Case study for developing Concept and Basic design of a Modular Dredging Pontoon Platform

1.Introduction

We have completed another interesting project for the development of concept and basic design of a Modular Pontoon platform. The planned area of operation of the vessel is the coastal waters of the Black Sea.

This case study introduces the steps involved in the design process and outlines the specifications of the task. We’ve been asked to create the concept design as a first step and thereafter proceed with the basic design. During the whole process one of the most important understanding was ensuring maximum safety while developing the most efficient design.

Our Hull and Steel Outfit department was trusted with the engineering of the:

single platform design
assembled modular platform (25 pontoons)
locking arrangements
control platform
modular railings
standard container steps for the installation of the mobile equipment, as the number and reinforcement during their installation in the deck of the pontoons is in accordance with the required safe load capacity
chains and other suitable standard elements with the appropriate load capacity attached to shaped „sockets“ in the deck for ensuring additional fixing of mobile equipment

Our Electrical and Automation department had the task to design:

electrical system
lighting
signal lighting
communication system

2. Overview of the technical specifications

The floating platform is a modular pontoon platform with spud pols. The platform consists of 25 single pontoons, divided into two types – Type I and Type II (20 pcs. – Type I and 5 pcs. – Type II)

2.1. Main dimensions:

Overall dimensions of the assembled platform:

Length L = 30.0 m
Width B = 16.0 m
Pontoon height D = 1.6 m
Displacement at draft 1.0m Δ = 462.48 t in saltwater

Pontoon dimensions Type I:

Length L1 = 6.0 m
Width B1 = 3.2 m
Board height D1 = 1.6 m

Pontoon dimensions Type II:

Length L1 = 6.0 m (bevel at 3.0 m)
Width B1 = 3.2 m
Board height D1 = 1.6 m (freeboard height at the end of the bevel 0.75 m)

Weight of a single pontoon Type 1 – 7.852 t

Weight of a single pontoon Type 2 – 7.293 t

Total weight of the assembled platform: 193.49

Our engineers wanted to develop the most efficient concept and this is the reason for choosing these particular dimensions of the single pontoons. The size of the pontoons allows:

Easy transportation and loading
Easy storage
Adjustable size of the platform based on the needs

Spud Poles

There are also 4 spud pols, powered by hydraulics, which are attached to the platform. The pylons have a maximum length of 15.0 m, are composed of sections with a length of about 3.0 m, this allows them to be assembled with a suitable length in each case. The maximum depth at which the platform can be used for anchoring is about 11.0 m.

2.2. Crew

The vessel does not have permanent crew accommodation as well as a permanent crew. During operation, it is serviced by about 5 – 10 people, depending on the task performed.

3. Loading Scheme

On the assembled platform it is planned to place:

mobile crane or excavator (for the initial calculations we use the overall dimensions and weight of the LIEBHERR LTM 1080/1 crane – loading capacity 80.0 tons)
diesel-electric generator with power 60 kW (+ 350 liters of fuel for it)
hydraulic station
control platform with a cabin 3.0×2.0 m
additional load – 40.0 tons of additional load on the platform deck has been added to the listed equipment in the weight calculations

* Total weight

Weight = 169.15 tons,
Draft = 0.37 m
Freeboard = 1.23 m

4. Locking devices

5. Additional elements

12 pieces of knitting bollards arranged according to the respective scheme. The bollards are fixed to certain single pontoons.
modular railings – attached with removable mechanical connections to the deck, which allows within certain limits to change their location on the platform depending on needs. Height of the rails 1100 mm from the deck.

All these elements are fixed with removable mechanical connections, which allows within certain limits to change their location on the platform depending on needs.

6. Stability and Strength calculations

One of the most important parts of our involvement in this project was the Forecast Stability in operation

Due to the reduced number and volume of the single pontoons, the stability of the platform was checked when the crane was working in the forward direction (according to the general arrangement) and on the starboard side. The weight, height, and distance of the lifted load are in accordance with the permissible requirements for the operation of the crane specified in the Technical Data.

Our engineers performed stability calculations for two loading scenarios. The purpose of the calculations is to determine the most appropriate positioning of the required equipment.