Construction of a cantilevered bow turret for FPSO

Courtesy of MODEC

FPSO Whakaaropai

Location: Maui B Field, New Zealand

Client Name: Shell Todd Oil Services Ltd.

Installation Date: August 1996

Water Depth: 110m (361ft)

Tanker Size: 135,510 dwt

Vessel Type: MODEC Converted FPSO

Storage Capacity: 750,000 bbls

Fabrication: External Cantilevered Bow - Singapore

Vessel - Singapore

External Turret Mooring Systems provide an excellent solution for a wide range of FSO/FPSO applications.

These proven single-point mooring systems permit the vessel to freely "weathervane" 360 degrees, allowing normal operations in moderate to extreme sea conditions. External turret systems are less expensive than internal turret designs and can be delivered in a shorter period of time, making them an excellent choice for many applications. External Turret Mooring Systems can be mounted at either the bow or stern of converted tankers or new-built vessels. External turret systems are designed and built for a few risers, in shallow water, for moderate environmental conditions but pending on some customer and market requirements, turrets could be designed and extended in technology for use in harsh environments and to support a large number of risers and flow throughput. The FPSO Whakaaropai (Maui-B), offshore New Zealand, was developed to withstand 10.6m significant seas and support two large risers in 110 meters of water. The turret mooring required the design and development of a high load capacity and fatigue resistant turret and turret support system.

Design Environmental Criteria (100-year storm) :-
Significant Wave Height: 10.7m (35.1f)
Wind Velocit: 40.2m/s (74.5 knots)
Current: 1.1m/s (2.2 knots)

Mooring System :-
10-leg Chain-wire-chain asymmetric catenary:
6-in. ORQ chain, 4.375-in. ORQ +20% top chain
5.5-in. 6-Strand wire rope, 24mt and 32mt High holding power drag embedment anchors

Fluid Swivel Assembly :-
Crude Oil: 1 x 12-in. piggable toroids
(680 psi design/1,025 psi test)

Produced Gas: 1x 6-in. piggable in-line (2,550 psi design/3,850 psi test)

Riser System :- 1 x 10.5-in. Flexible riser, 1 x 4.5-in. Flexible riser

When designing turret mooring systems for ship-shaped vessels, one of the most important vessel design factors affecting the mooring line tensions is the location of the turret. The farther forward the turret is located away from the mid-ship, the easier it becomes for the vessel to weathervane into an equilibrium heading under non-collinear environments.

However, the farther away the turret is placed, the more the vertical motions at the fairleads due to the vessel pitch will increase, which could have an adverse effect on the mooring line tensions in the line dynamic mooring analysis.  When considering the total impact of the turret on the hull, the bow turret has proven more cost effective in both benign and harsh environments.

The bow turret can be configured in two ways: Integral bow turret (built within tanker bow)  or the Cantilevered bow turret as in the Whakaaropai FPSO.

 

A fully weathervaning vessel has operation expense advantages over a controlled heading limited rotation vessel, but the inherent requirements of a swivel joint for each flow path imposes practical limitations on the number of flow paths that can be provided for a fully weathervaning vessel.

Whilst all turret systems are disconnectable, the term is only used for turrets having the facility for quick connection and quick disconnection (QCQDC). Most of the turret systems that have been designed for fairly benign weather and shallow water are disconnected when typhoon is expected.

 

In 1995, one of my first project in the shipyard's subsidiary is the construction of the 750ton gross weight turret which involves alot of thick welding ( on the chain table where steel thickness ranges from 4 to 6 inches ) and there is need to understand where to use temporary bracing ( using 6-8inch diameter heavy schedule pipes) to hold the chain table reinforcement structures to prevent weld shrinkage and unexpected weld cracks. This crack could be heard with loud "explosion" sound when it happened. The chain table is main core structure that seats the big 6 metre diameter roller bearing ( costing turret designer few mils to order ) and this roller bearing allows the turret to freely weathervane so that the tanker can take up the position of the least resistance to the prevailing weather, at all times. I recalled that the stud bolts for holding this big bearing is sized approximately 2.5inch diameter by 3feet length. One person would have hard time trying to carry this heavy stud.  Bolt tensioning by hydraulic system was done on these 100plus pieces of studbolts.This stretching/elongation is maintained by the head of the bolt and the nut on the joint thereby maintaining the joint at the desired tension (Bolt tensioning).To produce clamp load, the bolt must be placed in tension. If the bolt is not stretched then there is no clamping load. The bolt start to stretch elastically (not reaching the yield), proportional to the amount of nut advancement. As the nut is further turned by the "tommy bar" the threads of the bolt and nut are forced together under enormous pressure generating friction between the mating threads and also causing tensional twisting to the body of the bolt between the clamped surfaces. The bolt is experiencing two forces simultaneously, tension and torsion.
In a bolted connection, the bolt must be stretched sufficiently to produce static preload upon the connection that is greater than the expected external load rather than the joint assembly acting upon the bolt themselves. These external loads must be known so that the proper grade, size, diameter, thread pitch and number of fasteners can be chosen to create a safe joint or fastening.


As a rule, the joint will have been designed with sufficient fastener to apply the required clamp load at 65% of the fastener proof load stress figure i.e. well below the fastener’s yield point. There is also an auto-greasing system connected by stainless steel tubing with over hundred grease outlet points around the perimeter of the roller bearing and the timing of autogrease is done through the small auto programming pack.

 

Courtesy of Bolt tight

The chain-table forms the connection point for the anchor lines of the turret mooring system to the FPSO vessel. Mooring loads are transferred from the chainhawse connection points through the chain-table structure to the turret and the main weathervaning bearing into the ship’s bow structure. The chain-table also provides the entry points for the product risers and houses the foundations for the bend restrictors (as required). The chain table after fabrication weighs about 250tons and would required to be post-weld heat treated due to the welding sizes of exceeding more than 2 inches.  A temporary shed was moved into the workshop where the chain table was completed and prepared for gas fired to heat the 250ton steel to 650degree centigrade and holding at this temperature for two hours and then letting it cool down to ambient temperature.  About 200bottle of LPG gas with 3 to 4 gas burners were mobilised to do this PWHT treatment. Spent about $70k internal insulating the shed enclosure to keep the temperature inside and preventing much heat loss to the outside. After this heat treatment process, weld stresses relieved, an Australian machining company Furmanite was called in to carry out the laser level chain table bearing surface machining.

 

The Chainstoppers and Chainhawses :-

Ten chain hawse supports, each consisting of two cast steel pieces having a hook shape, are welded to the chain-table deck. The chain hawse assemblies complete with chainstoppers are fitted into the hooks via a self lubricated bearing which allows the chain hawse to rotate and align with the chains. A tubular guide trumpet ensures proper alignment of the chain during tensioning and helps the articulation of the chainhawses.

The turret also consist of a patented design Swivel Stack Assembly. The swivel stack assembly consists of an inner non-rotating ring and an outer rotating ring that encloses a toroidal shaped chamber. The individual swivel rings are stacked atop of each other to provide multiple independent flow paths. The inner and outer ring concentricity is maintained by triple race roller bearings. Seals around the periphery of the interface between the inner and the outer rings prevent leakage of the working fluid.

The swivel design is based upon the following guiding principles:

-Swivel redundancy

-Flow re-routing as back mode of operation

-Ease of maintenance with minimum intervention
-Maximum use of field proven designs

Some design the driving arrangement of the swivel stack as integral part of the overhead frame-work structure. An individual driving ring is supported at two opposite sides by a fork arrangement. Each swivel unit is therefore driven on both sides of the outer ring simultaneously resulting in a pure driving torque with no net shear being applied on the piping flanges.  The swivel sealing system incorporates double seal sets in each module. A leak detection system and recuperation system is built-in between the seals which collects any product fluid and returns it to the production flow.  

After completion of post weld heat treatment and special laser level machining done by Furmanite, the 250ton chain table is being moved out for the main hull assembly and installation of the main 6metre diameter slew roller bearing.

Installing the main turret hull to the chain table ( left hand side )

  

                         

                                                   Above is sample setup - not actual one as I could not find from my archives machining video of chain table

Furmanite Australia was engaged to carry out machining of the approx. 6m diameter chain table. At that time, the mobilisation and machining cost for the job was almost more than quarter mil. They supply and use a range of specialized self-levelling rotary milling machine fixed to a rotating beam arm. These are ideal for use in machining very large circular or irregular shaped surfaces. Circular faces up to 45m (150 feet) or rectangular faces up to 11.5m by 11.5m (38ft x 38ft) are able to be machined in a single set up. The machines follow a reference plane electronically, utilising the strength of the item being machined for support. This allows the use of lightweight machines. The machines are highly adaptable, allowing for machining of all faces                                                       from vertical to inverted.

The machine uses a laser controlled actuating system to raise and lower the cutting head which in turn maintains the flatness and “best fit” for the service.

Capacities and range of Machining could work up to :

• CLLM : 2.5m – 24m (8’ – 80’) diameter
• Low profile CLLM : 1.8m – 4.1m (6’ – 13.5’) diameter

Leonard T. Roe - An experience driller and toolpusher

In August 2004, I was on my way to Stavangar to attend the Offshore exhibition ( similar to that of OTC yearly held in Houston, though I had been to Houston many times but never been to OTC ever ) and I had made a purpose stopover trip to London Heathrow Terminal 3 for the first time to meet up Leonard Roe ( Len, in short after we known each other ) for an interview to be our drilling engineer. I got to know Len through his "Workover" drilling website and found him likely suitable candidate to fill our company's vacant post after speaking to some other candidates of similiar triats and experience.  A fit British army in old days, Len was a toolpusher in the early 70s' and had worked for Maersk back then. I landed at Heathrow airport, it was usual over crowded and packed and but somehow it was not that difficult to find Leonard at one of the counters where you book for a cab. At first sight, Len gave me the impression of the "roughneck" type with strong and big physique. We had some food in the hotel cafe and then we move on for an "informal" interview.  Len showed me his past credentials and his working experiences and his current work as drilling well control instructor and presenter. He had given me some of powerpoint presentations and he showed me very keenly and proudly his work, how he did his animations in powerpoint. I had the whole night assessing and understanding his working experience and his knowledge in well control and offshore drilling. Flew back to office after the purposed trip and discussed about Len's work to our management. After some track record checks and reviews, we finally hired Len in November that year. Len left us 2010 and had to return UK to further his treatment on his throat and I have no idea of his present condition whether he is improving or not. He has a son in the twenties and wife is in home care due to old age. Hope Len is still around and busy with his stuff on his website, www.drillfloor.com

Part of my in-between flight schedules while on way to ONS2004 exhibition:

Wed, Aug 25: SCANDINAVIAN AIRLINES, SK 0505

From: COPENHAGEN, DENMARK (CPH) map Departs: 2:55pm
Departure Terminal: TERMINAL 3 Gate: Check for latest information
To: LONDON HEATHROW, UNITED KINGDOM (LHR) map Arrives: 3:50pm
Aircraft: MCDONNELL DOUGLAS MD-90 JET Mileage: 594
Flight Time: 1 hours and 55 minutes

Thu, Aug 26: SCANDINAVIAN AIRLINES, SK 2520
From: LONDON HEATHROW, UNITED KINGDOM (LHR) map Departs: 10:45am
Departure Terminal: TERMINAL 3 Gate: Check for latest information
To: STAVANGER, NORWAY (SVG) map Arrives: 1:30pm
Aircraft: BOEING 737 JET Mileage: 554
Flight Time: 1 hours and 45 minutes

Leonard T. Roe

Rig manager and Drilling Superintendent

 

From November 2004 until November 2010 (6 one year contracts) held in the position of consulting Principal Engineer Drilling in Singapore to assist in setting up a drilling team.  This position involve the over view of the planning and designing of the rig floor and associated drilling components, and the systems associated with the Rig Technology of the many new builds, much of the onsite involvements carried out included, rig inspections during the construction phase, function testing installed equipment, and commissioning.

Offsite involvement included, sitting in on meeting with customers, checking and suggesting the rearrangement of drawings and layouts, writing seminars and lectures for both management and engineers as and when needed. Such seminars were run in Singapore, Abu-Dubai, and India. And would often include both yard personal and many of their customers.

Leonard was a freelance training instructor and consultant compiling and instructing/teaching aids for distant learning classes on rig design and functions while recovering from cancer, many of the subject can be seen below.

Some of his Lessons written in the past include:

Casing and Cementing

Fishing tools and their functions

Stripping and Snubbing

Bops' Atmospheric d-gasser and the Accumulator, kill and choke manifolds

Drill string Design

The circulating system

Drilling Hydraulic

Oil well completions and Workover

Introduction to casing while drilling

Rig Safety

Workover operations

Ton miles and wire line safety

Bulk Storage Systems

Mud Mixing system

Solid control systems Mud Cleaning and shaker area including D-gassers

Top Drive

Rotating Mouse Holes

Fox Holes

Pipe Deck Machines

Power Slips, PS30, PS21, PS16

Iron Roughneck TS80, AD4500, AD3200, Jim

Hydraulic Cat Heads

Hydraulic Power Units

Hydraulic stabbing boards

High Pressure Piping Systems this includes Valves, All manufactures

Conductor Tensioning Units (CTU)

Diverters Vetcogray and Cameron

Rig Pumps (fluid end and power end)

The crown and crown block assembles

The Stand Pipe Manifold

The choke Manifold

The trip Tank design an function

I have uploaded here some of Len's work below which he has given personally to me for sharing,
( P/s  the correctness of the information here below are not being counter-checked and to be used with discretion )  :

Rigfloor equipment2


Rig Controls at Drill Floor



Bulk Mud System


Optimizing Solids Control


Iron Roughneck


Slush Pumps


Top drive


What is an Accumulator1



Underbalanced Drilling


Surface Cement

RC Bits


Casing 2


Gas Cut Mud

Liners



Deepwater BOP Riser


Diverter Systems


Well Head

Propeller and hull wake resistance

In ship vibration, the propeller is normally the trouble source which can cause an excessive ship vibration problem. The consequences of excessive vibration in the ship's stern area can be very detrimental to the crews' comfort. Deterioration of the structural members can be accelerated as a result of fatigue caused by long term cyclic vibration. Excessive vibration can damage or adversely impact the performance of the ship’s mechanical and electrical equipment. Prolonged exposure to vibration can contribute to crew discomfort and increasing the opportunities for human error.

Increased flexibility of the hull girder of larger, and particularly longer, ships with a fine, underwater form can significantly increase susceptibility to vibration. Moreover, as the weight and distribution of steel within ship structures are optimized as shipbuilders attempt to control production and material costs, the probability for vibration-related troubles, particularly in the stern section of the vessel, increases. As the demand for higher service speeds for many of these vessels also increases, attendant increases in the propulsive power are required. This translates into higher loads on propellers, which in turn lead to greater propeller excitation and an increase in the risk of vibration and vibration-induced failures. These create an intense, fluctuating pressure impact on the ship’s hull.

There is now the availability of modern propeller design, moderate amount of sheet cavitation is often unavoidable in order to maintain the required propulsion efficiency. Reconciling the challenges posed by these conflicting technical and operational demands is essential if further improvements in the speed-power-size ratio are to be realized, particularly for large vessels.

To study and predict propeller-induced hull vibration is not simple. It is a synthetical analysis involving methodologies of many topics such as Computational Fluid Dynamics (CFD), Finite Element Method (FEM), and fluid cavitation dynamics. In propeller induced hull vibration assessment, the prediction of stern flow is central to the problem of unsteady propeller loads, cavitation, and propeller-induced hull pressure. The solution to these problems requires detailed knowledge of the turbulent stern flow (including thick and perhaps separated boundary layers), bilge vorticity, and propeller/hull interaction. Common in ship design, the technology for these predictions was mainly based on regression and empirical formulae. At best, the use of ship flow codes was restricted to potential flow calculation augmented by boundary layer predictions to approximate viscous effects. Propeller calculations were performed using empirically generated effective wakes, and the propeller’s interaction with the hull was approximated with a thrust deduction coefficient.

The use of CFD in ship hydrodynamics has increased in the marine field. This is due to continuous advances in computational methods together with the increase in performance and affordability of computers. Also, due to the emergence of many unconventional propulsor designs such as tractor PODs, tip plate propellers, and propellers with wake equalizing ducts/spoilers, empirical methods based on the historical databases developed for conventional propeller designs become questionable in the innovative designs. More sophisticated analyses based on direct simulation using CFD and FEA methods are required to associate with the model tests for propeller-induced vibration studies.

Nowadays, with advances in CFD techniques, more comprehensive analyses can be performed for propeller/hull interaction flow problems. It has been demonstrated that CFD simulation, particularly using RANS-based methods, can provide more flow details in understanding the complex propeller/hull interaction process. This paper provides an overview of the methodologies and the state-of-the-art computational analysis tools that ABS has developed in order to more accurately estimate propeller-induced hull vibration.

The sequence of comprehensive analyses in the integrated simulation system is summarized as follows:

1. Bare hull wake field (nominal wake) simulation

2. Simulation of wake field under propeller-ship hull interaction (effective wake)

3. Propeller performance analysis (thrust and torque coefficients, K T and K Q )

4. Propeller cavitation analysis (cavity patterns on propeller blades)

5. Hydrodynamic loading assessment (pressure on blades, propeller induced hull pressure and bearing forces/moments)

6. FEM analysis for vibration and stress on ship hull, shaft and propeller blades

Resistance and propulsion summary - With courtesy from Newcastle UponTyne University
Resistance Propulsion


Global vibration on container vessel - courtesy of Delta Marine Engineering

GlobalVibration Container Vessel


Lloyds Register Ship vibration - Courtesy of Llyods Register
LR ShipVibrationNotes




Vibration Analysis and Noise Rev1



Vibration Analysis

Turning 50 doesn't mean you are past your prime

Extracts and with courtesy of Sunday Times, 16th Sept 2012

It's never too late to achieve success, turning 50 plus doesn't mean you are past your prime - many successful entrepreneurs were late bloomers.

The corporate world is no exception. We tend to idolise the extraordinary achievements of entrepreneurs such as Apple's Mr Steve Jobs and Facebook's Mr Mark Zuckerberg when they peak early in their businesses. But this leaves the impression that if we fail to achieve success by a certain age, we will never make it.

There are many success stories involving late bloomers. Fast-food chains that dot our island Kentucky Fried Chicken was started by entrepreneur Harlan Sanders, the "Colonel Sanders" whose picture featuring his distinctive trademark goatee and white suit still appears on the company logo.

After spending nearly a lifetime trying out various jobs without much success - working as a farmer, a steamboat pilot and an insurance salesman - he finally hit the big time when he was 66, promoting his style of frying chicken. Then there is the ubiquitous McDonald's which is usually located side by side with Kentucky Fried Chicken. Milkshake mixer salesman Ray Kroc was 52 when he came across a small, thriving hamburger shop in southern California. He offered to be the shop's agent and later bought out its owners. The business prospered in his hands and was transformed into the world's biggest fast-food empire, as its restaurants with their familiar bright yellow arches planted themselves all over the globe.

In the financial world, few traders are aware of the remarkable story of Mr Roy Thomson, the man behind financial data provider Thomson Reuters.

Mr Thomson was a moderately successful radio station owner in Canada when he moved to Scotland after he turned 60, when his wife died and his business partner left to enter public life. He went on to create a media empire, buying up newspapers such as The Scotsman and The Times of London and numerous book publishers. In 2008, Thomson Corporation, the company he created, took over Reuters Group to form Thomson Reuters.

Even in our own backyard, there are examples of businessmen who achieved extraordinary success after reaching an age many regard as past their prime.

One good example is banker Wee Cho Yaw, who, when he was in his 70s, led his bank United Overseas Bank (UOB) to successfully out-bid DBS Bank for Overseas Union Bank in 2001.

It turned out to be a transformational deal which cemented UOB's position as a leading lender in South-east Asia.

There is also the example set by 68-year old Thai billionaire Charoen Sirivadhanabhakdi, the owner of Thai Beverage, who is currently engaged in a fierce tussle with Dutch brewing giant Heineken for control of Asia Pacific Breweries, the iconic maker of Tiger Beer. At an age when most people are supposed to be playing with their grandchildren, Mr Charoen is giving this European giant a run for its money, as he presses ahead with an audacious bid to become a leading brewer in Asia's fast-growing but fractured beer market.

It promises to be a battle of epic proportions which gets even a hard-bitten newsman like me all fired up with excitement over the outcome of the fight.

So, rather than succumb to the de-motivating belief that it is too late for any of us to do anything after a certain age, we should tell ourselves: It is never too late. Not even if we have turned 90.

We need to change our mindset - and believe that any deterioration a person may encounter past the age of 50 is really all in the mind.

Many people find that life is a lot easier after turning 50 years old. Suddenly you know who you are and what it is you want out of life; there isn’t anymore having to find yourself. It also seems as if you have a lot more control over your life than you once did. When we are young we seemed to be taken along by the tide and may be pushed into directions that we didn’t intend on going, but once you are older you have enough wisdom to know how to go against the tide and be exactly who you want to be.

Just because you are turning 50 years old doesn’t mean you have to look and feel like you are 50. If you eat right and get plenty of exercise you will probably look and feel years younger than what you are. There is no doubt that you are likely to have a few more aches and pains than you did 10 or 20 years ago, but all things considering, 50 should be a time you are looking forward and enjoy life as you wish to and do what you had wanted but did not get a chance due to your work life and see what you missed out in the past.

Self-worth quotables :-

“We cannot think of being acceptable to others until we have first proven acceptable to ourselves.”

― Malcolm X

“Life is too short to waste any amount of time on wondering what other people think about you. In the first place, if they had better things going on in their lives, they wouldn't have the time to sit around and talk about you. What's important to me is not others' opinions of me, but what's important to me is my opinion of myself.”

― C. JoyBell C.

“Sometimes the hardest part of the journey is believing you're worthy of the trip.”

― Glenn Beck, The Christmas Sweater

“If you wish to achieve worthwhile things in your personal and career life, you must become a worthwhile person in your own self-development.”

― Brian Tracy

“Most lives are not distinguished by great achievements. They are measured by an infinite number of small ones. Each time you do a kindness for someone or bring a smile to his face, it gives your life meaning. Never doubt your value, little friend. The world would be a dismal place without you in it. (tweaked version of a passage from Scandal in Spring)”

― Lisa Kleypas, Scandal in Spring

“A diamond doesn't start out polished and shining. It once was nothing special, but with enough pressure and time, becomes spectacular. I'm that diamond.”

― Solange nicole

Courtesy of Straits Times, Sunday, 18 November 2012 

Don't call me old...      

Being over 50 does not mean being over the hill, with many of the over-50 set defying ageist stereotypes

In his last job, resident technical officer Lee Joo Mong cycled to and from work every day for six months. It was about 14.5km or an hour each way from his three-room flat in Ang Mo Kio to his worksite at the Pan Pacific hotel.

His current worksite, Credo Residences, opposite the Ang Mo Kio MRT station, is just a 15-minute walk away. So Mr Lee cycles 32km, goes home for a shower and then walks to work.

On Sundays, he puts in an extra 112km on his bike around the island.The 59-year-old, who is single, says older people should not slow down.

"In fact, we should put in more effort to maintain the same level of fitness we had when we were younger," says Mr Lee, adding that in his physically demanding job, "I can do anything my younger colleagues can do".

Members of the over-50 set SundayLife! spoke to decry the notion that people past a certain age should prepare for life in a rocking chair.

Ageist attitudes persist in Singapore, says Mr Dennis Heath, a Singapore permanent resident of 10 years, who wrote to The Straits Times Forum page. The executive coach observed in his letter, published on Nov 5, that employers think that workers who are over 50 are past their sell-by date.

The 58-year-old Briton notices four ways that the "over-the-hill thinking" manifests itself: "They think older people are not as fit, not as tech-savvy, that we demand huge salaries because of experience and that we are set in our ways and refuse to learn new skills."  The owner of his own coaching company since 2006 puts paid to such ageist notions with a busy work, sports and social life.

He cycles or walks most mornings and trains with a dragon boat team twice a week. He also works out with weights in his Bedok condominium's gymnasium at least once a week.

Evenings find him at a concert or a movie with his Singapore girlfriend, aged 42, a voice-over artist.

He also started two part-time careers at 55 - as a television actor and voice-over artist.

A telecommunications industry veteran of 30 years, he had come to Singapore about 12 years ago to do international sales for a software company. It was just before the dotcom bust of 2001.

"Within 18 months, I had stock options worth nothing, no job and one month's redundancy pay," recalls Mr Heath, then 47. He went job-hunting for about one year. "There were no responses and I don't even remember having interviews," he says.  Finally, a headhunter friend persuaded an outplacement company to give him a chance. "Even then, it took the headhunter some persuasion to get the company to see me," he says.  But he got the business development manager job: His years of global sales experience were a match, despite his age.

Ms Annie Yap, group managing director of human resource company AYP Asia Group, says that employers' assumptions of veteran workers' sell-by dates are "not entirely accurate".

Ms Yap, 41, adds: "We have come across senior employees who want to continue their careers while taking as much as half their previous salary but they are overlooked by employers because of their age."

National University of Singapore sociologist Tan Ern Ser sees no reason that "50 is deemed to be old, given that current convention considers aged 65 and above as old".

Also, the "soft" retirement age of 62 is scheduled to be raised in the future.

In any case, age should not be the only consideration. He cites a running group, with whom he has jogged on Sunday evenings for close to 26 years. "The oldest member is close to 80 and he is still going strong, while someone in his early 50s has quit as he suffers from a serious knee problem," says Prof Tan.

At soyabean chain Super Bean International, where a quarter of its 550 employees in Singapore are older than 50, work has been streamlined so that each task - whether it is making pancakes or preparing soya milk - can be handled by anyone regardless of age.  Its managing director Kang Puay Seng, 52, sets an example - his younger colleagues often complain that he "walks too fast", he says, when they go to mega tradeshows abroad that are held in sprawling complexes.

Seniors SundayLife! spoke to say learning is important - at any age.

Ms Peggy Tan, a nurse of 25 years, received a World Health Organization scholarship to do a nursing degree at Curtin University at 42.  At 51, she received a scholarship from Nanyang Polytechnic, where she was lecturing, to do her master's in nursing at King's College London.

Now retired, the 68-year-old grandmother of three keeps busy planning monthly activities for the Australian Alumni Singapore as its vice-president.

Last Thursday, she organised a closed-door sales event for alumni members at a designer boutique.

The well-groomed Ms Tan has a piece of advice for seniors fighting ageist stereotypes. Sloppy dressing does not command respect.

She says: "I'm not the sort to go to the market in pyjamas."



Insights on Tender Assisted Drilling Vessel

Using a semi-submersible tender vessel for drilling from floating installations with dry wellheads in deepwater could be more cost-effective in benign climates such as in Southeast Asia, Brazil and West Africa, according to some well known drilling contractor. 

For example,  West Alliance, built by Keppel, delivered sometime in 2002. The design of this vessel, which is based on that of the West Menang, has been modified with larger columns and pontoons and incorporates a higher variable deckload and more storage capacity for liquid mud and brine.

The eight anchor winches are larger, compared to the wire currently used on West Menang and West Pelaut, which are also some of semisubmersible tender rigs owned by Seadrill. The mooring of tender rigs in deepwater has been facilitated by the development of lightweight mooring ropes such as Dyneema, which is made of high-modular polyethylene and polyester, combined with a pre-laid mooring system.

Two key questions arise in considering whether tender-assisted drilling is beneficial in these circumstances:

•Are there savings to be made compared with alternative solutions?

•Is it technically feasible, given that there is no experience of tender rigs working with deepwater floaters?

Cost savings

The major economic benefit of using a tender rig is that the cost of providing an integrated platform rig is avoided. Estimation made and was suggested that for a wellhead tension-leg platform (TLP), a saving of at least US$140 million (net present value) can be achieved.

This figure is made up of the cost of the platform rig itself and the reduction in the platform construction cost, which results from the fact that the TLP can be smaller. The operating weight of the self-erecting tender is only about one quarter that of a platform rig, while the size of the deck required for the derrick equipment set is also significantly smaller since mud systems, power, pipe deck, accommodation, and so on, are contained on the tender.

•Modec, which has developed the Moses wellhead TLP design

•Aker Maritime, which has delivered several Spar platforms.

The design criteria used in the studies were water depths of 6,000 ft for the Spar and 4,000 ft for the TLP. The key feasibility issue is whether the rig can be moored alongside a TLP or Spar in such a way as to maintain an optimal distance from the installation, neither approaching so close as to run the risk of colliding with it, nor moving so far that the lines carrying power, mud and other functions from the tender to the platform come under strain.

The design environmental conditions used were the 100-year storm conditions in Africa. Criteria for sea conditions were set at a significant wave height of 13.8 ft, a one-minute wind of 43 knots, and a surface current of three knots.

Mooring systems

For the TLP, the study considered a steel wire catenary system with the additional use of two pre-tensioned "stretcher" ropes between the tender and the platform. The stretcher ropes, the purpose of which is to further constrain the relative excursion between the tender and the platform, are 3 1/4-in. nylon rope pre-tensioned to a relatively low value - 50 kips. By maintaining positive tension in the stretchers it is possible to ensure that a minimum controllable distance is always maintained to the TLP. A Tension Leg Platform (TLP) is a vertically moored compliant platform. The floating platform with its excess buoyancy is vertically moored by taut mooring lines called tendons (or tethers). The structure is vertically restrained precluding motions vertically (heave) and rotationally (pitch and roll). It is compliant in the horizontal direction permitting lateral motions (surge and sway).

For the Spar platform study, a taut-leg mooring (TLM) system consisting of wire and polyester rope was used, which is similar to the mooring system adopted for the Spar platform. Studies showed that it is possible to moor the tenders in depths down to 6,000 ft by using a pre-installed mooring system combined with the semisub tender rig's own mooring system upgraded from 2 1/4-in. to 2 1/2-in. diameter wire rope. In the case of the TLP, the maximum relative distance was 84 ft and the minimum distance was 73 ft. In the Spar's case, the maximum relative distance was 105 ft when using 2 1/2-in. wire combined with 3-in. polyester rope and 92 ft when using 2 1/2-in. wire combined with 5-in polyester rope. The minimum distance was 36 ft. The Spar concept is a large deep draft, cylindrical floating Caisson designed to support

drilling and production operations. Its buoyancy is used to support facilities above the water surface [Glanville, et a1 1991; Halkyard 19961. It is, generally, anchored to the seafloor with multiple taut mooring lines. A third generation “cell” Spar was introduced in 2004. It performs similar to the other Spars, but it is constructed differently. The hull consists of multiple ring-stiffened tubes, or “cells”, which are connected by horizontal and vertical plates. This method of construction is cheaper than the traditional plate and frame methods. Because of the length of a Spar, the Spar hull cannot be towed upright. Therefore, it is towed offshore on its side, ballasted to a vertical attitude and then anchored in place. The topside is not taken with the hull and is mated offshore once the Spar is in place at its site. The mooring cables are connected with pre-deployed moorings.

                                                 Courtesy of Dietswell - Horse Shoe Tender Rig

The HS Tender




Tender Assist Drilling vessel erecting of DES onto platform. Courtesy Axon Energy, Youtube downloaded.

                                                        Courtesy of AXON Energy