Case Study: Engineering a Bespoke Boat Unloader System for PD Ports

Overview

Subco Engineering partnered with PD Ports to design and deliver a robust, rail‑mounted boat unloader system capable of transporting vessels safely and efficiently from quayside to workshop. The project demanded deep technical insight, adaptable engineering, and close collaboration across multiple disciplines. The resulting system provides PD Ports with a highly configurable, future‑ready solution engineered for reliability and operational safety.

The Client Challenge

PD Ports required a system to move a range of vessels — from smaller boats to those up to 35–40 tonnes — from the water into a maintenance shed. The solution needed to:

• Accommodate multiple vessel types, each with different hull geometries and masses
• Operate safely in challenging maritime environments with strict wind‑speed, load, and operational limits
• Interface with existing quay and rail infrastructure
• Provide a repeatable, dependable workflow for crews performing vessel transfers

Early assessments showed that critical loading assumptions (e.g., vessel weight readings) were sometimes inaccurate, meaning the engineering solution had to be robust enough to tolerate real‑world variability.

Our Approach

Subco Engineering delivered a phased design programme covering concept development, detailed engineering, and project close‑out. This structured approach ensured clarity, control, and adaptability throughout.

1. Front‑End Concept Development

The first phase included:

• Full load‑case modelling
• Basic trolley concepts and weight estimation
• Preliminary winch specification and ground loading assessments
• AutoCAD layouts showing rail locations, winch positioning, and diverter sheave arrangements

This established a strong design foundation and enabled PD Ports’ civils teams to begin early planning with accurate data.

2. Detailed Mechanical Design

The next stage translated concepts into engineered systems with defined geometry, components, and interfaces. Key elements included:

Dual‑Trolley System

• Two trolleys, adjustable from 5–8m centres, enabling flexible vessel support positioning
• Each trolley equipped with four wheels operating on A65 crane rail or BS113A flat‑bottom rail for maximum stability

Adjustable Support Cradles

• Multiple vertical and lateral supports to suit a wide variety of hull forms
• Lateral support angular adjustment between 95°–125° and height adjustment of approx. 500mm, ensuring a secure, tailored fit for each vessel type

Winch & Sheave System

• Dual winches providing controlled pull with defined operational and static load ratings
• Ground anchors, diverter sheaves, and tow points engineered for predictable and safe vessel movement under load

3. Safety & Operational Engineering

Operational limits were clearly defined, including:

• Maximum operational wind speed of 15 m/s and survival wind speeds up to 23.7 m/s
• Transverse and longitudinal load design criteria
• Clearly documented PPE and operational procedures within the O&M manual

Delivering the Final System

At project conclusion, Subco Engineering delivered a comprehensive package including:

• Full drawing set (PDF & DXF for fabrication)
• O&M manual for safe operation and maintenance
• Technical specifications and loading documentation
• Final engineering close‑out report summarising performance, lessons learned, and contractor feedback

The final close‑out documentation confirms the system comprises a rail‑mounted, dual‑trolley configuration with adjustable supports, moved by a paired winch system — purpose‑designed to reliably handle two main vessel classes with precision and safety.

Project Impact

The new boat unloader system provides PD Ports with:

✔ Greater Operational Control

Precise load distribution, modular cradle components, and controlled winch movement allow reliable vessel transfers independent of vessel type or hull shape.

✔ Improved Safety and Repeatability

Engineering controls and detailed O&M processes ensure teams can move vessels safely with consistent methodology.

✔ Future‑Ready Flexibility

The system’s wide range of adjustments enables PD Ports to support future vessels without major redesigns, protecting long‑term investment.

✔ Engineering Assurance

Subco Engineering’s detailed load cases, rigorous design checks, and structured project delivery provide clear traceability and confidence in system performance.