For a vessel to be assigned a freeboard and corresponding set of load lines she must satisfy the following principal factors.
· Structural strength of the vessel.
Vessels are to be constructed as per the requirements laid down by class and society to ensure strength and stability are sufficient for purpose intended. Vessels require to be surveyed at regular periods throughout construction, with all materials of sufficient structural strength as determined by both destructive and non-destructive testing.
· Preservation of reserve buoyancy.
All weather tight openings to have means of securing. All access hatches, ramps and doors must be secured to ensure no ingress of water. The height of all sills or openings is to be 350mm above decks. Hatchways to be of substantial construction with combings at least 600 mm in position 1, and 450mm in position 2. All hatch covers and their securing devices are to conform to the regs. Machinery space openings to be fitted with a watertight door with a sill height of 600mm in position 1 and 380mm in position 2.
· Physical means of preventing water into the hull.
All hatch covers, sounding pipes, vent covers or flaps to have watertight gasket fitted to ensure that they remain watertight. Vents to be 900mm above deck and have substantial covers, and air pipes to be 750mm have efficient means of closing them watertight.
· Safety of crew on the weather deck.
Vessels with small freeboard must have adequate means of allowing access around weather decks, either by way of raised and railed platforms or under deck walkways. All deckhouses are to be of efficient construction, with all handrails and bulwarks to have at least 1 metre height, and be constructed in accordance with the code.
Where necessary guardrails or lifelines are to be fitted above deck cargoes in the absence of any under deck walkways.
· Potential wetness of the weather deck.
As entrapment of water on the weather deck can have undesirable effects on stability, the regulations specify the dimensions of all scuppers, scuttles and freeing ports, both with hinged covers and open. The regulation also describes the requirement and dimensions for openings in bulwark and gives occasion when they should be substituted for rails due to anticipated water entrapment.
· Stability in the normal loaded condition.
The design of the vessel shall be such that during the probable loading conditions, the freeboard assigned shall ensure adequate stability at all times.
· Degree of subdivision and stability after suffering prescribed damage.
The assumptions made for the extent of the damage are that the vertical extent of the damage extends from the freeboard deck to the keel and transversely no more than one fifth of the vessel beam.
Type-B60 vessels up to 150m must survive flooding of any single compartment, and B-100 up to 150m vessels must survive two adjacent compartments flooding with the exclusion of the engine room.
Type B-60 and B-100 over 150m must consider the machinery room as a floodable compartment.
The minimum damage stability condition of equilibrium makes the following assumptions.
The final waterline flooding is below the lower edge through any down flooding may take place.
If no part of the deck is immersed, the angle of heel does not exceed 17°. If dei is reached, the angle of heel due to asymmetrical flooding does not exceed 15°.
The GM remains positive.
The minimum range shall be 20° and there shall be a min GZ of 0.1m. Area under the curve is to be at least 0.0175m-r.
b) Special requirements for timber load lines.
Vessel to have forecastle not less than 0.07L
Double bottom tanks fitted within the mid ship half length shall have longitudinal subdivision.
Bulwarks to be at least 1metre and strengthened by stays.
Timber is to be stowed to ensure that adequate stability is retained at all stages of the voyage and due consideration given to water absorption and free surface in slack tanks. Timber deck cargo is not to impair vision from bridge, impair weather or watertight integrity of vessel, and must not interfere with access to emergency steering or other spaces.
All lashings are to be of adequate strength to resist movement of the cargo in a seaway.
Stowage is to be in such a way that at no time does the max. Height exceed one third of the beam.
When the cargo occupies the whole of the uncovered deck of the vessel, access by means of a walkway with lifelines and handrails as near the centre of the vessel is to be fitted. All dimensions can be found in the regs.
Cargo to be stowed between superstructures must be packed as tightly as possible and extend over the entire length of the well.
Timber is to be secured at not less than 3 metre intervals and secured by lashings and eye plates. The regulation gives dimensions of plates and lashings.
2a) Fire protection Large Ships.
The purpose of the regulations is to afford the fullest fire protection, detection and extinction to vessels. The following basic principals lay emphasis on the regulations with due regard to the type of vessel and potential fire hazard.
Division of ship into main vertical zones by thermal and structural boundaries dependant on size.
Separation of accommodation spaces by similar means.
Restriction in use of combustible materials.
Detection of fire in the zone of origin.
Containing the fire in the space of source.
Protection of means of escape and access for fire fighting
Availability of fire fighting equipment.
Ignition of flammable cargo vapour to be minimised.
b) Structural methods of fire protection.
All bulkheads, decks, deckhouses and hull are to be constructed in steel. Aluminium alloys may be used if adequate insulation is afforded.
All category A machinery spaces are to be constructed in steel.
The hull and superstructure is to be divided into zones, which are to be of not more than 40 metres in length.
All vertical zones are to if possible to have divisional bulkheads one above the other. When this is not possible and they require to be stepped, adequate insulation must be afforded to the ‘stepped deck’.
Insulation standards required of an A class main zone bulkhead depends on the degree of fire risk in the associated compartments on each side. A table is available in MSN 1667.
3a) Classification of vessels.
Classification is not compulsory for any particular class or type of ship, but there is, a legal requirement for vessels in class to be constructed and maintained in accordance with one of the requirements of a recognized classification society.
In many cases classification may be a requirement of hull, machinery and cargo insurers or P & I clubs, with breech of this condition rendering the cover invalid
A vessel, which is not in class, is not seaworthy in the eyes of the law, and owners would find themselves liable for not just any losses or damage to their own vessel and cargo, but liable for the losses of any third party.
Ship classification concerns inspection of a ship through all stages of construction from design to completion, She is required to undergo regular inspection throughout its life to ensure that it is maintained to the required standards of the classification society. It is essential to insurers, bankers, charterers shippers and other parties in need of information about a vessel’s condition.
While it is not actually mandatory for a vessel to be in class, the major percentage of UK vessels adhere to the requirements of a classification societies structured system of construction, maintenance and inspection in order to assume the benefits of, amongst other things, hull, cargo and third party insurance.
b) Period of surveys under the harmonized system.
On completion and prior to going into service, every passenger vessel is required to have a full initial survey and inspection of the ships bottom. Every 12 months following the issue of this certificate the vessel is required to undergo a renewal survey and inspection of the vessel bottom.
After any repair or accident the MCA or Class may require an additional survey.
On completion and prior to going into service, every cargo vessel is required to have a full initial survey and inspection of the ships bottom. Successful survey will lead to the issue of a Cargo Ship Safety Construction Certificate which is valid for 5 years as long as the following conditions are met.
· On the first anniversary an annual survey.
· On the second anniversary either an annual or intermediate survey.
· On the third anniversary an intermediate or annual survey.
· Anniversary four is to be an annual.
· The fifth year brings the renewal survey.
Also included are two inspections of the vessel bottom within the five year period and not more than 36 months apart.
c) In water surveys.
Ships which are subject to the or Load Line Conventions must undergo two inspections of the ship’s bottom within a period of 5 years, and the maximum interval between these inspections is 36 months. One of these inspections shall be conducted out of the water, which should coincide with the renewal survey for Safety Construction or Load Line certificate, and the other intermediate inspection may be carried out in the water.
Ships which are more than 15 years old are not normally allowed an IWS. Oil tankers or bulk carriers, which are subjected to special surveys, are not permitted to have in water surveys.
More information regarding preparations and procedures during IWS may be found in MGN 217.
4a) Dry dock repair list.
The purpose of the dry dock specification is to ensure that all parties involved in the docking are fully aware of all items requiring survey and to what extent, if any, they are in need of repair.
Adhering to the spec. is the most effective way of ensuring that tasks are completed as planned.
The specification is prepared well in advance with the combined efforts of the vessel and superintendent. This spec is used to invite tenders, and is therefore important that it is as accurate as possible. The spec should be accompanied by all the required plans and drawings. Any extras should be covered with ‘variation to scope of works’ forms to avoid any confusion.
Due to the size and complexity of the scope of work, companies may wish to break the document down into more manageable sections, dealing with not only each department, but separate sections within each department.
b) Items surveyed below waterline.
The following is a list of the major items examined below the waterline.
· Hull plating cleaned, inspected and re-coated. Draught marks re applied.
· Anchor chain ranged and examined and lockers coated.
·All underwater valves and suctions overhauled as required. Sea bays cleaned and recoated.
·Fins extended, examined, tested coated and re-housed.
·Anodes replaced if necessary.
·Rudders and tail shafts removed and overhauled if required by spec. Clearances and bushes tested.
·Propellers cleaned and polished.
·Gratings removed and boxes cleaned and coated.
·Thruster gratings removed and blades inspected and cleaned.
STABILITY
ASSIGNMENT PAPER A
NORMAN MACDONALD
CLASS 2B
dariusz.lipinski