Spinnaker Trim from Dave Dellenbaugh's Speed & Smarts
For this reason, the art of spinnaker trim is far from an exact science. In fact, we won't even use quantitative numbers to describe spinnakers. We'll talk about general concepts and how certain controls affect trim and shape.
As you bear off, more of the flow becomes separated, until on a run most of the sail is stalled. The point here is not to say that spinnakers don't want attached flow. As with other sails, the more flow the better. It's just that flow is harder to get with chutes, so you have to be very careful not to overtrim. The last thing you want to do is help create separated flow.
Constantly play the sheet to keep the luff on the verge of curling. It's much better to keep the sail a little undertrimmed than take any chance of overtrimming. Of course, this means you have to keep a grinder ready to trim when the luff curls too much.
You can see how often spinnaker flow is stalled by placing telltales on the leeches, about a foot in from the edge. These telltales will actually help you keep the sail working when you're on a reach. As you bear off, however, the telltales will inevitably stall and lose their usefulness.
The basic principle behind spinnaker shape control is simple. The closer the leeches are to each other, the deeper the sail is. In this regard the spinnaker functions very much like a mainsail or genoa. For example, when you ease the main outhaul, the lower leech of the mains moves closer to the luff, and the sail gets fuller. The spinnaker is similar, except that its luff is not fixed to a forestay or mast.
Think of what happens when you lower the outboard end of the spinnaker pole. Both of the clews get lower (the leeward one not as much as the windward), and the leeches simultaneously get tighter. As the leeches get tighter, they move closer together, so the sail gets fuller.
Now raise the outboard end of the pole. As the clews move up, the leeches get looser and move apart from each other. So the sail gets flatter. It's important to understand that raising the pole flattens the spinnaker.
Pole angle -- When you are sailing with the apparent wind at 120 degrees or greater, the spinnaker pole should generally be square to your apparent wind.
For example, let's say you're racing on a broad reach with the apparent wind at 140 degrees. Your pole should be squared back so it makes a 50-degree angle with the boat's centerline. This will keep the pole 90 degrees to the apparent wind and project the chute as far as possible from the mainsail.
When reaching, however, the situation is a little different. Here your pole must be "oversquared" to keep the spinnaker flat. Squaring the pole to the apparent wind would produce a sail shape that is too deep and inefficient for reaching.
Pole height -- On a reach or broad reach, the newer chutes tend to be very forgiving of changes in pole height. Their clews seem to stay pretty even no matter what you do with the pole. Nonetheless, there is almost always an optimum height for the pole.
Setting the spinnaker pole height is a bit like moving the genoa lead. Your goal with the genoa is to find the lead position that makes the telltales break evenly all the way up and down the sail. The same is true with the spinnaker. You want to find a pole height that gives the luff a consistent angle to the apparent wind.
It's possible to put telltales along the spinnaker leeches to help with this. But since the flow around a chute is stalled so much of the time, you can't rely on telltales (except when reaching). A better guide is simply the curl along the spinnaker luff. Your goal is to make the luff curl as evenly as possible up and down the sail.
If you set the pole too high, the lower leech will curl before the upper leech. If you lower the pole too much, the upper luff closes down and will curl first. Don't be afraid to experiment and try to learn what setting is fastest.
Pole height on a beam or close reach depends partly on whether you lead the sheet over or under the boom. When it's led over the boom, your chute will have a high clew, flat foot and open head. This is a good attitude in heavy air, when the high clew opens up the leech to give you a cleaner exit. (Over-boom sheeting is not advisable on a fractional rig, as it will restrict the main boom too much.)
When the spinnaker sheet is led under the boom, the chute assumes a deeper, more powerful and easier to fly shape suitable for flat spinnakers and underpowered conditions. In this case, the pole needs to be lower. On close reaches (50 degrees to 90 degrees apparent) the need to trim the sheet hard sucks the clew down and also requires a correspondingly lower pole position.
Sheet lead -- In general, the sheet should lead to the stern for reaching. This keeps the leech from getting too tight and overpowering. As you square to a broad reach, move the lead forward to a snatch block on the rail. This adds power by preventing the leech from twisting off too much. It also helps stabilize the spinnaker's shape in waves.
Inboard pole end -- Always keep the inboard end of the pole even with the outboard end so the pole stays horizontal. This keeps the spinnaker as far away from the mast as possible. The inboard end should be adjusted automatically whenever the topping lift is changed; it shouldn't require an extra command from the helmsman or trimmer.
Depth -- As we discussed earlier, depth in the upper part of the sail is most affected by clew height. Raising the clews allows the leeches to open and the shoulders (the upper part of the leech) to spread out. These changes flatten the chute, contrary to popular belief. Lowering the clews pulls the leeches straighter and closer together, adding depth to the upper sections.
Depth in the lower half of the chute is controlled by the lead position, much like a genoa foot. Moving the sheeting position forward adds depth. Commonly, people lead the sheet too far aft on a broad reach, getting too flat a foot.
On a broad reach or run, depth is also affected by the angle of the spinnaker pole to the wind. As we discussed above, over-squaring the pole (trimming it beyond perpendicular to the apparent wind) forces you to trim harder on the sheet to keep it full, which in turn flattens the sail. This is a good idea in heavy wind and seas, when you don't want a full spinnaker rolling back and forth from side to side.
Under-squaring has the opposite effect. It allows you to pay out extra sheet, float the chute well in front of the bow and deepen the foot. This is often fast in lighter air and lumpy water.
Draft Position -- The position of draft in a spinnaker is controlled by the relative heights of the clews. The old maxim "make the clews even" is not so true any more. On a reach, judicious clew juggling affects the draft position. Lowering the tack moves the draft forward and adds twist. Raising the tack lets the draft aft. An all-purpose spinnaker should be flown on a reach with the clews even or the tack slightly lower than the clew, putting the draft at 40-50% aft.
The tack position (as adjusted by the pole) has a major effect on draft position, upper luff behavior, and the angle of attack of the head. For example, raising the pole moves the draft aft, flattens the entry at the shoulders and lets the upper luff sag to leeward. Upper luff sag has the effect of rotating the head aft, increasing its angle of attack, closing the leech and making the chute more powerful. Conversely, lowering the tack opens and depowers the upper leech.
Mainsail Trim -- The spinnaker bends airflow much more than a genoa, so trim your main appropriately. On a close spinnaker reach, trim the main almost as much as if you were beating, but watch the top batten telltale for signs of stall. Be careful not to over-vang. In light air, especially with fractional rigs, the upper spinnaker leech often sags into the main and closes down airflow. Trim and twist the main to re-establish flow.
The blooper -- It may seem suicidal, but flying a blooper balances your sail plan and dampens rolling. Use it. Trim the sheet through an end boom block, not straight to the stern. Raise the halyard more than in moderate conditions so as to keep the foot well clear of waves.
Working jib -- One effective tactic for reducing rolling in extreme conditions is to sheet your jib fore and aft in front of the mast, strapping it down with both sheets. This will work with or without a blooper.
Mainsail -- The main should be vanged hard enough to take all the twist out, or else the top sections will roll the mast to windward. Be sure that both vang and preventer can be released quickly. Assign someone to this job before you initiate a jibe broach. If you do jibe accidentally, beware of the boom; people have been killed this way.
The spinnaker -- Don't be afraid to use a smaller chute when the wind is forward of the beam. We tend to underestimate how powerful spinnakers can be, forgetting that just one broach can lose more distance than you can recover in a leg.
Obviously, you should depower the chute for heavy air reaching. Lead the sheet to the stern (and over the boom in some cases) to open up the leech. Keep the pole low to stabilize the luff, pull the draft forward, and open the leech. Flatten the chute by oversquaring the pole. If the boat is about to broach, the trimmer should jerk-ease the sheet a foot or more at a time to unload the rudder and regain control. Always dump the chute before a broach.
Staysail -- If you are only overpowered once in a while, set a small staysail under the chute. Dump the staysail in the blasts, and trim it during the lulls. Adding area to the forward half of your sail plan with the staysail helps to balance the helm. And the staysail, with its tack set well forward, gives you low-down power without much heeling force. Some boats fly a staysail with a reefed main for this reason.
Mainsail -- Your vang, whether mechanical or hydraulic, needs a quick release for power reaching. When a blast hits, ease the vang as well as the sheet. Releasing the vang luffs the upper half of the main immediately and lets you ease the boom farther without it hitting the water. Keep the outhaul or flattening reef tight to open up the lower leech. If the top of the main luffs consistently, reef it to cut down on windage and drag.
Preventing a Broach -- The release sequence before a broach must be perfectly clear to the entire crew; they'll be acting too rapidly to ask questions when the need arises. Here is what should happen:
We've learned that a sail is able to generate lift because it bends the wind, and we know that two sails generate more lift because they produce more bend in the wind. It follows, then, that three sails ought to bend the airflow most of all and generate the most lift.
You can actually see how much the wind flow is bent by watching how the mainsail must be trimmed farther inboard as the spinnaker and staysail are set. This increase in wind deflection is all to your advantage because it produces more lift. The trick, though, is avoiding excessive interference in such a crowded sail plan. With two slots instead of one, the importance of coordination and balancing the trims of all three sails is greatly increased.
Remember to check your speed a minute before and at least two minutes after setting the staysail. Don't be swayed by the crewmember who claims, 30 seconds after hoisting the staysail, that it's slowing you down. Just monitor your performance against other boats with a hand-bearing compass. To these suggestions we might add the obvious: watch what staysails, if any, other boats are setting. And don't be afraid to learn from their mistakes. The following factors have a bearing on the go/no go decision:
Wind angle -- Staysails are for reaching, not broad reaching. To get attached flow, the apparent wind angle must not be too far aft. If the angle is broader than 120 degrees, do not set a staysail. In the 90 to 120-degree range, use a staysail only if conditions are favorable (moderate to fresh wind with relatively smooth water). A Dazy staysail (with reduced LP and a high clew that sheets to the boom end) works best for these broad angles. In the 60 to 90-degree range, larger staysails work fine. They have no trouble obtaining attached flow, nor do they interfere with flow around the spinnaker.
Wind speed -- Staysails work best in moderate air, when there's enough breeze to lift each sail away from the other, but not so much to cause excessive heeling force.
In light air, the spinnaker cannot lift far enough from the staysail to avoid interference. Also, the staysail will not lift and twist itself enough to maintain attached flow in its upper sections. So don't use a staysail in light air.
In heavy air, you can hang onto the staysail by luffing or reefing the main. By luffing the staysail in the puffs to avoid broaching and trimming it in the lulls to add power, you can pull away from the competition. If you are continually overpowered, douse the staysail to reduce heeling forces and the possibility of broaching.
Sea Conditions -- Ideal staysail conditions are smooth seas. Rough water pitches the boat and disrupts airflow through the sails. Your top priorities in rough conditions should be steering and basic spinnaker trim, not worrying about a staysail.
What, then, are the ideal "go" conditions? 8-12 knots true wind speed; 65-80 degrees apparent wind angle; and smooth seas.
Dazy staysail -- This is the most versatile spinnaker staysail, and every boat should carry one. Named after Golden Dazy, the Holland two tonner designed for the Canada's Cup, the Dazy staysail has a full hoist with an LP in the 80-85% range and a high clew that sheets to the end of the boom. The Dazy is usually made of a light 1.0-1.7 ounce Mylar and cut very full. It will improve your staysail flying capabilities in light air and on broader points of sail. The Dazy also doubles as a windseeker in drifting conditions.
SLS (Special Little Staysail) -- This is a variation of the Dazy for fractionally rigged boats. It is a little smaller than the Dazy so it won't interfere with the main and spinnaker, yet it's big enough to add speed.
Tall spinnaker staysail -- This is a large sail that hoists to the masthead with an LP in the 90-130% range. It is normally made of 3 or 4-ounce Dacron or 3.2-ounce Mylar and designed to fly with a medium or heavy spinnaker. The Tall staysail's has a medium-full cut to give power on broader reaches without becoming too full in fresh air on a close reach. The clew is positioned high enough to permit end boom sheeting when the mainsail is eased to leeward of the lifelines. When built with a reef, it is called a "dual staysail" and can double as a genoa staysail.
Step 1 -- Set the tack position. The fore-and-aft position of the tack determines how much exposure the staysail gets at the expense of the spinnaker. In ideal conditions (close reach, fresh air, smooth water), tack the staysail well forward of the mast and rely on it to produce a great deal of power.
In marginal conditions, tack it farther aft to give the spinnaker more breathing room. The farthest aft legal tack position for your boat is determined by your rating rule. Athwartships, the correct tack position is on centerline for wind angles closer than a beam reach.
As you bear off and square the pole, tack the staysail to the weather rail as soon as the pole allows you to. On broad reaches, tack the staysail as far aft and to windward as the pole (and rule) permits.
Step 2 -- Set the proper sheet lead. When the boom end is trimmed inside the lifelines, sheet the staysail to the leeward rail. When the boom is eased outboard, sheet the staysail to the end of the boom to widen your sheeting base. If end boom sheeting moves your effective lead too far aft, causing excessive twist and not enough foot depth, raise the tack off the deck on a pennant until the staysail sets well again.
Set the fore-and-aft lead position for an even telltale break all the way up the luff or, to play it on the safe side, with the top luffing. A closed upper staysail leech is disastrous for airflow into the spinnaker head and must be avoided.
Step 3 -- Hoist the staysail. The staysail can be raised on either the genoa or spinnaker halyard. Have your bowman hold the luff of the sail tight as the mastman hoists. This will keep the staysail from hooking behind the spreaders.
Step 4 -- Coordinate all three sail trimmers. The spinnaker trimmer takes priority: give him or her an unobstructed view of the chute and an eager grinder. Periodically he should check his trim by asking the staysail trimmer to luff the staysail completely, then easing the spinnaker until it is on edge, and finally asking that the staysail be retrimmed.
If the chute begins to collapse, immediately dump the staysail to re-establish flow around the spinnaker. Don't trim until the spinnaker is pulling hard again. Always keep the staysail trimmed on the light side (windward telltales should be flying up) rather than overtrimmed. Luff the staysail when steering or trim becomes unsettled, and if in doubt, drop the staysail and work on your other two sails.
The mainsail is trimmed until backwind disappears, nearly on centerline for a close reach. As always, ease the vang until the top batten telltale flows, but no more.
The helmsman's responsibility to steer straight is triply important on a three sail reach. His sensitivity to the apparent wind angle versus the boat speed is vital to keeping the boat moving well. Since staysails work dramatically better on closer wind angles, consider the benefits of sailing slightly high of course for a bigger speed advantage.