How to operate an in‐mast furling system correctly

An in‐mast furling mainsail is an increasingly popular option. The advantages of such a system are clear: easy handling of the sail when setting, recovering and reefing. And once in harbour after a nice sail, there is no need to flake and cover up the mainsail on the boom. Once rolled up in the mast, it has stowed itself away. Easy!

The disadvantages, on the other hand, became less and less over the years as the furling systems developed. This concerns the mechanics in the mast, but also the cut of the sails themselves. A modern furling mainsail, especially one with full‐length vertical battens, sets as well as a conventional sail. And modern sailcloth also ensures that they can always be rolled up and unrolled reliably.

Advantages of a furling mainsail: Safe and easy handling without having to leave the cockpit.

How to operate an in-mast furling system correctly

Let's start with furling the sail. Only a tightly rolled up sail can be unfurled easily without jamming. The sail should be rolled up firmly and without creases. We achieve this by setting the boom vang tightly when furling and at the same time keeping tension on the outhaul line. We can see it often when furling a headsail: Without tension on the sheet, it rolls up loosely, with many creases and will become baggy. This does not look nice but otherwise it will not matter. With a mainsail in the mast, however, it can cause the sail to jam.

First, we turn the ship head to wind and then bear off a few degrees. If the sail in the mast is rolled up counter‐clockwise, we bear off to port. This keeps the sail free from the edge of the mast when furled. If it is rolled up clockwise, we bear off a few degrees to starboard. Then we set up the kicker so that the sail becomes flatter. Then we loosen the mainsheet and finally furl the sail, always maintaining some tension on the outhaul.

Everything tidily packed. Furling sails do not need to be packed or stowed.

Unfurling works in the same way, only the other way around, with one difference: this time the boom vang or kicker should be loose so that the boom can rise as the sail is unfurled, to make it easier. When the sail is fully unfurled, the sail profile can be perfectly adjusted by the tension of the foot (using the outhaul) and boom vang.

If the sail gets jammed during furling, it is probably due to the sail being rolled up too loosely, as mentioned above. In this case you should try to pull the sail tight on the roller profile inside the mast. To do this, hold the outhaul and roll up the sail again a bit, keeping the outhaul well under tension. Then unfurl again; if necessary, repeat this manoeuvre several times.

Another reason can be a backstay that is too tight. If the mast bends, the rolling profile inside will not be able to turn freely. Likewise, if the mainsail halyard is set up too tight it can cause the sail to throw horizontal folds and these get jammed. Rarely does it happen that the furling profile in the mast is too loose and has to be tensioned – but this is a job that you cannot really do yourself with on‐board equipment.

Furling mainsails with vertical battens have the same sail area as conventional mainsails.

Reefing a furling mainsail is of course very simple and works like furling. Ideally, you should also make sure that you reef the sail on the „right“ tack (depending on the direction in which the sail is furled, as explained above). Some sails have strips to indicate reefing points but it is entirely up to you and the wind conditions how far you reef.

The mechanics of a modern furling system are robust and reliable, but it certainly doesn’t hurt to remove the salt from the moving parts and also the blocks of the lines from time to time or to make it all nice and smooth again with a small drop of oil. It becomes more problematic when the sail itself is already old and blown out. If the cloth has been stretched a lot, it becomes more and more difficult to roll it up smoothly. In this case a new sail would certainly work wonders – for the smooth operation of the in‐mast furling as well as for the performance of your yacht!