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How to Reef the Mainsail

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Slab Reefing System
Reefing Main 2

© International Marine

Shown here is a simple slab reefing system you can easily install on your boat if you do not have one. If you already have a reefing system, be sure you understand how it works before you need it in rough conditions.

This illustration shows a single-line system. Larger boats often have a double-line system, in which a second reefing line is added (on the other side of the boom) to the second (higher) set of reef points. There are also variations in the use of a hook, or reefing horn, at the forward reefing point on the sail’s luff.

Here’s how the reefing line runs:
  1. From a fixed point on the port side of the boom (not seen here) the line rises to the aft grommet in the sail, called a reefing cringle.
  2. The line continues down the sail on the starboard side to a turning block mounted on the boom, then forward along the boom to another turning block.
  3. The line rises up to the cringle on the sail’s luff edge. In this illustration the line passes through a block on a reefing horn and then back down. Alternatively, the line may pass through the cringle (and down on the port side) in the same manner as it did through the luff cringle. The advantage of the horn with a block is reduced friction, and the horn can be raised to a higher reef point as well; the disadvantage is that a crew has to go forward to position the horn.
  4. Finally, the line comes down to a turning block at the base of the mast and back to the cockpit, where it can be taken in for reefing.

The next page shows how this looks with the reef in place.

Illustration with permission from The Seaworthy Offshore Sailboat by John Vigor, © International Marine.

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