Under Sails

After some intermediate steps and experiences with other yachts and boats, we have found a balance between these three poles on our F41 catamaran.

Effective are traditional sails such as gaff sails, which come close to an elliptical shape and can thus use the wind effectively. The performance of traditional triangular sails is limited. These were created by the competitive passion of the British, who developed balancing formulas for different ships during sailing races on the Thames.

(Sciarelli: „Lo yacht. Origine ed evoluzione del veliero da diporto“ (1970) https://www.amazon.de, Italian)
(Sciarelli: „Die Yacht. Ihre Herkunft und ihre Entwicklung“ (1973) https://www.amazon.de, German)

One of these formulas penalised the size of the gaff, which led to the current shape of triangular mainsails. Also, unlike gaff sails, triangular tall rigs are easier to operate by a smaller crew, but require stronger materials.

In modern rigs that are not constrained by racing measurement formulas, the gaff comes back in the form of the effective square sail – Well seen in the Americas Cup yachts, the Volvo Ocean Race (VO65 and Imoca 60) or the A Cat class.

Touring catamarans also have a corresponding sail batten in the top. Our mainsail is furled on a Leisure-Furl boom, which we have kept for comfort and cost reasons, even though this furling sail costs about 25% power – compared to a fully battened squaretop sail. In the meantime, we really like the stepless reefing option at the push of a button and have taken to reefing a little later than we would have to with a high-performance squaretop sail. This saves nerves and power. The only restriction is the amount of height on the wind that we can run with this sail. A high-end sail would probably go 5 ° higher. This is also due to the fact that the battens in a groove-guided sail can only exert half the horizontal pressure as a batten sitting in a furling car. So trimming the mainsail flat has its limitations.

The height on the wind is lower with a cat compared to slender monohulls. Therefore, investing in sails that promote height on the wind makes little sense. For example, 3D sails, which hold the profile shape chosen by the designer beautifully, are therefore superfluous for catamarans.

In the last three years, we have only once used our cat to the full height on the wind that our F41 can sail with its two daggerboards: We sailed upwind for two days on the English south coast at NW high on the wind. With reefed main and working jib, we still had 13 knots of speed in 22 knots of wind. However, this meant that every third wave rolled over into the cockpit and the spray from the port bow blew as a flag 15 metres astern. Arriving in Falmouth completely exhausted and soaked with salt water, we decided not to use this uncomfortable performance option of our boat in the future.

A flat sail trim on board a cat has different limitations than on monohulls. The large beam and design limitations do not allow for the rig tensions that are possible on monohulls. We have experienced older series catamarans that were so soft that we could screw the shroud tensioners completely loose without the wires coming loose, because the hulls simply sank down with them. If you then tighten the shrouds as much as you are used to on monohulls, the doors on these catamarans jam!

In catamaran rig designs, the mast profile is defined by the diamond stays. The mast is held only by the forestay and the windward shroud. The leeward shroud hangs loose. Some even tension it aft with long rubber bands to keep it from dangling. On our F31 trimaran, the windward shroud could be tensioned aft at a joint with an 8-fold shorn tackle, which trimmed the mast up to 12 degrees to windward. At 15 degrees heel, the mast was almost upright. This gave power – also because the aft tension in the rig meant that the two headsails (jib and code 0 on the jib boom) could be put through better.