Skysail Training


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Using telltales  Telling tales - /

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Sailing in light airs

Sail tuning - © Christian Brewer of Hyde Sails 1998  (now with Barton Marine)     

The most common question asked of sailmakers is how to get the best performance when sailing upwind.

As sailmakers we assess the characteristics of the mast and the type of boat as well as the type of sailing to be under- taken to determine the optimum shape and cloth specification. We then take into account slide types, number of reefs, tack offsets, clew height etc. as final detailing.

The Mainsail - What is the optimum shape?
We design our mainsail so that the maximum chord depth is between 45-50% aft of the luff at the mid way point and, as a rule of thumb, the bottom of the sail should be flatter than the top and the depth should be further forward at the bottom. The best place to view the chord depth and position on your yacht is to place yourself halfway along the boom and look directly upwards towards the headboard, racing yachts have draft stripes fitted at the 1/4, 1/2 and 3/4 heights of the mainsail luff for just this purpose.

From this pre-determined shape, we can use the sail controls to maintain the chord position and control depth and twist through the wind range.

THE MAIN HALYARD - always pull the sail up with enough tension to just eliminate the sagging between the slides. As the wind increases the maximum chord depth will migrate aft and we correct this by increasing the halyard tension. With age, the chord position migrates aft to such an extent that luff tension has no effect. When the chord depth has moved to 60% aft, it is time to consider a new sail.

THE OUTHAUL - As the wind increases we need to flatten the sail to reduce heeling, tightening the outhaul helps flatten the bottom third of the sail.

THE MAINSHEET AND TRAVELLER - Together these have a great effect on the twist of the leech and angle of attack of the mainsail. We use leech tell-tales to determine how much twist is required. The most important tell-tale is positioned immediately below the top batten, the rule of thumb here is to tension the sheet so that the tell tale is just flicking behind the leech occasionally. The traveller is used to get the boom onto the centreline in light to light/medium conditions. As the wind increases so does weather helm and heeling so we progressively ease the traveller down the track until a comfortable balance is achieved on the helm.

THE KICKING STRAP - Used in conjunction with the mainsheet, this control has an effect on twist in the sail, the more tension applied the tighter the leech becomes with correspondingly less twist. This control has more effect when the end of the boom is off the traveller line.

THE BACKSTAY - If an adjustable backstay is fitted, tensioning helps to bend the mast thus flattening the sail and opening the leech to reduce heeling and weather helm.

The Headsail - How do I trim my Genoa?
Most modern cruising yachts now come fitted with a furling headsail. The maximum chord depth for this sail should fall somewhere between 38-45% aft of the luff, and as with the mainsail, the sail should be flatter at the bottom than the head and the depth should be further forward in the base than the head. Again, you can view the shape of your sail by lying on the deck half way along the foot looking up towards the head of the sail. The depth of the sail is determined by the type of yacht but generally this sail is deeper than the mainsail.

To alter the chord position, depth and twist through the wind range, the following controls are used:

THE GENOA HALYARD – Tension the halyard just enough to see slight wrinkling on the luff of the sail off the headfoil. This tension is for light to light/medium airs, and as the wind increases, we tension the halyard to maintain the chord position and flatten the sail.

HEADSTAY TENSION – We cut a small amount of hollow into our headsails to compensate for the inevitable forestay sag when sailing upwind. If your sail appears to be too deep off the luff this will seriously affect your pointing ability can be remedied by applying more backstay tension. Alternatively, if the sail is too flat off the luff because of excess hollow will seriously affect the chord position, the boat will point but will not go forward.

LEAD POSITION - Tell-tales are the most important trim guide on the headsail. The objective is, when sailing close-hauled all three windward tell-tales should lift together when the boat is gently luffed into the wind. If the lead position is too far aft when sheeted in, the top tell-tale will lift first when luffing, conversely, if the lead is too far forward, the bottom telltale will stall, (see diagram)

The optimum flying position for the tell-tales when sailing upwind is to have all streaming with the windward ones at 40 degrees up from the horizontal and the lee ones streaming horizontally, perfect trim!

Perfect upwind trim is an interaction of the setting of both the mainsail and headsail, each affects the other, the ultimate aim is to have balance on the helm without excessive heeling, once achieved the boat is sailing at her most efficient and becomes a joy to sail!


Sailing in light airs -  ©  Keith Bater

“We stuck, nor breath nor motion;
As idle as a painted ship
Upon a painted ocean.”        Coleridge - The Rime of the Ancient Mariner      

Fortunately we do not have to suffer like Coleridge’s accursed seaman, but there will be times when getting the best out of your boat in light winds will yield benefits, and you do not have to be racing to see them.

Everyone has a limited tolerance for low speed sailing, and the engine will come on at 4 knots or less, whether it is to achieve a passage plan or from sheer boredom.  But cruising is still about efficient sailing, and finding an extra half-knot or more can be very satisfying

If you do race on occasions, then what follows might be even more useful.

The boat

Excess weight is as useful on a boat as a garden roller.  William Boeing said ‘Simplicate and add lightness’ which applies to yachts equally as well as aircraft.  Naval architects estimate that ships accumulate weight remorselessly at 2% or 3% per year, and some cruising boats do the same. Take any opportunity to get rid of weight.  The times we did really well in the Round the Island Race, the boat was relieved of as much excess weight as possible. The bower anchor, chain, water, fuel, spare sails, warps and dinghy were all easy to remove.  Pump the bilges.  The boat floated a few inches higher, and the difference in overall performance made it very worthwhile.  Boat speed, acceleration out of the tack and general responsiveness were all noticeably better.  The reduction in wetted area reduced drag, and scrubbing the waterline helped further.  If you have a smooth bottom (nothing personal intended..) that will help too.

Boats with a fixed prop will always have to contend with high drag, which has been likened to towing a bucket.  If the budget allows, consider a feathering or folding prop.  In light winds you will immediately see results.  Comparing the various alternatives can be hard work, but they all work and to a degree you get what you pay for. 

Make sure everything works smoothly and reliably – blocks, traveller, genoa cars, clutches, and winches.

Boat Trim

In general, get the transom out of the water by shifting weight forwards, this helps to reduce turbulent water and drag at the stern.  Some heel to leeward helps air flow over the sails as gravity helps the sail to keep shape, and can also reduce wetted hull area.  If the boom flops around, get someone to lean against it to keep it still.

Sail Trim

Fit tell tales behind the genoa luff and to the leach of the mainsail. They are vital for observing trim.  In light winds take some tension off the halyards, a few horizontal creases are allowable.

Ease the outhaul to allow some draft in the mainsail , this gives better acceleration particularly if the wind is fluky or the sea has any slop, and the boat is being stopped.  If the wind is very light or more consistent, or the sea is smooth, you can flatten the main to help the airflow and increase boat speed.

There is always an effect called ‘wind shear’, because the wind at the head of the sail is faster than at sea level, where surface friction slows the movement of air.  In light winds this effect is more pronounced and you need to let the sail twist at the head, so the top of the sail will point higher than the foot.  Upwind and off the wind, set the main traveller to windward so the sheet does not pull down on the boom.  Boom position will be a little more to leeward than normal. Don’t use the kicker; this allows the main to ‘twist’ in the upper section, so the angle of attack is higher at the head.  You can achieve the same twist effect for the genoa by moving the car further aft than normal.  

Make the sure the ‘slot’ between genoa and main is slightly open. A tight genoa and eased mainsheet will kill the boat speed.  When manoeuvring, get the main in before the genoa, or when easing sheets, genoa out before the main.  Don’t let any crew sit in the slot.

Always keep the boat moving, sail round in the tacks and bear away slightly with sheets slightly eased before coming back on the wind and bringing in the sheets. Avoid pinching too high, you will slow down and it will take time to accelerate.

If you can see wind on the water, use it.  It is more important to be where the wind is, than sail an absolutely correct course.  Or to put it another way, the correct course is where the wind is!   Similarly use the tide. At low boat speeds the tide has a much more important relative effect on your speed over the ground.  Get inshore when the tide is foul, further off when it is favourable. If racing, a kedge anchor is an essential weapon if you find yourself going backwards.  Before engines were in normal use, sailing ships and cruising boats kedged frequently.

Finally, sudden movements on the boat will disturb the sails and airflow, so give the crew plenty of warning if they need to move.  Keep rudder movements to a minimum and move the rudder slowly, they all add drag.  Avoid any hint of weather helm for the same reason.

If all else fails, ease any control at random, it is surprising how often it works.

A lot of this is obviously oriented to the racer, but a fair amount can be applied by the cruisers among us.  Even the Ancient Mariner might have found the ship moving!

posted 25th January 2012