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The main points of the risk-based approach are:


It is very important to properly characterize these risk-based guidelines as just that: a tool to be carefully applied, case by case, by the naval architect and the inspection authority, with sound technical judgment.

3.1 Terms of reference
The weathertight doors addressed herein are the following:

The reader should note that this methodology does not address interior doors, including fire zone doors, joiner doors, stairway access, and doors that are restricted to crew access. It may turn out, however, that this methodology can offer reconfiguration solutions that can be applied in these kinds of cases as well.

3.2 Characterization of risk factors
The proposed risk factors follow, with annotations showing the technical basis and supporting sources, for example, the Load Line Technical Manual or the Code of Federal Regulations:


3.3 Numerical valuation of risk factors
The proposed risk categories and factors appear below, with numerical values in square brackets (i.e., subject to review and revision). Again, it is important to properly characterize the risk guidelines as just that: a guiding tool to be carefully applied, case by case, with sound technical judgment. The risk values appearing below increase in magnitude with increasing risk and are absolute pre-weighted numbers.

i. Purpose & use of door (scoring range: 0 - 2)

  • [0] – Open only for embarkation/disembarkation, always closed during voyages
  • [1] – Open during voyages for passenger access to weather deck, e.g., “promenade deck”
  • [2] – Access to evacuation deck, required to be open in emergencies

ii. Door location (scoring range: 0 - 6)

Table 1. Door location risk scoring
Note: “Position 1” is between the bow and the point 0.25L aft of the bow;
“Position 2” is between the point 0.25L aft of the bow and the stern
Per definition of International Load Line Convention and the LLTM

  Height of deck at door < [8 feet] above waterline (WL) Height of deck at door >/= [8 feet] above WL
 
Position 1
Position 2
Position 1
Position 2
Facing outboard
[2]
[1]
[1]
[0]
Facing aft
[1]
[2], if <0.25L from stern; [1], if >/= 0.25L from stern
[0]
[1], <0.25L from stern
Facing forward
[6]
[4]
[3]
[2]
    1. For doors facing outboard, multiply score by [1.5] if the door is within [4 feet] of the deck edge.
    2. For all doors with low exterior exposure to the elements due to protective structural elements, multiply score by [0.67]. Discussion in 2.1 cites Subchapter S, K, and T language describing “exposed” locations. Such barriers would need to be in close proximity to the door, and preferably “upstream” in terms of the deck’s slope due to sheer and camber.

ii. Downflooding Potential

  • Downflooding (DF) path (scoring range: 0 - 6)


Table 2. Downflooding path risk scoring

X = distance from door to downflooding point
Y = height of downflooding point above deck

  X< [20 feet] X>/= [20 feet]
 
Y < [2 feet]
Y >/= [2 feet]
Y < [2 feet]
Y >/= [2 feet]
Manholes only
[1]
NA
[0.5]
NA
Protected
[2]
[1]
[1]
[0] 4
Unprotected
[6]
[4]
[4]
[2]
    1. Manholes only. Watertight, bolted, flush manholes leading to void spaces, tanks, and unmanned spaces, closed during voyages.
    2. Protected: Watertight or weathertight closures (doors or hatchways) with coaming at downflooding point(s)
    3. Unprotected: Joiner doors, ventilation openings to spaces below
    4. [0] – no pathway of any kind to watertight spaces below the passenger deck

iv. Area of operation
The aggregate scores for the above risk categories should be multiplied as follows for the OCMI designation of waters (that is, for the purposes of the stability regulations) in which the vessel is authorized to operate.

Total scoring range
The range of possible aggregate scores (“R”), before multiplying for the area of operation, is 0 – 16. The range of possible aggregate scores, after multiplying for the area of operation, is 0 – 24.


3.4 Doorway access solutions
The final step in the process is to identify the potential access solutions indicated by the total risk scores. In application, a solution may be selected for any risk score in or below its designated range. A high aggregate risk score may indicate the need to relocate the door and/or incorporate more protective features, to lower the score and consider the selection of a door with improved access.

The proposed menu of solutions follows:

Examples:

  • “Concept A” or B” exterior drains (see figures, Appendix A)
  • Gladding – Hearn exterior drainage detail on Flying Cloud (Appendix B, Figure 3)
  • Bulwarks, bulkheads, deck overhangs, etc. preventing passage of water to the door, especially from the direction of exposure, for example, from the bow for forward facing doors or from the stern for aft facing doors.

Aggregate risk score = [8 ? R ? 12]

This solution is for embarkation access only, that is, where the crew operates the door at known times and places only.

Aggregate risk score = [8 ? R ? 16]

Aggregate risk score = [16 ? R ? 20]

Aggregate risk score = [20 ? R ? 24]

3.5 Other doorway solutions
It may be fruitful to explore the possibilities for substitution of a watertight door with a minimally sized coaming, allowed in both the Subchapter T and K regulations (46 CFR 116.1160 and 179.360, respectively; see discussion, Phase 1 report). The currently available interpretation from Coast Guard safety personnel is that such substitution is meant specifically for vessels with licensed crew and other capable personnel (e.g., offshore drilling rig workers) aboard, who know how to operate a watertight door and can do so in emergency egress situations. This interpretation may be ripe for re-examination.
The use of such doors would raise other accessibility questions (hardware configuration and opening force); however, the result of the inquiry could be a set of new design requirements for consideration by watertight door manufacturers.

3.6 Embarkation doors at the deck edge
Many passenger boats have embarkation doors in the deckhouse side, at or very close to the deck edge and offering no weather deck access. Coamings are not the access barrier in these cases, but poorly designed gangways are. The problem most commonly seen is the double slope of the gangway and a short interior ramp meeting in an apex at the coaming (there are non-specification variations like the “whaleback” arching over the coaming). Gangways designed to provide proper slopes on both sides of the doorway and a proper landing over the coaming are the access solution, not removal or reduction of the coaming. A concept design appears in Appendix A, Figure 3.