Trim the gennaker: More speed and control

If the wind is too light for good speed under genoa and mainsail only, the conditions are often perfect for the gennaker. Nevertheless, many crews leave the colourful cloth in the bag. The fear of twisted sheets, unsuccessful jibes or a recovery manoeuvre that suddenly becomes hectic is too great.

The gennaker on cruising yachts is by no means just a sail for sporty crews. Properly prepared and neatly trimmed, it brings life to the boat in light winds and makes rough courses much more relaxed. The decisive factors are a clear sequence, the correct sheeting and an understanding of what the sheet, jib line, halyard and furler actually do to the sail.

A quick gennaker check is therefore particularly worthwhile at the start of the season. If you know the most important settings, you will set the light wind sail more often, sail more smoothly and retain more control when jibing and recovering.

The gennaker is increasingly replacing the spinnaker on cruising yachts. There are good reasons for this: For example, the ease of handling. The spinnaker pole, toppnant and downhaul, which are required for a spinnaker, are superfluous with a gennaker - even the barber haul can be dispensed with. You only need to operate two sheets. On very long courses without a planned jibe, you can even dispense with the windward sheet.

Another advantage of the gennaker is its extended range of use. With the early versions, which were a mixture of genoa and spinnaker, sailing on deep courses up to just before the wind was problematic; the bubble was increasingly covered by the mainsail as it dropped and lost its effect. The spinnaker was therefore favoured as it had better all-round characteristics. Modern cuts now allow the gennaker to rotate to windward and thus largely free itself from the cover of the mainsail.

Setting and retrieving has also become much easier. Gennakers can be fitted with a torsion cable in the luff and can then be furled and unfurled like a furling genoa. All you have to do to set or retrieve the gennaker is to operate the furled sheet.

By the way: A code zero can be an alternative to the gennaker. You can find out when this sail makes sense in our Special article.

The parts in this sail trim special:

• Trim the mainsail correctly
• Trim the genoa correctly
• Trim the gennaker correctly
• Trimming tips from professional Tim Kröger: Sail settings

Gennaker check before setting

• Are the halyard, sheets and halyard line free and not twisted?
• Is it clear whether the forestay is jibed inside or outside?
• Are both sheets long enough and guided correctly?
• Is the sheet clear for fast fiddling or casting off?
• Does the neck remain free of the forestay, pulpit and anchor fitting?
• Does the recovery hose or roller system function smoothly?
• Is the leeward sheet guided in such a way that it cannot fall into the water?
• Can the crew recover the gennaker quickly when the wind picks up?
• Has it been agreed beforehand who will steer, who will sheet and who will tidy up?
• Do you practise in moderate winds before pressurising the cloth?

Troubleshooting for the gennaker

Gennaker pole: when it helps and when it doesn't

This is why a gennaker pole is not necessary on normal displacement yachts - it is sufficient to attach the neck to a stub spit or the anchor fitting, it just has to remain free of the forestay. Very long gennaker poles, as seen mainly on skiff dinghies or sportier yachts, make little sense on cruising boats. On the other hand, a gennaker pole takes the cloth out of the cover of the mainsail. However, a displacement yacht cannot sail much faster than its theoretical hull speed, the length of its displacement shaft, allows. A larger gennaker would only have the consequence that this "sound barrier" would be reached a little earlier, but not shifted, but handling with a lot of cloth and early pressure would become much more difficult.

Although modern gennakers can be sailed very low, a special sailing technique is recommended when there is little wind: setting out in butterfly mode. Flat in front of the sheet, the gennaker is hauled as far abeam of the boat as possible using a spinnaker pole. As the foot is very long, a telescopic boom is recommended. This means that the mainsail no longer covers the bladder.

Sheet guide, jib line, barber hauler: what is responsible for what

There are two different types of sheeting. On cruising yachts without a long bowsprit, the sheeting has been used on the outside around the forestay. (1) around the boat. When jibing, the gennaker flies around the boat. If a gennaker pole is available, the sail is also jibed between its own luff and the forestay. The cloth can be firmly attached to the bow (2) be used, for example with roller systems, but it is better to use a neck line (3). It enables the gennaker profile to be trimmed and facilitates setting and recovery. Barber furler (4) are not absolutely necessary, but add a component to the trim repertoire. It is best to use snatch blocks on the sheet, as these can be attached and removed quickly. High loads can occur on the barber haul-out in strong winds, so it is best to operate this using a winch or tackle.

Angle of attack: Why the sheet must never be too tight

The sheet is used to regulate the angle of attack and the profile of the gennaker

The correct angle of attack is important, as a gennaker is flown around like a genoa and generates its propulsion through lift, not drag. In order to fill the cloth with wind after setting, the sail is luffed slowly and the sheet is tightened at the same time. As soon as the bladder fills, it must be dropped again and the sheet quickly furled - otherwise the buoyancy will act mainly to leeward, which can lead to strong heeling and a sun shot.

The sheet is furled until the luff of the gennaker starts to kill slightly, turning inwards. The ideal angle of attack is then found, similar to the gently killing windward leech of a genoa. As the outhaul moves forwards and upwards as the sail is fouled, the profile becomes rounder and opens up at the top of the leech, creating the desired shape.

Now the sheet can be actively furled by the trimmer by hand or winch, or passively, by taking up the sheet and the helmsman following the gennaker luff.
Important: Always have the sheet ready for casting off.

Neck line: How to change the profile and luff tension

With flat-cut gennakers, the profile can be influenced by the luff tension

Older gennakers in particular are often cut in such a way that the luff length corresponds to the distance between the head and tack attachment points. If the halyard and jib line of these sails are fully set, the luff is almost taut. This shifts the luff to windward, and with it the angle of attack becomes more acute. The sail is stretched overall, the width is reduced, the greatest camber depth moves forwards and at the same time the leech opens up in the upper area. The stronger the wind, the more the luff should be stretched. Although some height is lost due to the round profile, this is compensated for by the displacement of the leading edge and the forward-facing lift vector.

If the jib line is feathered a little, the profile compresses and becomes wider, but also flatter. The flat leading edge sometimes allows a little more height in light winds, but with increasing wind the sail moves to leeward and causes heeling.

Case tension: More rotation on low courses

The rotation of the gennaker head to windward can be influenced with the halyard tension

In modern cruising gennakers, the luff is cut about five to eight per cent longer than the maximum dimension between the head and the neck. This means that the luff cannot be pulled taut and some height is lost; only around 80 to 90 degrees to the true wind are possible. On the other hand, the sail is rounder, wider and turns clearly to windward on deep courses, almost like a spinnaker, and the bladder comes more out of the cover of the mainsail. This increases the projected area that is "visible" to the wind, and deep courses of up to 170 degrees wind angle are possible without a boom.

This rotation can be increased by slightly feathering the gennaker halyard. In most cases, a chop of two to three per cent of the luff length is sufficient, i.e. around 50 centimetres at 16 metres. This makes the luff even rounder and allows it to turn even more to windward. However, this also makes the gennaker a little less stable and requires more careful sailing.

Jibing with a gennaker: How to keep the sheet free

Only two sheets are to be operated, which can also be done single-handedly

When jibing, the gennaker shows its full advantage over the spinnaker in terms of handling. The barber haulers are furled and can be forgotten for the time being, only the sheets are important. Here, the gybe variant is shown around the outside of the forestay, as it makes sense on most cruising boats. It is important that the gennaker is jibed wide and quickly hauled tight on the new side. Otherwise there is a risk that the old sheet will fall into the water and get under the boat. The only thing that often helps is to unthread the sheet.

Important tip: Before jibing, the engine should be engaged backwards so that a folding propeller closes securely and a fixed pitch propeller is stationary - otherwise the sheet could wrap around the prop.

Gennakers with a furling system or a recovery tube can be recovered before the jibe in stronger winds and set again on the new bow, which is sometimes less stressful. Finally, the lee barber haul-out can be tightened again.

Catch-up: More control on low courses

The leech of the gennaker can be controlled on deep courses by using the leech

When sailing almost downwind, the sheet must be furled very far to enable the rotation described on the previous page. The tension on the leech decreases due to the increasingly blunt angle, the clew rises, the leech opens strongly at the top and releases pressure. A rounder profile at the top can be achieved by using a leech.

This is a trim line that is attached to the sheet by means of a block or loop and directed aft via a point approximately amidships. A midship cleat is also suitable for this purpose. When set tight, the angle of the sheet pull becomes steeper and the pull on the leech increases. However, inexperienced crews should initially dispense with the barber haul-out, as it must also be furled when luffing. Otherwise it causes a very closed profile and a lot of pressure to leeward.

Gennaker trim in video

Downloads for sail trim:

• Sail trim: Mainsail (pdf)
• Sail trim: Gennaker (pdf)
• Sails: Recovery hoses for space sheet sails (pdf)