01
What a marine warranty standard is, and where it sits
It is a set of requirements about how a marine operation is planned and what loads it is planned against. It is not a structural design code and it does not try to be one.
An onshore engineer meeting one of these standards for the first time usually looks for the member resistance formulas, does not find any, and concludes the document is incomplete. It is not: it is answering a different question.
A design code tells you what a member can take. Allowable stresses, resistance formulas, buckling curves, connection rules.
A marine warranty standard tells you what the operation has to be planned against. Load factors, load cases, the conditions under which an operation may proceed, and what evidence a warranty surveyor expects to see.
They stack. You still need a design code, and you apply it to a demand the warranty standard has raised.
01Why is this standard on your project?
- The operation is genuinely marine
- Its scope applies directly. A lift from or onto a floating vessel, a load-out, a transport, an installation.
- The client specification cites it
- It applies by contract, wherever the work happens. This is how it reaches a fabrication yard. The scope is marine and the obligation is contractual, and the contract wins.
- Somebody thought it was a good idea
- Ask what problem it is being used to solve. Applying an offshore factor set to a controlled onshore lift produces a heavier design and no more real margin. It is a decision that needs a reason.
02What does it replace?
- Nothing
- It sits on top of your design route. Member resistances still come from a structural code. The warranty standard raises the demand you apply it to.
- Your own dynamic factor
- Yes, and that matters. Applying both is double-counting. If the overlay supplies a dynamic amplification factor, yours comes off.
02
The three factors, and what each is for
Dynamic amplification, skew load, and a consequence factor that depends on which component you are checking. They are independent and they multiply.
Dynamic amplification. The extra force from motion of the crane, its support and the load. It depends on the item's weight and on the environment, and it falls as the item gets heavier because a heavy item is less responsive to the same crane motion.
Skew load. The load not sharing between its lift points as the geometry says. Sling length tolerance, fabrication tolerance in the attachment positions, and the indeterminacy of a four-point lift all contribute.
Consequence. What a failure of this particular component would mean. Lift points and their attachments carry a higher factor than the structure between them, because a lift point failure drops the load.
The three are independent, so they multiply.
Design demand on the overlay route
- is the characteristic load, weighed or calculated
- is dynamic amplification, from the weight and the environment
- is skew load factor
- is consequence factor for the component being checked
Onshore, on the worked lift point, those compound to 1.43.
The third factor is the one onshore engineers find most unfamiliar: the same lift produces different demands for different components. The beam and the padeye on it are checked against different multiples of the same load, because they have different consequences of failure. That is a deliberate feature and it is not something a single design factor can express.
03
What the overlay costs on real steel
The same 10 t spreader beam, three times: no overlay, overlay onshore, overlay offshore. The beam never changes.
Spreader Beam Design Calculator · computed at page render
The design route alone
A 10 t, 6 m spreader with slings at 60 degrees, on the below-the-hook route, with no warranty overlay.
| Axial compression | 3.7% |
|---|---|
| Major-axis bending | 10.4% |
| Padeye pin bearing | 50.8% |
| Padeye attachment weld | 55.7% |
Comfortable, and the governing check is the sling angle limit rather than any piece of steel. That is normal for a well-proportioned spreader.
Open this example in the calculatorSpreader Beam Design Calculator · computed at page render
The same beam with the overlay on, onshore
One field changed: the warranty overlay is enabled with an onshore environment. The section, the load, the slings and the padeye are identical.
| Dynamic amplification selectedat 10.5 t static hook load | 1.10 |
|---|---|
| Consequence factorlift points and their attachments | 1.30 |
| Compounded multiplier | 1.43 |
| Padeye pin bearingagainst 50.8% | 72.7% |
| Padeye attachment weldagainst 55.7% - now governing | 79.7% |
| Major-axis bendingagainst 10.4% | 14.9% |
Still passing, and the governing check has moved from the geometry to the padeye weld. That handover is a useful signal on its own: the overlay pushes the design towards the lift points, because that is where the consequence factor lands.
Open this example in the calculatorSpreader Beam Design Calculator · computed at page render
The same beam again, offshore
One field changed once more: the environment. Nothing physical is different from the first example.
| Dynamic amplification selectedagainst 1.10 onshore | 1.77 |
|---|---|
| Compounded multiplieragainst 1.43 onshore | 2.30 |
| Padeye pin bearingfailed | 116.9% |
| Padeye attachment weldfailed | 128.2% |
| Major-axis bendingthe beam is still comfortable | 23.9% |
The beam passes and the attachments fail. That is the shape of an offshore lifting device: the members are rarely the problem, and the lift points and their welds carry both the higher dynamic factor and the consequence factor on top of it.
Open this example in the calculator04
Meeting it onshore
It reaches a fabrication yard by contract, and the practical difficulty is not the arithmetic. It is that the factors were written for a world with different assumptions.
Four things an onshore engineer should know before working under one of these scopes.
The scope is marine and the obligation is contractual. The standard addresses marine operations. If the client's specification cites it for work in a yard, that is a contract term, and arguing about scope after the calculation is late.
The factors assume you cannot control conditions. Much of the conservatism exists because stopping an offshore operation to wait for a calmer day is never free. A yard lift with a wind limit, a controlled hoist and a planned stand-down is a different situation. That is a legitimate conversation to have with the warranty surveyor, and it is a conversation, not a unilateral decision.
A warranty surveyor is a reviewer, not an approver. They confirm the operation meets the scope. They do not take responsibility for the design, and a surveyor's acceptance does not make a calculation correct.
Ask what else the client has added. Corporate specifications routinely add factors on top: a minimum design category, an additional contingency, a proof test. These are the cheapest things on the project to discover early and the most expensive to discover at the review.
05
Reading a warranty scope before you calculate
Eight questions. Answering them takes an afternoon and it is the cheapest afternoon on the project.
Questions to answer before the first calculation
- 01Which document and which editionNamed on the calculation, with the edition, because factor tables change between editions.
- 02Which operations are inside the scopeThe lift, the load-out, the transport, the installation, or all of them. They are not all the same.
- 03Which environment column appliesOnshore, inshore or offshore, and who decided. It is worth more than any other single answer.
- 04Which components get the consequence factorLift points and their attachments normally do, and the structure between them normally does not.
- 05Whether the overlay supplies the dynamic factorIf it does, yours comes off. Applying both is the commonest double-count on these jobs.
- 06What the client specification addsA minimum design category, extra contingency, or a proof test regime. Discovered now, not at the review.
- 07What the surveyor expects to seeCalculations, drawings, certificates and a procedure, in the format they will actually accept.
- 08What the weather and sea-state limits areThey are inputs to the factors, and they end up in the plan as abort criteria.
06
Six ways a warranty scope goes wrong
Half of them are double-counting and half are scope.
1. The overlay's dynamic factor applied alongside your own. The single most common error, and it is invisible unless the load path is written out with each factor's owner named.
2. The overlay treated as a design code. It has no member resistances. A calculation citing it alone has not checked anything against a capacity.
3. The wrong environment column. At small weights the difference between onshore and offshore is more than a factor of two.
4. The consequence factor applied uniformly. It is component-dependent by design. Applying it to everything is conservative and it obscures why the lift points are heavy.
5. Scope discovered late. The standard is on the project because of a contract clause somebody read after the design was issued.
6. A surveyor's acceptance read as approval. They confirm the operation meets the scope. The design is still yours.
Common questions
- Is a marine warranty standard a design code?
- No, and expecting it to be one is why onshore engineers find it confusing. It sets out how a marine operation is planned and what loads it is planned against - load factors, load cases, the conditions under which the operation may proceed - and it supplies no member resistances at all. You still need a structural design code; the warranty standard raises the demand you apply that code to.
- Why does a marine standard apply to work in a yard?
- By contract. The scope of these standards is marine, but a client specification for modules destined offshore routinely cites one for the whole scope of work including fabrication and yard lifting. The obligation is then contractual rather than scope-based, and the contract wins. It is worth reading the specification's scope section before starting the calculation rather than after it.
- What are the three marine warranty factors?
- Dynamic amplification, covering the extra force from motion of the crane, its support and the load, which falls as the item gets heavier. Skew load, covering the load not sharing between its lift points as the geometry says. And a consequence factor that depends on the component being checked, with lift points and their attachments carrying a higher one than the structure between them because a lift point failure drops the load. They are independent and they multiply.
- How much does a marine warranty overlay add?
- On the spreader beam worked in this article, a factor of 1.43 on the demand for an onshore environment and 2.30 offshore, with the beam, padeye, slings and load all unchanged. That took the padeye attachment weld from 56 percent of capacity to 80 onshore and to 128 offshore, while the beam's own bending check stayed comfortable throughout. The overlay pushes a design towards its lift points, because that is where the consequence factor lands.
- Do I still apply my own dynamic factor under a warranty scope?
- No, if the overlay supplies one, and this is the commonest double-count on these jobs. The two are estimating the same physical allowance, so applying both inflates the demand without improving anything. The way to catch it is to write the load path out with each factor's owner named, at which point two entries doing the same job become visible immediately.
Sources
Every document below is linked at its publisher or regulator. Xarpis reproduces no standard text; where a clause is named, the identifier is given so you can find it in your own copy.
DNV-ST-N001Marine operations and marine warranty
DNV · paid document
The marine warranty standard behind most offshore lift factor sets: dynamic amplification, skew load and consequence factors, and the load cases a marine operation is planned against. Widely applied onshore by contract even though its scope is marine.
ASME BTH-1Design of Below-the-Hook Lifting Devices
ASME · paid document
Structural, mechanical and electrical design criteria for below-the-hook lifting devices, used alongside ASME B30.20 which carries the safety requirements. The current edition is BTH-1-2023; Xarpis implements the 2020 edition and says so on every result.
EN 13155Cranes. Safety. Non-fixed load lifting attachments
BSI (national adoption of the CEN standard) · paid document
The harmonised European standard for non-fixed load lifting attachments - the family a spreader beam or lifting beam belongs to. It carries the load basis and the proof requirements, not member resistances, which is why an EN route needs EN 1993 alongside it. Now published as EN 13155:2020+A1:2025.
EN EurocodesEurocodes: Building the future
European Commission, Joint Research Centre · free portal
The Commission's own Eurocodes portal: the structure of EN 1990 to EN 1999, the database of Nationally Determined Parameters, and the second-generation timetable. The standards themselves are sold by the national bodies, but the NDP database is free and is what decides which partial factors apply in your country.
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