«STRENGTH, CONSTRUCTION AND WATERTIGHT SUBDIVISION 2.1 Definitions (Regulation 2) The following notes are for the guidance of surveyors in the ...»
STRENGTH, CONSTRUCTION AND WATERTIGHT SUBDIVISION
2.1 Definitions (Regulation 2)
The following notes are for the guidance of surveyors in the interpretation of the
definitions of terms given in Regulation 2(2) of Part 1 of the Regulations when
calculating the maximum length of watertight compartments in accordance with
Schedule 2 to Merchant Shipping Notice MSN 1698 (M).
2.1.1 Machinery space
In the case of unusual arrangements, the MCA shall advise ship owners and shipbuilders of the limits of the machinery space to be taken for the purpose of the Regulations.
2.1.2 Margin line 126.96.36.199 For a ship which has a continuous bulkhead deck, the margin line is to be taken as a line drawn not less than 76 mm below the upper surface of the bulkhead deck at side, except that where there is a variation in the thickness of the bulkhead deck at side the upper surface of the deck should be taken at the least thickness of deck at side above the beam. If desired however, the upper surface of the deck may be taken at the mean thickness of the deck at side above the beam as calculated for the whole length of the deck, provided that the thickness is no greater than the least thickness plus 50 mm. See figure 188.8.131.52 a) and 184.108.40.206 b).
220.127.116.11 In the case of Ro-Ro ferries where the vehicle deck slopes downward forward of the collision bulkhead the margin line abaft the collision bulkhead may be carried forward as an assumed line above the rammed portion of the vehicle deck. See figure 18.104.22.168.
22.214.171.124 (i) If the bulkhead deck is not continuous, a margin line should be assumed which is at no point less than 76 mm below the upper surface of the deck at side to which the bulkheads concerned and the shell plating are carried watertight, special attention being given to the provisions of paragraph 6(1)(d) of Section 2 of Schedule 2 to Merchant Shipping Notice MSN 1698 (M). See figure 126.96.36.199.
(ii) Where a portion of an assumed margin line is appreciably below the deck to which bulkheads are carried, a limited relaxation may be permitted in the watertightness of those portions of the bulkheads which are above the margin line and immediately under the higher deck.
MSIS003/PT 2/REV 1.01/PAGE 1 OF 28 188.8.131.52 Where the bulkhead deck is stepped, as shown in figure 184.108.40.206, either level may be used as that from which the margin line is measured. If the lower level “A” is used the line of the bulkhead, and margin line, is projected to the shell. However, if the higher level “B” is adopted, the shaded portion shown must also be considered flooded for the purpose of satisfying subdivision (floodable length).
.1 For compartments A, B, C and G the margin line derived from Deck 2 may be used. For the remaining compartments the margin line derived from Deck 1 is to be used. The combined lengths C and D, F and G, and G and H are each not to exceed the permissible length determined by reference to the Deck 1 margin line.
.2 Openings in the shell plating below Deck 2 in these areas of the ship are to comply with Regulation 16.
Surveyors should note that as indicated in paragraph 1(4) of Section 1 of Schedule 2 to Merchant Shipping Notice MSN 1698 (M), the expression "passenger space" includes galleys, laundries and other similar spaces provided for the service of passengers, in addition to space provided for the use of passengers, but excludes baggage, store, provisions and mail rooms.
2.2 Application (Regulation 3)
It is to be noted that if a ship has certification as a Passenger Ship only, the requirements of the regulations are still to be complied with even when, for the time being, it may be carrying less than 13 passengers. The exception to this is when the ship is also certificated other than as a passenger ship.
2.3 Exemptions (Regulation 4) Pleasure vessels will only be considered for exemption on an individual case basis.
2.4 Strength of the Hull (Regulation 7) The structural plans and particulars are dealt with in paragraph 220.127.116.11 of these Instructions.
2.5 Watertight Subdivision (Regulation 8) 2.5.1 Floodable length 18.104.22.168 To enable the permissible length of compartments to be determined in accordance with Section 2 of Schedule 2 to Merchant Shipping Notice MSN 1698 (M), it is necessary to develop flooding curves which will indicate the floodable length at any point in the ship's length. Flooding curves should be developed by a method of calculation which takes into account the form, draught and other characteristics of the ship in question.
22.214.171.124 Alternatively, equivalent damage calculations may be accepted in lieu of the calculations referred to in 126.96.36.199.
188.8.131.52 Where any arrangement proposed includes the provision of a long compartment inboard of longitudinal bulkheads situated below the bulkhead deck, the surveyor should draw attention to the designer and owner that an alternative calculation needs to be made to show compliance with subdivision requirements. A long compartment is one which exceeds the length AB as shown in figure 184.108.40.206.1. The surveyor should also seek early assurance that they are aware of the MCA’s thinking and policy, as given below, regarding such arrangements. Details of the proposals should also be forwarded to Headquarters for comment.
MSIS003/PT 2/REV 1.01/PAGE 4 (i) Application of subdivision requirements to designs which incorporate long internal spaces is problematic because traditional subdivision calculations (flooding curves) were developed to assess the survivability of vessels subdivided by plain transverse bulkheads. The further the design of a ship departs from this idealised arrangement, the less effective the traditional subdivision calculations, incorporating equivalent plane bulkheads for example, are at predicting the survivability of the vessel following the flooding of spaces beyond any longitudinal division.
Consequently, where proposals are submitted for a vessel which incorporate one or more long internal compartments, such designs must be assessed for subdivision purposes by the application of alternative damage calculations.
(ii) The alternative calculation will be based on the consideration of side damages extending to the centreline (irrespective of any longitudinal bulkheads on the side of damage). Within this damage all spaces not protected by transverse bulkheads which extend transversely from shell to shell and vertically from baseline to the bulkhead deck will be considered flooded. This calculation is a separate calculation to that performed for normal damage stability considerations and as such, regardless of the compartmentation standard of the vessel, only one compartment damage will need to be considered for the purposes of this alternative calculation. However, where a transverse division of the long inboard compartment is not in line with the main transverse subdivision bulkheads, such division should be considered damaged. The extent of damage for this equivalent calculation will be from base line upwards.
(iii) Internal buoyant spaces should be considered to remain intact where they lie outwith the assumed damage extent. The method of allowances for local subdivision as set down in paragraph 2.5.6 shall not be applied. It may be necessary to consider damage from both sides of the vessel where internal buoyant spaces within the damaged compartment(s) are asymmetric, noting that the vessel will be permitted to heel during direct calculation and that this may affect margin line immersion.
(iv) Although traditional floodable lengths are not a regulatory requirement at trimmed waterlines, and on even keel residual stability requirements are not stipulated, these conditions should be considered when undertaking appropriate calculations for side damage penetration in excess of B/5. The valuable benefit of fitting B/5 longitudinal bulkheads should not to be degraded by the provision of overlong inboard spaces resulting in a reduction in survivability with regard to subdivision when compared to “conventionally” subdivided ships.
(vi) When requesting the submission of equivalent subdivision damage calculations for vessels with proposed long internal compartments, surveyors should advise the owners and builders of reasons for conducting such an examination. In any case where it does not prove possible to achieve agreement in meeting the recommended standards of residual stability, Headquarters should be consulted.
(vii) The recommended standards referred to in (vi) above are as follows:
(b) existing ships undergoing major modifications are to comply with SOLAS 90 at level keels and a minimum of STAB 80 over the operational trim range. In the case of Ro-Ro ships, STAB 80 may be accepted over the full range of trims provided that SOLAS 90 is attained by the date of compliance with the Stockholm Agreement determined in accordance with the A/Amax value. In any case, the required standard will be no less than that existing prior to conversion.
(c) Ships changing to UK flag are to comply with Res.A.265(viii) or SOLAS 90 over the full operational trim range.
2.5.2 Permeability 220.127.116.11 The assumed average permeabilities of portions of the ship forward and aft of the machinery space, will in general be determined by the appropriate formula given in paragraph 3(2)(a)(i) of Section 2 or paragraph 8(1) of Section 3 of Schedule 2 to Merchant Shipping Notice MSN 1698 (M).
For ships having unusual arrangements, where it is considered that the average permeability determined by direct calculation shall be greater than that given by the formulae, a detailed calculation will be required. After consideration, the permeability to be used will be agreed by the Administration.
18.104.22.168 The Certifying Authority will be prepared to consider applications for the use of a detailed calculation in any case where it can be shown that the average permeabilities of the portions forward and aft of the machinery space so obtained are less than those given by the appropriate formula, providing the permeabilities of the spaces within those portions are in accordance with either paragraph 3 or 8 of Schedule 2 to Merchant Shipping Notice MSN 1698 (M) whichever is applicable.
Note : For damage in way of side compartment shown shaded, bulkhead in position 2 would be considered damaged i.e. AFT & FWD holds flooded 22.214.171.124 For ships of Classes II and II(A), the subdivision of which is calculated in accordance with Section 3 of Schedule 2 to Merchant Shipping Notice MSN 1698 (M), the Certifying Authority must be satisfied that the greater part of the cargo space is occupied by cargo before either a permeability of 60% may be used in the formula in paragraph 8 or a permeability less than 95% may be used in the detailed calculation referred to in paragraph 8.
126.96.36.199 In ships which have a “long lowerhold”, as described in paragraph 188.8.131.52 of these Instructions, in which vehicles are intended to be carried, the permeability of the space is to be taken as 90%.
2.5.3 Factor of subdivision 184.108.40.206 Where in ships of Classes II and II(A) the carriage of appreciable quantities of cargo in spaces below the bulkhead deck will render it impracticable to apply a factor of subdivision not exceeding.50 aft of the collision bulkhead, consideration may be given to the calculation of a factor of subdivision in accordance with paragraph 9(2) of Section 3 of Schedule 2 to Merchant Shipping Notice MSN 1698 (M) (the cargo clause) at the request of the owner. Full details of all cargoes intended to be carried by the ship in normal service conditions should be submitted by the surveyor to Headquarters for consideration. Cargo carried above the bulkhead deck cannot be taken into account in a submission relating to paragraph 9(2).