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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

Note: The stock sail plan for the L42 is unbalanced resulting in an underpowered jib and significant weather helm. To address this issue and improve performance, the main needs to be slightly underpowered through reefing and/or increasing twist as described below. If the boat does not feel balanced and the weather helm is significant, your main is overpowered and needs to be adjusted.

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 or 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). The traveler is placed to windward so that the boom is high when centered and the top of the main twists to spill air in heavy wind. If you need more twist simply move the traveler more to windward and ease the sheet so that the boom remains centered. When bearing off, simply ease the traveler as needed.

Going downwind in strong to moderate winds (<20 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 (>20 knots): weather helm is especially noticeable when downwind in strong winds. Reef early and deeply to control the main’s power. You also need to flatten the main’s draft and increase twist to depower the sail. The L42 does not have enough controls to easily flatten the draft but you can increase twist by moving the traveler to windward (even as much as centerline but not past it) and easing the sheet so that the boom returns to its original location.

PRO TIP: Think of the traveler as having two functions: 1) changing the angle of attack (by changing the boom location on a horizontal plane) and 2) changing the sail’s twist (by changing the boom height). When you move the traveler without moving the mainsheet, you are using the traveler primarily to change the angle of attack because you will be moving the location of the boom on the horizontal plane. When you do this the twist will remain mostly intact. However, if you move the traveler while also manipulating the mainsheet, you are using it primarily to impact twist by lowering or raising the boom. What do I mean by “manipulating the sheet”. I mean taking in or easing the mainsheet as you move the traveler so that the boom stays at the same angle of attack but it will move up or down on a vertical plane. Here is how you increase or decrease twist: to increase twist you want to raise the boom. You do this by increasing the distance between the traveler and the desired boom location (angle of attack). So for example, if I want the boom to be centered but I want to increase twist, I would move the traveler to windward and ease the mainsheet so that the boom stays centered but at a higher location. The higher boom opens the top of the sail. To decrease twist, you want to lower the boom height. You do this by reducing the distance between the traveler and the desired boom location. In the example above, I would move the traveler to leeward while taking in the mainsheet so that the boom angle of attack is in the original location but at a lower height. The main sheet will then be tight, which would lower the boom and close the top of the main (reducing twist).

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. Depower the main by increasing twist. To increase twist, you need to raise the boom. You do this by increasing the distance between the traveler and the desired boom location. For example, if you want the boom centered, you move the traveler significantly to windward of the center line (2-3 feet) and ease the main to keep the boom centered. This will cause the boom to rise increasing twist on top of the sail and spilling wind. See Pro Tip above.

Reducing main sail power in gusts

As I mentioned above, when the wind is above 18 knots the traveler should be to windward of the center line 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 without a proper clew board. If your jib has a clew board, then you increase twist by attaching the jib in the lower clew attachment points. If you want to decrease twist, you connect the jib to the highest points, which increases leech tension.

If your self-tacking jib doesn’t have a clew board, the only thing you can do is play with the self-tacking track. The location of the track cart has some impact on twist but not as much as a clew board. 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. The leech line is used to control the fluttering of the leech. It is usually left alone because it does not truly impact shape or twist enough. However, if it is completely 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 to get a clew board.

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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