Section 4 Fragmentation protection

4.1.1 This section does not deal with the loss of structural strength due to material perforation. It is only concerned with fragmentation protection of equipment and personnel within critical compartments and potentially critical pipe and cable runs.

4.1.2 Fragment and small arms penetrators can be stopped by the use of structure designed to prevent penetration, either through the use of increased thickness of normal structural materials, suitable siting of compartments, addition of armour (non-structural) materials, or even the use of armour material that can take structural loads.

4.1.3 The Rules give design data based on fragment penetration equations for three representative threats. The selection and use of fragment penetration equations or computer modelling for other threats will be considered provided they are carried out by a competent body which has relevant experience and employs recognised procedures.

4.1.4 For fragmentation protection to be effective, materials within the ship forming part of the ship’s equipment and outfit shall be of a type that is not prone to the generation of secondary fragments or ‘splinters’. Materials such as wood, brittle plastics and brittle cast materials are not to be used in protected compartments. Where the use of such materials is essential, consideration may be given to the use of bonded splinter-retaining membranes.

4.1.5 RATTAM is defined as the response to attack on ammunition and describes protection fitted externally to the ship to prevent the penetration of particular threats which may cause damage, principally to magazines. Similar protection may also be fitted to protect other critical compartments, both are covered by the SP notation.

4.2.1 The threat may be classified as either small arms fire or fragments from the casing of shells or warheads (‘shrapnel’ or ‘splinters’) capable of perforating the ship's structure and thus causing damage to equipment or casualties amongst personnel.

4.2.2 Three levels of protection are shown in Table 2.4.1 Fragment threat types. They are from a combination of internally and externally detonating threats. Alternative levels will be considered in accordance with Vol 1, Pt 4, Ch 2, 4.5 Structural requirements 4.5.2.

4.2.3 The actual threat level and type used in the calculation and the areas of the ship to be protected are to be specified by the Owner and will remain confidential to LR.

4.2.4 The Level I threat is assumed to detonate on impact with the ship’s structure in the act of which it will penetrate the outer skin of the vessel. Fragmentation protection will reduce the risk of fragments penetrating additional compartments. The ends, internal sides and decks of critical compartments are in general to be fitted with protection, an example of which is shown in Figure 2.4.1 Level I arrangement, see also Vol 1, Pt 4, Ch 2, 4.3 Notation assessment levels and methodology 4.3.2. The outer skin of the ship may be strengthened to resist the shell in accordance with the requirements for the SP notation, however it will usually require a significant amount of armour.

4.2.5 Level II considers a threat posed by an externally detonating shell. Strengthening is, in general, to be fitted to the external skin of the ship to protect the critical internal spaces, an example of which is shown in Figure 2.4.2 Level II arrangement, see also Vol 1, Pt 4, Ch 2, 4.3 Notation assessment levels and methodology 4.3.2. For this level of protection a stand off distance for the weapon is to be specified by the Owner.

4.2.6 The Level III threat is a generic weapon based on a sea skimming anti-ship weapon with a semi armour piercing, (SAP) warhead that detonates within the hull. Fragmentation protection is intended to reduce the risk of fragments penetrating additional compartments. The considerable amount of protection required will normally mean that protection is only fitted at zone boundaries to limit the longitudinal spread of fragments. See example in Figure 2.4.3 Level III arrangement and also Vol 1, Pt 4, Ch 2, 4.3 Notation assessment levels and methodology 4.3.2.

4.2.7 The examples given in Figure 2.4.1 Level I arrangement show a compartment immediately under the main deck with deckhouse over subject to a side-on attack. Where the critical compartment is fitted directly below an external deck, in a deckhouse or the threat is directly above the compartment, protection is to be arranged using the principles given in examples in Figure 2.4.1 Level I arrangement.

Figure 2.4.1 Level I arrangement

Figure 2.4.2 Level II arrangement

Figure 2.4.3 Level III arrangement

4.3.1 The fragmentation protection FP1 and FP2 notations are assigned for ships which have protection fitted to resist fragments from the casing of a shell or warhead. The small arms protection, SP notation is assigned for ships fitted with protection to resist the penetration of small arms fire into the hull. For ships where the fragmentation resistance is carried out using the Tables and graphs of this section an FP1 notation is assigned. Where fragmentation testing or analysis is used to determine the fragmentation resistance required a FP2 notation is assigned.

4.3.2 The pressure produced by a Level I threat is such that an IB notation is not required. The Level II threat is external and of a level such that an EB notation will not be required. A Level III threat will require the effect of the internal blast pressure on the structure to be considered and IB and RSA notations will generally be required.

4.4.1 For each threat level it will be necessary to identify the critical compartments requiring protection, plus the critical pipe and cable runs where appropriate. Plans are to be provided showing the location and manner of all fragmentation and terrorist attack protection.

4.4.2 Where alternative tests or calculations have been carried out full details are to be submitted. They are to include details of the organisation involved, their experience, test or calculation procedures and the program or equations used.

4.5.1 Where different threats, materials or multiple plate arrays are fitted alternative methods may be used to determine the fragmentation resistance, for example:

• Penetration equations.
• Finite element and fluid-codes.
• Experimental methods.

Ascending the levels of calculation complexity is not simply a matter of increased cost in design, the increased complexity potentially offers the reward of reduced protection requirement for the given threats.

4.5.2 Armour spaced normal to the threat can reduce the total thickness by up to 30 per cent. It may also be effective for bullets provided the gap between plates is greater than 1,0 m.

4.5.3 For Level I fragmentation protection, the equivalent thickness of steel is to be in accordance with Table 2.4.2 Level I fragmentation protection.

4.5.4 For Level II fragmentation protection, the equivalent thickness of steel is to be determined from Figure 2.4.4 Level II fragmentation protection.

4.5.5 For Level III fragmentation protection, the equivalent thickness of steel is to be determined from Figure 2.4.5 Level III fragmentation protection. Protection will normally be required to be provided by several bulkheads or specific armour and the graph can serve only as a guide. The structural protection for this type of threat will generally be specially considered based on the particular weapon characteristics and protection arrangements. It should also be noted that many modern missiles generate controlled fragments which will need special consideration.

4.5.6 The graphs are produced based on a 50 per cent probability of perforation for penetrators perpendicular to the target.

Figure 2.4.4 Level II fragmentation protection

Figure 2.4.5 Level III fragmentation protection