All the new bits of rudder shaft and tiller attachment were fitted over the last week (more on that later) and, in order to fit them in, it was necessary to cut a slightly larger hole in a bit of deck that had been caulked and sikaflexed. The bit cut away gave a cut through view of how the deck will look… 
This section is a new bit so has a straight seam rather than the “y” shaped seam in most of the deck. None thesis the principle is the same. The depth of the seam is plugged with the caulking cotton. This helps plug up the depth, provides a barrier should any water get in, and is a flexible material allowing the deck to shrink and expand as the weather changes. The sikaflex (historically this would have been tar) sits on top and – crucially – meets both top edges of the deck either side of the seam. The cross section shows that this has worked as planned. Best of all, when I tried to pull the seam apart and tugged and twisted it in ways that the deck would never actually move….  It was stuck fast and didn’t budge an inch. Good stuff indeed!