Engineering a Bespoke Forestay Attachment & Mastering “Wet Preg”

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Key Topic: Replacing our catamaran’s aluminum beam with carbon fiber meant reinventing how critical components attach. For the forestay, this led to a unique engineering solution: a custom transverse pin and slot system that channels load directly into the unidirectional carbon of our recycled America’s Cup mast. This video and post also dive into the professional composite technique of “Wet Preg,” where we pre-assemble the entire carbon fiber reinforcement patch in the laminating room for perfect resin control and accuracy before vacuum bagging it into place.

Author: Shayne and Anna

Replacing our catamaran’s original beam with a carbon fiber one meant reinventing every attachment point from scratch. For the critical forestay connection, we engineered a unique solution that leverages the unique properties of our recycled America’s Cup mast carbon. This process also gave us the perfect opportunity to demonstrate a professional composite technique known as “Wet Preg,” which gives unparalleled control over resin content and laminate accuracy.

The Engineering: A Unique Forestay Pin Solution

The challenge was to transfer the immense load from the forestay into the carbon beam and, ultimately, into the seagull striker and martingale. Working with the existing geometry of our recycled mast sections required a custom approach.

Our solution was a transverse pin and dual-slot arrangement. This design allows us to transfer the load directly into the large unidirectional carbon planks from the original mast, efficiently channeling the force through the entire structure. The pin itself is crafted from 19mm Nitronic rod, salvaged from our old rigging, making it a true example of upcycling.

The Technique: “Wet Preg” for Perfect Patches

For the reinforcing patches around the forestay pin, we used a method called “Wet Preg” (or “Kiwi Preg”). This technique bridges the gap between standard wet layup and factory pre-preg (pre-impregnated) carbon fiber.

Here’s how it works:

  1. Template Creation: A precise template is created, marking the exact size and stagger for each layer of the carbon patch.
  2. Pre-Wetting: The carbon fiber is cut and wetted out on a table, allowing for perfect resin control and elimination of dry spots.
  3. Pre-Assembly: Using the template, the entire multi-layer patch is built and stacked with perfect overlaps on the laminating table, sandwiched between two pieces of plastic.
  4. Application: This pre-assembled, wet “puck” is then carried to the job site and applied in one go before being vacuum bagged.

The key advantage is knowing the fiber-to-resin ratio is correct before the laminate even touches the part, resulting in a stronger, lighter, and more professional finish.

A Crucial Upgrade: The Inner Forestay Point

A key part of this project was adding an inner forestay attachment point on the longeron. This allows us to fly a storm sail or trinket in heavier air—a crucial safety and performance upgrade for offshore sailing. Instead of reefing our large headsail and compromising its shape, we can now easily switch to a smaller, more robust sail designed for strong winds.

Conclusion: Problem-Solving with Advanced Composites

This project exemplifies the problem-solving at the heart of our refit. By understanding the materials and advanced techniques like “Wet Preg,” we can create custom, high-performance solutions that are both strong and elegant. The new forestay attachment is not just a copy of the old one in a new material; it is a completely re-engineered system designed to make Paikea safer and more capable.

Catch up on the entire Front Beam Project:

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