Trimming an asymmetrical

Sail Trim

Dave Flynn of Quantum Sails offers advice on the trim and take-down of asymmetrical spinnakers.

Most performance racers now fly asymmetrical spinnakers off a bowsprit or prodder, but these versatile sails can also be flown off a pole like a traditional symmetrical spinnaker.

Setting

• Set on a broad reach, where the mainsail will blanket the sail.

• Secure the bag near the middle of the foredeck.

• Attach both sheets to the clew, leading the lazy sheet around in front of the headstay.

• Attach the downhaul. If there is a bowsprit, lead the downhaul over the sheets (inside gybes), if no bowsprit, lead the downhaul under the sheets (outside gybes).

• Attach halyard, making sure the halyard is outside and in front of the headstay.

• Pre-pull the downhaul so that the tack will be about a metre off the deck, but pre-pull the clew back to the shrouds.

• Hoist rapidly.

• When the sail is fully hoisted, trim the sheet.

A spinnaker sock may be used to keep  the sail from filling while you hoist. If using
a sock, secure the sock control lines to the mast after hoisting.

Trimming

Ease the sheet out until the sail luffs (curls) along the leading edge. Trim in just enough to stop the sail luffing. A periodic curl is good; this indicates the sail is just on the edge of luffing. As with all sails, over-trimming is the most common problem. When in doubt, let it out.

For reaching, tighten the downhaul and lower the tack to pulpit height to minimize luff sag. This will pull the camber (draft) forward and open the leech.

The tighter the downhaul, the more genoa-like the shape will be. Though it is
a function of breeze velocity and the design range of the sail, in lighter winds you can use most asymmetricals as close as 50 degrees apparent wind angle.

For running and broad reaching, ease the downhaul, allowing the tack to float up 4-6’ off the deck. This will allow the sail to lift up and the luff to rotate out to weather, away from the blanketing effect of the mainsail. It will also create a more spinnaker-like (symmetrical) shape.

If using a spinnaker pole to control the tack, set the pole just above the pulpit for close reaching. Gradually bring the pole aft, keeping it perpendicular to the apparent wind angle (just as with a symmetrical sail), and raising it gradually to keep the tack approximately level with the clew.

Another useful technique at broader angles is to “twing”, or move the sheet lead forward. (See diagram). This keeps the clew from rising up and dumping off the leech, making the sail more symmetrical and powerful.

How deep (broad) an angle you can sail is largely a function of breeze velocity. The lighter the air, the higher the angle (closer to the wind) you will need to sail to keep the asymmetrical full and pulling. To find the optimum angle for a given breeze velocity, start with the sail full and pulling and bear off slowly until the clew begins to droop and the sheet begins to lose pressure, then head back up until the sail is solid and fully pressurised. This magic edge changes with velocity. You will be able to sail lower angles in the puffs, but will have to head up in the lulls.

Gybing

Asymmetrical spinnakers are gybed, not tacked. Start with the sail fully loaded. Bear off slowly, easing the sheet as smoothly and quickly as you can without collapsing the sail. The trick is to use the sheet pressure to get the sail out in front of the boat. If the sail is not eased out before the boat gets downwind, it will collapse and fall into the headstay. As the boat passes through dead downwind, release the old sheet completely and take up on the new sheet.
The sail is gybed outside and in front of the headstay when the tack is set on the stem.
If you have a long enough bowsprit, you can gybe inside the tack downhaul. No matter which system you use, turn from a broad reach to a broad reach slowly but smoothly. Do not stop in the middle of the turn, or you will encourage the sail to get wrapped around the headstay. Watch the sail and slow the turn slightly as the clew gets to the headstay and is pulled around. The lighter the air, the higher the reaching angle you will need to sail, both at the outset, and as you exit the gybe. In very light air, you may have to physically help the sail around the headstay.

Take Downs

1. Bear off to a broad reach (10-20 degrees up from a dead-run is best).

2. Grab the lazy sheet just in front of the main boom.

3. Release the downhaul, or the active sheet, completely and gather the sail behind the mainsail using the lazy sheet.

4. Ease the halyard as fast as the sail can be gathered.

5. Stuff the sail down the companionway or forward hatch as you gather. Putting the sail in the bag later is easier than trying to do it on deck if there is a lot of breeze.
A spinnaker sock can be pulled down over the sail first to keep the sail from blowing out of control while being gathered. Release the sheet, and pull the sock down, then gather the sail.

Racing take downs can be done in two other variations. First, a weather take down, where the lazy sheet or a special take down line is led around the headstay. The sheet is released, and the sail is pulled around the headstay to weather and gathered.
Another option is the “envelope” drop. Here, the lazy sheet is brought completely around to the leeward side and led through the foot of the mainsail (works with loose-footed mainsails only). The tack is released completely and the sail is gathered through the foot of the mainsail and down the main companionway hatch. This type of take down is particularly effective in windy situations on bigger boats.