It is useful at the outset to state the essential safety precepts in regard to watertight integrity, as expressed in national and international regulations and safety instruments. In the strict physical sense, the vessel consists of a watertight hull envelope and weathertight topside. The safety philosophy is to:
- Keep water off the decks, through assignment of freeboard, the height of the deck above the water
- Get water off the decks, via freeing ports and other drainage features, and transverse and longitudinal deck slopes, known as camber and sheer
- Keep water out of interior spaces by proper design of structures and closures
- Control any water that does get in through protection of downflooding paths, subdivision of compartments below, and pumping arrangements
2.1 “Door design solution”
The primary goal of the Access Board was the door design solution, meaning proper independent access through any weathertight door used by passengers. The desired outcome was a design or designs of coaming-less doors where the marine safety inspector would otherwise specify a coaming. The initial consideration of such solutions in the Phase 1 report included conceptual alternate water barrier arrangements and alternate deck drainage arrangements.
The difficulty in seeking an engineering solution lies in the fact that the Coast Guard cannot quantify the hazard that coamings are meant to protect against, that is, the volumes, heights, and velocities of water on deck, and the frequency and duration of exposure. The watertight integrity and coaming regulations include no preamble and have no supporting analysis characterizing the hazard. Therefore, development, and approval, of “equivalent” alternate designs on the basis of first principles would be fraught with technical uncertainty.
The Coast Guard’s thinking on watertight integrity is grounded in the analogous regulations of the International Load Lines Convention, as expressed in the Load Line Technical Manual (USCG-M-1-90) and their regulations in 46 CFR, Subchapter E, Part 42. Doors and coamings are covered in the “conditions of assignment” (as described in the Phase 1 report), as are other topside structures, openings, and closures. Recent developments involving ocean-going ships covered by the Convention have tended towards strengthening conditions of assignment regulations rather than searching for alternate, equivalent solutions. The hazards addressed for such ships are likewise non-quantified, and the loss of many bulk carriers at sea, notably the Derbyshire, led to a re-examination and enhancement of regulations for the strength of closures, particularly cargo hatch covers.
These findings led to a decision to concentrate on the reconfiguration solution, rather than a pure engineering solution to a non-quantified problem.
2.2 “Reconfiguration solution”
The reconfiguration approach aims at access solutions by mitigating the hazard of water ingress and reducing risk, by protective placement of the door and minimization and control of water entry. The Phase 1 report showed in several cases that Coast Guard safety inspectors have de facto approved equivalences, based on common sense and without technical substantiation on the record. The risk management approach proposed here is a logical, risk-based guide to arrangement and design practice, building upon the ad hoc approaches developed in recent years among designers and Coast Guard inspectors. The outcome in past cases has been the elimination of coamings or the acceptance of other access designs based on several factors considered in an assessment of safety equivalency. This approach addresses manual doors only and does not include the access solutions suggested by the Passenger Vessel Access Advisory Committee (PVAAC).
The new approach assesses risk on a relative, quantitative scale, based upon several configuration and operations aspects. The results guide the designer to one or more intermediate design solutions or a finding that coamings must be included, as per the regulations. The intended result is a suggested solution or choice of solutions that must also be subject to sound judgment by the designer and safety inspector on a case-by-case basis.
The particulars of this approach are based upon several sources:
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The “Load Line Technical Manual” (USCG-M-1-90, 1990), for vessels with load lines, including those in ocean service. Chapter 4 addresses relaxation of some conditions of assignment in cases where the door is favorably located, e.g., when the vessel has increased freeboard relative to that required or extra deck height, the latter affecting doors located higher on the superstructure.- Title 46 of the CFR, watertight integrity regulations of Subchapters K, T, and S. While the regulations do not explicitly address safety equivalences and the circumstances under which they are approved, they do provide insight into the relation of hazard and risk to the door’s location. The regulations are discussed in detail in the Phase 1 Report.- The “Phase 1” report for this project, which included:
- Detailed presentation of the relevant doorway and coaming provisions U.S. regulations and the international code, including the hazards and risks addressed.- Case studies of Subchapter K and T vessels that have weathertight doors without coamings. These included visits to the boats, review of plans, Coast Guard Certificates of Inspection, and stability letters, and discussions with designers, operators, and Coast Guard inspection personnel.- Detailed presentation of the relevant access specifications and earlier efforts by industry and government experts to find mobility access solutions for weathertight doors with coamings.
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Discussion of the methodology with naval architects prominent in the passenger boat field, their review of the risk-based approach, and revision of the methodology in accordance with questions and comments received.
The Phase 1 work also revealed several ideas for intermediate access solutions, including doors with reduced height coamings and mitigating design features, such as removable coamings, double doors in sequence, and ADAAG-compliant short length ramps and platforms. These design features fit more aptly in the context of reconfiguration solutions, as improved doorway access options
