Solving Boat Shower Drainage with Cardboard, CAD, 3D Scanning & 3D Printing

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The Hybrid Design Workflow: Building a Boat Shower Floor with Cardboard, CAD, and 3D Scanning: Walk through the hybrid design process for a custom boat shower floor. See how cardboard prototyping, CAD, 3D scanning, and 3D printing combine to solve complex drainage and access problems in a marine refit.

Author: Shayne and Anna

Introduction

Designing a complex, one-off part for a boat interior—like a shower floor that must drain perfectly, provide access, and integrate plumbing—requires more than guesswork. It demands a methodology that bridges intuitive understanding and digital precision. For our latest refit project, we employed a hybrid workflow, moving seamlessly from physical prototyping to advanced digital verification and fabrication. This post breaks down that process, from “Cardboard Assisted Design” to the final 3D print preparation.

Phase 1: Cardboard Assisted Design (The “Other” CAD)

Mock up of shower floor concept prior to CAD drawing

It all starts in the real world. Before a single polygon is modeled, we create full-scale mock-ups using foam board and cardboard. This “Cardboard Assisted Design” phase is irreplaceable for:

  • Ergonomics & Spatial Awareness: Understanding how the floor feels in the space, the reach to the hatch, and the overall scale.
  • Initial Problem Solving: Quickly testing ideas for drainage direction and hatch placement in three dimensions.
  • Creating a Template: The cardboard model provides the exact outline and key landmark locations to transfer onto the final foam core material.

This hands-on stage informs every digital decision that follows, grounding the design in physical reality.

Phase 2: Translation to Digital CAD

The cardboard model provides the essential framework, which is then digitized. In the computer-aided design (CAD) software, we build upon this foundation with precision:

3D CAD model showing shower hatch, toilet placement and carbon drainage tube.
  • Defining Drainage Geometry: We model exact falls (slopes) by creating tapered wedge sections in the foam core. The design features a central valley to collect water from both the fore and aft sections of the floor, mitigating issues from boat trim changes.
  • Hatch Engineering: The large inspection hatch is more than a hole. Its design includes:
    • Seal Compression Stops: Small steps in the hatch surround prevent over-compression and damage to the neoprene seal.
    • Flow-Through Geometry: Ramps and radii in corners prevent water and scum from pooling, ensuring everything drains into the gutter.
    • Dual Retention: The model accommodates both a simple bungee cord system and a backup mechanical hook-and-wingnut option.
  • Integrated Systems Design: The sump is modeled with a steep fall and a step to hold a stainless steel mesh hair trap. A carbon fiber tube is routed through a bulkhead, separating the wet collection area from the dry pump location—a critical lesson learned from past flooding experiences.

Phase 3: Verification with 3D Scanning

Overlay of CAD shower model on 3D scanned point cloud of boat hull

Even with careful measurements, the curved, organic shapes of a boat hull can differ from idealized CAD models. To ensure a perfect fit for bulky components like the toilet, we employed 3D scanning.

  • We scanned the specific compartment, creating a “point cloud” reality check.
  • This scan was imported into the CAD environment, where we could overlay our designed components.
  • The result was twofold: confidence that the toilet placement was feasible (no clashes with the actual hull), and the ability to tweak nearby bulkhead models to match the boat’s true shape. For complex refits, scanning is an invaluable tool for bridging the digital/physical gap.

Phase 4: Preparing for Fabrication – 3D Printing the Mould

With the design verified, the CAD model shifts from a virtual part to a tool for making the part. The negative space of our drain and sump cavity is used to create a positive mould.

  • The complex mould geometry is split into sections that fit within the build volume of our FDM 3D printer.

Conclusion

The journey from a rough cardboard mock-up to a ready-to-print mould file exemplifies modern practical fabrication. It combines the irreplaceable tactile feedback of physical prototyping with the accuracy, testability, and fabrication power of digital tools. This hybrid approach—Cardboard, CAD, Scan, Print—ensures that the final composite part isn’t just theoretically sound, but perfectly suited to the real-world, irregular environment of a boat. It demonstrates that thoughtful process is the most critical tool in the builder’s kit.

More Floor Construction

Building new composite floors has helped us make big gains on our quest to remove weight and lighten Paikea.

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