UK Sailmakers' Encyclopedia of Sails

6.1 - Spinnaker Setup and Trim

The steps in preparing to set a spinnaker and their most efficient sequence varies depending upon the boat, the crew and the conditions. The basic steps and their sequence are:

1. Attach the turtle. On boats under 30 feet, it can be clipped in the bow pulpit. On larger boats (and small ones when it’s blowing hard) the turtle should be hooked at the rail or to the middle of the foredeck about halfway between the mast and headstay. Make sure that the head and both clews are outside of the bag.

2. Position the spinnaker pole so that the out-board end of the pole is over the side of the boat that will be the windward side when the spinnaker is hoisted.

3. Lead the guy through the outboard end of the pole and then attach it to the spinnaker.

4. Fasten the sheet to the sail. Double-check to be sure that it is not tangled with the life lines.

5. Attach the pole to the mast and raise the inboard end of the pole to the height which seems appropriate.

6. Attach the topping lift and foreguy and hoist the pole at right angles to the mast.

7. Attach the spinnaker halyard.

When racing and the boat is heeling over, it’s important that the bowman keep his or her weight to windward while setting up the spinnaker. To do this, the bowman has to break up the jobs listed above, and do them on two different tacks. For instance, when rounding the windward mark to port, have the bowman clip the spinnaker bag to the port rail while on your final port tack to the mark. This way he can hook on the turtle and attach the sheets and guys while on the windward side. When you tack to starboard, he can get the pole ready while keeping his weight to windward. If he has to do any of the rigging at the bow, he should plan out his moves ahead of time so that he spends the least amount of time possible on the bow, i.e., if he has to lead the sheets around the forestay, have the cockpit crew make sure the lines are untangled so that they’ll run free when he pulls on them. Weight on the bow, no matter how light, disturbs the helm.

The Set

The sequence of the actual set depends on whether the spinnaker is set flying or stopped in rubber bands. In either case, do not to trim the chute fully until the halyard is hoisted and cleated.

TO SET FLYING

1. Trim the spinnaker guy so that the clew of the spinnaker reaches the jaw of the pole when the pole is laying against the headstay.

2. Trim the spinnaker sheet until the clew is just past the shrouds.

3. Hoist the spinnaker all the way up, then drop the jib.

4. Trim the spinnaker to the wind.

TO SET STOPPED

Having the sail stopped in rubber bands is some-times used when setting a spinnaker in heavy winds. The rubber bands keep the sail under control and break away when your crew trims the sheet.

1. Trim the spinnaker guy so that the clew of the spinnaker reaches the jaw of the pole when the pole is laying against the headstay.

2. Trim the spinnaker sheet until the clew is just past the shrouds.

3. Hoist the sail until it is all the way up.

4. Over-trim the sheet to break open the stops.

5. Trim the sheet and the guy as required by the wind, starting with the guy first.

6. Drop the jib.

TRIMMING THE SPINNAKER

The tools available for maintaining the proper trim of a spinnaker are limited; they consist of pole position and sheet position. Pole position is variable both fore and aft and up and down. Sheet position is varied primarily by pulling it in or letting it out. Normally, the sheet is led to the leeward rail, at or near the stern, but sheet position can also be varied by the use of a spinnaker twing (a block and tackle that changes the lead angle of the sheet). A forward lead is only recommended when running in strong winds to help stabilize the spinnaker.

The spinnaker is a versatile sail which can be used when the wind is blowing anywhere from 60 to 180 degrees off the bow. Optimal sailing angles are determined by wind strength. In stronger winds, you won’t be able to fly the spinnaker as close to the wind because your boat will be overpowered by the spinna-ker at the closer angles. If the wind is too light, sailing at the broader angles will be too slow. 

At the forward end of this range, from 60 to 130 degrees, the wind will be flowing across the spinnaker from the luff to leech. (The principles involved in trimming a genoa are also applicable here.) At some point behind 130 degrees, or thereabouts, the wind blows directly into the sail and ceases to move across it. The sail is then said to be “stalled”, and the principles of trim change accordingly. 

REACHING TRIM

When the wind is flowing across the spinnaker from luff to leech, reaching considerations apply. If the wind is forward of abeam, the pole should be close to the headstay. “Close” means as close as possible to the headstay without allowing the two to touch. If the pole does rub against the stay, there’s a risk of damage to the pole, the rig, or both. Fore and aft position is controlled by the afterguy. The sheet should be trimmed just enough to prevent the sail from collapsing. The trim should be constantly tested by easing the sheet slightly until the luff commences to curl, then trimming again when the curl becomes excessive.

Put telltales on the leeches of the spinnaker midway between the head and clews. When reaching, read the telltales as you would on a jib. Keep both the windward and the leeward telltales streaming straight back. When both are streaming aft, the leading edge of the chute will curl some — but don’t worry. A little bit of curl is fast.

Pole height is adjusted by means of the pole lift and foreguy. In any given wind condition, the clew will find its own height. It is commonly recommended that the pole height be adjusted to match that found by the clew. In that condition, the draft will be approxi-mately in the center of the sail, which is the right place for it. If the pole is slightly lower than the clew, the sail will become asymmetrical, with the draft slightly forward of the center. This asymmetrical trim will be faster on close reaches. Putting the pole higher than the clew moves the draft behind the middle. But this always produces slow going: NEVER CARRY THE POLE HIGHER THAN THE CLEW.

At all times, sufficient tension should be maintained on the pole lift, the foreguy and the afterguy to keep the outboard end of the pole firmly in position. When all other adjustments have been made, the inboard end of the pole should be moved up or down on its track to keep the pole perpendicular to the mast. Remember that adjustments to the inboard end are a low priority item. Unless it’s grossly out of position, meaning feet, not inches, don’t waste time on it until everything else is set correctly.

As the wind moves aft, ease the sheet, while at the same time bringing the pole aft. If the pole is correctly placed fore and aft, the depth of the draft in the sail will be uniform from the top to bottom, and the luff of the sail will extend directly upward from the end of the pole. If the pole is too far forward, the pocket in the lower part of the sail will be too deep, and the luff will angle out to windward from the end of the pole. If the pole is too far aft, the foot of the sail will be too flat, and the luff will angle off to leeward from the pole end.

RUNNING TRIM

When on a run, with the wind blowing directly into the sail, it is desirable to present as much area as possible, subject to certain limitations. The pole should be kept as far aft as possible without making the foot too flat or causing the luff to be other than straight up from the pole end.

On a run, in a good breeze (you shouldn’t be on a run unless the wind is blowing over 14 knots), the clew may seek to rise higher than is desirable. If the foot gets too high, you lose projected area. Therefore, move the spinnaker sheet lead forward to keep the clew down. That way you won’t have to raise the pole too high.

Even in a “stalled” sail, there is some flow of air along the leeward side of the sail and therefore some aerodynamic force, which increases the wind’s normal force. This flow occurs at the sides of the sail, moving from both leeches for a short distance toward the center of the sail. A flatter sail projects more area, hampering flow on the leeward side of the sail. A fuller sail projects less area, but generates more flow. A similar flow of air also moves over the top of the sail and down the front toward the center. This overhead flow travels further and is more powerful than the flow at the sides. If the foot of the sail is held too low, this overhead flow will be curtailed; if not low enough, too much projected area will be lost.

Proper downwind trim involves balancing the extra thrust resulting from the aerodynamic forces acting around the edges of a deeper setting against the greater projected area obtained with a flatter setting. Normally, best results are obtained at the flatter end of the range, but remember that it is quite possible to trim the sail too flat or have the foot too low. Thus, the only way to find the best shape is to experiment while watching your speedometer.