Zeilschool Amsterdam RYA trainingscentrum

RYA ZEIL TRAININGEN

 CWO CURSUSSEN

 
 
RYA zeezeilschool  RYA Zeilschool   Nieuwsbrief

Performance Racing Trim
by Bill Gladstone

 

Chapter 5 - Genoa Trim & Controls

5.1 Introduction
5.2 The Genoa Trimmer
5.3 Genoa Power
5.4 Sail Selection
5.6 Reaching Trim
5.7 Conclusion


 

Introduction

Genoa trim is a never ending process; the genoa sheet and other controls require constant attention to maintain optimum shape and performance. Every fluctuation in conditions requires a corresponding change in trim. Don't expect huge leaps in speed. Work for a boat length here, and a few feet there. Great trim is the sum of many small adjustments. It adds up.

This chapter will start with a look at the role of the jib trimmer in upwind performance. From there we will consider the sources of genoa power and proper sail selection. Next, we will look at each genoa control. We will start from the initial set of each control, and then move on to refined sail trim, matching genoa shape to sailing conditions.

 Fig. 1. Genoa trim is a never ending process of trim and fine tuning to match sail shape to the prevailing conditions and performance goals.

In subsequent chapters we will explore mainsail trim and helming. Later, in Chapter 8, we will also explore upwind performance problems and suggest methods for resolving them.

 

The Genoa Trimmer

The genoa trimmer guides the boat upwind. Through sail trim, and through communications with the driver, the genoa trimmer guides the boat to the optimum balance of speed and pointing.

The genoa trimmer monitors performance moment to moment, using one or all of the following:
  • Comparison to other boats.
  • A target boat speed standard.
  • Immediate past performance (i.e.: How are we doing now compared with a moment ago?).
  • The boats feel. A good trimmer will be able to feel a loss of power before it shows up as a loss of speed.
Based on current performance the trimmer directs adjustments to improve (or maintain) performance. Changes include adjustments in genoa trim, changes in mainsail trim, and changes in driving style. It is critical for the trimmer to communicate the current state of performance, to suggest the means to improve, and then to report on progress as adjustments take hold. As we explore genoa trim further we will look at the specific adjustments which might be called for in a variety of conditions.

 

Genoa Power

There are three sources of sail power: Angle of attack, shape, and twist.
Angle of Attack
The genoa derives power first through angle of attack. Trim the sail in, and you add power. Let the sail out and you reduce power. Heading up also reduces angle of attack and power.

Angle of attack is increased by trimming the sheet or by falling off.
Shape
Deeper sails generate more power. Flat sail shapes generate less power (and less drag). Genoa depth is adjusted through a variety of controls, including headstay sage, lead position, and sheet trim.

Fig 3.
Angle of attack changes with trim and steering angle. Here Boat A is trimmed to a narrow angle of attack, while Boat B, with the lead outboard and sheet eased, is trimmed to a wider angle of attack.

Fig 4. Sail Shape: Boat A has deep genoa shape, for extra power. Boat B has a flat genoa shape, preferred for smooth water and heavy winds.

 

 

 

 

Twist: -
A closed leech generates more power. A twisted, or open leech, spills power. Genoa twist is controlled through lead position and sheet trim.

Fig 5. Twist: Boat C is trimmed for power, with little twist. Boat D's genoa is twisted open, spilling power.

Initially the sheet's primary impact is angle of attack, pulling the sail in. As the sail nears full trim the sheet increasingly pulls the sail down (not in). At this point the primary impact of trim is a change in twist.

Total Power, Mix of Power
The trimmers job is to achieve the correct total power in the sail, and also the correct mix of power from each source. Sail Selection and Sail Controls
Each genoa control impacts sail power in a number of ways. Of course, the biggest impact on power is the choice of which genoa to fly. The next section will look at sail selection. The subsequent section will cover sail controls one by one.

Fig 6. Twist versus Angle of Attack: Boat E has a wide angle of attack. - the entire sail is open, while Boat F has twist - the upper leech is open, but the lower part of the sail is trimmed inboard.

 

Sail Selection

The first step in genoa trim is to choose a sail based on conditions. Each sail has a designed strength and performance range. The optimal safe wind range for a given sail is available from the sailmaker, though with modern materials sail strength is less an issue than size and shape. The sail will be wrong from a performance standpoint before you threaten its strength. [This statement is not a warranty. Do not blow out your sails.] At the crossover between two sails several secondary factors influence the decision.

Sea State

Generally, in waves or chop use the bigger sail for extra power. In smoother water a smaller sail with a shorter overlap is preferred for close sheeting and high pointing ability. In big waves some skippers prefer a smaller jib which allows them to steer around big waves; while others rely on a big jib for power.

Trend of Conditions

No surprises here: If the breeze is building then use the smaller sail. In a dying breeze use the larger sail. Notes that sea state and breeze trend factors tend to coincide. In a building breeze seas will not have built up. In a dying breeze there will be left over seas.

Beware. Do not start with a smaller sail because you anticipate the wind building into its range. Use the smaller sail only if the wind is already in its range and you expect it to continue to build.

Performance Records

The band of uncertainty will become narrower as you become more familiar with your boat. Good record keeping can accelerate this process.

Two notes here: 1) Good record keeping can also help you in subsequent sail purchases. If you find you want to carry one sail up into the range where the next sail would supposedly be better then report this finding to your sailmaker. This information will help in the design of future sails.

Note 2) Once you know the exact crossover wind speed for each sail in your inventory, it is time to get a new boat. Sometimes you can delay this by changing your sail inventory.

Testing

Prior to a race test your options before making a decision. Head out to the starting area an hour early to test out different headsails. Tuning up with both sails against another boat is particularly valuable.

Better still, do your testing in practice against a well sailed sistership. You should sail with different sails, and then both switch. When you find which sail is faster do further testing to optimize performance with both boats using the same sail.

Fig. 7 Sail selection is based on wind strength, sea state, and the trend in conditions. Careful record keeping can help us know the proper sail selection.

Halyard

The halyard is used to position the draft. Working from our initial trim settings, this is a two part process.

Initial Trim

Set the halyard to remove wrinkles from the luff of the jib. In light to moderate conditions it is better to leave the halyard too loose - leave a few wrinkles. In heavier air a firmer halyard is needed - remove the wrinkles.

Draft Maintenance

As wind strength changes halyard tension is adjusted to keep the draft in position. As the draft blows aft halyard tension is increased to hold the draft forward. As the breeze dies the halyard is eased to match the reduced loads in the sail. Our goal in this first stage is simply to keep the draft in its designed position.

Draft Tuning

Once we have finished draft maintenance we can fine tune our sail shape to suit conditions. More halyard tension will pull the draft forward. This creates a rounder entry shape which makes steering easier, particularly in waves.

Easing the halyard will allow the draft to move aft, resulting in a flatter, or "finer" entry. This fine entry will result in a closer pointing shape, but with a narrow steering groove. In easy steering smooth water conditions this softer halyard will allow for better pointing.

To achieve proper halyard tension we must balance pointing ability with groove width. A flat entry which we cannot steer to will be slow; a round easy-to-steer entry will not allow us to point.

Fig. 9 Boat A - Draft aft creates narrow angle of attack. Boat B - Draft forward and wide angle of attack.

Measuring and Duplicating Halyard Settings

The best way to measure halyard settings is with a mark on your headstay and corresponding marks on your sails. This is easier and more accurate than number strips on deck matched to marks on the halyard. It also encourages pit crew to keep their heads up, looking forward during the hoist, which is good.

First, put a one inch wide mark on your headfoil six or more feet above the deck - as high as you can reach conveniently. (Your headfoil should be fixed in place. If properly installed it should not move up and down on your headstay.) Next, set each jib (in appropriate conditions) and set the halyard tension properly. Mark the jib luff to match the mark on the headstay. At the sail's upper end you may need to pull a little above the mark, and at the low end you will want the halyard slightly eased from this setting.

Fig. 10 Use marks on the sail and foil to set halyard tension.

These marks are particularly valuable when setting the jib prior to a spinnaker takedown. It is very hard to judge appropriate upwind halyard tension with the sail loosely sheeted on a reach.

One more trick: Overhoist the sail slightly and ease down to the mark. This helps assure even cloth tension over the length of the luff.

Headstay Sag

Headstay sag controls depth of draft, particularly in the forward part of the sail. As with halyard tension and draft position, controlling depth is a two stage process.

Initial Trim

Set the headstay sag with backstay or running backstay. Set at one quarter max tension in light air; progressively more for stronger breeze.

Depth Maintenance

As the wind strength changes loads in the sail change, and sag changes. As the wind builds we must add headstay tension to keep the same sail shape. Similarly, as the wind dies the headstay must be eased.

Depth Tuning

More sag adds depth and power; for extra speed in waves, and better acceleration. A tight headstay creates a flat shape. The flat shape will be faster and higher pointing in smooth water.

Fig.

 Fig 11a - A tight headstay creates a flat closewinded, low drag shape best for heavy air and smooth water.

 Fig 11b - A sagged or loose headstay produces a deeper, more powerful shape, best suited for light to moderate winds and chop.

Fig 11c - This figure shows a deep sail shape silhouetted over a flat shape. As the breeze changes the headstay sag will change due to changing sail load. Adjustments will first be needed simply to maintain shape. From there sail shape can be fine tuned to the conditions.

A secondary affect of headstay sag is a change in entry shape, similar to halyard control. More sag creates a rounder entry; a tighter headstay creates a flatter entry. Consequently any adjustment in sag should be followed by a check of halyard tension to be sure entry shape is proper.

Tightening the headstay flattens the entry; and the halyard may need to be snugged to put some shape into the front of the sail. Sagging the headstay rounds the entry. A matching ease on the halyard can prevent the entry from becoming too round.

Genoa Leads

Moving the fairlead changes genoa shape and power. The goal of initial trim is to achieve the designed shape. We'll fine tune from there

Initial Trim

Set the jib fairleads so the sail has a fair curve and even shape from top to bottom. When the sheet is trimmed the jib telltales should break evenly from top to bottom. (As you pinch up above closed hauled the upper telltales will luff before the lower ones.) The leech of the jib should match the shape of the main.

NO, the telltales will not all break together. The upper telltales will luff first, and the break will spread down.

 Fig. 12 - The jib telltales will NOT all break at the same time. The upper part of the sail will break first. and the luff will spread down form there.

Balance of Power

The jib leads balance high and low shape in the sail. Our goal is to set the lead so the sail shape matches the wind from top to bottom. When the lead is set properly the inside telltales will break smoothly, starting from top and moving down.

Moving the lead forward makes the sheet pull down more on the upper part of the sail, trimming in the top. Moving the lead aft will cause the sheet to pull back on the foot, like an outhaul, without trimming the upper part of the sail as much.


Tuning to Conditions

In waves and chop pulling the lead forward adds power throughout the sail. The top of the sail is trimmed fully, and the foot of the sail takes on a round, powerful shape. In moderate winds the leech will trim within a few inches of the top spreader, while in light air it may be as far as a foot off. The foot of the sail will carry perhaps two feet of depth over a ten foot chord length. Only when the lead is in its forward most position will the entire luff break at once - the way basic sailing texts say they should.

In smooth water move the lead aft to open up the sail. This allows the genoa to be trimmed in closer to the main without clogging up the slot. The foot is stretched flat. Overlapping genoas will trim against the shroud base. The telltales break first aloft, and the lower telltales may even be partially stalled while the uppers spin. This flatter shape allows harder trim and thus higher pointing.

In over powering conditions move the lead aft to flatten the foot of the sail and spill open the top; reducing power throughout.

 Fig 13 - moving the genoa leads changes the shape and power of the foot and leech of the genoa. Boat A - Moving the lea aft flattens the foot and opens the leech, reducing power. Move the lead aft to reduce heeling when overpowered and for closer pointing in smooth water. Boat B - Moving the lead forward adds shape and power in the foot and up the leech. Move the lead forward for extra punch in waves.

Adjustable Jib Leads

Adjustable jib lead systems allow you to adjust the lead position on a loaded jib lead. This allows the lead to be adjusted to changing conditions and situations. For example, the lead can be pulled forward for extra acceleration out of a tack. As speed builds the lead is eased to its normal position. Similarly, the lead can be pulled forward to add power when approaching a tough set of waves, or the lead can be eased aft to spill power in a puff.

Inboard and Outboard Leads

An inboard lead position allows for closer pointing in ideal smooth water moderate air conditions. With the main and jib both trimmed flat move the lead inboard a few inches. (Drag it inboard with a hook around the sheet.) Your goal is to improve pointing without any sacrifice in speed. Be prepared to ease out immediately if (when) you lose speed. Speed first - pointing second. Keep speed, then try to squeeze up. On many boats it is difficult to improve pointing due to limitations of the keel.

In heavy air an outboard lead de-powers the slot. With an overlapping genoa and the main traveler down the slot will be clogged. Move the lead outboard to open the slot for speed and to reduce heeling. The danger here is a loss of pointing ability. Before moving the lead outboard try first to de power by easing the sheet a few inches while leaving the lead in its regular (aft) heavy air position. Only in extreme conditions - when you ought to have a smaller sail - is an outboard lead effective.

In very light air an outboard lead prevents the slot from being clogged and eases flow. Hold the lead outboard and reach off to build speed. Once you have speed then try pointing (back to the harbor). Repeat from above: Speed first.

From our initial set we can fine tune shape to suit conditions. Each control can be fine tuned; and as we adjust one we will need to check the impact on others. As stated above, genoa trimming is a never ending process.

Genoa Sheet

Sheet trim is the primary control of jib shape. The sheet effects the depth, power, angle of attack, and the shape of the slot. When the sheet is properly trimmed the genoa will have smooth even shape, parallel to the main. The main may show the first signs of backwinding.

Initial trim

Initial trim will put the upper genoa leech a few inches off the top spreader as the foot nears the shroud. (Obviously this is a rough approximation - yours may vary.) You will find you point higher and lose speed as you trim. When additional trim does not improve pointing the sail is overtrimmed. Ease slightly and continue the search for the best mix of pointing and boat speed. Play the sheet constantly to keep optimum speed and pointing.

One or Two Inches

The difference between fair trim and good trim is only an inch or two of sheet. About right does not cut it. Two inches too tight and you will be slow. Too loose, and your pointing will suffer.

The difference between good trim and great trim is effort. Get good speed and test extra trim. Try for extra pointing without sacrificing speed. If speed suffers ease for a moment to build speed, and try again.

 Fig. 8. The genoa sheet is the primary control. the sheet affects power, shape, and angle of attack. Trim the sheet so the genoa shape balances speed and pointing, and play the sheet with each change in conditions or performance - easing to build speed and trimming to point higher when speed is good. Be prepared to check the sheet trim with every change in secondary controls. Any change in the halyard, headstay, or lead will affect the sheet.


In final trim the difference between fast and slow is only a couple of inches. Here, Boat A is eased for acceleration. Boat B is fully trimmed for high pointing.

The genoa sheet must be played with each fluctuation in conditions or performance. In a lull, or when the boat is slow, the sheet should be eased. As a puff hits the sheet may need an initial ease, and then trim as the boat accelerates.
Keep working, and remember - speed first, then pointing.

Secondary Affects

Sheet trim must be checked after every other adjustment or change.

Raising the halyard raises the head of the genoa, and increases the distance from the clew to the head of the sail. To keep the same leech shape the sheet would have to be eased as the halyard is raised. The reverse would hold if the halyard were eased.

Tightening the headstay is similar to tightening the sheet, except the sail is pulled from the luff rather than the clew. To maintain trim as the headstay is tightened the sheet must be eased. If the sheet is not eased the entire sail will be trimmed in. (And vice versa for more headstay sag.)

Adjusting the sheet lead directly affects the sheeting angle. Any lead adjustment will require some sheet adjustment. As the lead is moved forward the sheet may need a slight ease; as the lead is moved aft the sheet generally needs trim.

Never Relent

Don't cleat the jib sheet, and don't hang out to leeward. The jib trimmer should be the last crew to the rail. As long as conditions allow, keep the jib trimmer to leeward, working on trim. Once the rest of the crew are fully hiked the jib trimmer should hike too. But don't cleat the sheet. Bring the tail along. That way the sail can be eased without delay, and without the trimmer moving off the rail.

 

Reaching Trim

A high clewed Reacher or Jib Top is designed for jib reaching, with extra roundness and power forward. Lacking such a specialty sail, you will have to make do with a standard genoa, trimming it as best you can for the reach.

Barber Hauling

Using a standard genoa on a jib reach the lead must be moved outboard and forward. You chase the clew of the sail with the lead. It also helps to keep the halyard firm to hold the draft forward and too prevent the back of the sail from becoming too round. 

Fig. 14

 

As the genoa sheet is eased on a jib reach the genoa lead is must follow the sail outboard and forward. Boat A - If the lead is not moved the jib foot will be too round, and the leech will spill.

If the lead is not moved as the sheet is eased, then the top of the sail will twist open, spilling power, and the bottom of the sail will hook in toward the boat, creating excess drag.

At the Cusp

There is a limit to how low you can reach effectively with a genoa. As you push the lead forward in an effort to keep the top of the sail trimmed you make the foot increasingly round.

As you reach the lower limit of effective reaching trim you have two choices:

One is to set your spinnaker - particularly if you carry an asymmetrical spinnaker. If the angle is too close for a chute then the alternative is to head up slightly to keep the jib working effectively. As you gain height you will eventually be able to reach down and set a spinnaker. This is the only time a direct route is not fastest on a reach.

Reacher

If you carry a high clewed Reacher or Jib Top the exact lead position depends on the wind angle. Set the sheet lead well aft, and rig a choker to pull the sheet down. Adjust the choker so the sail luffs evenly from top to bottom. This arrangement is better than a fixed lead, as it allows easy adjustment as wind angle and wind speed change.

 Fig. 15 A reacher is designed for reaching, with a hight clew and powerful shape. Sheet it aft, and choke the sheet to adjustable sheeting angle.

Genoa Staysails

Although they have gone out of fashion, some old IOR boats with huge J dimensions still carry genoa staysails.

The genoa staysail can be set between the jib and main, creating a double head rig. Tack it on the centerline at 40 - 50% of J aft, and sheet it evenly between the main and genoa. Try it. If you go faster keep it up; if it makes you slower take it down.

(WOW!) If you own one of these relics take care of it - you certainly don't want to have to replace it. It may also be time to think about a newer boat, where you don't need to carry so many sails to sail fast.

Fig 16 The genoa staysail depicted here may be the last one you see. Give it a close look...

 

Conclusion

Genoa trim is a never ending battle to match sail shape to the conditions of the moment. The genoa trimmer leads the boat upwind, guiding the driver up or down, depending on performance.

Later, in Chapter 8, we will revisit genoa trim as we consider overall upwind trim solutions in a variety of sailing conditions.

 

previous next

CWO zeilschool

Zeil mee naar Engeland!

RYA zeezeilschool

SPECIALS

Wedstrijdzeilen

RYA SHOREBASED COURSES

 
 
 
 

Copyright: Waypoint Amsterdam Zeilschool