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Tips on Sailing a Small Trimaran                                             

PART 4      Sailing in Waves … Upwind & Downwind

First, permit me a personal flashback. My first introduction to this fascinating subject was around 1955.   If I close my eyes, I can still visualize a table in a local British pub, with the noted British small boat designer Ian Proctor* and the local ’golden boy’ John Oakeley, discussing Ian’s newest designs and how to sail them in waves.  At 22, John was a crack 12ft National and Merlin-Rocket skipper based at the Hamble River SC where I sailed.     Here’s a pic from those days of how I remember John.  (He went on to become one of Britain’s finest sailors, later knighted and was a skipper chosen to represent Britain in an America’s Cup challenge).   It was a fascinating ‘meeting of the minds’ that encouraged me to pay attention to the subject over the coming years.  

  *designer of the Osprey, Wayfarer, Gull, Topper & others, from which over 60,000 boats  were built.

Both Ian and John went on to become authors of their own books and some still sit in my bookcase.   Ian also encouraged me with something else.

“While you cannot see either wind or current, you can certainly see their effects;  so use your eyes to learn all you can from how things that you can see, interface and are affected by them”.

Ian constantly did that, so I know he would appreciate the small video clips I’ve included below ;)   His books became full of illustrations of curling winds & currents and how they can dynamically affect our sailing efficiency.    

His 1953 book on Sailing Wind & Current is still a fascinating read.

First, let’s agree that even though there are both good and poor ways to sail in waves, sailing in flatter water is almost always faster (except if surfing downwind), so keep this in mind when planning your course.  The effect of waves on a boat will also vary with boat shape and weight, with slim vertically-sided boats like the W17 doing relatively better than others with more vee’d sections and higher keel rocker.

Before we get into the ‘how’ of sailing with waves, we need to grasp a basic understanding of what waves are and how they move, both real and apparent,  so let’s dig right into this.

Wave Basics

First let me say that despite all the theories out there, there’s really NO ‘standard’ wave in the real world, even though we’re going to try and simplify things by showing one here.   Each one varies in height and length and they can grow and dissipate in remarkably short time.    Open water waves are in fact one of the most complex bodies to analyze on this planet and, like leaves on a tree, not only do they both grow and die repeatedly, but there are probably no two exactly alike.   


Although wind is the prime driver, they are also affected by numerous other factors like varying gravitation forces, proximity of the seabed, magnetic fields, water temperature, specific gravity and so on … all subtle forces and influences that we cannot even readily see, let alone evaluate accurately.   

Even in the photo of this small wave sample, one can hardly find 2 waves alike and the sample ‘contour chart of ocean waves’ certainly further confirms the variation to be expected.

One of the most common forces that upsets ‘the perfect theoretical wave’, is another wave that moves over the same surface from a different direction, caused perhaps by reflecting off steep cliffs, some nearby headland, strong turbulent winds, or even by a large boat passing.  Even in the open ocean away from land, waves vary constantly and sometimes unexplainably compound in height to create the occasional ‘rogue wave’.   All we can really be certain of, is that ‘natural waves will grow and decay’ and are primarily a response to wind over the surface.

“Whew!” … with that intro, one may wonder if it’s even worth writing about this at all!    Well, I still think so, as there are certain characteristics of waves that need to be understood, with ‘better or worse’ ways of dealing with them, regardless of their variable size or irregularity.

First, let’s consider this typical quote that I’ve seen on line in several versions.

“Just took one look at the waves travelling past my harbor entrance at 7-8 knots and I knew it would be useless to go out, as I can only make 5kts with either my motor or sailing to windwardl”.

So where do you stand on this?   If it makes sense to you, then read on.  If not, then jump this section entirely as you’ll not need it.

Versions of the above quote are surprisingly common from those new to sailing but even persist with a few sailors who have not studied the subject.    This section should help.

What I will try to show the reader is this.  The problem with the quote is that while waves may ‘appear’ to move at 7-8 knots, the actual water you will be moving through is hardly moving at all and most of the resistance you will feel is from wind resistance, not adverse wave speed.   So here goes.

First, let’s do a little visual experiment.    Imagine something like a clothes-drying rack with a strip of heavy plastic or tarpaulin hanging over it.    Let it sag as per this sketch, to look like the trough of a wave with the end rods being the crests.   Now take a free length of rod and starting at the end ‘A’, sweep the rod under the plastic, horizontally over towards ‘B’.   You will create a simulated crest travelling from A to B, but the surface, although moving slightly back and forth as it moves up and down, does not itself move with the visually moving simulated wave crest.   While a real wave is more complex than that, the surface affect is somewhat similar.

First, as the total volume of water is not changing every minute, there must always be a trough below the mean waterline that offsets the raised water in the crest.

                         (In above sketch, R is radius of a circle that has a circumference of L, and H = wave amplitude)

For well over a century now, naval architects have used the assumption that waves take on a profile as created by a trochoid – the trace of a point on a rolling circle.   It’s not 100% precise but close enough (see sketch above) and if one notes the small arrows, clarifies that the direction of surface water particles actually change momentarily as ‘the wave’ passes …. moving WITH the wave near the crest, but AGAINST the wave in the troughs, so that the water mass between each peak effectively returns to its original location before the wave passed.    If this trochoidal plot and rolling circle makes little sense to you, think of it this way.

In the above sketch, the wave is coming from the right.   So the water-surface-height at any one spot on the wave, will soon change to be whatever it is to the right-hand side of that spot.  So on the right-hand side of this sketch, the crest will soon replace the trough so the water-surface-height will be rising (just as the arrows show).  But on the left-hand-side, the trough will replace the left-hand crest, meaning the water-surface-height must drop … again as indicated by the trochoidal  arrows.      Still unsure about this?     

This short video should also help.  Here you’ll see a leaf right at the surface.   Light enough to be easily moved by any water movement, but almost totally out of any wind.  

                             [When this YouTube stops, another YouTube may appear on totally another theme!  I will try to fix that.  Until I do, please hit REPLAY (bottom left) and then again for (PAUSE) to Stop and re-set the video, and then continue reading]       

You will see the leaf move forward ‘just a little’ with the wave crest (to the left) but then pull back in the trough (to the right), so overall, it just stays where it is while the crests just keep rolling by … a clear demonstration that those seemingly high speed waves are NOT the moving mass of water they first appear.    To see this for yourself, throw in a small 50mm square of plywood and watch it.

But sometimes, a secondary system of waves can come in at a different angle and ride on the back of another wave, creating a steeper one with even more speed.   When the wind is also strong, the top crest can be rolled-over, forming breaking whitecaps.  Now these whitecaps DO try to stay on the moving crest, meaning that the whitecaps actually DO move at the apparent wave speed, so, for as long as they stay, whitecaps justify a LOT more attention and respect.    

Here’s a short video showing this.   The crests of these waves are starting to curl over and if a leaf were to be caught in the ‘whitecap’, it would suddenly take off just like a surfer.  In the video, you’ll see that the foaming crest or ‘whitewater’ IS now moving with the apparent wave speed, until it falls off the back of the wave and then dissipates.  


So why all this explanation ?   It’s to help clarify what is happening at different parts of every wave, to better understand the suggestions below, on how to sail both against and with waves to your best advantage.

SAILING upwind against waves

The first thing I would suggest, is to do all you can to have good speed.   Trying to ’pinch and inch’ your boat to windward at slow speed just does not work when waves are slamming you back.  You need some weight and speed to punch through.    A fine boat like a slim trimaran hull with a L/b ratio of 9 or more will certainly help, but if you’re in a mono, keep your weight as far forward as the freeboard will allow, as that weight will not only help you punch through the rough stuff but the hull shape now presented to the waves will also be finer and pass through more easily.

With a trimaran like the W17, I like to keep the mainsheet traveler slightly to leeward and then have the mainsheet tensioned to keep the leech fairly tight.  Sail with the upper windward jib telltale slightly lifting to assure you’re not close to stalling the sail and if you DO find you need to bear off a little, ease off the sheets a little to match.   If you’re overpowered, ease out the mainsheet more to feather the leech but pick a comfortable speed for good steerage, neither too slow nor too fast.   Avoid white crests if you can or cut into them nearly head on … quickly bearing away after you make the initial cut.

With a slower monohull, I’d suggest to have the traveler closer to midships but with fuller, more twisted sails than you might set in smoother water.   Easing off the outhaul slightly can also give a little more fullness & drive, but only ease a little.

For the jib, the sheet lead can be slid aft a little, to not only keep a parallel slot with the main but to also permit you to sail ‘up and off’ the waves without risking a stall.  (A stall will occur if your sail is too tight or flat, relative to your heading with the wind).   As each boat and rig varies slightly, experiment a bit with the above as a base. Particularly with monos, while fullness should not be excessive, slightly fuller sails can work better upwind in waves than having them too flat.    The top telltale on the mainsail should be streaming aft all the time.  When steering over waves we need to recall what was explained earlier in this article; that surface water is moving downwind at the crest but upwind in the trough. So one needs to sail ‘a wiggly course in order to spend as little time as possible in the adverse crest but more in the quieter trough water that may even be moving with you.  The diagram above will show how this works.

Always keep in mind that excessive use of the rudder will add a braking force, so whatever can be done to help turning through boat balance and sail trim, will reduce rudder use and potentially improve your speed.   So to luff, allow the boat to heel a little, but to bear off, keep the boat flat by hiking out and ease off the mainsail.     If it’s really bumpy with waves and you’re changing direction through quite an angle, you risk to stall the main if you have hammered it down too tight.   So ease things out a little in such conditions and set the jib to match.   Better to have sails too-far-out than too-far-in.

Sailing in Light Air and a Chop       

This is one of the toughest sailing challenges and few sailors have the concentration to excel in such conditions.  It also doesn’t help when your telltales aren’t working or that your sails are being thrown out-of-shape by wave action.

Try to keep the flow around both sides of the sail as consistent as possible as this will help to keep your drive and speed more constant.  This is more important than just a few high-speed bursts, as being slowed nearly to a standstill and then having to re-accelerate back up to speed, is slower overall.     Particularly in very light winds, keep the boat, mast and sails as ‘still’ as possible.

Trim the boat to heel to leeward a little and keep the bow well down and the transom out. This will help you to steer when there’s hardly enough wind for it.   Get a firm sense of where the wind is coming from, and even if it’s not always visible on the water or sails, ‘assume’ it’s there unless other signs clearly show it’s moved and move VERY slowly around the boat to not disturb the precious but invisible air flow.   Again, keep the mass of your boat moving at all costs even if very slowly.   It’s only then you will have steerage to make adjustments to any wind changes. 

If there are waves along with little wind, it may well pay to spread out your crew weight to dampen the ends and reduce the bobbing …. the contrary of what you would do in stronger wind, when you generally want to sit close together to keep the ends light.   Either way, I suggest to keep the bow down lower than the stern.

Push the jib sheet lead forward and ease the outhaul on the mainsail, making certain that the sail has good camber by manually pushing the clew forward. If you sheet sails too tightly you will see the leeward telltales rise, indicating a stall and a large loss of power. Only trim sails in when you sense a speed increase and be prepared to ease them out again if the speed drops.

In very light wind and a chop, keeping some twist in the leech (particularly with a beamier monohull) will allow for best flow and better suit the varying angle of attack caused by the wave action on the boat. But be ready to tighten the leech and reduce twist as the speed and wind picks up.    Follow the general track over the crests as shown in the above sketch and play the mainsheet by tightening a little where you sense good speed but ease off again if you’re slowed up.  Keep weight forward.

If the waves are very irregular and you see no pattern to sail across, try to aim for the lower spots and steer to miss the highest ones.  It’s crucial to maintain good speed though and not pinch too close to the wind, as you need good steering to able to pick your way through this wiggly course.

Sailing Downwind in Waves

This is another exciting part of sailing

Handling a strong gust … should one luff up or bear away ?  This is often a difficult call as there are many variables …...  a major one being the angle you are sailing to the true wind.   If you’re sailing above a beam reach, it’s generally quicker and safer to ease up into the wind to spill some off the leech, but be prepared to haul in the mainsheet to tighten the leech once the main gust has passed.  What is NOT a good idea is to round up into the wind too fast as centrifugal forces then add to the heeling effect of a gust and risk to capsize you.    Ease off the mainsail (and any overlapping foresail) until it luffs and then turn slowly upwind until you’re close to 50 deg. off the wind, then, with things more under control, haul the sails back in to keep the speed up to work through the wave tops. 

If you’re already heading slightly below 90 deg to the wind, you have the option of bearing off but be aware that if the wind is strong, it will try to bury the bows so make sure your mainsheet traveller is out as far as possible but do not allow too much mainsail twist (ie: keep mainsheet fairly tight but with the mainsheet traveller fully out).  Also, move all your weight rearward as you bear off and keep the boat flat.   Before doing this, make a quick check of a land reference point and the true wind direction to make sure you don’t bear off too much and accidentally gybe.

Let’s now consider that ‘the rhumb line’ (the line that takes you directly to where you want to go), is directly downwind.   With a monohull, you might sail directly on that line, using a spinnaker or boomed-out foresail, but with a multihull it’s generally faster to sail higher, on a broad reach and periodically gybe.  Look ahead for flatter areas, especially for the gybe.     Riding waves is great fun but you need speed to catch them and if you don’t have it, it’s best to not deviate far from your line to find a wave that just throws you up-and-down.  To keep the speed as constant as practical, luff up a little in the lulls and bear away in the gusts.     A lot of energy is wasted if the boat has to be constantly accelerated, so striving for a more constant speed is more efficient.

If you’re sailing slower than the waves are coming at you from behind, it can help your speed downwind if you can place your transom in front of the larger waves.   But as soon as you start to feel the thrust, throw your weight rearwards to lighten the bow so that it can lift more easily.  If you need just a little more speed to stay with the wave, momentarily turn slightly to a reach and once matching the wave speed, bear away again.

If you are using a boom vang, tighten it to try and hold the increased speed.  If there’s enough speed to potentially catch the wave in front, look for a low spot to break through.   If you do break through, throw your weight forward as you cross the crest and then back again as you start to ride down.    (Ian Proctor used to say ‘it’s like jumping a horse in a steeplechase’ ;-)

Once you’re surfing, turn more to a reach to stay as long as possible on the face of the wave.   If your speed is faster than the wave, look for a low place to break through.   If the wave is faster, sail as fast as possible by reaching in the troughs, but bear away as the wave crest reaches the transom and ride as long as the speed is up but go back to a reach as the crest passes under the boat and your speed slows.

I hope I've covered the basics but if high performance sailing really interests you, here are 3 or 4 books worth reading:

Sailing wind and Current …. by Ian Proctor

High Performance Sailing …. by Frank Bethwaite

      Go for the Gold …. by Garry Hoyt


This is Downwind Sailing …. by John Oakeley  (good for regular spinnaker handling)

Although the above series covers many things unique to the small trimaran, for time-honored Sail Trim Basics, there are now some excellent YouTubes, particularly those by North Sails who are arguably the worlds expert on sails, especially since developing their 3D technology now used by most top-flight boats post 2015.   Here are some favorites I can recommend.

Trimming your sails.  Although this is mainly for monohull rigs with a flexible mast, not for rigid rotating wingmasts … the end target is much the same.   So references to boat heel, backstays, spinnaker poles etc. will not apply, but there are still many excellent sail adjustment basics here that are well worth understanding, learning and practicing.

And for Trimming your Asymmetrical, here is a very thorough (one hour!) analysis ..  …again by North Sails

Hope you enjoyed this series and please send in your comments and any of your own experience. And remember, ‘practice makes perfect’, but as wave & wind conditions are NEVER the same, one never stops learning ;)

   See other parts of this Series,

Part 1:  Basic Sail Attachments;  Sail Tension & Shape;  Setting Sails;  Booms;  the Jib;  Boat Trim;   Sail Trim & Sail Camber;   Sailing Downwind     

Part 2:  Tacking;   Mainsheet & Leech;  Mainsail Foot tension;  Bearing off;  Wing Masts – Control & Adjustment;  Mast Section shape;   Mast rotation adjustment;  Mikelin

Part 3:   Tell-Tails;  Tell-Tails Location;  Tell-Tails Upwind;  Tell-Tails Off the wind;  Popular Sayings

Part 4:  Waves;   Wave Basics;  Sailing in Waves;  Sailing upwind  against Waves;  Sailing in light air & chop;  Sailing downwind in Waves


(Your comments, personal tips and questions are always welcome ..

"New articles, comments and references will be added periodically as new questions are answered and other info comes in relative to this subject, so you're invited to revisit and participate." —webmaster