Join Date: Oct 2007
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I have experienced the same effect many time. The following is a mental experiment to try.
Your boat is trimmed properly for wind coming from 60 degrees off the bow.
The boat is not moving (lets assume it is held back for some reason) This not moving constraint is not necessary but makes it easier to visualize.
The wind starts low and gradually increases
The wind hitting the sail exerts a force against the mast (the force against the mast is what ultimately moves the boat).
That force is composed of two vectors.
One vector attempts to tip the boat over.
One vector attempts to move the boat forward.
The weight of the keel resists the vector to tip the boat over.
As the wind increases the force to tip the boat will increase.
At some point the healing of the boat will be excessive.
At that point you have two three choices.
Spill the wind by easing the sheets
Reduce sail by reefing
Or do both
All of these three choices will reduce healing but also reduce the force attempting to move the boat forward.
At some point the force moving the boat forward will be so low it will not be enough to overcome all of the forces that exist to keep the boat stationary.
It is pretty obvious that even in perfect conditions on a beam reach with flat seas and steady wind there is a minimum amount of sail area required to got any boat to move at all. IE a clean-ex will not sail a 30 footer.
Also as the wind increases and the sail is reefed nothing improves but lots of things detract from efficiency.
The sail bags (unless you have a hi-tech racing sail)
Your halyard stretches.
A reefed sail is seldom the perfect shape.
The mast bends (can be a good thing but often not.)
Waves and chop builds
All these things slow you down.
I remember being disappointed about how badly several boats would point when the wind exceeded their sweet spot, usually about 14 knots for Catalina's 25,27,30.
A boat that would point through an arc of 90 degrees in perfect conditions would be hard-pressed to manage 120 if it had to be reefed.
Your experiencing the same thing but instead of pointing it is being manifest as a slowdown.