Deck Maintenance & Surveys

A cargo hold is only as watertight as its weakest closing appliance, and on a general cargo or bulk carrier that appliance is the hatch cover. Cargo claims for wet damage trace back to the coaming and cover joint more often than to any other part of the hull, which is why a surveyor will go to the hatches before almost anywhere else on deck.

The joint works as a system, not a single part. The compression bar, welded along the coaming or the cover panel, presses down onto a continuous rubber packing when the cover is dogged down by the cleats; the packing deforms to close the gap, and the drainage channels carry away whatever spray or rain still gets past the first line of defence, routing it overboard through non-return valves rather than into the hold. If any one part of that chain is out of adjustment — a low cleat, a hardened or perished packing, a blocked drain channel — the others cannot compensate for it, and the joint leaks somewhere along its length even though it looks sound everywhere else.

• Chalk test — a chalk line run along the compression bar, cover closed and dogged, then reopened to see whether the line has transferred continuously onto the packing. It proves the bar is contacting the packing with even pressure along its length. It proves nothing about whether that contact actually excludes water.
• Hose test — a jet of water played over the closed joint from a set distance and pressure, with someone below checking for ingress. It is a direct test of leakage, but it is weather-dependent, labour-intensive, can force water into insulation or electrical runs nearby, and is restricted in some ports for exactly that reason.
• Ultrasonic test — an ultrasonic transmitter is placed inside the closed hold and a receiver is run along the joint from the outside; where the packing seals properly the signal is blocked, and where there is a gap the receiver's reading rises above a set threshold. It is the only one of the three that gives a number, and that number can be logged, trended, and used to pinpoint exactly which frame or corner needs attention.

None of this removes the value of the other two. A chalk test is quick enough to run before every loading, and a hose test is still asked for at some surveys because it tests the assembled system under an actual head of water rather than an acoustic proxy for it. But when the question is whether the joint meets the standard, ultrasonic testing is the test that actually measures it, and it is the one to reach for when the chalk test looks marginal or the cargo is sensitive to wetting.

Lifesaving and firefighting appliances are maintained on a fixed calendar, not on how they look. The intervals are short at the bottom of the hierarchy and get longer, more thorough, and more likely to involve a shore technician as you go up it — and every level produces a record that has to exist before the equipment can be said to have been maintained at all.

• Weekly, on board — visual checks of lifeboats, rescue boats and their launching arrangements; engines run under load; davits and falls given a general look-over.
• Monthly, on board — a fuller inspection logged against a checklist: extinguisher pressure gauges and seals, EEBDs, immersion suits, fire hoses and nozzles, emergency lighting.
• Annual, ashore — an approved service station strips, tests and re-certifies inflatable liferafts, hydrostatic release units, fire extinguishers and similar equipment, and issues the certificate that goes back aboard with the item.
• Five-yearly — davits and falls undergo a load test above the boat's maximum permitted load, confirming the winch, brake and wire can still take the working load with margin, not just that they turn freely.

That has a blunt consequence. If the annual service was carried out but the certificate is still at the agent's office, or the load test happened but the tag was never transcribed into the PMS, the finding is a deficiency — not a caveat, not a note to chase up later. The equipment's actual physical condition does not enter into it at that point; what is being inspected is whether the paperwork proves the interval was met. Keeping the certificate folder current and matched to the equipment on board is as much a part of maintaining lifesaving appliances as greasing the davit trackways.

Paint is not decoration on a ship's structure; it is the only thing standing between bare steel and an electrolyte that never stops working on it. Once a coating system breaks down — mechanical damage, a holiday left in the original application, cathodic protection that has run out of anode — the steel underneath starts wasting, and it often does so invisibly, under paint that still looks intact from a few feet away.

That is why thickness measurement, not visual inspection, actually settles the question. A UT gauge reads the remaining metal thickness at a grid of points, and that reading is judged against two numbers: the as-built thickness, which shows how much has already been lost, and the class renewal (minimum permissible) thickness, which is the figure the surveyor actually cares about — cross that line and the plate or frame must be renewed regardless of how much service life the owner had hoped to get from it.

Surveyors grade coating condition simply — good, fair or poor — and that grading is not just descriptive, it drives how much of the tank gets gauged and how the survey scope for the whole ship is set. A tank graded poor typically brings a much heavier thickness-measurement programme with it, because a failed coating is read as an early warning that the steel behind it may already be wasting faster than the calendar interval suggests. Recoating before that grading is reached is far cheaper, in both money and downtime, than chasing a diminishing margin with thickness gauges at every survey after.

Anchoring and mooring equipment wears rather than corrodes, in the main, and that distinction changes how it is surveyed. A cable's chain links rub against each other and against the windlass and hawsepipe every time the anchor is worked, and that mechanical action thins the metal steadily over years of service in a way that has nothing to do with coating condition.

At dry-docking the cable is ranged out on deck, cleaned, and gauged rather than simply looked at. The reading that matters is diameter measured across the link at right angles to the stud, taken clear of any weld flash — measuring along the stud, or over a flash mark, both read artificially high and can let a genuinely worn link through. The worst-worn length of cable, not a convenient sample, is what gets gauged, because that is the length that will actually fail first.

The cable is also re-marked at this point — paint or wire markings at each shackle join, so that whoever is on the windlass brake at sea can read off how much cable is out without counting shackles from memory under pressure. Mooring lines and wires get their own version of the same logic: synthetic rope is checked for chafe, UV degradation and broken yarns rather than gauged, wire rope for broken strands and corrosion at the core, and the windlass brake itself is periodically tested to confirm it still holds its rated load rather than simply that it grips.

Every interval described so far — hatch cover tests, LSA/FFA servicing, thickness gauging, anchor cable ranging — only has value to a survey if it is written down at the time it happens. The planned maintenance system is the ship's own record of its own compliance, and a surveyor reading it is really asking one question: does this record actually reflect work being done continuously, or was it assembled just before the survey?

That question has a tell. Records entered in a single sitting the week before survey, clustered in timestamp and identical in tone, read exactly like what they are. A record built up honestly over months has the untidy rhythm of a working ship in it — jobs deferred and picked up again, defects raised and closed weeks apart, readings that vary slightly from one round to the next because different people took them. Contemporaneous entry is not a bureaucratic nicety; it is what makes the record credible evidence rather than a document produced to pass an inspection.

For the mate, this makes the PMS a standing responsibility rather than a pre-survey scramble: flagging overdue items as they fall due, chasing certificates back from agents and service stations before they go missing, and keeping everything indexed so that when a surveyor asks for the extinguisher service records or the last three years of thickness readings, the answer is a folder, not a search.

A dry-docking is a fixed, expensive window with a yard's schedule and a yard's price list attached to it, and the document that controls what happens inside that window is the dock specification. It is written and agreed before the ship arrives, and it is, in every practical sense, a contract: whatever it does not cover is not included, and the yard is entitled to price anything outside it as a variation order, on their terms, once the ship is already alongside and has nowhere else to go.

• Scope — every job listed item by item, drawn from survey requirements, owner's wish list and deferred maintenance, not a general description of "hull works".
• Access and staging — where scaffolding, staging and lighting are needed, and who is providing them.
• Blanking and isolation — sea inlets, overboard discharges and other openings that must be blanked before the dock is flooded down or work begins on them.
• Gas-freeing and enclosed-space entry — tanks and spaces certified safe for entry and hot work before anyone is sent into them.
• Acceptance criteria — the standard each job is measured against to be signed off as complete, agreed in advance rather than negotiated at handover.
• Supply — who provides paint, anodes, spares and consumables, since a yard supplying them prices them, and a ship supplying them has to have them there on time.

Writing this document is where the whole chapter comes together — the hatch cover ultrasonic readings, the coating condition grading, the thickness measurements, the anchor cable's condemning margin all feed into what actually needs to be in scope. A dock specification assembled from a genuinely current PMS and survey record is precise because the ship already knows what it needs; one assembled in a hurry from memory is where scope gets missed and costs get discovered afterwards.

The three examples below work through the reasoning behind a thickness reading, an anchor cable gauging, and a PMS forward plan — layered, multi-step problems of the kind the exam actually sets, rather than a single formula substitution.

Worked example 1

Coating wastage rate and remaining margin to renewal thickness

A cargo hold side shell plate was 12.0 mm thick when built. Eight years later, at the ship's special survey, ultrasonic thickness measurement finds it averaging 10.8 mm. Class's renewal (minimum permissible) thickness for this plate is 9.0 mm, and the ship's next special survey falls at the normal 5-year interval. The coating in this tank was assessed as 'poor' at this survey. Estimate how long the plate has before it reaches renewal thickness at its present wastage rate, and say whether it will pass the next special survey.

Given

As-built thickness t₀ = 12.0 mm Measured thickness now (age 8 years) t₁ = 10.8 mm Class renewal (minimum permissible) thickness t_min = 9.0 mm Special survey interval = 5 years Coating condition in this tank = poor

Required

Estimate how long the plate has before it reaches renewal thickness at its present wastage rate, and say whether it will pass the next special survey

1. Find the average wastage rate.

   Wastage=t₀ − t₁ =12.0 − 10.8 =1.2 mm over 8 years Rate=1.2 ÷ 8 =0.15 mm/year

   The metal lost since build, divided by the years it took, gives a straight-line rate — the only rate available in the absence of a full history of yearly readings.

2. Compare the current thickness to the renewal thickness to see how much margin is left before the plate would be condemned.

   Margin=t₁ − t_min =10.8 − 9.0 =1.8 mm

3. Divide the remaining margin by the wastage rate to project the years remaining.

   Years to renewal=1.8 ÷ 0.15 =12 years Wastage over next 5-year cycle = 0.15 × 5 =0.75 mm Projected thickness at next SS=10.8 − 0.75 =10.05 mm (> 9.0 mm — passes)

   Then check that projection against the next survey cycle.

AnswerOn a straight-line projection the plate has about 12 years to renewal thickness and would pass the next special survey with roughly 1.05 mm to spare — but see the trap.

The trap: that straight-line rate was set before the coating failed; with the tank now graded 'poor', corrosion is free to accelerate, so the 12-year projection is optimistic — the sound response is to recommend coating renewal now, not to trust the extrapolation forward.

Worked example 2

Anchor cable wear against the condemning diameter

During dry-docking the mate ranges the port bower anchor cable on deck for survey. The cable is 50 mm nominal diameter, and the condemning limit set for this cable is 12% diameter wear. The worst-worn length is gauged at three points, giving diameters of 46 mm, 45 mm and 44 mm. Decide whether the cable passes, and by how much.

Given

Nominal (as-fitted) diameter d₀ = 50 mm Condemning limit = 12% diameter wear Gauged diameters at worst length = 46 mm, 45 mm, 44 mm

1. Set the condemning diameter first.

   d_min=d₀ × (1 − 0.12) =50 × 0.88 =44.0 mm

   So each reading can be judged against a fixed figure rather than converting a percentage every time.

2. Average the readings taken across the worst-worn length.

   d_avg=(46 + 45 + 44) ÷ 3 =135 ÷ 3 =45.0 mm

   It is the worst length of cable that is gauged, and its average that is judged — not a single most-convenient reading.

3. Compare the averaged reading to the condemning diameter.

   Margin=d_avg − d_min =45.0 − 44.0 =1.0 mm Wear so far=(50 − 45.0) ÷ 50 × 100 =10%

   And separately state the wear reached so far against the 12% limit.

AnswerCable passes — 10% wear against a 12% condemning limit, 1.0 mm of diameter in hand — but it is close enough to flag for re-ranging at the next dry-docking rather than waiting the full interval.

The trap: gauging across the weld flash, or along the line of the stud rather than perpendicular to it, both read artificially high and can pass a link that has actually worn past the limit.

Worked example 3

Scheduling LSA/FFA servicing against an approaching survey

The chief mate reviews the PMS forward plan ten weeks before the annual survey. Records show: the lifeboat davit/falls load test (5-year interval) was last done 252 weeks ago; the portable fire extinguishers' annual service (52-week interval) was last done 48 weeks ago; and the EEBD inspection (monthly, treated as a 4-week interval for planning) was last done 5 weeks ago. Work out which items fall due before the survey, and which need action right now.

Given

Survey due in 10 weeks Davit/falls load test: interval 260 weeks (5 years), last done 252 weeks ago Extinguisher annual service: interval 52 weeks, last done 48 weeks ago EEBD inspection: interval 4 weeks, last done 5 weeks ago

1. Find how much interval remains on each item by subtracting elapsed time from the interval.

   Davit test remaining=260 − 252 = 8 weeks Extinguisher service remaining=52 − 48 = 4 weeks EEBD remaining=4 − 5 = −1 week (already overdue)

   A negative result means the item is already overdue, not merely approaching.

2. Compare each remaining figure to the 10-week window to the survey.

   8 weeks<10 weeks → davit test falls due before survey 4 weeks<10 weeks → extinguisher service falls due before survey EEBD already overdue → due immediately, independent of the survey date

   Anything due inside that window must be actioned before the surveyor is aboard, not left to the ship's normal rhythm.

3. Order the three by urgency and note which needs the longest lead time to arrange.

   A shore contractor for the load test cannot usually be booked at short notice.

AnswerAll three items fall due before the survey: EEBD inspection today (already 1 week overdue), extinguisher service within 4 weeks, davit/falls load test within 8 weeks — book the load-test contractor now, since that lead time is the tightest against the survey date.

The trap: treating the davit test as the least urgent because it has the longest remaining time — it is actually the one with the least slack once the contractor's own booking lead time is subtracted from the 8 weeks available.