autopilot to course downwind is that incorrect sail trim tends to have a bigger effect on boat performance than upwind.

While upwind, setting the autopilot to steer to a compass might mean the boat ends up slightly luffing or footing for a time, the likelihood is it will only scrub a small amount of boat speed and significant change is quite quickly noticeable.

Downwind, however, it is easy not to notice that you have become significantly overtrimmed with the boat sailing a set course.

5. Autorouting

A key feature, which has seen significant improvement in recent years, is auto routing software.

With most systems now able to take into account forecasting and tidal information this has become increasingly accurate and useful for cruisers.

Toby Heppell mugshot

Toby Heppell got his first boat aged four and grew up sailing on the East Coast. He has been a sailing journalist for over 15 years. Credit: Richard Langdon

‘Once you have relatively accurate polars inputted, then autorouting becomes a really useful tool,’ says Eeles. ‘We have information from Predict Wind going into our systems and tidal information too, all of which can provide a really accurate ETA and ideal course to steer. Now, you can usually do your passage plan using autoroute on a PC or tablet at home and when you arrive it will instantly appear on your boat systems [provided you have an internet connection].

‘It’s really useful to have autorouting software, which considers wind, tide, VMG and boat performance, but what I find most interesting are the times it wants to send me a route I would not have naturally chosen. 
I will often tweak the suggested route to better fit what I think should be a good route but it is really interesting to see a route that looks to be much further to sail, but because of a variety of factors should be quicker.’

Autorouting serves as a good summation for the electronic aids many of us have on board but might not always use.

Ultimately, we are still at the point where just trusting the numbers is not possible without time 
and effort invested in calibration.

It’s easy to feel there is an element 
of sailing by numbers involved in using software but in truth the human element remains so significant that we are still a long way from that.

Most of us have a range of electronic devices on board, which offer any number 
of functions.

Investing a bit of time into setup makes these tools vastly more useful and can help your sailing by challenging preconceptions, doing some of the hard work for you or just offering confirmation 
that your instincts are right (or wrong).