From tooling-driven constraints to robotic LFAM: engineering the next generation of marine stern structures

Engineering function and structural requirements of marine stern sections

Stern sections are load-bearing structural assemblies positioned at the aft end of the hull, forming the interface between the vessel’s primary structure and the propulsion system. In motorboat configurations, they integrate mounting areas for engines or outdrives, reinforcement zones for mechanical loads, hydrodynamic transition surfaces, and functional apertures for drainage or system routing. Their geometry directly affects flow separation, pressure distribution, propulsive efficiency, and wake characteristics, making dimensional accuracy and surface continuity critical from a hydrodynamic standpoint.

From an engineering perspective, these components must withstand static and dynamic loads transmitted by the propulsion system, cyclic vibrations, localized stress concentrations, and long-term exposure to saline water, UV radiation, and thermal variations. Structural stiffness, interlaminar strength (in composite solutions), tight geometric tolerances, and marine-grade surface finishing are mandatory to ensure mechanical integrity, proper hull integration, and long-term durability in aggressive environments.

Conventional manufacturing practices to date

Conventionally, stern sections are produced using mold-based composite manufacturing processes such as hand layup or vacuum infusion on dedicated female molds. This workflow requires the prior fabrication of master plugs and tooling, typically via CNC machining followed by manual surface preparation and coating. Such tooling represents a significant capital investment and introduces extended lead times before part production can begin.

The process is inherently labor-intensive and sequential, with limited flexibility for design updates once molds are completed. Any geometric modification requires tooling rework or complete replacement. Furthermore, trimming, mold preparation, and finishing operations contribute to material waste and increased cycle times. These constraints become particularly critical in medium-batch or customized production scenarios, where tooling amortization and process rigidity negatively impact cost-efficiency and responsiveness.

Process optimization through robotic LFAM

To overcome the structural and economic limitations of mold-based composite manufacturing, Caracol produced the stern sections by leveraging its robotic LFAM platform for composite production, Heron AM. This approach enabled direct manufacturing of the component in glass fiber reinforced thermoplastic composite, eliminating the need for dedicated tooling and decoupling production from mold fabrication constraints.

LFAM was selected for its high material deposition rate, process stability, and multi-axis robotic control, which allow the fabrication of large structural parts with controlled bead geometry and repeatable dimensional accuracy. The additive strategy enables near-net-shape production, reducing intermediate steps and minimizing material overuse typical of subtractive or mold-based methods. The adoption of ASA reinforced with 20% glass fiber ensured an adequate stiffness-to-weight ratio, thermal stability, and environmental resistance compatible with marine operating conditions.

Technical Data

• System: Heron 300 – HV extruder
• Nozzle size: 3 mm
• Material: ASA + 20% GF
• Printing time: 14 h
• Weight: 9.5 kg
• Size: 780 × 270 × 610 mm

Following the additive phase, the components underwent support removal and precision machining of functional interfaces. A controlled marine finishing cycle was then applied, including progressive sanding, vinylester-based surface correction, and final coating with either gelcoat or epoxy primer and paint to meet structural protection and surface quality standards required in boatbuilding.

Quantifiable industrial benefits and performance gains

The integration of Heron AM into the production workflow yielded measurable improvements across key manufacturing parameters. By eliminating mold production and significantly reducing manual composite layup operations, the process reduced non-value-added steps and compressed the overall production timeline.

The project achieved:

• Waste reduction up to 30%
• Lead time reduction up to 60%
• Cost reduction up to 60%

These results derive from optimized material deposition, tooling elimination, reduced manual labor, and a controlled 14-hour production cycle. LFAM is increasingly establishing itself as a scalable industrial technology capable of solving real manufacturing challenges, combining structural reliability, geometric freedom, and process repeatability within a fully digital workflow suited for demanding production environments.

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