The first series of 3 photos shows a modification for the bow tube to help stiffen the boat by upgrading the attachment. The usual attachment is with a single bolt at each bow; the mod replaces the stock tube with a new tube cut to fit (within class rules) and attached by through bolting two bolts at each bow.
The second set of 3 photos shows the next phase of stiffening the boat by through bolting the cross tubes via portholes added to the doghouse. If you have an older boat with water logged foam that needs to be removed, this mod would best be done when the decks have been lifted from the hulls.
The replacement of the bow tube requires the re-routing of the forestay bridle as shown in the last row.