Figure 1. Fender connection module

Figure 2. Fender connectors engagement in progress

ABSTRACT

Marine platforms such as pontoons or barges often need to be joined together to create a larger overall working surface such as bridge, a floating base or a floating causeway. This paper introduces a novel design concept. The key technical challenges for constructing such large platforms in rough seas are discussed. The design concept amalgamates multiple functional requirements, such as rapid self-alignment, impact attenuation and rigid engagement, into an integrated design. The engineering process from concept generation, model testing, detailed design and evaluation, material selection, prototyping and sea trials are presented. Potential applications for offshore operation are illustrated.

Han Lei

INTRODUCTION

Joined platforms at sea can be used as floating bridges or causeways to create ship-to-ship, ship-to-shore as well as shore-to-shore links. However, one of the key technical challenges in constructing such joined floating platforms lies in the connector design which must address the difficulties related to the relative motion between two floating platforms, particularly during the connection process in rough seas. The connector design must also be able to sustain the dynamic forces as a result of the wave motion both during the connecting process as well as after the connection has been established.

The relative vertical motion of two platforms in choppy sea can be more than 0.5m (as has been observed during sea trials). In such conditions, it is very difficult for an operator to judge exactly when the two platforms are aligned in order to secure the platforms together manually. It is also very dangerous for the operators working at the edges of the platforms as the platforms not only move up and down but can also knock against each other. Such violent motion can potentially cause serious or fatal injuries to operators who may lose their balance and fall into the gap between the two platforms.

There are several patented designs which have addressed the various problems with connecting two platforms in rough seas. They include the patent specifications of US 4290382, US 3386117, US 4695184, JP 20203488 and US 5606929. These patented devices utilise guided coupling pairs which allow for two platforms to become increasingly aligned as they are brought together. However, the coupling pairs are rigid by design and can cause significant impact loading on each other, particularly when the engagement process is not completed.

This paper presents a securing system (granted Patent No. 109504) - fender connector module. It is able to provide an alignment function and also absorb the severe impact loading between two platforms.

CONCEPT DESIGN

Fundamentally, an ideal securing system should have the following functions:

• Self-alignment
• Impact attenuation
• Rigid engagement
• Adequate strength

The system should facilitate the securing of two floating platforms in rough water with minimum effort in the shortest time. The system, once interlocked, should provide a stable working surface and survive in rough seas without any structural damage.

Design principles

The dynamic motion of the floating platforms is the primary concern. When a specific operational sea state and the main parameters of the platform have been defined, the dynamic motion of the platform at sea can be predicted, from which the operational tolerance of the connecter modules can also be defined.
The following principles were used for guiding the conceptual design development:

Systematic Design Approach

Among the four principal design requirements, 2 and 3 are contradictory because characteristics of elasticity and rigidity are in opposition in a single material. While we can go for a "smart" composite material which could adjust its hardness on demand, its cost-effectiveness would however be questionable. This was the key challenge that the design had to resolve.

An integrated and optimal design is derived by achieving the four required functions without compromising individual performance. Staging the functional requirements and separating the features into different components were the main ideas leading to the design development

Conceptual Design

The conceptual design was generated based on the principles discussed and is illustrated in Figure 1.

The connector comprises 'D' fender and a 'V' recess fixed to one side of the marine platform, and two Rigid Stoppers and two Side Recesses fixed next to the 'D' fender and the 'V' recess respectively on the same side of the marine platform. As illustrated in Figure 2, the 'D' and 'V' coupling members on two different platforms have a complementary relationship and can be moved from an unengaged position to a fully engaged position by the movement of the two platforms towards each other at the water level plane. The freedom of movement between the two coupling members decreases as they become engaged. The Rigid Stoppers and Side Recesses will create a rigid coupling to prevent relative vertical and longitudinal movement, as the freedom of movement between the 'D' and 'V' coupling members nears complete engagement. The 'D' member is made of a resilient yet flexible material (e.g. rubber) and can withstand impact loading between the two platforms. Securing means - Locking Bars - are included to secure the floating marine platforms together in the transverse direction.