Скачать или смотреть The Mainsail Paradox: Lessons from the Europe Dinghy

Thoughts on the Europe mainsail to mast stiffness question covering:
What the ideal set up feels like
The paradox of the mainsheet (mast stiffness matters)
Mast stiffness changes leech tension NOT mast bend
How to adapt for imperfect mast stiffness
Golden ratio of mast stiffness to righting moment

What the ideal set up feels like
With the correct combination power builds as you sheet on with the boom reaching the deck when the sailor is exerting their maximum righting moment. The mast stiffness is holding just enough leech tension that the sailor has adequate but not excessive twist. I think many people know this feeling, but the real problem is attaining the feeling and communicating a good set up so it can be replicated across a fleet with a range of equipment and sailor sizes.

The mainsheet paradox
The reason mast stiffness is so critical and also why such a range of sailor weights can be competitive in the Europe is due to the paradox of the two contradictory effects that mainsheet has on the boats upwind power.
The first effect of mainsheet as the boom moves toward the deck is it applies tension to the leech, reducing twist and increasing the angle of attack the sail presents to the wind which in turn increases power, especially up high. This increases heeling moment and the feeling of being powered up.
The second conflicting effect of sheeting the mainsheet and bringing the boom to the deck is that it tensions the leech which pulls down and backwards on the mast tip. This bends the mast, stretching the sail fabric horizontally along the chord between the mast and the now taught leech. This reduces the camber (depth) of the sail and reduces the power it produces.
If the mast is too soft you sheet the boom to the deck, removing all camber and power from your sail, before you build enough leech tension to reduce twist and lean your body weight against. Conversely, if the mast is too stiff as you sheet the boom down you build power too quickly as twist is reduced but the mast does not bend, leaving you with an overly deep sail which has lots of drag upwind.

Mast stiffness changes leech tension NOT mast bend
It is best to think of mast stiffness controlling leech tension, rather than mast bend. People wrongly think because their mast is soft and bendy, it will bend more with sheet tension and therefore flatten their sail more. This is not the case. If you have two mast, one stiff and one soft and hoist a sail with the same leech length on both, with the same rake and sheet the boom to the deck, then both masts will have identical total bend. The difference will be that the stiffer mast will put more tension into the leech.
Mast bend is really a question of geometry, so if the geometry remains the same (leech length and rake) then the mast will bend to same position.
This is important as it means lighter sailors with softer mast DO NOT need more luff curve. Adding more luff curve for a light sailor with a soft mast will only make their sail deeper and overpower them further. The converse is true for a heavier sailor with a stiffer mast. A given sail design should have a similar luff curve for all masts with only small tweaks made to accommodate for where that bend occurs (is it relatively bender up high or down low).

How can we adapt to a mast which is too stiff or soft?
If your mast is too soft and does not create enough leech tension with the mast set in the design rake position (and hence bend) then you can rake forward. However, be aware this will overbend your mast.
If your mast is too stiff and you are becoming overpowered to soon with a straight leech that you can’t open up through hiking then you can consider raking you mast back to reduce the relative distance between the boom and mast tip when sheeted to the deck. However, be aware this will under bend you mast.

The Golden Ratio – leech tension from mast V leech tension from righting moment
The Golden Ratio is leech tension generated by mast stiffness versus the leech tension generated by hiking. This should be comparable across sailors of different sizes.
To measure the ratio you will need a load cell and data capture.
Step 1: Measure your leech tension from mast stiffness alone with boat head to wind and boom 1-2mm off the deck.
Step 2: Sheet again to the exact same position, hike hard upwind for 1 minute. Take a average of the leech load.
Step 3: Calculate the righting moment leech tension by subtracting the base tension from the sailing fully hiked tension.
Step 4: Express the base tension and the righting moment tension as a % of total sailing leech tension.

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