Basic naval architecture chapter 9

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BASIC NAVAL ARCHITECTURE:

CHAPTER IX BASIC NAVAL ARCHITECTURE 17/01/2013 LOKESH KUMAR MYLAPILLI

SUBDIVISION & FLOODABLE LENGTH :

SUBDIVISION & FLOODABLE LENGTH 17/01/2013 LOKESH KUMAR MYLAPILLI

Subdivision & Floodable length:

Subdivision & Floodable length Floodable length, or subdivision requirements, specify a number of compartments for which a ship must be able to sustain flooding of and remain afloat. Subdivision requirements are subject to IMO, classification, and flag state regulations. A factor of subdivision is calculated for the ship, describing the number of compartments which would be bilged or flooded. 17/01/2013 LOKESH KUMAR MYLAPILLI

Subdivision & Floodable length:

Subdivision & Floodable length A factor of subdivision is calculated for the ship, describing the number of compartments which would be bilged or flooded. A floodable lengths curve is calculated, inclusive of allowable permeability, either in order to place subdivision bulkheads or verify their compliance. 17/01/2013 LOKESH KUMAR MYLAPILLI

Maximum permissible length of compartments :

Maximum permissible length of compartments Ships are to be as efficiently subdivided as is possible having regard to the nature of the service for which they are intended. The degree of subdivision is to vary with the length L S of the ship and with the service, in such manner that the highest degree of subdivision corresponds with the ships of greatest length, primarily engaged in the carriage of passengers. 17/01/2013 LOKESH KUMAR MYLAPILLI

Maximum permissible length of compartments :

Maximum permissible length of compartments The requirements reported are used for calculating the maximum permissible length of a compartment having its centre at any point in the ship's length L S . The maximum permissible length of a compartment having its centre at any point in the ship's length L S is obtained from the floodable length, by multiplying the latter by an appropriate factor called the factor of subdivision. The factor of subdivision is calculated using the criterion of service . 17/01/2013 LOKESH KUMAR MYLAPILLI

Floodable length calculation :

Floodable length calculation The floodable length at any point of the length L S of a ship is to be determined by the method of calculation specified below which takes into consideration the form, draught and other characteristics of the ship in question. In a ship with a continuous bulkhead deck, the floodable length at a given point is the maximum portion of the length L S of the ship, having its centre at the point in question, which can be flooded under the definite assumptions set forth without the ship is being submerged beyond the margin line. 17/01/2013 LOKESH KUMAR MYLAPILLI

Floodable length calculation :

Floodable length calculation In the case of a ship not having a continuous bulkhead deck, the floodable length at any point may be determined to an assumed continuous margin line which at no point is less than 76 mm below the top of the deck (at side) to which the bulkheads concerned and the shell are carried watertight. Where a portion of an assumed margin line is appreciably below the deck to which bulkheads are carried, the Society may permit a limited relaxation in the water tightness of those portions of the bulkheads which are above the margin line and immediately under the higher deck. 17/01/2013 LOKESH KUMAR MYLAPILLI

Permeability:

Permeability The definite assumptions referred to relate to the permeability of the spaces below the margin line.. In determining the floodable length, a uniform average permeability is to be used throughout the whole length of each of the following portions of the ship below the margin line: The machinery space as defined The portion forward of the machinery space The portion aft of the machinery space. 17/01/2013 LOKESH KUMAR MYLAPILLI

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The uniform average permeability µ throughout the machinery space is to be determined from the formula: Where: a : Volume of the passenger spaces, as defined, which are situated below the margin line within the limits of the machinery space c :Volume of "tweendeck spaces below the margin line within the limits of the machinery space which are appropriated for cargo, coal or stores v :Whole volume of the machinery space below the margin line. 17/01/2013 LOKESH KUMAR MYLAPILLI

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Where it is shown to the satisfaction of the Society that the average permeability as determined by detailed calculation is less than that given by the formula, the detailed calculated value may be used. For the purpose of such calculation, the permeability of passenger spaces is to be taken as 0.95, that of all cargo, coal and store spaces as 0.60. The permeability for double bottom, fuel oil and other tanks may be taken as 0.95. 17/01/2013 LOKESH KUMAR MYLAPILLI

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Except as provided in the case of special subdivision, the uniform average permeability m throughout the portion of the ship forward or aft of the machinery space is to be determined from the formula: Where: a :Volume of the passenger spaces, as defined, including the volume of spaces for the accommodation and use of the crew, forward or aft of the machinery space v : Whole volume of the portion of the ship below the margin line forward or aft of the machinery space. 17/01/2013 LOKESH KUMAR MYLAPILLI

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In the case of special subdivision required, the uniform average permeability, m throughout the portion of the ship forward or aft of the machinery space is to be determined by the following formula: Where: b: Volume of the spaces below the margin line and above the tops of floors, inner bottom, or peak tanks, as the case may be, which are appropriated for and used as cargo spaces, coal or fuel oil bunkers, store-rooms, baggage and mail rooms, chain lockers and fresh water tanks, forward or aft of the machinery space v:Whole volume of the portion of the ship below the margin line forward or aft of the machinery space. 17/01/2013 LOKESH KUMAR MYLAPILLI

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In the case of ships engaged on services where the cargo holds are not generally occupied by any substantial quantities of cargo, no part of the cargo spaces is to be included in calculating b. In the case of unusual arrangements the Society may allow, or require, a detailed calculation of average permeability for the portions forward or aft of the machinery space. For the purpose of such calculation, the permeability of passenger spaces is to be taken as 0.95, that of spaces containing machinery as 0.85, that of all cargo, coal and store spaces as 0.60, and that of double bottom, fuel oil and other tanks at such value as may be approved in each case. 17/01/2013 LOKESH KUMAR MYLAPILLI

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Where a "tweendeck compartment between two transverse watertight bulkheads contains any passenger or crew space, the whole of that compartment, less any space completely enclosed within permanent steel bulkheads and appropriated for other purposes, is to be regarded as a passenger space. Where, however, the passenger or crew space in question is completely enclosed within permanent steel bulkheads, only the space so enclosed need be considered as a passenger space. 17/01/2013 LOKESH KUMAR MYLAPILLI

Factor of subdivision:

Factor of subdivision The factor of subdivision is to depend on the length L S of the ship, and for a given length is to vary according to the nature of the service for which the ship is intended. It is to decrease in a regular and continuous manner: As the length L S of the ship increases, and From a factor A, applicable to ships primarily engaged in the carriage of cargo, to a factor B, applicable to ships primarily engaged in the carriage of passengers. 17/01/2013 LOKESH KUMAR MYLAPILLI

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The variations of the factors A and B are to be expressed by the following formulae, where L S is the length of the ship as defined. For LS equal to or greater than 131 m: For LS equal to or greater than to 79 m: The factor of subdivision is to be calculated as reported hereafter, using the criterion of service (criterion numeral ) 17/01/2013 LOKESH KUMAR MYLAPILLI

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A)The subdivision abaft the fore peak of ships of 131 m in length and upwards having a criterion numeral of 23 or less is to be governed by the factor A given by the above formula; of those having a criterion numeral of 123 or more by the factor B given by the above formula; and of those having a criterion numeral between 23 and 123 by the factor of subdivision F obtained by linear interpolation between the factors A and B, using the formula: Nevertheless, where the criterion numeral is equal to 45 or more and simultaneously the computed factor of subdivision F is 0.65 or less, but more than 0.50, the subdivision abaft the fore peak is to be governed by the factor 0.50 . 17/01/2013 LOKESH KUMAR MYLAPILLI

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B) Where the factor F is less than 0.40 and it is shown to the satisfaction of the Society to be impracticable to comply with the factor F in a machinery compartment of the ship, the subdivision of such compartment may be governed by an increased factor, which, however, may not exceed 0.40. 17/01/2013 LOKESH KUMAR MYLAPILLI

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C) The subdivision abaft the fore peak of ships of less than 131 m but not less than 79 m in length having a criterion numeral equal to S, where: is to be governed by the factor unity; of those having a criterion numeral of 123 or more by the factor B given by the above formula, of those having a criterion numeral between S and 123 by the factor F obtained by linear interpolation between unity and the factor B using the formula: 17/01/2013 LOKESH KUMAR MYLAPILLI

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D) The subdivision abaft the fore peak of ships of less than 131 m but not less than 79 m in length and having a criterion numeral less than S, and of ships of less than 79 m in length is to be governed by the factor unity, unless, in either case, it is shown to the satisfaction of the Society to be impracticable to comply with this factor in any part of the ship, in which case the Society may allow such relaxation as may appear to be justified. 17/01/2013 LOKESH KUMAR MYLAPILLI

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E) The provisions reported in d) are to apply also to ships of whatever length, which are to be certified to carry a number of passengers exceeding 12 but not exceeding: or 50, whichever is the lesser. 17/01/2013 LOKESH KUMAR MYLAPILLI

Criterion of service:

Criterion of service For a ship of given length the appropriate factor of subdivision is to be determined by the criterion of service numeral (hereafter called the criterion numeral) as given by the following formulae: 17/01/2013 LOKESH KUMAR MYLAPILLI

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where: C S : Criterion numeral M : Volume of the machinery space, in m 3 , as defined with the addition thereto of the volume of any permanent fuel oil bunkers which may be situated above the inner bottom and forward or aft of the machinery space V : Whole volume of the ship below the margin line, in m 3 P : Whole volume of the passenger spaces below the margin line, in m 3 , as defined, including the volume of the spaces for the accommodation and use of the crew P 1 : Factor, to be taken equal to: P 1 = K N Where the value of KN is greater than the sum of P and the whole volume of the actual passenger spaces above the margin line, the figure to be taken as P 1 is that sum or two thirds KN, whichever is the greater K = 0,056 L S L S : Length of the ship, in m, as defined, N : Number of passengers for which the ship is to be certified. For ships not having a continuous bulkhead deck the volumes are to be taken up to the actual margin lines used in determining the floodable lengths. 17/01/2013 LOKESH KUMAR MYLAPILLI

Special requirements concerning Ro-Ro passenger ship subdivision:

Special requirements concerning Ro-Ro passenger ship subdivision A) Where in a portion or portions of a ship the watertight bulkheads are carried to a higher deck than in the remainder of the ship and it is desired to take advantage of this higher extension of the bulkheads in calculating the floodable length, separate margin lines may be used for each such portion of the ship provided that: 17/01/2013 LOKESH KUMAR MYLAPILLI

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The sides of the ship are extended throughout the ship's length L S to the deck corresponding to the upper margin line and all openings in the shell plating below this deck throughout the length L S of the ship are treated as being below a margin line. The two compartments adjacent to the "step" in the bulkhead deck are each within the permissible length corresponding to their respective margin lines, and, in addition, their combined length does not exceed twice the permissible length based on the lower margin line. 17/01/2013 LOKESH KUMAR MYLAPILLI

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B) A compartment may exceed the permissible length determined from the requirements provided the combined length of each pair of adjacent compartments to which the compartment in question is common does not exceed either the floodable length or twice the permissible length, whichever is the lesser. If one of the two adjacent compartments is situated inside the machinery space, and the second is situated outside the machinery space, and the average permeability of the portion of the ship in which the second is situated differs from that of the machinery space, the combined length of the two compartments is to be adjusted to the mean average permeability of the two portions of the ship in which the compartments are situated. Where the two adjacent compartments have different factors of subdivision, the combined length of the two compartments is to be determined proportionately. 17/01/2013 LOKESH KUMAR MYLAPILLI

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C) In ships of 100 m in length and upwards, one of the main transverse bulkheads abaft the fore peak is to be fitted at a distance from the forward perpendicular which is not greater than the permissible length. D) A main transverse bulkhead may be recessed provided that all parts of the recess lie inboard of vertical surfaces on both sides of the ship, situated at a distance from the shell plating equal to one fifth the breadth of the ship, as defined and measured at right angles to the centreline at the level of the deepest subdivision load line. Any part of a recess which lies outside these limits is to be dealt with as a step in accordance with e). 17/01/2013 LOKESH KUMAR MYLAPILLI

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E) A main transverse bulkhead may be stepped provided that it meets one of the following conditions: The combined length of the two compartments, separated by the bulkhead in question, does not exceed either 90 per cent of the floodable length or twice the permissible length, except that, in ships having a factor of subdivision greater than 0.9, the combined length of the two compartments in question may not exceed the permissible length; additional subdivision is provided in way of the step to maintain the same measure of safety as that secured by a plane bulkhead; The compartment over which the step extends does not exceed the permissible length corresponding to a margin line taken 76 mm below the step. 17/01/2013 LOKESH KUMAR MYLAPILLI

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F) Where a main transverse bulkhead is recessed or stepped, an equivalent plane bulkhead is to be used in determining the subdivision. G) If the distance between two adjacent main transverse bulkheads, or their equivalent plane bulkheads, or the distance between the transverse planes passing through the nearest stepped portions of the bulkheads, is less than 3.0 m plus 3 per cent of the length L S of the ship, or 11.0 m whichever is the lesser, only one of these bulkheads is to be regarded as forming part of the subdivision of the ship in accordance with the provisions of Maximum permissible length of compartments , Floodable length calculation , Permeability, Factor of subdivision . 17/01/2013 LOKESH KUMAR MYLAPILLI

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H) Where a main transverse watertight compartment contains local subdivision and it can be shown to the satisfaction of the Society that, after any assumed side damage extending over a length of 3.0 m plus 3 per cent of the length L S of the ship, or 11.0 m whichever is the lesser, the whole volume of the main compartment is not flooded, a proportionate allowance may be made in the permissible length otherwise required for such compartment. In such a case the volume of effective buoyancy assumed on the undamaged side may not be greater than that assumed on the damaged side. I) Where the required factor of subdivision is 0.50 or less, the combined length of any two adjacent compartments may not exceed the floodable length. 17/01/2013 LOKESH KUMAR MYLAPILLI

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THANK YOU 17/01/2013 LOKESH KUMAR MYLAPILLI

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