LATEST NAVAL ARCHITECTURE MMD ORAL Q & A PART-3

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(a) Explain the purpose of a collision bulkhead.

(b) Describe with the aid of sketch the construction of a Collision bulkhead paying particular attention to the strength and attachment on to it and to the adjacent structure.

(c) Sketch and explain about the purpose of wash bulkheads fitted in cargo oil tanks

(a) Purpose of collision bulkhead

  • To limit the extent of flooding and
  • To strengthens the fore end structure of the ship
  • To protect cargo, bow of ship damage.
  • To resists the effect of pounding and panting

(b) Collision bulkhead

  • Foremost major watertight bulkhead.
  • Extend to uppermost continuous deck.
  • Plating 12% thicker than other watertight bulkheads.
  • Located at a distance of L/20 from forward perpendicular of ship. (L = Ship length)
  • Locate not less than 5% and not greater than 8% of ship’s length from fore end of load waterline.
  • Stiffened by vertical bulb plates (stiffener) spaced about 600 mm.
  • Fit horizontal plating (stringer) because of excessive taper on plates which occur with vertical plating

(c) Wash Bulkhead

  • To reduce the surge of liquid when ship rolls and pitches.
  • To reduce dynamic impact of the liquid on surrounding structure.
  • To reduce free surface effect on ship stability
  • In tanker design, not only reduces dynamic cargo pressures, but also increases longitudinal strength of structure.

1. What is the purpose and construction system of bilge keel? Explain with sketch in detail.

2. Sketch and describe briefly

(a) Bilge Keel

(b) Duct Keel

(c) Chain Locker

(d) Hawse pipe

1. Bilge Keels

  • Direct resistance between bilge keel and water comparatively weak effect.
  • Slightly increase ship’s period of roll.
  • Increase water pressure over large area of ship’s hull, this pressure act in such direction as to damp rolling
  • Increase wave making resistance.
  • Upset transverse streamlines of ship’s hull, set up eddy currents.
  • Fit to turn of bilge.
  • Attach to continuous flat bar, welded to shell plating.
  • Generally extended over to 1/3 to ½ ship’s length amidships.
  • Fit to resist rolling, external to hull, create resistance to ahead rolling.
  • Size of bilge keel restrict due to ship’s speed.

2. (a) Bilge Keels

  • Flat keel fit along bilge radius either side of ship nearly half its length.
  • Bilge keel fit at right angle to bilge radius plating.
  • Outer joint of bilge keel rivet or lightly welded.
  • Outer joint easy to break and hull undamaged.
  • Doubling plate welded both end of bilge plating and tapper at both ends.

Purpose of bilge keel

  • Reduce ship rolling
  • Give longitudinal strength to bilge strake

(b) Duct keel

  • Consist of two center girders and extends from E/R length to forward hold.
  • Width not more than 2 m allow for duct.
  • Keel and tank top’s center, strake must strength either by supporting members in duct or by increasing thickness of plates.
  • Allow oil and water pipes beneath hold spaces and protect against cargo damage by leakage.
  • Watertight manhole door provides forward end of ER and each of C/H as entrance.
  • Ventilation fan and lighting fit for entering in duct keel

(c) Chain locker

  • Fit forward collision bulkhead between upper deck and second deck.
  • Watertight door fit at upper deck.
  • It size is adequate to house all anchor cable and still leave empty space above.
  • It should reduce height of centre of gravity of considerable mass of cables.
  • A perforated floor is fitted at bottom to provide drainage well and out of mud and water.
  • At top center have spurling pipe, made of heavy plate with chaffing ring on lower edge.
  • The final link of anchor cable secure inside of it.

(d) Hawse pipe

  • Hawse pipe fitted to smooth running of anchor cable and to maintain water tightness of forecastle.
  • Chafing ring fit to top of each hawse pipe.
  • Have thick plating which attach to doubling plate at forecastle deck, reinforced strake of plating at side shell
  • Construct mild steel tube with casting in one complete unit for each side of ship
  • A sliding plate cover is shaped to fit over cable and close the opening when ship is at sea.

With reference to the oil tankers, define the following terms

(a) SBT (Segregated ballast tank)

(b) CBT (Clean ballast tank)

(c) LOT (load on top)

(d) IGS (Inert gas system)

(a) Segregated Ballast Tank (SBT)

  • A ballast tank, which is
  • Completely separated from cargo oil and oil systems
  • Permanently arranged to carriage of ballast or cargoes (oil)
  • Segregated ballast lines pass through cargo oil tanks they are to be of steel and thickness (not less than 16 mm) with welded or heavy flanged joints.
  • The amount of ballast required for safe and efficient sailing is
  • 35 ~ 40% of deadweight under good weather conditions
  • 50 ~ 60% when heavy weather

(b) Clean Ballast (CBT)

  • Dedicated clean ballast is the ballast in a tank which
  • Since oil was last carried therein,
  • Cleaned for using dedicated clean ballast only.
  • Selected adequate capacity and comply with the relative draught and trim requirements in tanker.

(c) Load-on-top (LOT)

  • Oil and water mixture from ballasting and cleaning to be collected in slop tanks.
  • This mixture pumped ashore at loading ports which have special reception facilities to prevent oil pollution at sea.
  • If the mixture cannot be pumped ashore, the new cargo can be loaded on top and pumped ashore at the discharge port.

(d) Inert gas system (IGS)

  • For safety of fire and explosion risks, Inert Gas Systems are fitted on oil tankers.
  • A petroleum cargo oil tanker give out flammable vapors.
  • In the absence of Inert gas, any source of ignition cause atmosphere within a tank to explode.
  • Inert gas has insufficient oxygen to support combustion.
  • Inserting in tanks means cutting one side of fire triangle, avoiding any chances or fire or explosion.

(a) Sketch & describe two types of the rudder & forces exerted on it.

(b) Sketch & describe separate rudder carrier & stuffing box.

(a) Two types of rudder & forces exerted on it.

  • Rudder is used to steer the ship. Turning action is largely dependent on rudder area
  • Required area of rudder, varies with different type of vessels, desired manoeuvring ability and general ship design impose restrictions.
  • In practice rudder area is usually related to, area of immersed middle plane.
  • When rudder is turned, from centerline plane to any angle, water flows round rudder and creates additional resistance on side of centerline.

 Force which acts on rudder parallel to centerline has two components:

(1) Force created by streamlines formation round rudder, i.e. due to change in direction of the water;

(2) The suction on the after side of the rudder caused by the eddying.

(b) Separate rudder carrier and stuffing box

  • Depending on rudder type and arrangement, rudder weight carried by the pintle and by a rudder carrier within hull.
  • In spade type rudder, full weight of rudder is carried by the carrier.
  • A rudder carrier and stuffing box be may combined or separate items of equipment

Rudder carrier

1. Major part of rudder’s weight is transferred to lower bearing surface of rudder carrier through Cone.

2. Upper part of rudder carrier is keyed to stock so that they turn together.

3. Lower half of carrier is bolted into a heavy insert plate on deck of steering flat.

Watertight stuffing box

1. A separate watertight stuffing box is fitted where the stock enters the rudder trunk.

2. This arrangement provides access to a greater length of the rudder stock, removes need for a watertight construction of carrier bearing & reduces unsupported length of stock.

(a) How to identify the Un-balance rudder, Semi-balance rudder and Balance rudder?

(b) Sketch and describe any type of un-balanced rudder.

(a)

The rudder is used to steer the ship.

1. Unbalanced rudder – A rudder with all of its area, aft of the turning axis

2. Semi-balanced rudder – A rudder with a small part of its area, less than(<) 20%, forward of the turning axis

3. Balanced rudder – When 25% to 30% of the area is forward of the turning axis there is no torque on the rudder stock at certain angles

(b) Un-balanced rudder

  • A rudder with all of its area, aft of the turning axis is known as ‘unbalanced rudder.
  • Constructed with double plate and internal webs stiffening.
  • Lifting hole and drain plug are provided at rudder.
  • Rudder and the lower part of stock are connected by horizontal coupling.
  • Rudder weight rest on bearing pintle.
  • To prevent the rudder from jumping, the locking pintle is fitted with bolts and nuts to upper rudder arm.
  • All pintles must be tapered in the upper part to hold them fast in the rudder arm.
  • Pintle must be of same depth as the gudgeon in which they turn and are fitted with liners to reduce wear.
  • Eddy plate or fashion plate is welded at the forward end of rudder to give the stream line water flow to rudder.