OWS / Sewage / Marine Environment — Most Asked Questions
28 questions asked about ows / sewage / marine environment across the General and Fn 3 papers, heaviest first. 1 of them are must-master.
Learn the system first
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1 Annex 1 discharge criteria
Also asked: “Annex 1 special area discharge criteria”, “what is Annex-1 and discharge criteria?”, “Rise of floor Annex 1 discharge criteria”
Answer
Machinery-space bilge water may go overboard only en route, through working oil-filtering equipment, at 15 ppm or less, with auto-stop — tankers face extra cargo-area conditions.
- Ship proceeding en route; mixture processed through oil-filtering equipment; oil content 15 ppm or less without dilution.
- On tankers the mixture must not come from cargo pump-room bilges nor be mixed with cargo-oil residues; nothing at all discharged in Antarctic/Arctic waters.
- A 15-ppm automatic stopping device is fitted; the separator runs only under Chief Engineer/Master authority with date, time, duration and position logged.
- Tanker cargo-area discharges add: outside special areas, over 50 miles from land, en route, instantaneous rate within 30 litres per nautical mile plus total-quantity limits.
Surveyor follow-up: the 15-ppm alarm sounds mid-discharge — what stops, what is logged, and can you restart by switching to the spare unit?
Full theory: When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas -
2 Orb part 1 entry
Answer
Part 1 logs every machinery-space oil move in lettered codes: C for bilge to slop tank, D and E overboard through the separator, G for accidents, H for bunkering.
- Code C: bilge water discharged to slop or holding tank — time, position and quantity.
- Codes D and E: overboard through filtering equipment — start and stop times, auto-stop performance, 15 ppm proof.
- Code F: separator failure — when it failed, when restored, and why; Code G: any accidental or exceptional discharge with full circumstances.
- Code H: bunkering — time, place, quantity and hose connections; every line signed by the officer and master.
Surveyor follow-up: separator auto-stop tripped mid-discharge — which code, and what three times go in the book?
Full theory: When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas -
3 Entries in orb
Also asked: “Enteries in orb”
Answer
Part 1 logs every machinery-space oil move by letter: ballast, dirty water, bilge, overboard, failures, accidents and bunkering.
- Code A: ballasting or cleaning fuel tanks; Code B: discharging dirty ballast or cleaning water from them.
- Code C: bilge water collected to slop or holding tank; Codes D and E: overboard through filtering equipment with times and 15 ppm proof.
- Code F: separator failure with stop and restore times plus reason; Code G: accidental or exceptional discharge with full circumstances.
- Code H: bunkering with time, place and quantity; every line tank-to-tank, signed by officer and master.
Surveyor follow-up: auto-stop tripped mid-discharge — which code, and what three times go in the book?
Full theory: When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas -
4 Ballast water management
Answer
Ballast water management stops invasive species hitching a ride: a shipboard plan, a record book, exchange or treatment to D-1 and D-2 standards.
- Every ship of 400 gross tons and up carries a ballast water management plan, record book and certificate.
- D-1 exchange: 95% volumetric exchange by sequential empty-refill, flow-through or dilution methods, recorded by pump hours.
- D-2 performance: treatment systems landing organisms below set limits — the modern compliance route.
- Never transfer untreated ballast between incompatible zones; log every uptake, treatment and discharge.
Surveyor follow-up: exchange done mid-ocean but the treatment plant faulted — compliant or not, and what goes in the book?
Full theory: When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas -
5 Discharge criteria,engine room bilges
Answer
Bilge water goes overboard only en route through working filtering gear at 15 ppm or less — five conditions, all met.
- Ship proceeding en route outside 12 miles with the mixture through compliant filtering equipment.
- Oil content 15 ppm or less without dilution, proved by the monitor with automatic stop.
- Never from cargo pump-room bilges on tankers nor mixed with cargo residues.
- Special areas add the same bar with tighter watch — log time, position and quantity every discharge.
Surveyor follow-up: 15-ppm alarm sounds mid-discharge — what stops, what is logged, and can you restart on the spare unit?
Full theory: When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas -
6 ORB weekly entry
Answer
Sludge retained on board is logged at least weekly: tank identity, capacity, quantity kept and how the rest left the ship.
- Record sludge from fuel and lube purification plus machinery-space residues with tank names and capacities.
- Log total retained quantity at voyage end and at least once a week — weekly on short voyages too.
- Each disposal notes date, method, quantity landed or burnt and quantity remaining.
- Bilge, bunkering and accidental-discharge entries beside it carry their own dates, positions and signatures.
Surveyor follow-up: sludge quantity unchanged for three weeks with the purifier running daily — normal or missing entries?
Full theory: When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas -
7 With reference to an OWS
Answer
Answer any OWS reference with stages, monitor and law: gravity, coalescer and polish to 15 ppm with auto-stop and record book.
- First-stage gravity with baffles and float venting; second-stage coalescer joining fine drops to drainable size.
- Polishing filter and 15 ppm monitor with automatic stop on exceedance or failure.
- Operate to the five discharge conditions — en route, through working gear, clean of cargo bilges and residues.
- Log every run by code in the Oil Record Book with times, positions and quantities.
Surveyor follow-up: apply that frame to the separator in front of you — stages, monitor and discharge law first.
Full theory: How Oily Water Separation Works — Gravity, Coalescence and Why Turbulence Ruins It -
8 Dimensions of standard discharge connection for sewage
Also asked: “Sewage shore connection dimensions”
Answer
Sewage lands ashore through one standard flange: 210 mm outside on a 170 mm bolt circle with four 16 mm bolts.
- Outside 210 mm with inner bore to pipe size up to 100 mm maximum in steel with flat face.
- Bolt circle 170 mm with four 18 mm holes slotted to the edge, 18 mm slot width.
- Flange 16 mm thick with gasket for 600 kPa service; small ships may reduce to 38 mm bore.
- Dedicated trades may fit administration-accepted quick couplings instead — standard remains the fallback.
Surveyor follow-up: reception hose will not mate with the ship flange — adapter, reducer or new flange, and who provides it?
Full theory: MARPOL Annex IV — Prevention of Pollution by Sewage from Ships -
9 Oil discharge criteria for engine room in spcl area
Answer
Special areas keep the same 15 ppm bar with tighter watch: en route, through working gear, clean of cargo bilges.
- Ship proceeding en route with the mixture through compliant filtering equipment.
- Oil content 15 ppm or less without dilution, proved by monitor with automatic stop.
- Never from cargo pump-room bilges on tankers nor mixed with cargo residues.
- Log time, position and quantity every discharge — special-area entries read first at inspection.
Surveyor follow-up: 15-ppm alarm mid-discharge inside a special area — stop, log or switch units?
Full theory: When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas -
10 Oily discharge criteria in special area?
Also asked: “Ows discharge criteria in special area ?”
Answer
Special-area discharge is machinery-spaces-only at 15 ppm: en route, filtered, monitored and logged.
- Only machinery-space bilges — cargo-area mixtures stay aboard for reception in special areas.
- En route with working oil-filtering equipment and 15 ppm proved without dilution.
- Automatic stop on exceedance or monitor failure with Code F entries for every stop.
- Positions inside the area boundaries logged start to finish — outside the line is a different law.
Surveyor follow-up: inside a special area with clean effluent — discharge or hold, and what position proves it?
Full theory: When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas -
11 Orb how many
Answer
Two record books cover oil: Part I machinery spaces on every big ship, Part II cargo and ballast on tankers.
- Part I for every oil tanker of 150 gross tons and every other ship of 400 gross tons and up.
- Part II additionally for oil tankers recording cargo and ballast movements tank to tank.
- Entries by letter code with dates, quantities, positions and methods in chronological order.
- Each operation signed by the officer, each page signed by the master — accuracy limits noted, not hidden.
Surveyor follow-up: 300-gross-ton bulker with one book aboard — Part I, Part II or both, and why?
Full theory: How Oily Water Separation Works — Gravity, Coalescence and Why Turbulence Ruins It -
12 Oil discharge criteria
Answer
Machinery bilges leave only through 15-ppm gear: en route, filtering, auto-stopped above 15 ppm — tankers add the mile rules.
- Machinery effluent passes oil-filtering plant to 15 ppm maximum with an auto-stopping device on excess.
- Small ships without auto-stop keep special-area discharges aboard — no stop device, no special-area pumping.
- Oil-tanker cargo areas add the full set: outside special areas, beyond 50 miles, en route, 30 litres per mile and total limits.
- Prove by record book, monitor printout and stopped-discharge drill — the surveyor fails paper without the test.
Surveyor follow-up: 15-ppm alarm with discharge still flowing outside special areas — monitor, stop device or crew, and what now?
Full theory: MARPOL Annex I — Prevention of Pollution by Oil -
13 Ballast Water Management . D1 and D2?
Answer
D1 swaps the ocean, D2 cleans it: exchange 95% mid-ocean until treatment plants meet the organism counts.
- D1 exchange runs sequential empty-refill, flow-through overflow or dilution pumping to 95% volumetric replacement.
- D2 treatment meets discharge organism and microbe limits through approved plants with a ballast record book.
- Ships past 400 gross tons carry a BWM plan, record book and certificate under the 2017 convention.
- Answer with your plant and method — sequential, flow-through or treated — with the log pages that prove the last exchange.
Surveyor follow-up: D1 logged inside 50 miles with the treatment plant bypassed — exchange, treatment or detention first?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
14 Annex 5 discharge criteria for seca and non seca nd annex 4 discharge criteria?
Answer
Garbage and sewage are graded the same way: distances outside a special area, and much tighter rules or a ban inside one.
- Annex V garbage: plastics are prohibited outright, dunnage beyond 25 miles, and other refuse and food waste beyond 12 miles.
- Commminuted or ground garbage may go beyond 3 miles and must pass a 25 mm screen; special areas bite first.
- Annex IV sewage: comminuted and disinfected discharge past 3 miles and above 4 knots; untreated past 12 miles.
- In special areas the tighter requirement applies, and a ship with no storage in the area must retain the discharge.
Surveyor follow-up: food waste overboard at 8 miles in a special area — is the distance, the grinding or the area the failure?
Full theory: MARPOL Annex V — Prevention of Pollution by Garbage from Ships -
15 Anx 1 discharge criteria+ special area definition and difference between area and other area
Answer
A special area is a defined sea where the oil discharge rules tighten: everywhere else the general Annex I limits apply.
- Special areas are listed by name — the Mediterranean, Baltic, Red Sea, Black Sea and North Sea, the Gulf of Aden area, and the Antarctic.
- In them, machinery bilge discharge is effectively stopped: the 15-ppm allowance is withdrawn and effluent is retained.
- Outside them, machinery-space bilge may go overboard at 15 ppm or less without dilution, en route, and not from cargo pump-room bilges.
- Oil tankers are bound by the separate cargo-area rules: 15 ppm, 30 litres per mile, beyond 50 miles, and further tightened at sea in ballast.
- So the difference is the area and the rule, with the record book saying which area the ship was in at the time of the discharge.
Surveyor follow-up: discharge logged at 15 ppm with the ship inside the North Sea — which annex and which area rule apply?
Full theory: MARPOL Annex I — Prevention of Pollution by Oil -
16 Ballast water management plan and use on my ship
Answer
The BWM plan is the ship’s written method: exchange or treat, with the records that prove which was done and where.
- Ships past 400 gross tons carry a ballast water management plan, a record book and a certificate under the convention.
- D1 exchange means 95% volumetric exchange by sequential, flow-through or dilution methods, done away from the coast.
- D2 treatment meets the discharge organism counts through an approved type-approved plant on board.
- Use it on the ship: the plan decides the method, the exchange is logged with tanks and position, and the samples are the proof.
Surveyor follow-up: exchange logged inside 50 miles with the plan permitting it — is the plan, the practice or the record wrong?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
17 Bilge from m/c space discharge criteria within and outside special areas
Answer
Outside special areas, 15 ppm en route; inside them, the 15-ppm allowance is withdrawn and the discharge is stopped.
- Outside: processed bilge from machinery spaces may go overboard if the oil content without dilution is 15 ppm or less.
- The bilge must not come from cargo pump-room bilges, must not be mixed with oil residues, and the ship must be en route.
- Inside a special area that 15-ppm allowance does not apply, so the effluent is retained in the bilge or sludge tank.
- On ships over 10 000 gross tons the alarm and automatic stopping device are what enforce the rule in practice.
Surveyor follow-up: bilge logged at 14 ppm inside a special area — is that 15 ppm or a special-area breach?
Full theory: MARPOL Annex I — Prevention of Pollution by Oil -
18 Discharge criteria for omds
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19 If you are taking lo in drum, will you enter in orb?
Answer
Yes — taking lube oil in drums is a machinery-space oil operation, so it goes into the Oil Record Book Part I.
- Oil Record Book Part I is kept by every ship of 400 gross tons and above other than an oil tanker.
- The entry records the type of oil, the quantity, the date and time, and the tank it went into.
- Keep the supplier’s delivery note or drum receipt with the entry as the supporting document.
- A drum simply stowed for later use is not yet an operation; the moment it is transferred, the book is opened.
Surveyor follow-up: drum transfer done with the note filed and the ORB blank — which document is the surveyor holding you to?
Full theory: MARPOL Annex I — Prevention of Pollution by Oil -
20 Orb categories all ?
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21 Orb entry code
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22 Regulation and recent amendment for garbage
Answer
Annex V bans plastics outright and grades everything else by distance: ground 3 miles, other refuse and food waste 12 miles, dunnage 25.
- Plastics may not be discharged at all, and floating dunnage, lining and packing material must be more than 25 miles offshore.
- Paper, rags, glass, metal bottles and crockery may go overboard comminuted or ground beyond 3 miles.
- The same refuse unground, and food waste not comminuted or ground, need more than 12 miles from shore.
- Comminuted or ground garbage must pass a screen of 25 mm mesh or less, and special-area rules bite before the general distances do.
Surveyor follow-up: comminuted food waste landed at 5 miles with the screen logged 40 mm — what fails, distance or mesh?
Full theory: MARPOL Annex V — Prevention of Pollution by Garbage from Ships -
23 Separator capable of achieving 15 ppm on type C emulsion
Answer
The separator must be able to hold 15 ppm on a type C emulsion — the toughest case, which is why the test sample is not clean water.
- A type C emulsion is a stable, finely divided oil-water mix that does not separate on standing — the hardest case to treat.
- The separator is proved with the 15 ppm alarm unit and the automatic three-way changeover in the overboard discharge.
- Charge the test gradually from the separator to the bilge tank and operate the unit, watching the alarm and the changeover.
- A separator that only reaches 15 ppm on clean water is not proved — the emulsion is the test, not the appearance of the outlet.
Surveyor follow-up: 15 ppm alarm clear on clean water with the emulsion test never run — what has actually been proved?
Full theory: Inside the Oily Water Separator — Plates, Probes, Relief Valve and Siphon Breaker -
24 Sewage tank entry wat u precautions (decider
Answer
A sewage tank is an enclosed space with a gas of its own: permit, test, ventilate, and nobody goes in without a breathing set ready.
- The tank is isolated and gas freed, with the permit and a gas free certificate before the cover is lifted.
- Test for oxygen, flammables and hydrogen sulphide — sewage gas is toxic long before it is flammable.
- Ventilate continuously, work with the attendant and lifeline at the hatch, and keep a self-contained set on the entrance.
Surveyor follow-up: sewage tank entered with an EEBD and no attendant at the hatch — is the set enough for this gas?
Full theory: Safety on the Sewage Plant — Gas Hazards and Enclosed Space Entry -
25 The oily water separator must pass through the minimum discharge limit of 15ppm
Answer
The separator discharges only at 15 ppm or below, and the alarm unit is the thing that proves it — not the gauge on the discharge.
- The oil content meter reads the effluent and the automatic device stops the discharge above 15 ppm.
- Beyond 15 ppm the three-way valve sends the effluent to the bilge tank, not overboard.
- So the limit is enforced by the equipment, and the test is whether that equipment works when the alarm is challenged.
- In port the overboard discharge is closed altogether — a separator is not a licence to discharge alongside.
Surveyor follow-up: 15 ppm unit bypassed in port with the overboard valve open — is that a legal setup on any ship?
Full theory: Inside the Oily Water Separator — Plates, Probes, Relief Valve and Siphon Breaker -
26 What is dcs
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27 What is noxious liquid substance
Answer
A noxious liquid is one that endangers marine life or human health if discharged: MARPOL Annex II sorts them X, Y, Z and D by hazard.
- Category X presents a major hazard and justifies prohibiting discharge from tank cleaning and deballasting entirely.
- Category Y presents a hazard, Z presents a lesser hazard, and D the smallest of the four, each with its own discharge conditions.
- The conditions set out maximum quantities and concentrations, and apply differently outside and inside special areas.
- Annex II governs ships carrying these substances in bulk; the chemical tanker’s IBC standard follows the same hazard classes.
Surveyor follow-up: a Category Y cargo being discharged inside a special area — which condition controls, and which annex?
Full theory: MARPOL Annex II — Noxious Liquid Substances in Bulk -
28 Wt is ballast water management plant....in..ur ship..is there?
Answer
A ballast water treatment plant is the D2 side of the convention: filter, then kill, then prove the count before discharge.
- The plant is filtration — strainer and filters to remove organisms and sediment — followed by a killing step.
- The kill may be UV dose, active substance, electrochlorination with deoxygenation, or an approved physical system.
- It is type-approved, and the commissioning test is what proves the D2 organism and microbe counts are met.
- On the ship: name the plant type, where it takes suction, where it discharges, and where the record book entries go.
Surveyor follow-up: treatment plant in operation with no commissioning test on board — is the system approved, or unproved?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.