Dyneema in the Cold

Dyneema experiences a negative linear thermal expansion coefficient in the direction of the fiber. What this means is that it stretches as it cools. Minor differences in temperature will not create an appreciable difference in length, leading to loss of tension, but more drastic differences will.

What this means is that your rigging will go slack during the winter which is of little consequence since the sailing season ends before it gets cold enough to notice the difference. I tensioned my rigging when it was between 60F and 80F. Now that the temperature has dropped down to below 20F, we are seeing an appreciable slackness in the standing rigging. 

The headstay which is usually bar tight in the spring, summer, and fall, is now loose. I can easily pull down on the headstay's deadeye and create this much gap (nearly 6mm or 1/4") with one of my arms and little effort. I needed an incredible pulley system to achieve the necessary tightness when the rigging was installed in warmer weather. 

If I were inclined to sail on these freezing days, I would need to tension the rigging again. By waiting for the warmth to return before I set sail again, I don't need to do such adjustments. When the air warms again, rigging will once again regain its pre-established tension without being touched.

The other option I have available on these frigid days is to tighten the rigging by hand, when the warmth returns, the rigging will be tighter than I could have ever dreamed of achieving. This is nice from the standpoint of "achieving sufficient tension" but this unnecessary tension can lead to greatly increased forces exerted on the rigging which can lead to premature failures of the fittings.

Rigging tensions, as everything else on the yacht, is a double edged sword. More tension equates to more forces which leads to greater loads and stresses, which leads to premature gear failures. Always be mindful of how tight your stays are and remember that the mast fittings and chainplates have to distribute these great loads.