The Engineering Behind Our Bulletproof Composite Chainplates

/ Boat Systems and Upgrades, Bulkhead, Chainplates, Paikea Refit, Rigging & Systems, Working with Composites / By

Author: Shayne and Anna

Key Topic: Replacing our catamaran’s rotten, failing chainplates became an exercise in advanced composite engineering. By moving from a traditional bolted stainless steel strap to a fully integrated carbon fiber chainplate laminated within a new foam-core bulkhead, we eliminated the weak points of the old system. This post breaks down how distributing massive rigging loads over a vast, bonded surface area—rather than concentrating them on bolt holes—creates a connection that is not just a repair, but a permanent, bulletproof upgrade.

In our last post, we showed the fabrication of new carbon fiber chainplates for Paikea. This wasn’t just an upgrade for the sake of it; it was a necessary solution to a critical failure. The original system—a stainless steel strap bolted through a plywood-cored bulkhead—had served for over 30 years. But time and moisture took their toll, the plywood core rotted away, and the integrity of the entire rigging attachment was compromised.

The evidence was clear: the bolts were slowly but surely pulling upwards, allowing the entire chainplate to move. We needed a solution that was not only a repair but a long-term improvement. Our answer was to build a new, integrated system: a carbon fiber chainplate laminated directly onto a new section of foam-cored, e-glass bulkhead.

The Critical Question: How Does It All Stay In?

The most common question we received after the build was a logical one: How does this new bulkhead section, which is simply butt-jointed to the old structure, resist being pulled through the deck under the immense load of the rig?

The answer lies in a fundamental principle of composite engineering: load distribution.

Unlike a bolted connection that concentrates stress on a few small points, our composite solution spreads the load over a massive area. We don’t rely on the compressive strength of bolts through core material; we rely on the incredible shear strength of the bond between the carbon chainplate and the surrounding fiberglass.

The Secret: A Structural Sandwich

The key is how we integrated the carbon fiber chainplate. We didn’t just glue it to the surface; we sandwiched it between two layers of e-glass double-bias (DB) laminate.

  1. The First Layer: A bed of DB glass was laid on the new foam bulkhead, creating a perfect bonding surface.
  2. The Carbon Core: The unidirectional carbon chainplate was bonded to this first layer.
  3. The Second Layer: Another layer of DB glass was laminated over the carbon, encasing it completely.

This process effectively doubles the bonding surface area that transfers the load from the chainplate into the bulkhead. The load travels from the shroud pin, down the carbon fibers, and is then efficiently distributed through the DB glass into the entire bulkhead structure, and from there, into the hull and deck.

Beyond the Bulkhead: A Holistic Load Path

The bulkhead itself is more than just a mounting point; it acts as a vital structural web. Its primary role is to stabilize the hull panels, preventing them from flexing. The chainplate loads are distributed into this stiff web, which then transfers them throughout the boat’s structure via carefully designed taping that connects the new bulkhead section to the old, and to the hull and deck.

This creates a continuous, robust load path that is far superior to the original design, which relied on the limited bearing strength of rotten plywood.

Proven in Practice

This isn’t just theoretical. We’ve already sailed Paikea hard, putting the new chainplates under full rig load with the hull skimming the water. The system performed flawlessly, without a hint of movement or concern. It’s a solution we have total confidence in.

Exploring Different Composite Chainplate Designs

Inside Carbon Race Boats: The Engineering Secrets Production Builders Should Use

The beauty of composite construction is its adaptability. The principles of large bonding areas and efficient load distribution remain the same, but the execution can vary based on the boat’s design.

While our solution attached the chainplate to a bulkhead, another common and effective approach is to bond a long, tapered carbon plate directly to the hull side. This is often seen in modern race boats where bulkheads may not be in the ideal location for rigging loads.

If you’re interested in seeing this alternative approach, we documented the inside of a high-tech carbon race boat in the blog post Inside a Modern Carbon Fibre Race Boat: Chainplates & Structure

Conclusion: A Stronger Foundation for the Future

By moving from a failed mechanical connection to an integrated composite solution, we haven’t just fixed a problem—we’ve eliminated it. The new chainplates are lighter, stronger, and immune to the rot that doomed the originals. They represent a permanent, bulletproof foundation for Paikea’s rig, ensuring safety and reliability for the adventures to come.

The Permanent Fix: Carbon Fiber Chainplates & Bulkheads

Our temporary chainplate repair, securing the rig with upgraded bolts for an Atlantic crossing, had reached its limit. The underlying rot in the bulkheads, a legacy issue of the original construction, was now compromising the core structure. This project documents the only permanent solution: the complete removal of the failed plywood-cored bulkheads and the engineering, fabrication, and installation of monolithic carbon fiber chainplates. This is not a repair; it is a fundamental redesign that eliminates rot and creates a stronger, more reliable rigging foundation for Paikea.

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