Chain plate / bulkhead structure

[Brion Toss]

Hello,
Great question. First, all bulkheads athwart the mast act as spreaders; it’s just that with the cables on this boat the vertical load component is largely removed from the bulkheads. But the bulkheads still have to deal with the consequences of horizontal loads, and this is where the tabbing comes in, keeping the hull/rig system intact, while the weather chainplates try to pull the bulkhead inboard (with some up, too), and the keel tries to pull the weather side of the hull down. Perhaps the deformation is less with the cables you mention; it was developed to allow for lighter hull structures without loss of stiffness. But the tabbing is far from decorative.
Overall, if the hull scantlings reflect the advantages of this configuration, I’d say the tabbing is just as significant as with a conventional setup.
Fair leads,
Brion Toss