Bulkheads, Pipes & Fittings (General) — Most Asked Questions
19 questions asked about bulkheads, pipes & fittings (general) across the General and Fn 4b and Fn 3 papers, heaviest first.
Learn the system first
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1 Single phase inductn motor?
Answer
Single-phase motors start by faking a second phase: a capacitor-shifted auxiliary winding drags the rotor round until it can run alone.
- Two stator windings 90 degrees apart on the same supply, one in series with a capacitor for phase shift.
- Capacitor-start: auxiliary winding drops out once running — good only for light loads.
- Capacitor-start-run keeps it in circuit for heavier duty with better torque and power factor.
- Shipboard homes: fans, small pumps, workshop tools and domestic gear where three-phase is not run.
Surveyor follow-up: single-phase fan hums but will not start until spun by hand — winding or capacitor, and what do you megger first?
Full theory: Electric Drives for Deck Machinery — Motors, Converters and Stalling -
2 Reduction gear ratio
Answer
Reduction gearing trades rpm for torque: engine speed over propeller speed, often two to eight on geared diesels.
- Ratio above one lets engine and wheel each spin at their best efficiency together.
- Medium-speed diesels commonly reduce two to eight times to the shaft; turbines need far deeper cuts.
- Shaft-generator take-offs reverse the maths with step-up to alternator speed.
- Hunting-tooth ratios avoid repeat meshing wear — state engine rpm, shaft rpm and ratio together.
Surveyor follow-up: engine 750 rpm on a 150 rpm shaft — ratio, and what breaks if the pinion strips?
Full theory: Marine Propeller, Rudder and Steering Gear -
3 Fwg less production
Answer
Low fresh-water output means lost vacuum, hot shell or choked ejector: salinity, flow and air leaks in that order.
- High salinity from defective salinometer, cool shell or hot jacket water dumps good water back.
- Falling flow from dead distillate pump, open drains, scaled tubes, low jacket flow or leaking solenoids.
- Lost vacuum from open breaker, weak ejector pump, choked nozzle or leaking gaskets.
- Prove by shell temperature, vacuum gauge and salinity trend before opening a single joint.
Surveyor follow-up: salinity high with vacuum normal — temperature, flow or tubes, and what do you throttle first?
Full theory: Fresh Water Generator — Vacuum Boiling, Operation & Faults -
4 Fwg production low
Answer
Low distillate means weak vacuum, scaled plates or a drowning condenser — feed, heat and extraction must match.
- Prove ejector vacuum first: air leaks, worn nozzles and low motive flow kill boiling at low temperature.
- Descale evaporator plates — carbonate, magnesium and sulphate scales throttle heat transfer as temperatures rise.
- Balance feed against output and keep the distillate pump extracting at production rate so the condenser never floods.
- Hold salinity below limits with the dump open while high, closing to the tank only when the meter proves clean.
Surveyor follow-up: vacuum good but output still falling with rising jacket temperatures — scale, feed or extraction?
Full theory: Fresh Water Generator — Vacuum Boiling, Operation & Faults -
5 Sounding pipe const
Also asked: “Construction of sounding pipe”
Answer
Sounding pipes are straight, small and striker-plated: deck cap to tank bottom so the tape tells the truth.
- Run pipes as straight as possible, at least 32 mm bore — 65 mm through refrigerated spaces that can ice.
- Fit striker plates of full thickness under every open end so the bob never dents the tank bottom.
- Cap on deck with self-closing, labelled covers; pair with air pipes at the tank’s high far end above deck.
- Sound beside the suction and vent paths where levels truly sit, not where trim and structure lie to the tape.
Surveyor follow-up: sounding pipe with no striker plate and a missing cap — sound, repair or condemn first?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
6 Audit conducted on ship
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7 Bunker tank sounding pipe contruction
Answer
A bunker sounding pipe is a fire hazard in a straight tube: it gets a self-closing cover, a striker plate and, where fitted, a flame arrestor.
- The pipe runs straight to the tank bottom with a bore of at least 32 mm, and a striker plate of adequate size and thickness beneath.
- The deck cover is self-closing so a lifted or dropped sounding rod cannot leave the tank open to vapour.
- The sounding rod is long enough to stay below the gas seal, so the tank vapour cannot travel up into the accommodation.
- That combination — cover, striker plate, rod length and gas seal — is the whole of the construction, and each is a survey point.
Surveyor follow-up: bunker sounding pipe found with a hinged cover and no striker plate — what has been lost?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
8 Db tank vent pipe location ? Reason?
Answer
The double-bottom vent goes at the highest point, at the end opposite the filling pipe, so trapped air escapes as the tank fills.
- Air pipes are fitted opposite the filling pipe and at the highest point of the tank.
- Every double bottom, deep tank reaching the ship’s side, or tank run up from the sea is led above the bulkhead deck.
- Oil, cofferdam and pumpable tanks are led to open deck where a leak cannot endanger a space.
- A vent at the wrong end traps air, gives a false sounding and stops the fuel or water from flowing as intended.
Surveyor follow-up: fuel tank will not fill through the sounding pipe — the vent, the filler or the vent height?
Full theory: Double Bottom Structure and Bottom Framing -
9 Describe how gas sealing takes place in 2S engine. Function of stuffing box and piston rod. The efficiency of the engine depends upon the effective sealing between the piston and liners. Leakage will reduced compression
Also asked: “Describe how gas sealing takes place in 2S engine. Function of stuffing box and piston rod. The efficiency of the engine depends upon the effective sealing between the piston and liners. Leakage will reduced compression pressure & power will lost. Piston rings seal the gas space by expanding outwards due to the gas pressure acting behind them”
Answer
Sealing is pressure acting on the ring: gas above and behind it forces it down and out to the wall, which is why free ring movement is essential.
- Piston rings give a gas-tight seal between piston and liner, the seal occurring by gas pressure above and behind the ring.
- That pressure forces the ring down and out towards the cylinder wall, so free ring movement is what makes the seal at all.
- Ring movement is described as loose, sluggish or stuck, and is checked by pressing each ring with a wooden stick through a scavenge port.
- Leakage past the rings cuts compression and wastes the charge, so a sluggish ring is a power fault and not just a wear note.
Surveyor follow-up: rings free but the liner polished in a band — is it the ring, the liner or the oil that is sealing?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
10 First valve 1 is to be opened. Then CO2 passes through a non return valve and opens
Answer
The release sequence is fixed: pilot gas, valve 1, master valve, then valve 2 through the time delay to the bottle heads.
- One pilot bottle valve is opened, and the CO₂ reaches the two valves marked 1 and 2 in the release cabinet.
- Valve 1 is opened first; the gas passes through a non-return valve and pneumatically opens the master valve.
- With the master valve open, valve 2 is opened, supplying pilot gas to the main bottle head assembly through a non-return valve and the time delay unit.
- The pressure-operated cylinder valve in the head then lifts and the main bottles discharge to the manifold — the sequence is what the surveyor tests.
Surveyor follow-up: valve 2 opened before valve 1 with the master valve shut — what has happened in the manifold?
Full theory: CO2 Fixed Fire-Fighting System on Ships -
11 How to achieve tier 3 (secondary nox reduction methods
Answer
Tier 3 NOx is cut after the cylinder: SCR on the exhaust gas stream, plus a particulate filter for the soot trade-off.
- Secondary reduction treats the exhaust gas after it leaves the engine, instead of modifying the combustion itself.
- Selective catalytic reduction injects a reductant — usually urea or ammonia — over a catalyst that converts NOx into nitrogen and water.
- The catalyst needs its own temperature window, and too much reductant escapes as ammonia, so dosing is controlled on temperature and speed.
- SCR alone cuts NOx but adds ammonia slip, and EGR lowers NOx at the cost of soot — so a particulate filter restores the particulate performance.
Surveyor follow-up: SCR fitted with ammonia measured at the stack — what has the reduction cost in exchange?
Full theory: MARPOL Annex VI — Air Pollution: SOx, NOx & Exhaust Gas Cleaning -
12 Provides sealing between Scavenge space and Crankcase
Also asked: “• Provides sealing between Scavenge space and Crankcase”
Answer
The stuffing box is the boundary: it seals the piston rod so the crankcase oil and the scavenge gas never meet.
- The stuffing box seals the crankcase from the scavenge space in a two-stroke engine, and stops oil being carried over.
- It also prevents accumulated deposits and excess cylinder oil entering the crankcase, which keeps the sump clean.
- New designs add a gas-tight top scraper, a large drain area, stronger springs, a bronze ring and hardened rod in way of the box.
- So the sealing is two-sided: it keeps crankcase oil out of the scavenge and scavenge gas and dirt out of the crankcase.
Surveyor follow-up: scavenge air coming past the piston rod into the crankcase — is the packing, the scraper or the rod surface?
Full theory: Crosshead Assembly, Guide Clearances & Piston Rod Stuffing Box -
13 Radar trunk space and it's sealing
Answer
A radar trunk is sealed to the deck it penetrates, and the sealing has to stop both fire and water without blocking the cable entry.
- The trunk carries the scanner cable and any feeder through the deck or bulkhead, and the space around it is sealed at the penetration.
- The sealing has to be fire-tight as well as weathertight, because an unsealed trunk is a chimney between the accommodation and the weather deck.
- Where the trunk opens into a space, that opening is a boundary and is sealed to the same standard as the bulkhead it passes.
- And the cable entry itself is through a sealed gland or stuffing box, so the trunk sealing and the cable sealing are two separate jobs.
Surveyor follow-up: trunk sealed with foam and the cable gland left open — which half of the sealing has been done?
Full theory: Ship Bulkheads: Watertight, Corrugated and Fire -
14 Reduction ka something he wantwd to hear voltage drop 1/root3
Answer
The √3 is the three-phase step: you calculate the drop in one core, then multiply it by √3 to get the line voltage drop.
- The voltage drop in one cable core is calculated first as current times the resistance of that core.
- Then the three-phase line voltage drop is the core drop multiplied by √3 — note the introduction of the √3 when considering the three-phase condition.
- Worked through: 180 A through 0.018 Ω gives 3.24 V in the core, and √3 times 3.24 V gives 5.6 V across the line.
- So a reduction scheme that quotes a line drop must show the √3 step, or the answer is a core drop dressed up as a line drop.
Surveyor follow-up: cable quoted at 5.6 V drop and a measured end voltage 3.24 V low — where has the √3 gone?
Full theory: Switchboards & Protection — MSB to Emergency Bus -
15 The combustion gases exert pressure behind the piston rings and push towards the liner for proper sealing
Also asked: “• The combustion gases exert pressure behind the piston rings and push towards the liner for proper sealing”
Answer
Gas pressure is the seal: the load above and behind the ring presses it against the liner, which is why the ring must be free to move.
- Combustion pressure above the piston and behind the ring forces the ring down and out against the cylinder wall.
- The seal is therefore pressure-dependent — a static ring with no pressure behind it is not sealed at all.
- Ring groove depth gives that pressure somewhere to act, and a ring that binds in the groove cannot respond to it.
- So a compression drop with the rings fitted correctly points at the ring groove, the liner surface or the fuel, not the ring itself.
Surveyor follow-up: compression falling with rings free and grooves within limits — where else does the pressure go?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
16 What safeties are given on vent piper on deck in fuel oil tanks?
Answer
Fuel tank vents are flame arrested, screened and weatherproof: nothing must let a flame or a spark reach the vapour.
- The vent outlet is a flame arrestor or wire gauze so a passing flame cannot reach the vapour inside the tank.
- A hood or mushroom cowl keeps water and debris out while the free area stays generous enough to breathe.
- The height above deck is set by rule — not less than about 760 mm on the freeboard deck, 450 mm on the superstructure deck.
- The outlet is led to a safe position where a leak or vapour cannot reach a doorway, accommodation or a source of ignition.
Surveyor follow-up: fuel tank vent found without a flame arrestor — is the tank isolated, or is the vent a live vapour line?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
17 Who conducts it
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18 Why engine room sounding pipe are self closing but deck side not
Answer
A sounding pipe in the engine room is fitted with fire and gas to keep a flame or vapour out — a deck tank has no such hazard.
- The engine-room sounding pipe terminates below the floor, and its deck flange is self-closing so the space cannot be filled with vapour.
- A flame arrestor and a gas seal complete the fitting, and the sounding rod is kept long enough to stay below the seal.
- A deck-side tank vent is simply an open air pipe with a hood — its vapour is already in the open air.
- The difference is the hazard: a deck tank breathes safely, while an engine-room pipe passes into a manned space.
Surveyor follow-up: engine-room sounding pipe found open with the rod short of the seal — is it a fire risk, a gas risk, or both?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
19 Why self closing arrangement in sounding pipe and cross
Answer
The self-closing arrangement exists so the sounding pipe cannot become a permanent flame, gas or oil path into a manned space.
- A self-closing cover on the sounding pipe closes the moment it is lifted, so the pipe does not stand open.
- The gas seal below stops fire and vapour travelling up the pipe into the space above.
- Without it, a dropped rod, a displaced cover or a fire in the tank would put flame straight into the engine room.
- The arrangement is proved on the routine: the seal is filled, the cover closes, and the rod reaches the bottom of the tank.
Surveyor follow-up: gas seal dry on a sounding pipe with the cover removed — is it a fire risk, a gas risk, or both?
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.