There are four basic trimming tools that need careful attention in order to get the best from the spinnaker. These are pole height, pole position fore and aft (angle of attack), sheet tension and sheet angle.
|Correct pole height and the right angle fore and|
aft are critical components of spinnaker trim
Usually, the pole will already be up (or will at least be in the process of going up) when the spinnaker is hoisted. The pole should be set to a pre-determined or default height that you know is more or less correct, make sure that the pole topper is marked accordingly! Once the sail is up and filled it is time to start fine tuning. On most boats the first point of reference is usually the relative clew heights. Use this as a guide by all means, you probably won’t be too far wrong but do not use ‘even’ clew heights as gospel! Another useful indicator is the orientation of the centre vertical seam in the sail. This should be more or less perpendicular to the water. When combined with the other trimming aids which we’ll come to shortly, this is probably a better reference than relying on the height of the clews. However, the most useful indicator of whether or not the pole is at the correct height is the way that the luff of the sail breaks as the sheet is eased. What you are aiming for is a nice even break from top to bottom or a break that begins just above the mid point; if the pole is too high the top of the sail will lift and twist off and the sail will collapse from the bottom. If the pole is too low the top of the sail will be pulled towards the boat causing the break to begin higher up. In other words, if the top of the sail is breaking too early then the pole needs to go up a little. So, in order of priority, to set the pole height correctly, firstly look at how the luff is breaking, secondly check that the centre seam is vertical, and thirdly use the clew heights as a reference.
Within its range of settings, the pole height will need to be raised and lowered (i.e. adjusted) according to wind speed, sea state and wind angle. In lighter airs the pole needs to be lower to maintain some tension in the luff, keep the sail stable and hold the draft forwards towards the luff. The same applies to sloppy or choppy conditions; the sail will be more stable and easier to fly with a lower pole.
The pole height of course does have a bearing on the aerodynamic shape of the sail though this is more of an issue when reaching when you actually have air flowing over the sail, i.e. the sail is behaving like an aerofoil rather than a ‘barn door’ in downwind mode. Setting the sail with a lower pole pulls the draft forwards in a similar way to pulling on the Cunningham in a mainsail or increasing halyard tension in a headsail. Pulling the draft forwards flattens the back of the sail, encourages it to twist which helps to depower it. Similarly, raising the pole flattens the entry meaning that you can point higher but it will also let the draft creep aft which will increase drag and heeling moment. Again there is a balance to be found, this time between being able to point and managing heel.
If the inboard end of the pole is set on a track, i.e. it is movable, then make sure that the pole is set to horizontal which will help to project as much of the sail as possible from behind the mainsail.
As a rule of thumb, the pole should be positioned fore and aft roughly perpendicular to the apparent wind, use your burgee or wind indicator as a guide. Another useful reference point is that the main boom and the spinnaker pole should be more or less in a continuous line through the mast though in reality the spinnaker pole will likely be just forward of this point. The general idea is to square the pole back as much as possible in order to present more of the spinnaker before the wind. However, it is easy to over do this and the pole should never be squared aft to the degree where the foot of the spinnaker ends up being pulled tight against the forestay. Having the pole too far aft will also make life difficult for the sheet trimmer as the luff of the sail will be continually twitchy.
The sheet trimmer and guy trimmer need to continually communicate in order to get the most out of the sail and the sheet trimmer in particular also needs be having an almost continual dialogue with the helmsman in order for trim to be most effective. As with pole height, the position of the pole relative to its base position may depend to some degree on sea state and wind conditions. For example, in sloppy conditions when the boat is bouncing around it may well be easier for the trimmers (as well as faster) for the pole to be set just a little further forwards than usual in order to keep the sail drawing effectively.
Spinnaker trim is a dynamic process; the sheet should be continuously moving in order for the overall trim to be optimal. The trimmer should ease the sheet slowly and smoothly until the luff just starts to curl and then trim it on just a touch to prevent the curl from becoming excessive. As soon as there is no curl the sheet is eased again and the whole process continues. The guy trimmer is also looking to move the pole aft where possible and needs to monitor what the sheet trimmer is doing. The sheet trimmer should be talking to the helmsman about ‘feel’ and ‘pressure’. If the sheet feels too light the trimmer needs to let the helmsman know so that he can steer a little higher (tactics and other boats permitting). Once the speed has built and the pressure in the sail feels better the trimmer can let the helmsman know that he can come down a couple of degrees. Again, the whole process is continuous.
There is no magic angle to sail, it will depend on the type of boat, wind speed, wave state and position of other boats but hard work, good communication and appropriate focus will certainly get the boat to the leeward mark more quickly than those adopting a more passive approach.
On most boats the spinnaker sheets are led aft to a turning block somewhere near the back of the boat. This kind of set up may be fine some of the time but leaves no room for adjusting the downward component on the sheet tension which in turn controls how the leech of the sail twists and behaves. Therefore, assuming class rules allow it, the spinnaker sheets should be led through adjustable ‘twinning lines’ (‘twinners’ or ‘twings’) which provide the sheet trimmer with a greater degree of control over the overall sail shape. If the sheet lead is too far aft the clew of the sail might be inclined to lift up causing the leech to become too twisted with this in turning having a bearing on how the luff is shaping up. The tack of the sail might in this instance appear to low, the trimmer calls for the pole to be raised to ‘get the clews’ level and the whole sail ends up being set too high with subsequent loss of performance. Of course it is also possible to have the lead too far forwards in which case the leech of the sail will become too tight and the sail will be pulled to leeward, again compromising performance.
As with the other points above, get the luff correct first and then use the twinners to fine tune the leech. Bear in mind that the twinners will often be used as a means of moving the sheet lower away from the boom. That’s fine in principle but take care that the shape of the spinnaker isn’t being compromised at the same time.
Mark the pole topping lift and downhaul so that they can be pre-set into a position that is more-or-less right as you approach the windward mark and before the spinnaker is even hoisted.
As the pole is being moved fore and aft the pole downhaul will also need continual adjustment. Make sure that its default position is on hard to prevent the pole bouncing.
Similarly, put some marks on the ‘lazy guys’ at a position which you know provides the bowman with just enough slack to complete a gybe.