Headsail Trim - Getting it all together
by Andrew Dove, Area Manager North Sails Caribbean on 9 Dec 2007
Getting the tensions right will optimise your headsail’s performance SW
You may have been cruising for years, but are you getting the best out of your sails? An extra helf knot can help make the difference between getting to shore before dark, or beating that storm that is threatening. It can also sometimes help turn a six day sail into a five day sail, expecially if you have a personal rule(as we do) not to go into strange anchorages in the dark.
Andrew Dove, Area Manager for North Sails Caribbean, writes this week about getting the trim of your headsail right to go smoother and faster.
The Headsail is most probably the principal driving force of your boat, from reaching to going hard onto the wind. To maximise the drive, you have three principal parameters to master—the Halyard Tension, the Car Position, and the Sheet Tension.
Halyard Tension:
If your boat has a furling unit or a Tuff Luff type extrusion, then initially hoist your sail to full hoist without any real tension. Point up until you are sailing a windward course sheet in, then tension the halyard until you remove any horizontal folds.
Do not over tension, as this will do little more than increase the wear and strain on your sail. Sail shape can be modified around this standard adjustment. Certainly in light airs a fuller shape, even with a few small horizontal creases, will be fast. If you ease halyard tension, be careful when you furl as you may induce a halyard wrap. If you have a hanked on headsail the same logic applies, but you will most probably need a little more tension to avoid bellowing of the luff between the hanks.
As a general note, halyard tension is easy to adjust with a good halyard and impossible with an old or stretchy one.
When partially furling, horizontal or oblique creases may appear in your sail. It is often possible to absorb these with a little luff tension. A poorly designed flattening system will create oblique creasing and your sail maker can generally, with a small intervention, correct this.
When adjusting the halyard tension, do ease the sheet a little and luff gently. It is useful to put a mark on your halyard at the clutch or other practical place to enable rapid halyard set up.
The Car position
As a general rule the initial car position can be set such that the extrapolation of the jib sheet cuts the luff at just over the half height. If there is a good breeze move the car back a little. This will help the leech to twist, allowing air to flow more freely, reducing heel and increasing speed.
If you are not hard on the wind, move the car forward to maintain reasonable leech tension and add shape into the lower sections of the sail. As you bear further away, move the car forward if you can fit an out board sheet to allow slot or gap between the foresail and the main. With greater flow the boat gains on drive and stability.
On furling headsails you need to move the car forward as you furl the sail to maintain a correct sheeting angle. Use the same basic rule of the prolongation of the sheet to the luff as your guide.
The Sheet tension.
This adjustment depends upon your relative angle to the wind and its strength. On the wind you will generally sheet in until the leech of the sail sits close to the most prominent spreader end. As you bear away ease the sheet such that the luff is at the limit of back winding. To be more precise one needs a little help. Most sails should have telltales. Otherwise know as tufts, indicators, flappers or woollies. These are generally either in wool or nylon and can be simply stuck to the sail. If you do not have any most sail makers will either give them to you or sell them cheaply. These can be positioned roughly 10% back from the luff at a height of say 25, 50, and 75% of the luff. One is stuck each side of the sail, either back to back or one slightly above the other. Do avoid positioning near a seam as the telltale will get caught up on the stitching.
The telltales indicate the direction and quality of the air over the sail. Without over complicating things, the usage of the telltales is a little different if sailing hard on the wind or freed and sailing for speed. The telltales near the luff of the sail are used as a steering aid when sailing upwind. If you are pointing too high the windward telltales 'stall', i.e. point straight up or stream forwards or twirl around restlessly. If you are sailing too low the leeward telltales hang down and die, and the whole foresail is about to stall.
The windward telltales indicate different things depending of the wind strength. In light winds your heading is correct generally when the windward telltales are just about to twirl. In medium winds the best speed made good is achieved when the windward telltales jump up at steady intervals. In heavy winds heal becomes more of a factor and the windward telltale may often be disturbed.
Otherwise if sailing freed then basically the sheet should be adjusted to maximise flow over the sail. If the windward telltale points upwards then you need to sheet in. If the leeward telltale drops then ease the sheet. Having three levels of telltales is the key to adjusting the car position. If you luff slightly all being perfect the windward telltales should lift all at the same time. If the higher telltale lifts early you should sheet a little further forward. An early reaction of the lower telltale suggests that you should move your car a little further aft.
Other factors
Once the basics are sorted the leech and foot line of your headsail should be adjusted. The foot line is rarely so important, though should be tightened such that any foot flutter is removed. The sheeting position has an effect on the foot tension.
Of probably greater importance is the leech line adjustment. Here again I return to one of my recurring nightmares, bad halyards. If halyard tension is lost then the leech will flutter. If a sail has a reasonably smooth exit on the leech then the leech line tension will need to be increased as the wind builds.
If your sail is really full or built out of a stretchy low performance fabric then its depth may be adequate to not require leech line tension. If the load line that runs just few within the sail is shorter than the curve around the leech then the leech will flutter and line tension will be needed until the outer curve becomes the shortest distance in space between the head and the clew.
A very full poorly designed cruising headsail may by its depth have a tight leech. The leech tapes may become tight as the sail cloth of the sail itself stretches, or more precisely the tapes may shrink at a greater rate than the body of the sail. A tight leech or the need for excessive leech line both create disturbance in the air flow and a slow sail. These issues can generally be corrected by your sail maker.
Depending on your rig good forestay tension is a key to sailing well to windward. If you can adjust your backstay then do try to maintain forestay alignment with increased tension. As you adjust check your rig and mast reaction. Again do not hesitate to ask for help. In the Caribbean we have some very competent riggers and if all fails ask your sail maker as a second best option.
To finish this section on the headsails, a few words on furling. You should come off the wind, ease the sheet and begin to furl. Keep a little tension on the sheet to ensure a smooth furl. We have a number of sails where the white UV cover is furled on the inside by mistake so do furl with the UV cover on the exterior of the sail and your sail flattening system should be on the inside. If it's hard to furl your sail away then bear away a little more and ease the sheet a little more. Before you force, however, look up and check that the halyard is not wrapping around the furling unit. If furling is still difficult have
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