Handbook of Offshore Engineering, Vol 1

HANDBOOK OF

OFFSHORESURVEYING

VOLUME I

EDITORS

H-J LEKKERKERK

M.J. THEIJS

PROJECTS,

PREPARATION

& PROCESSING

Skilltrade provide courses, training and assessment in:

- Introduction Hydrography Course

- Hydrographic Survey Course - Category “B” (recognised by the FIG, IHO,ICA)

- Subject Courses: Positioning, Multibeam Echosounder, Side Scan Sonar, Tides or Earth Science

- Company specific Courses

- Survey Engineer Course

- General courses: Culture & communications, International Business, Project Management,

Change Management & Survey software

- Personnel Assessment, Appraisal & Competence Support

- GIS course

Course References:

Acergy - Survey Basics, Theory and Software

- 3-week course

AllSeas - Personnel Assessment, Hydrography and Survey Engineer

- 3-week courses

Boskalis & Van Oord - Cultural Communications

- 2-day course

Gardline - Geophysical Survey Engineer

- 3-week course

ReadWellServices - Geodesy, Theory of Errors and GPS

- 1-week course

SAIPEM - extended Introduction Hydrography

- 1-week course

Seaway Heavy Lifting - Survey procedure & Survey Equipment

- 2-day course

Contact:

For a complete overview of all our courses please contact us on [email protected]

! Skilltrade BV - 1 -

COLOFON

Editors: Huibert-Jan Lekkerkerk Maarten-Jan Theijs

Chapter Title Author(s)

1 Introduction to Hydrography Huibert-Jan Lekkerkkerk; Tim Haycock

2 Nautical charting Cor Mallie; IHO survey manual

3 Dredging Huibert-Jan Lekkerkerk; Willem van der Lee

4 Inspection Pieter Jansen; Tim Haycock

5 Survey for Offshore Installation Tim Haycock

6 Rig Moves Tim Haycock

7 Cable and Pipe lay Pieter Jansen; Tim Haycock

8 Remotely Operated Vehicles Pieter Jansen; Paul van Waalwijk van Doorn

9 Personnel and Organisation Pieter Jansen; Huibert-Jan Lekkerkerk

10 Geotechnical Survey Fugro

11 Seismic Survey Robert van der Velden

12 Land survey Huibert-Jan Lekkerkerk; Peter Veldkamp

13 Gravity & Magnetic Survey Pieter Jansen; Aad van Dam

14 Project preparation Pieter Jansen; Fugro; Huibert-Jan Lekkerkerk

15 Survey Operations Huibert-Jan Lekkerkerk; Pieter Jansen; Arie Goedknegt

16 Processing and Reporting Huibert-Jan Lekkerkerk, Maris; Cor Mallie; Pieter Jansen;

Peter Veldkamp

Photo’s and drawings: Skilltrade BV unless stated otherwise

Copyright © Skilltrade BV, 2nd

edition, 2011

ISBN: 978-90-816591-1-6

This book has been carefully prepared from the best existing sources of information available at the time of preparation but

Skilltrade BV does not guarantee the accuracy of the book nor the limits, extent or position of any drawings/illustrations represented therein nor does Skilltrade BV assume any responsibility or liability for any reliance thereon. The information contained in this document is subject to change without notice.

The information contained in this document is the exclusive property of Skilltrade and/or the respective authors. This work is protected under copyright law of the Netherlands and the copyright laws of the given countries of origin and applicable international law, treaties and/or conventions. No part of this work may be reproduced or transmitted in any form or by any given means, electronic or mechanical, including photocopying or recording, or by any information storage or retrieval

system, except as expressly permitted in writing by Skilltrade BV.

Note-1: we have made every effort to refer all articles, text and pictures to the right person and company. In case you are of the opinion that we have missed something please inform us by sending an email to [email protected]

Note-2: in case you find an error or a mistake in this Handbook please inform us by sending an email to [email protected]

Note-3: to order additional copies of the Handbook visit www.skilltradebookstore.nl

Skilltrade BV P.O. box 111 2250 AC Voorschoten

The Netherlands

Tel: +31 (0)71 561 1365 Fax: +31 (0)71 561 1503

Email [email protected] www.skilltrade.nl

HYDROGRAPHIC SURVEY CATEGORY “B” COURSE

In 2001 Skilltrade BV started with sharing the knowledge and experience its people had with

others, ipso facto trading information. This resulted in a 2day general course “Introduction

Hydrography” and evolved into very specific courses like Multibeam Echosounder, DGPS, RTK,

SSS and Tides. Later on it emerged that there was a requirement for 5d Offshore Construction

Surveyor and Surveyor Dredging courses, Company specific courses and the assessment of

personnel. Hundreds of people have been trained on these courses to date.

Skilltrade BV joined forces with the STC Group to develop a Hydrographic Survey Course. On

the 1st of July 2008 our Hydrographic Survey Course received international recognition from

the IHO-FIG-ICA International Advisory Board on Standards of Competence for Hydrographic

Surveyors and Nautical Cartographers as a Category “B” course.

The 13-week Hydrographic Survey Category “B” course runs twice a year and starts, with

adequate registrations, every year in January and August (www.skilltrade.nl). To date over 60

individuals have been trained on this course.

We like to thank the following companies and all of our former students for their continuous

support and involvement in our Hydrographic Survey Course.

Maarten-Jan Theijs MBA BSc.

Course Director

[email protected]

Van Oord

QPS

DEEP BV

Reson

Port of Rotterdam

Noordhoek Survey BV

IxSea

Nortek BV

Swedish Maritime Authority

Ashtech

Sonardyne

Seatronics

Meteo Consult

AllSeas

Nautronix

Rijkswaterstaat, Northsea dep.

Boskalis

CDL

Hydrographic Service RNN

Boskalis

MMT AB

Stema

Deltares

Geometius

Visualsoft

Seaway Heavy Lifting

EIVA

Kongsberg

piLot Survey Services

MDL

Heerema

Global Marine

AGIP KCO

Acergy

Tesla Offshore

SwetsODV van Laar

Gardline

SAIPEM

Marine Sampling Holland


CONTENTS

1 INTRODUCTION TO HYDROGRAPHY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.1 Definition and scope of hydrography 7 1.2 Industry / Project types related to Hydrography 8

2 NAUTICAL CHARTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.1 Data Production 13 2.2 Nautical Information System (NIS) 13 2.3 Data Quality for charting purposes 15

3 DREDGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.1 Introduction 18 3.2 Construction 19 3.3 Wet earth moving 23 3.4 Environmental dredging 23 3.5 Geotechnical Design Issues for Dredging works 24 3.6 Geotechnical issues for nearshore structures 27 3.7 Dredges 31 3.8 Calibration of dredging equipment 32 3.9 Types of vessels 34 3.10 Survey in support of coastal management 36 3.11 Survey Execution For dredging 39

4 INSPECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4.1 Route Survey 41 4.2 Site Survey 45

5 SURVEY FOR OFFSHORE INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 5.1 SPAR / Floater Installation 50 5.2 Structure Installation 51 5.3 Suction Pile Installation 54 5.4 Platform Foundation design issues 55 5.5 Anchoring design issues and installation constraints 57

6 RIG MOVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 6.1 Preparation 60 6.2 Mobilisation 60 6.3 Jack-up rigs 62 6.4 Semi-Submersible rigs 63 6.5 Reporting 64

7 CABLE AND PIPE LAY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 7.1 Pipe / cable lay terminology 65 7.2 Foundation design issues and installation constraints 67 7.3 Pre-Lay Survey 69 7.4 Pipeline Installation 70 7.5 Trenching Support 76 7.6 Pipeline Ploughing and Backfilling 76 7.7 As-Laid Survey 77 7.8 As-Trenched Survey 78 7.9 Pipeline Inspection Requirements 78 7.10 Umbilical and Cable Lay Support 80

8 REMOTELY OPERATED VEHICLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 8.1 Why ROV’s 84 8.2 ROV types. 85 8.3 Dive Procedure 93


9 PERSONNEL AND ORGANIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 9.1 Project organization For dredging 96 9.2 Project organization For Offshore projects 97 9.3 Functions 97 9.4 Personnel Competency 100

10 GEOTECHNICAL SURVEY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 10.1 Geotechnical survey for construction 102 10.2 Geotechnical survey and laboratory testing 103

11 SEISMIC SURVEY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11011.1 Reflection seismic 110 11.2 Refraction seismic 112

12 LANDSURVEY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 12.1 Control Surveys 113 12.2 Construction support 116 12.3 Other landsurvey project types 117

13 GRAVITY & MAGNETIC SURVEY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 13.1 Gravity survey 118 13.2 Magnetic survey 118

14 PROJECT PREPARATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 14.1 Tendering 119 14.2 Office Preparation 119 14.3 Accuracy, Quality Control, and Quality Assurance 123 14.4 Quality Assurance Documentation 124 14.5 Acts and Regulations 128 14.6 HSE 131 14.7 Communication 135

15 SURVEY OPERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 15.1 Survey Specifications 140 15.2 Statistics 141 15.3 Equipment selection 155 15.4 Survey Lines. 160 15.5 Mobilization 164 15.6 Interfacing of equipment 167 15.7 Telemetry 171 15.8 Data collection 175 15.9 Survey control 183 15.10 Demobilization 184

16 PROCESSING AND REPORTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 16.1 Processing 185 16.2 Data validation 188 16.3 Interpolation 201 16.4 Digital terrain models 205 16.5 Data Management techniques and Data Quality Control 209 16.6 Volume Calculations 215 16.7 Presentation 220 16.8 Reporting 230

Skilltrade BV - 7 -

1 INTRODUCTION TO HYDROGRAPHY

1.1 Definition and scope of hydrography

According to the on-line Britannica Encyclopaedia, hydrography is: “The art and science of compiling and producing charts, or maps, of water-covered areas of the Earth's surface”. The latter is correct but incomplete as hydrography as perceived by the industry also includes amongst others charting of the water column parameters, geology of the seabed sediments and positioning issues. A more official definition is given by the International Hydrographic Organisation (IHO):

"Hydrography is the branch of applied sciences which deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers, as well as with the prediction of their evolution, for the primary purpose of safety of navigation and all other marine purposes and activities, including economic development, security and defence, scientific research, and environmental

protection."

1.1.1 International Hydrographic Organization

The International Hydrographic Organization is an intergovernmental consultative and technical organization that was established in 1921 to support safety of navigation and the protection of the marine environment. States can become a member of the IHO and are usually represented through the Hydrographic Office or equivalent organization of that member country.

Competency and branches The day to day operations of the IHO are run by the International Hydrographic Bureau (IHB) which is located in Monaco and functions as a secretariat to the IHO. The IHB is managed by the Directing Committee consisting of three Directors elected at the International Hydrographic Conference held every 5 years. The IHO distinguishes a total of 197 competencies divided over 12 main subjects and 7 branches as shown on the figures below. Associated fields are earth and environmental sciences. Engineering geology and geotechnics become involved whenever construction related design activities would be performed on the basis of the data acquired. Generally hydrographic data is part of a larger set including geophysical, geotechnical, oceanographic and meteorological data.

Figure: Competence and Branch overviews (Source: IHO)

! Of the branches listed, nautical charting and military hydrography are generally not or only partly performed by the civilian market. As a consequence only the remaining 5 are considered in this handbook; with an emphasis on offshore construction and dredging. ! Coastal zone management is primarily related to dredging associated with shoreline protection and

harbour construction. The hydrographic content is large and generally sophisticated due to the detailed design requirements and the measuring accuracies during the execution of the work. ! Offshore seismic has a limited hydrographic scope that primarily consists of positioning of vessel,

guns and streamers by means of surface and acoustics positioning techniques. ! Offshore Construction has a wide range of hydrographic requirements in a pre-design phase, followed

by a more positioning related scope during the installation phase. Owing to the amount of remote intervention tasks, survey activities are generally linked to the use of Remotely Operated Vehicles (ROV), which complicate the interfacing, and to a lesser extent the calculations involved. ! Remote sensing is only used in a few hydrographic applications but the processing and GIS

techniques used in remote sensing can be applied widely throughout the entire field of hydrography

Skilltrade BV - 18 -

3 DREDGING

3.1 Introduction

Offshore or nearshore dredging programmes entail lowering of the seabed and disposal of the dredged material to another (approved) location. In some cases, seabed lowering is the main objective, such as for the creation of a harbour basin, an approach channel, or for a pipeline trench. In other cases, reclamation of soil is the main objective and seabed lowering is just a means of mining the material.

Geotechnical investigations are always needed at the seabed lowering site and often also at the disposal site. The seabed lowering site may sometimes be chosen at an earlier stage than the disposal site, or vice versa.

The area covered by a dredging project may be very large compared to the area required for offshore or nearshore structures.

The dredging process usually comprises four main stages: ! excavation, comprising the loosening, fragmentation or cutting of the soil or rock ! raising the excavated material to the surface by hydraulic or mechanical methods ! transport of the excavated material to a reclamation or disposal area ! disposal or use of the dredged material.

Each stage requires specific knowledge of the soil or rock properties of the site. One of the following types of equipment is typically employed for the first and second stages: ! Trailing suction hopper dredger. ! Stationary suction dredger. ! Cutter dredger. ! Dredging mill. ! Grab on pontoon or on vessel (with or without hopper). ! Backhoe on pontoon or on vessel (with or without hopper).

Figure: 3 different types of dredgers often used (left: hopper; middle: cutter; right: backhoe)

If (hard) rock needs to be removed and cutting is not possible or suitable, the dredging activity may be preceded by breaking the rock with explosives.

The third stage (transport) does not require additional equipment when a hopper dredger, or other vessel capable to transport the dredged material, is used. In case of stationary dredgers, this stage may require separate (hopper) barges, berthing alongside the dredger, or pipelines in which the material is transported as a soil-water slurry.

The fourth stage (disposal) may be done using bottom doors (hoppers), pumps, specially shaped pipe-ends (sometimes onshore; sometimes attached to a special pontoon), grabs or other equipment. The choice of dredger type, and other equipment, largely depends on the soil and rock characteristics and on the environmental conditions, such as water depth, current, sand transport and waves. Trailing suction hopper dredgers are virtually the only type of equipment capable of operating in the open sea. Heave compensators and floating pipelines may assist in facilitating the operation of other types of dredgers working at sea, but waves always seriously limit the choice of equipment.


4 INSPECTION

Inspection surveys are performed to determine the state of the seabed and are usually followed by construction or dredging works. Depending on the demands the inspection survey can comprise anything from a simple bathymetric survey using single beam echosounder to a multi-disciplinary project. The following types of inspection survey and their requirements are described in this chapter: ! Route survey ! Site survey ! Seismic survey ! Geotechnical survey ! Magnetometer survey ! Gravity survey

4.1 Route Survey

4.1.1 Survey requirements

Careful use of available data in many cases can be used for efficient planning of site specific studies and can reduce the scope of a dedicated site investigation.

A route survey is performed in the early stages of a pipeline installation project and is usually executed 6 months to 2 years before the actual pipeline installation. From this survey the pipeline engineers will determine the optimum pipeline route and determine ‘depth of burial’ according to the seabed properties. In cases where the environment is very unstable, e.g. strong currents, sand dunes and tidal effects, the project team may want to gather environmental data by placing current and tidal gauges along the route.

In general sense a Route Survey will attempt to establish some or all of the following: ! The topography and character of the seabed, ! The composition of the layer of sedimentary material immediately beneath the surface of the seabed, ! The presence of debris on the seabed, ! The confirmation of the positions of existing sub-surface structures, including pipelines, cables,

templates and wellheads.

Figure: Side Scan Sonar picture of debris on the seabed, existing pipeline (www.klein.com)

The project engineers of the pipe lay construction company will assess all the reported findings. Of particular interest is the topography along the proposed pipeline route. A longitudinal profile, derived from a digital terrain model, provides every meter along the proposed route an absolute depth reading. This data forms the basis for the pipeline stress analysis and free span determination can already be calculated from this information. It is therefore imperative that the digital terrain model (DTM) is as close to reality as possible. To achieve this objective it is important not to overly smooth the DTM, and it would perhaps be wise to specifically generate a non-smoothed DTM derived longitudinal profile specifically for this purpose. Consultation with the project engineers on this issue is advised. It may occur that the proposed route will be amended due to the reported preliminary findings on board. These route changes can be caused through the findings of boulder areas, pockmarks (holes in the seafloor where gas or liquid rise) or rocky outcrops, basically any hostile environment for the installation of pipelines..


5 SURVEY FOR OFFSHORE INSTALLATION

5.1 SPAR / Floater Installation

Tethered structures are employed in deep-water environments where conventional Platform designs are impractical. A typical example is the Heidrun Tension Leg Platform in the Norwegian sector of the North Sea, shown below along with the associated offshore storage and load-out facilities (SPARS / Floating Production Storage Offloding oiler - FPSOs)

Figure: Heidrun Platform; Heidrun Platform loading schematic

On installation of Tethered (Floating) Platforms or SPARs, the mooring system will already be in place and the primary task is to ballast the structure and hook up the Mooring lines. The mooring system typically comprises of Anchor piles, Pile chains and mooring wires. The Survey team will usually be on the Installation vessel and information is gathered remotely from the structure under tow and the Anchor Handling Tugs (AHTs). FPSOs are in general self-propelled.

The Geodetic reference systems will be in absolute co-ordinates and the only relative distances observed might be Fanbeam observations to assist the DP system on the Installation Vessel. Preparation Tasks will comprise the installation of the equipment packages and testing of sensors. ROV mounted sensors will need to be zeroed or aligned for heading and depth data. Data to be used for the display on the Survey monitors should include the Anchor pile locations, chain catenaries information and suspended buoyancy arrangements.

The preparation tasks by the Survey team include: Checking the Geodetic data, KP system and Target co-ordinates provided Checking that the C-O's and scale corrections to the individual sensor units are applied and re-

calibrated if necessary. This applies to the ROV sensors and LBL array checks if used, as well as the surface systems.

Check communications and Video overlay information required from ROV control Preparation and mounting of the Platform or SPAR mounted sensors Measuring offsets to a datum position on the Platform or SPAR

On commencement of the tow out, the AHT and Structure Telemetry systems need to be tested. On arrival of the Installation Vessel on location an ROV survey is carried out on the anchor array and any new debris or obstructions to the running of the anchor wires inspected. On arrival of the Structure on location, ballasting (usually upending by release of buoyancy tanks in the case of SPAR structures) is carried out and the hook up to the mooring system commences.

Figure: Tow-out and installation of SPAR (image courtesy of Heerema)


7 CABLE AND PIPE LAY

7.1 Pipe / cable lay terminology

The following typical lay terminology for the surveyor on a lay-barge will be explained. The “new words” are used in the sequence of the lay i.e. from stem/bow to stern.

Figure: Lay terminology and barge layout

!Joint: Length or section of pipe: 12.5 m. Pipes are stored in a pipe racks at/near the bow of the barge !Weight coat: Concrete mantle around the pipe attached to outside steel. Typical length: 12.0 m !Pulling Head: Is a solid section of tubular steel with a large eye-pad to its end. The other end is

welded to the first joint. ! A/R wire (Abandon and Retrieve Wire): Steel cable(s) that connect the pulling head to the DMA. !DMA: Dead Man Anchor: A 5 tonnes block of concrete used to secure the A/R wire during the

initiation of the pipe lay. The DMA is normally placed a pre-determined number of meters behind the KP 0.000. !Line Up Station (LUS) or Beadstall: Location on the lay-barge where a joint will be welded to the

previous joint. The joint to be welded will be aligned to the already/previous joint in such a fashion that there is a predetermined space between the 2 joints and that the new joint is level with the previous joint. On more primitive barges a person named “Spacer” was in control of this activity. The exact location of the LUS in local or real-time coordinates is very important (for the surveyor) as from this location the length of the last joint of a pipeline will be determined. (Hell will break loose if the surveyor calculates the lay-down joint erroneously).

Figure: Welding station


9 PERSONNEL AND ORGANIZATION

Personnel are a key factor for successful project execution. It is very important to allocate responsibility to personnel as this eliminates any ambiguity. The responsibility of personnel is captured in the functional descriptions and these reflect the position, authority and reporting line(s) within the company. With these guidelines laid down for each individual, a clear understanding of relationships and communication lines is achieved. These must be chosen such that they will reflect the company organization.

Each person has his or her specific assignment; this can be going offshore as Surveyor or be the Base Surveyor in the office or anything else your company wishes you to do. These specific assignments are captured in the job description, and will outline the tasks involved inclusive of reporting line(s). This does not mean however that one should confine oneself to the tasks outlined in the job description. The job description is a guideline, whenever one feels that he can help his colleague, this should be done if it does not hamper regular operations (with the exception of safety issues where help should be immediately).

Specific functions require certain training and experience. In light of the ISO 9000 (2000) standards personnel competency is a requirement within Management Systems, and is outlined in the paragraph on Personnel Competence.

9.1 Project organization For dredging

A large number of dredging projects are run by so-called combinations. In these combinations a number of dredging companies participate to be able to complete a large project. One of the companies will be the main contractor and supply the project manager. The other departments are divided between the different companies. Personnel from all the partners are used for each department.

Figure: project organization typical dredging project

Project

manager

Survey Electronics Super

intendent

Engineering QA / HSE

Chief surveyor

Account

Administration

Electronics engineer

Surveyor 1

Surveyor 2

Data processor 1

Data processor 2

Equipment 1

Master

Navigation

Engineer

Dredging operator

Equipment 2

Worksmanager


10 GEOTECHNICAL SURVEY

Knowledge of sea bed geology, morphology, properties, and sea bed dynamics is essential for planning of infrastructural projects as deepening, widening and maintenance of shipping routes, offshore artificial islands, coastal extensions, windmill parks, pipeline and cable routes, sea bed structures, fisheries, mineral exploration and so on. The sediments occurring at and below seabed are highly depending on the environment of deposition: shelf, slope, deep sea, deltaic and the hydrodynamic circumstances of the sea as currents, waves, long shore transport etc. Based on geophysical surveys with multi beam, side scan sonar and seismic systems a seabed-sampling plan can be made.

Plan

Data-

acquisition

Data storage and

interpretation

Development

data products

Figure: Scheme showing the successive steps of a survey

Depending on the aim, a choice has to be made which sampling method and system will be used. For instance on a shelf near by the coast coarse sediments will occur, while near the shelf edge finer sediments will be present. At the slope the same process takes place. At the upper part the sediments will be coarser than at the middle or lower part of the slope. In the deep sea pelagic muds occur, partly derived from the slopes by turbidity currents and partly by sedimentation of organic skeletons of microorganism, and fine dust particles dropping to the ocean floor from the water column.

Figure: Scheme showing the occurrence of the different sediment types and minerals at the shelf, slope and deep sea

10.1 Geotechnical survey for construction

Usually a development and production plan for a platform must include a detailed geotechnical evaluation of the platform's foundation based on analysis of one or more soil borings from the site.

In addition, it is a must to perform sufficient geological/geotechnical sampling and testing of foundation soils to thoroughly categorize foundation engineering conditions within the proposed pipeline corridor. The principal purposes of the geotechnical survey are to:


14 PROJECT PREPARATION

14.1 Tendering

Every company that wants to trade needs to provide a service. And in order to provide this service a proposal needs to be made outlining exactly how and when it is executed. The client will then award the contract to the successful bidder. The criteria where upon the client selects his sub-contractor do vary but it is usually the price of the bid, which is the governing factor. There are certainly other criteria, which the clients will take into consideration, they can be the following: ! The available resources of the sub-contractor at time of execution, ! The technical proposed standard for execution of the works, and ! The financial health of the sub-contractor.

Especially when the works to be executed are large then the available resources and financial health of the sub-contractor are seriously taken into consideration, as the client wants to know whether the sub-contractor has the necessary resources and finances when projects overrun or partially/totally fail. The client does not want to be brought into a position where they need to go out for tender again to finish the works because the sub-contractor is bankrupt.

In order to prepare a proposal, the client has to provide the sub-contractor with an ‘Invitation To Tender’ (ITT). In the document all relevant information is provided to prepare the proposal. In case areas of the ITT are unclear, clarifications can be asked of the client. The client will respond to the sub-contractor and provides the clarification to all other tenderers as well. With all the provided information it is the task for the sub-contractor to prepare a concise and competitive tender.

The internal tendering process of the sub-contractor needs to be such that the services match the client’s requirements. When the ITT is received, the sub-contractor will analyse the documents and various company departments will be invited to provide their specific input. When all the information is collated into a document, it is usually checked independently within the company. Part of the tender preparation is a risk analysis and the head of tendering will assess this information to judge whether the proposal is fit for issue. When all aspects of the proposal have been carefully examined and approved it may be issued to the client.

When, at the tendering stage, items of the project have been overlooked they have subsequently not been priced either, making the likelihood far greater for being accepted by the client as a competitive tender. When the tender then is awarded great financial difficulties may arise from that mistake. The proposal however is binding and has to be executed according to the client’s scope of work for the sum of money, which is detailed in the proposal. Needless to say that from the onset such a project will become a great loss.

14.2 Office Preparation

14.2.1 General

Once as project has been sold and handed over to the project manager, he will investigate the requirements. A generic approach does apply to the project preparations and the build up to the actual mobilization. The following steps can be distinguished: ! Office preparation (e.i. tender, contract, procedure) ! Definitions (e.g. scope of work, time scale, equipment, personnel, costing, safety) ! Project Plan (e.g. works, quality, SoW, project specifics, procedures, operating instructions, standards) ! Check of supplied data and information ! Equipment selection ! Health, safety & environment ! Applicable Acts & Regulations ! Quality Assurance ! Project deliverables which define the overall set-up of the system and the way the data will have to be

managed.

What ever the type of project, method of data collection (manually or automatically) or part of the world the project is in, the above does apply. The time spend for a proper preparation easily pays itself back in the execution phase of the project.


15 SURVEY OPERATIONS

15.1 Survey Specifications

Requirements for hydrographic surveys arise as the result of policy decisions, product user reports or requests, national defense needs, and other demands. The inception of a specific hydrographic survey project follows an evaluation of all known requirements and the establishment of priorities. Among the many objective and subjective factors that influence the establishment of priorities are national and agency goal, quantitative and qualitative measures of shipping and boating, the adequacy of existing surveys, and the rate of change of the submarine topography in the area.

To accommodate in a systematic manner different accuracy requirements for areas to be surveyed, four orders of survey are defined by IHO in publication S-44 edition 98. As these specifications are created with nautical charting surveys in mind, most clients in the offshore construction and dredging industry will have specifications that go beyond the special order of the IHO. In some countries additional orders have been created for easy project specification. Notwithstanding this limitation on the IHO orders, the items mentioned are well worth considering in every survey specification.

Order Special 1 2 3

Examples Harbours, berthing areas, and associated critical channels with minimum under keel clearances

Harbours, harbour approach channels, recommended tracks and some coastal areas with depths

up to 100 m

Areas not described in Special Order and Order 1, orareas up to 200m water depth

Offshore areas not described in Special Order, and Orders 1 and2

Horizontal accuracy 5

2 m 5 m + 5% of depth 20 m + 5% of depth

150 m + 5% of depth

Depth accuracy (reduced depths)

1,5a = 0.25 m b.= 0.0075

a = 0.5 m b.= 0.013

a = 0.1.0 m b.= 0.023

Same as Order 2

100% bottom search Compulsory2

Required in selected areas

2May be required in selected areas

Not applicable

System detection capability

Cubic features > 1 m

Cubic features > 2 m in depths up to 40 m; 10% of

depth beyond 40 m

3

Same as Order1

Not applicable

Maximum line spacing4

Not applicable, as 100% search compulsory

3 x average depth or 25 m, whicheveris greater

3-4 x average depth or 200 m,whichever is greater

4 x average depth

Notes:

! To calculate the error limits for depth accuracy the corresponding values of ‘a’ and ‘b’ listed in the table have to be introduced into the formula

!22 )( depthba +±

! For safety of navigation purposes, the use of an accurately specified mechanical sweep to guarantee a minimum safe clearance depth throughout an area may be considered sufficient for Special Order and Order 1 surveys. ! The value of 40 m has been chosen considering the maximum expected draught of vessels. ! The line spacing can be expanded if procedures for ensuring an adequate sounding density are used.

The figures should be interpreted as follows: ! spacing of sounding lines for single beam sounders, and ! distance between the outer limits of swaths for swath sounding systems. ! All accuracy’s are stated to the 95% confidence level

15.1.1 Special Order

Hydrographic surveys approach engineering standards and their use is intended to be restricted to specific critical areas with minimum under keel clearance and where bottom characteristics are potentially hazardous to vessels. These areas have to be explicitly designated by the agency responsible for survey quality. Examples are harbors, berthing areas, and associated critical channels.


! Trunnion (cutter suction dredge) Vessel offsets are often measured twice by independent personnel in order to confirm the measurements.

15.6 Interfacing of equipment

To read out the sensors data it is necessary to define the communication of the software with the sensor. There are several important things when defining the communication. ! Choose the right cabling. ! Choose the right system / right driver in the software ! Choose the right communication parameters / settings ! Choose the right use of the data messages

15.6.1 Connection and cabling

The correct type of cabling used to connect a sensor with the acquisition computer depends in the first place on the sensor. Most sensors in hydrography use communications according to the serial principle. Another regularly used type of communications is the network TCP/IP protocol.

Analog-Digital conversion Some telemetry systems have an analog input for instance some tide gauges using pressure sensors with a analog output this output can be a direct input to the telemetry system.

Figure. tide gauge

In the telemetry the analog output will be the input for a analog to digital converter which will have a serial output connected to the transmitter

Figure: Analog-Digital conversion

This signal will be the input for the transmitter and can be made analog again if necessary on the receiver side by using a digital/analog converter or can be used as input for a computer.

Serial communication Serial communication has the advantage of covering large distances (up to tents of meters.) The cables are relatively easy to be made (do it yourself) and exist of a cable with 9 or 25 pins connectors. Onboard survey vessels, the 9 pin connectors are used in general, because it is easier to lead them through small holes. You can use converters when the sensor has got a 25 pins connector.

Documents

Handbook of Offshore Engineering, Vol 1