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If a mast bends beyond what the mainsail can adapt to (beyond the luff curve built into the sail), the sail shape will distort and become inefficient.

See the drawings of typical over-bend creases and what the cause might be. Thanks to Ian Pinnell from P&B Sails

The way a 5O5 mast is generally rigged it is easy to get the mainsail too flat in the bottom and middle sections while having the top relatively full.

Too much bend in the middle where the spreaders are? The spreaders are too long for those conditions. Rake less or move shroud bases aft.

Too much bend at deck level? Pull the ram down to straighten the mast at deck level. it is easy to think “I need more mast bend I shall ease the ram. This is the opposite of what you need to do.

Too much Vang can also over-bend a mast.

Not enough power, particularly in the lulls? Make sure you have sheeted the jib on properly to ensure the top luff tell tale is flowing. Make sure yo have pulled the boom back to centre, eased cunningham and rig tension (and maybe vang).

In this photo the boom is not pulled in all the way so the crew cant lean harder and harness the wooer available.

Every time the crew needs to stop leaning the boom should be pulled in hard so crew can continue to lean as hard as possible.

This requires constant communication between helm and crew.

The mainsail may need to be flatter but it is likely you are sheeting the jib too far inboard or too tightly.

Check that the jib leach tell tale is flowing. If it inst you likely have the jib over sheeted and you should ease the jib sheet.

If that isn’t the problem, then sheet the jib further outboard by moving the Barber Hauler.

STILL WORK IN PROGRESS

Mast is bending down low even with ram on because it is touching the back of the mast gate. 

Mast too bent when raked. This happens because the spreaders are pushing too much on the middle of the mast….

Jib leach too open when mast raked.

Sails too full or flat

                 Sails have too much or too little twist

                 Sails incorrectly sheeted

Boat isnt balanced

OVERBEND CREASES AND CAUSES

Photos thanks to Ian Pinnell

P&B Sails