the largest anchors ever - · pdf filecould not take it on the ship they had offered....

Anchounter 42 April 2007

A MEETINGGROUND FORANCHORAND MOORINGNEWSPUBLISHEDBY VRYHOFANCHORS

THIS ISSUE

• SUBSEA TENSIONING• DRAG EMBEDDED PLATE ANCHORS• INTERMOOR FOURCHON FACILITY• API RECOMMENDATION

The 75 tons anchors are the biggestin Vryhof’ history and believed thebiggest in the offshore industry.Vryhof did produce a 65 ton StevprisMk3 in the 1980s and later even a 60

ton Stevshark was built, however thecurrent ones include 15 tons ofballast and are thus actually 75 tons.

With records like this, normally oneuses superlatives, compare it to thesize or weight of the Eiffel Tower.Stuff l ike that. Well , to speak inaviator terms, the anchors wing spanis 12 meters (that’s one heck of astretched limo) or their weight equals35 American cars.

Vryhof Anchors long standing clientRasmussen Equipment Co. located inSeattle Washington (USA), was todeliver the anchors to MansonConstruction Company Inc. a US-based international contractor activein offshore, dredging, bridge buildingetc. Manson’s client was the BoeingCompany of America, which needs nointroduction, whose client was MDAto moor their new SBX.

Transport of the anchors was to govia the Panama Canal, then right upto Seattle not exactly your averageoffshore destination. From there theywere to load out for the second legof their travels to Alaska.

Continued on next page

TThhee llaarrggeesstt aanncchhoorrss eevveerr !! In january 2007 Vryhof loaded out 8 huge 75 ton Stevshark anchors from themanufacturing plant in Rotterdam, readying them for a very, very long haulthrough the Panama Canal to their final destination in Alaska. Eh ... Alaska?Are offshore developments speeding up such that they need anchors? No, notto worry you are not missing a boat; this simply concerns a secret mission.

Booth 2331

5007 Anchounter #42 25-04-2007 12:15 Pagina 2

MDA, SBX, VA STK 75 T. Thisstarts to sound like a JamesBond Movie. Well , partlythat fits. The anchors are to become part of theInternational Missile DefenseSystems, or more precise tomoor a Sea-Based X-bandRadar.

It does make an interestingcombination, where themost hyper-tech industrychooses the most traditionalhigh-tech way of mooringsystem around. Anchors.

Transporting SBX anchors“If you have transportedanchors as often as we have, you might call it aroutine operation.”, says BGTTransport Director HansVerrijp when he criticallyfollows the load out of theSBX anchors in Rotterdam.Vryhof and BGT Transport goback a long way and havetransported anchors overroad, rail, through mountainspasses (more than just once!)

by airplane,helicopter andyes also overwater. Someanchors aremore difficultthan others.But not so much becauseof extremed i m e n s i o n s .Let’s not forget

that transportation efficiencyis nowadays one of the designcriteria. “We learned of the record sizeanchors last October and weregiven a time window of early2007 delivery”, says Hans “andwe can normally live with a timewindow like that. Generally westart setting off the possible wayof transport against the cost, arather important driver. In thiscase the dimensions more thanthe weight were criteria thatlimit the choices, so that wecould not transport over roadand then the destination,Seattle, doesn’t leave very many

variations either. It’s one straightline to Panama, followed by astraight line up North. I mean,no real use into looking atcrossing Canada is there?”As it turned out there was onlyone liner available for that routeso we did secure a quote in timeto assure the client we wouldget his anchors to Seattle. Whenwe later specified the loads; 8flukes of 40,8 tons and 8 shanksof 34.2 tons and they looked atthe dimensions, sure enoughthey suddenly discovered theycould not take it on the shipthey had offered. “Capacityproblems do not leave muchspace for negotiating …” grinsHans “so that we had to becreative and after a while settled

for two different calls of thevessel to Vlissingen (Flushing)harbour in the South West ofHolland. On January 15, just before theload out was to commence, twoanchors were assembled on thequay side for the shooting ofsome commemorative photoswith the client reps present andthe fabrication plant staff on thephoto too! The second load left29th of January and all weretransferred to the ocean liner onFebruary 7 with ETA in Seattleon March 15.

The trip is via Mazanillo,Panama Canal, Topolobambo,Los Angeles, Oakland, SanFrancisco, Vancouver and then afree out delivery in Seattle.Some delay occurred during thefirst leg but all is set for a 22March delivery.

And the secrecy Hans? “Vryhofdid explain about that and we stuck to it. And now wereceive reports on the vessel’swhereabouts on a daily basis.”

Rotterdam

Panama

Los Angelos

Seattle


ANCHOUNTER 42

Photo: Anchor manufacturing

plant crew, Vryhof staff and

client representatives at a short

commemorative photo shoot.


The proof testing ofinstal led anchor points for permanently mooredfaci l it ies such as CALMbuoys and FPSOs is a criticalaspect of the overallcertification and approvalprocess for these systems.For drag embedment anchorsolutions, the proof testincludes setting the anchorsinto the seabed andensuring they do not dragbeyond allowable l imits.Where vertically installedanchor points are involved,such as driven piles orsuction anchors, the prooftest performs the dual roleof not only verifying theanchor point capability butof also embedding themooring line at the pile intothe seabed in a characteristicinverse catenary curve. Theloads required are oftenhigh, typically being 80% ofthe maximum intact designload, and the hold period forthe proof test is dictated byclass society rules, rangingfrom 15-30 minutes.

The StevtensionerApplying these (substantiallyhorizontal) proof loads inthe field requires highbollard pull vessels, or bymeans of cross-tensioning ondeck using a crane, f ixedwinch or chain jack system.However, subsea tensioningcan offer significant timeand cost benefits andreduced risk over otherconventional mooring systemproof testing methods, usinga device l ike the VryhofStevtensioner. This is basicallya chain shortening clutch,

which passes chain throughit in the slack condition butlocks onto the chain underload. An anchor l ine isattached to one side of theStevtensioner, an opposedanchor l ine is passedthrough it and up to thesurface. A vertical pull onthis riser induces more thandouble that pull in thehorizontal legs, just like abowstring.

The BenefitsThe potential benefits of subsea tensioning are numerous, particularlysaving time and moneyduring installation. It can be applied to al l types of mooring systems andanchors provided a workingchain section is included, inshallow or deep waters. In

symmetrical systems anchorscan be cross-tensioned as opposed pairs, halving the number of tensioningoperations required, orindividual anchors can betensioned using a temporaryreaction anchor. The loadsseen at the installation vesselare reduced, reducing thesize of equipment requiredand more importantlylowering risk to equipmentand personnel. The reducedrequired vertical pull enablesa wider range of vessels tobe considered for tensioningoperations, and obviates theneed for bollard pull orcrane capacity in excess ofrequired installation load.Subsea tensioning can beperformed from anchorhandling vessels or modestcrane barges, helping to

Subsea Tensioning for Cost-Effective Installation


ANCHOUNTER 42

reduce overall installationcost. The load in thehorizontal anchor leg canbe measured at theStevtensioner by means ofan integral load cell andthe data recorded in realtime on deck via anumbilical cable or acousticmodem in deeper waterdepths. Subsea tensioningequipment is relativelycompact in size so can besent by air freight toreduce mobilisation time.

The Tensioning ProcessOnce the anchors havebeen laid on the seabed,or piles installed and themooring l ines laid, theStevtensioner is connectedand deployed to theseabed. The tensioningprocess involves repeatedlyheaving up and slackingback the Stevtensioner in ayo-yo action to removeslack from the system andprogressively build up theload in the horizontal legsuntil the required tensionis achieved. Typically 4-6yo-yo cycles are neededand cross-tensioning a pairof anchors takes around 6 hours from connectingthe Stevtensioner to de-rigging it (depending onsystem parameters).

Example CALM buoyinstallationThe installation of a CALMbuoy typifies the benefitsof subsea tensioning,where a six-leg symmetricalspread mooring requiresonly three tensioningoperations to proof testthe system. In March 2006the Vryhof Stevtensionerwas used on such a projectoffshore Libya, where acomplete CALM buoymooring was instal led,

proof tested and hookedup in only 16 days,including 2 days transittime from the mobilisationport of Malta, and 2 daysof weather downtime. Six1.5m diameter piles weredriven 15m into theseabed, s ix 300m long92mm diameter studlessanchor chains laid, cross-tensioned with theStevtensioner to 200tonnes, and the buoyconnected, all in only 12

operating days on site.This was completed by theSaipem 3000 crane vesselfor ENI Oil.

The Complete ServiceVryhof Anchors providecomprehensive subseatensioning services for the instal lation of al loffshore mooring systems,including feasibility study,equipment hire, andprovision of supervisorypersonnel offshore. Arange of Stevtensionersare held in stock to coverchain sizes up to 135mmand loads up to 1000tonnes can be handled.

active chainpassive chain


Introduction.When using drag embeddedplate anchors (for example the Stevmanta VLA), a keyparameter is the relationshipbetween the generatedultimate pull-out capacity (UPC)and the applied installation loadat the anchor shackle (Finst). Incommon design practice forthese anchors, the ratio UPC /Finst ranges between 2 and 3.5depending on anchor resistanceand soil properties. This articleexamines the influence ofvarious anchor geometry andsoil parameters on this ratio.

UPC and installation load.The UPC of a plate anchor isdefined as:

[1]

whereNc = bearing capacity factorsu = undrained shear strength at

penetration depthA = plate area

The load at the anchor shackle(Finst ) required to penetrate thedrag embedded plate anchor to penetration depth can beevaluated with the followingrelationship (see also DNV 2002,appendix H). Assumptions madein deriving the relationship :• the undrained shear strength

of the soil is constant withdepth

• the sensitivity of the soil isconstant with depth

• the anchor penetrates parallelto the fluke

• the weight of the anchor isneglected as the influence onanchor behavior is very small

[2]whereµ shearing ;i = the area of shearing

surface i relative tothe fluke area (A)

µ bearing ;j = of bearing surface jrelative to the flukearea (A)

st = the sensitivity of the soil= the angle between the

fluke surface and theapplied mooring line force

By combining equations [1] and[2], the following relationship isfound between the UPC and Finst :

[3]

Evaluation of the ratio UPC / Finst .The ratio of UPC / Finst will be evaluated for a number of different cases. The bearingcapacity factor (Nc ) has been taken equal to 12, aconservative assumption basedon recent research.

Case 1. An infinitely thin platewith the mooring line forceacting directly on the plate. Inthis case there are no bearingforces and there is no effectfrom the shank. The ration ofUPC / Finst has been evaluatedfor a number of different valuesof st and mooring line anglesvarying from 0 to 90 degrees.

Figure 1 shows the results of theanalysis. In table 1 the results arepresented for mooring lineangles varying between 40degrees to 65 degrees which isthe normally used range forplate anchors in clay.

Table 1 - UPC / Finst forvarying and st – thin plate

s t = 1 s t = 2 s t = 4

40° 4.6 9.2 18.445° 4.2 8.5 17.050° 3.9 7.7 15.455° 3.4 6.9 13.860° 3.0 6.0 12.065° 2.5 5.1 10.1

Case 2. A typical dragembedded plate anchor has atotal shearing area equal to 2.7times A ( = 2.7) and atotal bearing area equal to 0.15 times A ( ∑ = 0.15). Theratio of UPC / Finst has beenevaluated for a number ofdifferent values of st andmooring line angles varyingfrom 0 to 90 degrees. Figure 2shows the results of the analysis.In table 2 the results arepresented for mooring lineangles varying between 40degrees to 65 degrees which isthe normally used range forplate anchors in clay.

Table 2 - UPC / Finst for varying and s t – typical anchor

s t = 1 s t = 2 s t = 4

40° 2.1 3.0 3.845° 2.0 2.8 3.550° 1.8 2.5 3.255° 1.6 2.3 2.860° 1.4 2.0 2.565° 1.2 1.7 2.1

Case 3. The anchor from case 2 isevaluated in a soil with asensitivity of 3 while the bearingarea is varied. The shearing areais constant (2.7 times A). In table3 the results are presented formooring line angles varyingbetween 40 degrees to 65degrees.

Drag Embedded Plate AnchorsRatio between installation load and Ultimate Pull-out Capacity (UPC)


ANCHOUNTER 42

Table 3 - UPC / Finst for varying and bearing area

_0.1 0.15 0.2

40° 4.4 3.4 2.845° 4.0 3.1 2.650° 3.7 2.9 2.355° 3.3 2.5 2.160° 2.9 2.2 1.865° 2.4 1.9 1.5

Case 4. The anchor from case2 is evaluated in a soil with asensitivity of 3 while theshearing area is varied. Thebearing area is constant (0.15times A). In table 4 the resultsare presented for mooringline angles varying between40 degrees to 65 degrees.

Table 4 - UPC / Finst for varying and shearing area

_2 2.5 3

40° 3.7 3.5 3.345° 3.4 3.2 3.050° 3.1 2.9 2.855° 2.8 2.6 2.560° 2.4 2.3 2.165° 2.1 1.9 1.8

Conclusions.From the analysis, thefollowing can be concluded.• For drag embedded plate

anchors the ration betweenthe ultimate pull-outcapacity (UPC / Finst ) isdependant on anchorgeometry and soil properties.

• The ratio UPC / Finst increaseswith increasing soilsensitivity.

• The ratio UPC / Finst increaseswith decreasing mooringline angle ( ), i.e. withsmaller fluke/shank angle.

• The ratio UPC / Finst increaseswith decreasing bearingarea.

• The ratio UPC / Finst increaseswith decreasing shearingarea.

• A ratio UPC / Finst of 2 to 3.5is a typical value for deepwater applications, i.e. soilwith high sensitivity.

References.DNV Recommended PracticeRP-E302 (2002), Design andInstallation of Plate Anchors inClay, 2002. Høvik.

0

1

2

3

4

5

0 10 20 30 40 50 60 70 80 90

installation angle [degrees]

UP

C /

Fin

st

St = 1 St = 2 St = 4

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90

installation angle [degrees]

UP

C /

Fin

st

St = 1 St = 2 St = 4

Figure 1 – infinitely thin plate without shank Figure 2 – typical drag embedded plate anchor


We are pleased to announcethat Kevin Firth has joined the Vryhof team to furtherstrengthen the commercial and

business development functions.Kevin will work on all Vryhofproducts and services but hisprimary focus will be the

expanded development of theDeepRope polyester mooringline offering in the widest sense.

Many Vryhof clients willdoubtless remember Kevin fromhis former lives at Bridon andMarlow Ropes where he wasinvolved in too many deepwatermooring projects to rememberover a 20 year period.

Kevin has returned from a fouryear sabbatical in subseaproduction systems and nowclaims a Christmas Tree isn'talways green with brightlycoloured lights and baubles!Already the expanded team isworking well with the winningof the contract for the FPSOGimboa moorings ropes fromSaipem. Kevin looks forward tore-forging old acquaintances atOTC and beyond.

Kevin Firth joining the Vryhof team

Kevin knows the ropes and will

provide an important addition to

the Bexco/Vryhof relationship.


ANCHOUNTER 42

The price of oil is fluctuating,changing almost every day.Why? There is no directreason for that. One daythere are reports that theconsumption is declining.The next day it is beingreported that demand willexceed production. Oneincident results in a higherprice almost overnight.

At the time of writing thisarticle the price is again wellabove $60.- per barrel, afterhitting the $50.- not too long ago. Basics for energydemand are still very muchrelated to demand bynations like India and China.Those economies are stillgrowing at a very fast paceand there are no signs this will change in theforeseeable future.

It is expected that the Indianeconomy will surpass theeconomy of the U.S. by 2050.The Chinese will achieve thatby 2035.

The Indians will use 3 timesmore crude oil by 2020 thanthey do now. With 70% of itsoil imported, this will putpressure on the supply ofMiddle Eastern oil, possiblyresulting in a race for supplyfrom those sources.

It was reported that Chinaholds in excess of 1000 billionUS dollars and this will notstop.

ONE THOUSAND BILLION,how many zero’s is that ?

For resources, China isfocussing on Africa, wherethey buy raw materials, whileinvesting a lot of money inseveral African countries,building roads etc. Thisindicates that their economywill grow at the fast pace wehave been used to. Anotheritem of concern is how thisgrowth will influence theenvironment. There areconcerns that the impact willbe enormous.

Ethanol fuel ? Corn growers especially inthe U.S. benefit from giantincreases in the price. As aresult, the corn as basis offoods becomes more costly.For instance the price oftortilla’s in Mexico, food for the poor, has risendramatically. Corn prices havesoared 119 % since late 2005.This while the tortilla accountsfor half of the calories theaverage Mexican consumesevery day. The rise in cornprices is also believed to

influence the Peso , which has fallen against the USdollar as one of the fewcurrencies. This is seriousbusiness for the secondbiggest economy in SouthAmerica.

Bio-fuel, using waste insteadof corn, is heavily subsidized.The cost price however ismuch higher than that ofcorn based production. Still,Ethanol accounts only for afraction of the energydemand.

Thailand plans to allowimport of palm oil. Thisbecause they most likely cannot produce enough palm oilthemselves for their biodieselmanufacture.This in spite of the fact thatimporting the oil will be atsubstantial higher prices thanif manufactured locally.In addition a shortage of palm oil for cookingpurposes is expected.

In Brazil ethanol is madefrom sugar cane, which ischeaper than US corn ethanoland has hardly any effect onfood commodity prices.

Last little fact.The European Union havepassed a bill to reduce theannual CO 2 emission by 20 %.This will most likely meanthat they want to reduce cars running on diesel (rathercommon in Europe), whereasthey have promoted the use of diesel run cars in theseventies.

In conclusion, for now I willcontinue driving my car, whichruns on regular, althoughunleaded, gasoline at amodest speed of 90 - 100kilometers / hour, on a sunnyday, without any head windand no traffic to speak of,averaging 6 kilometers to theliter.

Just like I guess most of youwill do.

Jan Mouthaan

The World according to...Numbers and little facts.


InterMoor was founded in2004 when Acteon purchasedthe assets of Technip OffshoreMoorings. Since then, InterMoor hastripled its business due to the market conditions andbeing made an independentcompany. This expansion is a combination of organicgrowth, investment in mooringhardware and infrastructure,and Acteon’s acquisitions ofvarious companies.

Due to the strong marketdemands in the Gulf of Mexicoafter the disastrous hurricane

season in 2005, InterMoor is inthe process of acquiring anadditional $20 million in mooringhardware. The hurricanes havechanged mooring practices in theGulf of Mexico such that many ofthe rigs have upgraded fromeight point mooring systems totwelve point mooring systems.This, along with the continuingincrease of subsea infrastructure,has created a strong demand forpreset mooring systems, which isa large part of InterMoor’sbusiness. Parts of this hardwareare a purchase of 32 anchorsfrom Vryhof. The anchors beingpurchased are Stevpris NG andStevmanta anchors.InterMoor is constructing a new

960,000 square feet (89,197square meter) facility in Fourchon,more than 2. 5 times the size ofthe current facility. The newfacility will allow to better servethe Gulf of Mexico clients for loadout and storage facilities. A heavylift crane will be added.

Outside of the U.S. market,InterMoor do Brasil was formedin September 2006. From Rio deJaneiro full service mooringcapabilities will be offered. Someof these services through FlukeEngenharia, who is a licensedVryhof fabricator.

In Europe, the acquisition ofTrident and Aquatic made byActon last year, complimentInterMoor’s global mooring andsubsea installation business.Trident Offshore of Aberdeenspecializes in the design andinstallation of mooring systemsfor drilling rigs and floatingproduction units. It also relocatesdrilling rigs and providesnavigation and positioningservices. Trident is well respectedin the international mooringsbusiness – the company has astrong presence in the North Seaand has also worked offshoreWest Africa, South America andChina – and has built areputation for its marine

engineering skills and projectmanagement capability.

Aquatic is a flexible pipelay andretrieval specialists with theprovision of their large poweredreel systems. These systems canalso be used for the deploymentof spiral strand wire or polyesterfor mooring systems. Aquatic hasextensive engineering andoperational capabilities thatsupport a flourishing offshoreconstruction business.

InterMoor is also activelyworking with two other Acteoncompanies to provide unique

solutions for the offshore oil and gas industry. With Menck, the supplier of deepwater under-water pile driving hammers, theydevelop operational proceduresand technology for theinstallation of driven piles andconductors from lower costalternative vessels. 2H Offshore,the deepwater riser specialistcompany, and InterMoorcollaborate in various issues thatrelate to both mooring andrisers, including mooringintegrity management.

All of this expansion makesInterMoor better suited toprovide the industry with morecost efficient solutions.

InterMoor Fourchon Facility


ANCHOUNTER 42

The 1st MODU recommendedpractice, released in 1987 by API, specified a designenvironment lower than the five to ten year returnperiod in the present version of the API RP 2SK,principally driven by theMODU mooring capabilitiesavailable at that time. The latest version of the recommended practice"Design and Analysis ofStationkeeping Systems forfloating Structures", API RP2SK, dated October 2005incorporates already moresevere metocean designdata.

The mooring fai luresoccurring during theHurricanes of 2004 and2005 suggested that thedesign recommendationswere not sufficientlyeffective. The OffshoreOperators Committeelaunched a Joint IndustryProject entitled "US Gulfof Mexico (GOM) MooringStrength Reliabil ity"(MODU JIP) that started in September/October2005 with the task to improve the designrecommendations for the2006 hurricane season. Thisal l happened in closecooperation with API whowould publish the newrecommendations.Studies were init iated.Mooring fai lures wereanalysed using measureddata obtained from thehurricanes, common practiceson mooring inspectionwere evaluated, historicaland recent weather data

were analysed again and combined in a newdatabase, methods ofmooring design werecritically looked at, morefocus was given to the riska mooring can impose onits surrounding.

All these studies will bringus also a big step forwardin the design methodologyof moorings, but athorough study takes time,more time even if theproblems are complex and if there are manyparticipants and interestedparties. The workgroupthat compiled the latestedition of API RP 2SK was asked to continue their work and proposerecommendations for the2006 hurricane season.Init ial ly the proposedrecommendations were tobe part of a commentaryto the existing RP 2SK, buttime was insufficient andthe recommendationswere published in May2006 as a separatedocument supplementingthe latest edition of RP2SK; "Interim Guidance forGulf of Mexico MODUMooring Practice - 2006Hurricane season" API RP95F, first edition.The workgroup RP 2SKcontinued their taskpreparing the completedocument as a commentaryto the RP 2SK. Agreementwas reached on increasedmetocean design data, oncalculation methods andmooring analysis, on riskassessment, on mooring

system improvement, onmooring installation andinspection, on anchorsystem considerations and even on most of the wording of therecommendations.

Although progress of theworkgroup was good, oneessential issue was pushedforward but still remainedto be decided on: thedesign return period. Someparties are of the opinionthat the present returnperiod of 5- to 10-yearshould be increased to 50- or 100-year or even more; other parties believe that the increased met-ocean design data andincreased factors of safetyalready result in asufficient increase ofmooring strength withrespect to the present RP2SK and that a returnperiod between 5 and 50would be preferred.

It has been decided not towait for the results of thediscussion on returnperiods and for now goforward on the same basisas proposed in the InterimGuidance 2006. It seems as if the RP 2SK workgroupdocument will be publishedas a 2nd edition of the"Interim Guidance for Gulfof Mexico MODU MooringPractice – 2007 HurricaneSeason" showing a requiredreturn period larger orequal to 10.

The result of thementioned design returnperiod discussion may bepublished in the "InterimGuidance 2008", buthopefully much earlier in a f inal document of"Commentary" added toAPI RP 2SK.

By Gijs Degenkamp

API recommendationHurricane Moorings - Interim Guidance Revisited


P.O. Box 109

2900 AC Capelle a/d Yssel

The Netherlands

Phone: +31 10 266 8900

Fax : +31 10 266 8999

E-mail : [email protected]

www.vryhof.com

Vicinay-Cadenas S.A., theSpanish manufacturer andsupplier of mooring chain,represented by VryhofAnchors in the Netherlands,has opened an ultramodernForging Plant close to thetown of Galdames, some 30 kilometers from Bilbao,Vicinay’s home town. Theplant was developed as to be able to cope with anincreasing order portfoliofrom the offshore industrythat apart from chain alsoincludes forged mooringcomponents.

The production floor layoutof the new plant wasprimarily driven by Vicinay’smanagement plan - based on OHSAS 18001:99 - that notonly includes the obviouslarger production capacity wonthrough higher efficiency, butbalances these parameterswith matters such as health & safety, environmentalconsiderations such as the useof eco-friendly fuels.

The new plant is designed toan annual output of 800tonnes of items between 40and 2.500 kilograms.

New Vicinay Forging Plant


the largest anchors ever - · pdf filecould not take it on the ship they had offered....

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