{"id":51736,"date":"2026-04-17T23:44:04","date_gmt":"2026-04-17T22:44:04","guid":{"rendered":"https:\/\/maritimehub.co.uk\/?p=51736"},"modified":"2026-04-17T23:44:04","modified_gmt":"2026-04-17T22:44:04","slug":"psv-cargo-runs-whats-on-deck-and-why","status":"publish","type":"post","link":"https:\/\/maritimehub.co.uk\/psv-cargo-runs-whats-on-deck-and-why\/","title":{"rendered":"PSV Cargo Runs – What’s on Deck and Why"},"content":{"rendered":"
\n

ON DECK -> Offshore Deck Operations<\/p>\n

Position on Deck<\/strong><\/p>\n

Operation Group:<\/strong> Offshore \/ Cargo<\/p>\n

Primary Role:<\/strong> Safe and sequenced delivery of deck cargo and bulk products from quayside to offshore installation<\/p>\n

Interfaces:<\/strong> Logistics coordinator ashore, installation OIM\/crane operator, deck crew, DPO, cargo shipper, mud engineer, base dispatcher<\/p>\n

Operational Criticality:<\/strong> Absolute \u2014 the PSV is the installation’s supply chain; if it fails, the rig stops drilling<\/p>\n

Failure Consequence:<\/strong> Unsecured cargo shifts in a seaway, causing list, structural damage, or loss overboard. Bulk cross-contamination renders expensive drilling fluids unusable. Mis-sequenced deck loads delay crane operations at the installation, extending the vessel’s time alongside in deteriorating weather windows.<\/p>\n<\/div>\n

A platform supply vessel is not a ferry. It is a floating warehouse that must deliver its stock in the right order, in the right condition, into the hands of a crane operator who cannot wait.<\/em><\/p>\n

Introduction<\/h2>\n

The PSV cargo run is the most routine offshore operation there is. It is also the one most likely to be treated casually. A vessel loads at a supply base, makes a sea passage of anything from four to thirty-six hours, arrives at an installation, and discharges. It does this again, and again, and again. The repetition breeds familiarity. Familiarity breeds the assumption that nothing will go wrong because nothing went wrong last time.<\/p>\n

But the cargo run is where logistics planning, deck seamanship, bulk fluid management, and dynamic positioning all converge in a single evolution. Each of those disciplines has its own failure modes. When they compound \u2014 a mis-declared weight on a container, a lashing that wasn’t tensioned, a cross-contaminated mud tank \u2014 the consequences arrive suddenly and without negotiation. The weather doesn’t care that the cargo plan looked good on the office screen.<\/p>\n

This article addresses what actually goes on deck and in the tanks of a working PSV, what discipline is required to get it there safely, and why the transition from sea passage to the 500-metre zone is the moment that exposes every shortcut taken at the berth.<\/p>\n

Contents<\/h2>\n
    \n
  • 1. The PSV as a Logistics Platform<\/li>\n
  • 2. Deck Cargo: What Goes On and What It Weighs<\/li>\n
  • 3. Bulk Cargoes: What’s Below Deck and Below the Waterline<\/li>\n
  • 4. The Cargo Manifest and the Shipper’s Responsibility<\/li>\n
  • 5. Deck Load Planning: Sequence Before Space<\/li>\n
  • 6. Sea-Fastening Discipline<\/li>\n
  • 7. Bulk Transfer Operations at the Installation<\/li>\n
  • 8. The 500-Metre Zone and the Transition<\/li>\n
  • 9. Closing Reality<\/li>\n<\/ul>\n

    1. The PSV as a Logistics Platform<\/h2>\n

    A platform supply vessel exists to keep an offshore installation operational. That is its entire purpose. It is not primarily a ship that makes voyages; it is a delivery system with a propulsion plant attached. Understanding this shapes everything about how a PSV is loaded, sailed, and worked alongside.<\/p>\n

    The modern PSV \u2014 typically 70 to 95 metres, 3,000 to 5,000 DWT \u2014 is purpose-built around a flat, unobstructed cargo deck aft of the superstructure and a complex array of bulk tanks beneath it. The deck is a loading platform. The tanks are a liquid and powder warehouse. The DP system exists to hold the vessel steady while the installation’s crane strips the deck and the hoses transfer what’s below.<\/p>\n

    Everything about the vessel’s design is a compromise between cargo capacity and seakeeping. A big open deck catches wind. A full set of bulk tanks raises the centre of gravity if loaded carelessly. The vessel must be stable enough for a potentially rough crossing yet arrive in a condition that allows safe cargo operations \u2014 which means controllable draughts, manageable freeboard, and a predictable motion characteristic when holding station.<\/p>\n

    The logistics chain ashore \u2014 the base dispatcher, the operator’s logistics coordinator, the mud company, the fuel supplier \u2014 all depend on the PSV to translate their planning into physical delivery. When that chain works, it is invisible. When it breaks, a drilling rig costing hundreds of thousands of pounds a day sits idle waiting for cement, or pipe, or the wrong grade of mud gets pumped into the wrong tank because somebody at the base didn’t label a manifold correctly.<\/p>\n

    2. Deck Cargo: What Goes On and What It Weighs<\/h2>\n

    A PSV’s cargo deck will carry almost anything the installation needs that won’t fit in a tank. The typical load mix on a drilling-support run includes some combination of the following:<\/p>\n

      \n
    • Drill pipe and tubulars \u2014 heavy, long, and prone to rolling if not chocked and lashed properly. Typically racked in pipe baskets or secured in bundles on dunnage.<\/li>\n
    • Cargo carrying units (CCUs) \u2014 open-top and closed containers, half-heights, baskets, skips. These carry everything from drilling consumables to food stores to hazardous chemicals in IBCs.<\/li>\n
    • Mud tanks and tote tanks \u2014 portable tanks of drilling fluid additives, brines, or specialty chemicals. Heavy when full. Often poorly marked.<\/li>\n
    • Hose reels, BOP parts, wellhead equipment, Christmas trees \u2014 irregular shapes, extreme weights, each requiring bespoke securing arrangements.<\/li>\n
    • Waste skips \u2014 returning dirty, often overloaded, sometimes with undeclared contents. A perennial problem.<\/li>\n<\/ul>\n

      The critical issue is weight. Not volume. A PSV’s cargo deck is large enough to accommodate an impressive amount of equipment by area. But the deck’s rated loading \u2014 typically expressed in tonnes per square metre \u2014 and the vessel’s total deadweight are the real constraints. A deck that looks half-empty may already be at its structural or stability limit if what’s on it is dense steel.<\/p>\n

      Pipe is the classic trap. A few racks of 5-inch drill pipe will consume a modest amount of deck space but a disproportionate amount of the vessel’s cargo capacity by weight. If the load planner is thinking in square metres rather than tonnes, the vessel can end up overloaded before the last container is swung aboard.<\/p>\n

      Every item on that deck has a certified weight. In theory. In practice, the declared weight on a CCU is only as good as the shipper’s scales and the shipper’s honesty. Containers that arrive at the quayside marked at 8 tonnes and weigh 12 tonnes are not rare. They are a fact of offshore logistics. The vessel’s chief officer has a right and a duty to reject any unit whose weight cannot be verified or whose condition is suspect. That right is exercised far less often than it should be.<\/p>\n

      3. Bulk Cargoes: What’s Below Deck and Below the Waterline<\/h2>\n

      The bulk cargo system on a PSV is what separates it from any other vessel of similar size. The tank arrangement beneath the cargo deck typically includes dedicated capacity for:<\/p>\n

        \n
      • Drill water<\/strong> \u2014 large-volume, low-value, but essential. Used for mixing drilling fluids and general rig operations. Often the single largest bulk cargo by volume.<\/li>\n
      • Potable water<\/strong> \u2014 segregated from drill water by regulation and common sense. Cross-contamination is not an inconvenience; it is a health hazard.<\/li>\n
      • Fuel oil<\/strong> \u2014 marine gas oil for the installation’s power generation and machinery.<\/li>\n
      • Liquid mud<\/strong> \u2014 active drilling fluid systems. Multiple grades may be carried simultaneously in segregated tanks. Contamination between grades can cost hundreds of thousands of pounds in lost product and rig time.<\/li>\n
      • Brine<\/strong> \u2014 completion fluids, often calcium chloride or calcium bromide solutions. Extremely expensive per cubic metre. Corrosive. Must be kept segregated from everything else.<\/li>\n
      • Dry bulk<\/strong> \u2014 cement, barite, bentonite. Carried in pneumatic tanks and discharged by air pressure. Segregation between products is essential; a tank of cement contaminated with barite is useless to anyone.<\/li>\n<\/ul>\n

        The tank arrangement is fixed by the vessel’s design, but the loading plan is different every trip. The chief officer must know exactly what is in every tank, how much of it there is, and what sequence it will be discharged in. The cargo documentation system \u2014 tank loading plans, ullage reports, bulk cargo manifests \u2014 must reflect reality, not what was planned ashore.<\/p>\n

        Stability is calculated on the basis of actual tank contents. A PSV with partially filled mud tanks on a beam sea will develop free-surface effects that significantly reduce GM. This is not theoretical. It is the reason PSVs have capsized.<\/p>\n

        4. The Cargo Manifest and the Shipper’s Responsibility<\/h2>\n

        The cargo manifest is the legal and operational document that defines what is on board. It should list every deck unit by identifier, description, weight, dimensions, and hazard classification. For bulks, it should state product type, volume, specific gravity, and destination tank on the installation.<\/p>\n

        The shipper \u2014 the party consigning the cargo \u2014 has a legal responsibility under the Merchant Shipping regulations and the IMDG Code (where applicable) to provide accurate information about weight, contents, and hazard classification. The reality is that this responsibility is routinely discharged with varying degrees of rigour. Manifests arrive late. Weights are estimated. Hazard declarations are copied from the last shipment without checking whether the contents have changed.<\/p>\n

        A signed manifest is a warranty. If the declared weight is wrong and the vessel is overloaded, the shipper is liable. But liability after the event does not prevent the event. The chief officer loading cargo at 0300 in the rain, against a sailing deadline, with a dispatcher pushing to get the last skip aboard, is the last line of defence.<\/p>\n

        That line of defence must hold.<\/p>\n

        A container that is 40% heavier than declared will shift in a seaway even if lashed for its declared weight. The lashing was correct on paper. The physics was not.<\/p>\n

        5. Deck Load Planning: Sequence Before Space<\/h2>\n

        The most common error in PSV deck load planning is treating it as a packing problem. It is not. It is a sequencing problem. The question is not "does it fit?" but "can the installation’s crane take it off in the order they need it?"<\/p>\n

        An offshore installation crane operates under constraints that the vessel cannot control: weather limits, simultaneous operations on the drill floor, crew change helicopter windows, permit-to-work schedules. The installation will specify a discharge priority. Urgent items \u2014 perhaps a replacement pump, or a cement batch needed for a well operation starting at dawn \u2014 must be accessible first. That means they must be loaded last and positioned where the crane can reach them without moving other cargo.<\/p>\n

        This is where the load plan becomes a three-dimensional puzzle solved backwards. The first item needed at the installation goes on deck last, positioned outboard and aft where the crane has a clear pick. Items needed last go on first, inboard, stacked if stability and lashing allow.<\/p>\n

        When the load plan is done well, the vessel arrives, the crane lifts in sequence, and the operation is efficient. When it is done badly \u2014 or when late-arriving cargo forces a re-plan that nobody communicates to the installation \u2014 containers must be shuffled on deck alongside the rig, wasting crane time in weather that may be deteriorating by the hour.<\/p>\n

        Deck load planning is not a deckhand’s job. It is the chief officer’s responsibility, executed in consultation with the base dispatcher and the installation logistics team. It requires knowledge of the vessel’s stability at every stage of discharge, the crane’s safe working load at the relevant radius, and the physical characteristics of every unit on deck.<\/p>\n

        A plan that exists only in someone’s head is not a plan. It is a hope.<\/p>\n

        6. Sea-Fastening Discipline<\/h2>\n

        A PSV that sails with unsecured deck cargo has already failed. Not "is at risk of failing." Has failed. The failure occurred at the berth, when lashings were not applied, not tensioned, or not checked. The consequences simply arrive later, at sea, when the vessel rolls and something moves.<\/p>\n

        The standard securing arrangements for PSV deck cargo involve combinations of:<\/p>\n

          \n
        • Chain lashings<\/strong> \u2014 used for heavy units, pipe racks, tanks. Secured to deck pad-eyes with load-rated shackles and tensioned with bottle screws or lever binders. Chain does not stretch. It either holds or it fails at the weakest link \u2014 often the shackle or the pad-eye weld.<\/li>\n
        • Webbing straps<\/strong> \u2014 used for lighter CCUs and baskets. Faster to apply than chain. Subject to chafe damage, UV degradation, and loss of tension over time. Must be checked and re-tensioned during the voyage.<\/li>\n
        • Wire lashings<\/strong> \u2014 less common now but still seen. Prone to kinking and difficult to re-tension without the right tools.<\/li>\n
        • Chocks and stoppers<\/strong> \u2014 timber dunnage, welded stoppers, or manufactured chock systems used to prevent lateral movement at the base of cargo units. Lashings resist overturning and lifting forces; chocks resist sliding. Both are needed. One without the other is incomplete.<\/li>\n<\/ul>\n

          The number and SWL of lashings required for a given unit depend on its weight, height, position on deck, and the expected accelerations during the voyage. NWEA guidelines and the vessel’s Cargo Securing Manual provide the framework. But the framework only works if the lashings are actually applied, are in serviceable condition, and are tensioned to the correct degree.<\/p>\n

          A chain with a bent link is not a lashing. A webbing strap passed over a container corner without a corner protector will chafe through in a moderate sea. A bottle screw that hasn’t been greased in six months won’t tension properly and will seize when someone tries to release it at the installation.<\/p>\n

          Sea-fastening is not the last job before sailing. It is one of the most critical jobs in the entire cargo run. The master and chief officer should inspect every lashing before departure and record the inspection. If the vessel sails and a lashing fails, the question will not be "was the lashing adequate?" It will be "did anyone check?"<\/p>\n

          7. Bulk Transfer Operations at the Installation<\/h2>\n

          Bulk transfer alongside an offshore installation is where the greatest potential for costly error exists. The products are expensive, the consequences of contamination are severe, and the operation happens through hoses and manifolds that cannot be visually inspected once connected.<\/p>\n

          The process follows a standard sequence: the vessel makes up alongside or holds on DP at a specified standoff distance, hoses are connected to the installation’s bulk transfer points (typically via a crane-assisted messenger or a dedicated hose-handling system), and product is pumped at agreed pressures and flow rates while both parties monitor tank levels.<\/p>\n

          Pressure management is critical. Over-pressurising a hose or an installation receiving tank can cause a burst line, a spill, or a structural failure in a tank. Maximum pump pressure and flow rate are agreed before transfer begins. The vessel’s pump operator and the installation’s mud engineer or tank operator must be in continuous communication throughout \u2014 and that means dedicated radio channels, not shared working frequencies cluttered with crane talk.<\/p>\n

          Cross-contamination is the operational nightmare of bulk transfers. It can happen in several ways:<\/p>\n

            \n
          • A hose that previously carried one product is connected for a different product without being flushed.<\/li>\n
          • A valve on the vessel’s manifold is lined up to the wrong tank.<\/li>\n
          • Residual product in a vessel’s tank \u2014 not fully stripped on a previous discharge \u2014 mixes with the new load.<\/li>\n
          • A dry bulk line that carried cement is used for barite without being blown through with air first.<\/li>\n<\/ul>\n

            Any one of these can render a tank of product unusable. A contaminated tank of oil-based mud or a batch of calcium bromide brine ruined by a few hundred litres of drill water represents a loss that can run to six figures. The drilling programme may stall while replacement product is mixed or shipped.<\/p>\n

            Line-up checks before every transfer are not optional. They are the single most effective control against cross-contamination. Both the vessel crew and the installation receiving party should independently verify that the correct tanks, valves, and hoses are aligned before any pump starts. The check must be physical \u2014 someone walking the manifold and confirming valve positions \u2014 not a verbal confirmation from someone who thinks they remember from last time.<\/p>\n

            8. The 500-Metre Zone and the Transition<\/h2>\n

            The 500-metre safety zone around an offshore installation is a legal boundary. It is also an operational threshold that separates two fundamentally different modes of operating the vessel.<\/p>\n

            On passage, the PSV is a ship. It navigates, it keeps watch, it follows COLREGS, and its cargo sits lashed and inert on deck. The primary risks are weather, traffic, and machinery failure.<\/p>\n

            Inside the 500-metre zone, the vessel becomes something else: a servicing platform holding station in close proximity to a fixed structure, subject to the installation’s operational authority, with its deck about to become an active crane-working area and its manifolds about to be connected to another facility’s piping systems. The risk profile changes completely.<\/p>\n

            The transition from passage to approach is the moment that reveals the quality of every decision made at the berth. If the deck cargo is properly secured, the vessel arrives with everything where it should be, ready for an orderly discharge. If lashings have worked loose, if a container has shifted even slightly, the crew now face a rectification task alongside a live installation, possibly in a seaway, with the crane standing by and the OIM asking when operations can start.<\/p>\n

            Before entering the zone, the vessel must have permission from the installation. The DP system must be proven \u2014 trials completed, references checked, position-reference systems verified. The approach procedure, the agreed heading, the standoff distance, the escape route in the event of a DP failure \u2014 all of this must be confirmed and understood by the bridge team before the vessel crosses the boundary.<\/p>\n

            A vessel that enters the 500-metre zone without having completed its DP checks, or with deck cargo in a doubtful state, or without a clear plan for the sequence of operations, is introducing risk into an environment that has no tolerance for improvisation.<\/p>\n

            The zone boundary is where discipline either exists or is exposed as absent. There is no middle ground at 500 metres.<\/p>\n

            9. Closing Reality<\/h2>\n

            A PSV cargo run succeeds or fails long before the vessel arrives at the installation. It succeeds or fails at the supply base, when weights are verified or assumed, when lashings are applied and tensioned or merely draped over cargo for appearance, when bulk tank line-ups are walked and confirmed or left to the last person who touched the manifold.<\/p>\n

            The sea passage is not a pause between loading and discharge. It is the test. Every inadequate lashing, every mis-declared weight, every rushed load plan is subjected to the forces that the North Sea or the South Atlantic or the Gulf of Mexico impose without negotiation. What was marginal at the quayside becomes dangerous at sea.<\/p>\n

            A PSV that arrives at the 500-metre zone with its cargo intact, its tanks correctly segregated, its load plan aligned with the installation’s discharge priorities, and its DP system proven is a vessel that has been operated by people who understand what the job actually requires.<\/p>\n

            A PSV that arrives with a shifted container, a suspect lashing, or a cargo manifest that doesn’t match reality is a vessel that was failed by everyone who touched it ashore and on board.<\/p>\n

            The cargo run is routine. The standards required to execute it safely are not.<\/p>\n","protected":false},"excerpt":{"rendered":"

            Deck cargo, bulk transfers, and sea-fastening discipline on platform supply vessels: what actually matters on an offshore cargo run.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"fifu_image_url":"","fifu_image_alt":"","c2c-post-author-ip":"2a02:c7c:2ef8:2400:931:afb1:9971:4a62","footnotes":""},"categories":[1,14],"tags":[9402,9398,9312,9399,9389,8176,9401,9400],"class_list":["post-51736","post","type-post","status-publish","format-standard","hentry","category-latest","category-on-deck","tag-500-metre-zone","tag-bulk-transfer","tag-cargo-securing","tag-deck-cargo","tag-offshore-deck-operations","tag-psv","tag-sea-fastening","tag-supply-vessel"],"acf":[],"_links":{"self":[{"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/posts\/51736","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/maritimehub.co.uk\/?rest_route=%2Fwp%2Fv2%2Fcomments&post=51736"}],"version-history":[{"count":1,"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/posts\/51736\/revisions"}],"predecessor-version":[{"id":51737,"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/posts\/51736\/revisions\/51737"}],"wp:attachment":[{"href":"https:\/\/maritimehub.co.uk\/?rest_route=%2Fwp%2Fv2%2Fmedia&parent=51736"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/maritimehub.co.uk\/?rest_route=%2Fwp%2Fv2%2Fcategories&post=51736"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/maritimehub.co.uk\/?rest_route=%2Fwp%2Fv2%2Ftags&post=51736"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}