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How to trim the sails on a Lagoon 42 cruising catamaran

Here are some basic tips for sail trimming on our Lagoon 42 catamaran Blue Buddha. Although some of these tips are unique to the Lagoon 42 sail configuration, they apply to most cats with aft mast configurations like most new Lagoons. Feel free to ask questions via the comments features.

Trimming the mainsail for performance

The procedure to trim the mainsail varies based on whether you will be going mostly upwind or downwind and whether you have moderate or strong winds.

Going upwind in moderate winds (<18knots): the standard procedure to trim the mainsail when on a beam and reaching is to center the traveler and trim the main sheet as needed until the upper tell tails fly nicely. Then adjust the angle of a tack, as needed, with the traveler (not the main sheet). You use the traveler instead of the mainsheet because moving the traveler will have less impact on sail twist than adjusting the mainsheet. By making adjustments with the traveler, you will be able to maintain the correct twist for the wind speed.

Going upwind in strong winds (>18knots): start with the traveler 2 feet (60cm) to windward of the centerline, center the boom (sheet in hard), and then ease the traveler as needed when bearing off.

Going downwind in moderate winds (<18 knots): start with the traveler halfway between the center line and the leeward end of the traveler, then ease the main sheet until the sail barely touches the shrouds

Going downwind in strong winds (>18knots): start with the traveler and the boom centered (sheet as hard as possible) and then move the traveler to leeward until the upper section of the mainsail barely touches the shrouds. This will create a flatter main at the correct angle of attack.

Avoid main-only sailing

If you try to sail Blue Buddha with the mainsail only in higher winds (>15 knots), you will quickly realize that the boat does not want to bear away (i.e., does not turn away from the wind) and will instead strongly fight you to turn to windward (excessive weather helm). This will happen even when you have a very flat main. To avoid excessive weather helm, simply do not sail with the main only and instead always deploy the jib after rising the main. The reason for this is due to the design of the boat. The location of the mainsail in the Lagoon 42, and similar new Lagoons, causes the position of the Center of Force to be significantly aft of the midpoint of the boat. The center of force is the location on the side of the boat where the sideways wind force is concentrated. If this location is too aft of the midpoint, the wind is essentially pushing the stern of the boat to leeward, which turns the bow of the boat into the wind. This is what creates weather helm. To fix this, you need to move the center of force forward and the easiest and most effective way to so is to deploy the jib. If you still experience significant weather helm after deploying the jib, your main is still overpowered and you can follow the tips below on how to reduce weather helm.

Excessive weather helm reduces your speed

Read this article on weather helm on the L42 for more information.

When the boat has excessive weather helm, the rudder will be open trying to keep the boat on course and will essentially act as a brake that will significantly slow down the boat. The Lagoon 42 has an underpowered jib and an aft main, which results in a very aft center of force and a perfect storm for weather helm. Thus, addressing whether helm is necessary for most points of sail and most wind speeds (although you will see an increase in weather helm as the wind speed increases). You can determine the degree of weather helm by looking at the center mark of the helm. It should not be turned more than 45-70 degrees to leeward to keep a straight course. If you see the mark at 90 degrees or more, then you have excessive weather helm and your speed is suffering.  Here are the three key tips to move the center of force forward and decrease weather helm:

  1. Never sail with main only on the L42.
  2. Take another reef on the main. At 18+ knots, reefing the main will actually produce higher speeds because it will significantly reduce weather helm (see reefing guide below).
  3. Flatten the main. To flatten the main you need to increase tension on the main sheet. When reaching in high winds, the traveler should be moved to windward past the centerline. At 18+ knots when reaching, the traveler should be about 2 feet or 60cm to windward and the boom should be centered. When on a beam, the traveler should be centered and the boom just off center to leeward. When downwind, sheet in the main hard while the traveler is centered and then ease the traveler to the correct trim as needed. Overall, trim the sails with the traveler keeping a tight main sheet, which will flatten the sail and reduce weather helm.

Reducing main sail power in gusts

As I mentioned above, when the wind is above 18 knots the traveler should be 60cm to windward and the boom should be centered. In a sustained gust, ease the traveler up to the centerline. This will lift the boom slightly, increase twist, and drop some wind from the top of the main. If you need to spill more wind, ease the main sheet. Do not ease the traveler past the centerline in this situation as this increases mainsheet tension that flattens the sail preventing wind from being spilled. The reason why you ease the traveler to the center line but not beyond has to do with the shape of the traveler in relation to the boom swing. Because the traveler is straight, when the boom is moved from the centerline with the traveler the distance between the traveler cart and the gooseneck increases. This forces a tightening of the main sheet lowering the boom, which increases leech tension and flattens the sail. Although you want flat sails in strong winds, you want to increase twist to spill wind during gusts.

Controlling the twist of the jib

Blue Buddha is rigged with a self-tacking jib which can be difficult to properly shape for those not familiar with how to use the self-tacking track. The track works this way: Move the track to windward to increase twist and to leeward to decrease twist. How do you know if you need to increase or decrease twist? Pay attention to the tell tails and follow this technique:

  1. Place the track cart so that it is leeward of center.
  2. Trim the jib so that the lower tell tails are both flying in parallel.
  3. Look at the mid and upper tell tails.
    1. If the windward tails are flying parallel to the boat but the leeward tails are not, you need to increase twist by moving the clew cart to windward. This almost never happens.
    1. If the leeward tails are flying parallel to the boat but the windward tails are not, you need to decrease twist by moving the cart to leeward.
  4. After moving the cart, trim the jib for the lower tails and check the upper tails again.

Don’t forget to check the leech tension line. This is a cord that can be adjusted on the clew of the sail. If it is too loose, your sail will luff on top even when properly trimmed!

In our experience, the standard jib that comes with the L42 tends to have too much twist when reaching, especially at higher winds and thus requires the cart to be all the way to leeward. In fact, my experience with the L42 is that at moderate and high winds, even with the cart at the most leeward position, the jib still has too much twist for perfect trimming although the trim is “good enough” for cruising. For this reason, we most often simply leave the carts at the most leeward position when sailing as we never need to increase twist. When we replace our jib, we will make sure the sail designer knows how to work with self-tacking jibs to make sure the sail is cut properly so that it will flatten when the cart is fully to leeward.

Tack to safely change the jib cart position

If you need to change the position of the jib cart to adjust the twist of the jib in strong winds, simply tack, adjust the cart, and then tack back.

Here is the reefing guide we used in Blue Buddha. This is different than our original guide and includes changes we made after sailing 200nm in quite strong winds (up to 30 knots).

Upwind Reefing Guide

Speed (knots) Sails Main Traveler
<18 Full Move to windward as speed increases, up to
18-25 1 reef main Full Jib 60cm to windward. Boom centered.
26-30 2 reef main 75% jib 60cm to windward. Boom centered.
30-35 3 reefs main 75% jib Centered. Boom 1m to leeward.
35-40 3 reefs main 40% jib Centered. Boom 1m to leeward.
40+ 3 reefs
No Jib
“Park the Boat” All the way to leeward. Sheet main hard. Helm to windward.

Downwind Reefing Guide

Speed (knots) Sails Main Traveler
<20 Full Up to 1m to leeward as
wind speed increases
20-25 1 reef main Full Jib 1m to leeward
26-30 2 reefs main 75% jib Fully to leeward
30-40 3 reefs main 40% jib Fully to leeward
40-45 No main 60% jib Centered. Tight topping lift and main sheet.
46+ Bare Poles. Drag Drogue if surfing above 15 knots Centered. Tight topping lift and main sheet.

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