Reefing is the way to reduce sail area quickly when your boat becomes overpowered. When buying a mainsail, your UK Sailmaker will determine how many rows of reefs are needed. Buying more reefs than necessary adds expense and extra weight to the sail.

Most buoy racers buy a sail with a single reef or no reefs at all, because they are concerned about adding too much weight to the sail. A single reef will be used on most boats in winds around 25 knots since most racers put up smaller genoas before reefing.

A second reef is used in winds blowing close 30 knots — conditions where most day races have been cancelled. Those doing distance races need a second reef.

A third reef is only used by sailors who venture offshore.  

A double-reefed mainsail and heavy weather jib on a J/133

When tying in a reef diamond, make sure to tie around the sail only and not around the boom. This way you are less likely to rip the sail if you go to shake the reef without untying the reef diamonds.