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Publication Title | SOME IMPORTANT NAVAL ARCHITECTURAL TERMS

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SOME IMPORTANT NAVAL ARCHITECTURAL TERMS

February 2009

Page 1(6)

ITEM

EXPLANATION

A-, B- and C-class divisions

SOLAS has tables for structural fire protection requirement of bulkheads and decks. The requirements depend on the spaces in question, and are different for passenger ships and cargo ships.

A-0, A-15, A-30, A-60:

Shall be constructed of steel or equivalent material, shall be constructed to prevent passage of smoke and flame for 1 h in Standard Fire Test, shall be insulated so that the average temperature of the unexposed side does not rise more than 140 C (any point no more than 180 C) above the original temperature within 0, 15, 30 or 60 minutes.

B-0, B-15:

Shall be constructed to prevent passage of flame for 0.5 h in Standard Fire Test, shall be insulated so that the average temperature of the unexposed side does not rise more than 140 C (any point no more than 225 C) above the original temperature within 0 or 15 minutes. Shall be constructed of approved non-combustible materials (However, combustible veneer may be used).

C:

Shall be constructed of approved non-combustible materials (However, combustible veneer may be used).

Alternative Design, Alternative Arrangements

Regulation allows for designs and arrangements which are not according to SOLAS requirements, providing an analysis is made that shows the proposed alternative design or arrangement is, with regards to safety, at the same or better level than the SOLAS requirement. Example of an alternative design are lifeboats with a higher than 150 person capacity.

Attained Subdivision Index, “A”

According to probabilistic damage stability rules the vessel’s probability to survive a flooding damage (collision, grounding) is calculated with formula:

=

where:

i represents each compartment or group of compartments under consideration.

pi is the probability that only the compartment or group of compartments under consideration may be flooded.

si is the probability of survivability after flooding of the compartment or group of compartments under consideration.

The “A” is calculated for three different drafts and summarized with a weighted formula. If the “A” ”R” (R=required subdivision index), the vessel fulfills the requirement. Typically the vessel’s GM-limits for damage stability are adjusted so that “A”=”R”.

Ballast Water Convention, Ballast Water Treatment, BWT

New regulation requiring ballast water treatment systems on all ships (new and old), in order to avoid harmful organisms spreading from one location to another. Typically the treatment is by filtering and UV- light.

B/5, Breadth divided by 5, B/5-line

Imaginary line used in ship design and damage stability calculations: according to old rules, no damage extends inside the B/5-line (e.g. on a vessel with breadth of 32.2 m, maximum extent of any damage is 6.44 m from ship’s shell). Due to this, bilge main lines, fuel tanks, etc. are normally located inside this B/5. New probabilistic rules have made this rule obsolete on new ships.

Block Coefficient, CB

Important coefficient which describes the fullness of the hull: a lower coefficient means typically lower resistance. CB = Displacement Volume / (L x B x T). A typical figure for a cruise vessel is e.g. 0.65. Other often used coefficient is CM, Midship Section Coefficient, which describes the fullness of Midship Section.

©2009 Foreship Ltd.

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