Under Coast Guard domestic regulations, certain doors in passenger vessels leading from the outside (“the weather”) into passenger accommodation spaces must have sills (also known as coamings) of varying heights to prevent the entry of water. However, under the American with Disabilities Act Accessibility Guidelines (ADAAG), an accessible door cannot have a threshold that is higher than 1/4 inch or 1/2 inch, if beveled. If ADAAG threshold provisions were applied to passenger vessels, at certain doors, the coaming requirement and ADAAG threshold requirement would conflict. The following sections detail the provisions of the Coast Guard regulations and the ADAAG guidance, as well as summarizing the current practice in the U.S. passenger fleet.

2.1 Relevant Coast Guard Regulations and Practice
It is useful at the outset to set the U.S. passenger fleet and the Federal regulations within the larger context of the international fleet and its safety codes, and to provide some definitions of marine safety concepts as they relate to the most elemental need: to keep water out of the boat and preserve the integrity of the “watertight envelope” provided by the hull. The hull structure consists of the shell, its bottom and sides, and the main deck, and it carries the payload by displacing water (except in cases of “lift” craft such as hydroplanes and hovercraft, a very small minority of passenger vessels). Its geometric and loading configuration defines its stability and provides reserve buoyancy for safe responses to external forces such as waves, wind, and water on deck.

The very first marine safety regulations resulted from the Merchant Shipping Act of 1871 (Great Britain), which addressed seaworthiness and later were substantially adopted as the first international code, the International Load Line Convention (ILLC). The essence of the ILLC was to provide for adequate hull structure and reserve buoyancy, prevent overloading, and to ensure watertight integrity. A significant feature of the latter was to address water that gets on the “weather decks”, by rain, spray, and, most importantly, boarding waves. For merchant cargo ships, storm-driven waves sweeping the deck (also known as “green water”) are a serious hazard to this day. The danger is twofold: accumulation of water on deck and downflooding into spaces below. Both degrade reserve buoyancy and stability.

The ILLC addresses this hazard through the “conditions of assignment”, a detailed set of specifications for all structures above the main deck and all openings into the hull and superstructure, including cargo hatches, doorways, ventilator pipes, port holes, and others. The conditions of assignment aim to provide topside design features that will prevent entry of water and shed it quickly over the side; many of these are adapted for use in the CFR’s subchapters addressing ship safety in general and passenger vessel safety in particular. The CFR covers nearly all of the United States passenger vessels operating in United States waters. The ILLC pertains only to a handful of United States vessels operating on international voyages, as well as all of the foreign flagged cruise ships operating from U.S. ports.

Properly designed topside structures and openings are “weathertight”. The distinction between watertight and weathertight is the following:

2.1.1 Code of Federal Regulations
The relevant issues in the CFR for these purposes are the definitions for all types of passenger vessels, areas of operation as applied to Certificates of Inspection (COI) and for the purposes of stability requirements, and the weathertight door coaming regulations themselves. Passenger vessel definitions
The definitions for passenger vessels are found first in 46 CFR, Part 70, Table 70.05- 1(A) “Classes of vessels examined or inspected under various Coast Guard regulations. Discussion for these purposes is confined to vessels whose primary purpose is carriage of passengers and does not include oceanographic research vessels and other commercial vessels that sometimes carry passengers for hire, for example, tankers or fishing boats. The table defines, in descending order of size, Subchapter H, Subchapter K, Subchapter T, and Subchapter C passenger boats.

The definitions and particular subchapter citations follow, along with examples of each: Areas of operation
The CFR and Coast Guard certification and inspection regime takes a dual approach to areas of operation, affecting all passenger vessel types, and in addition allows for a certain amount of judgment by the Officer in Charge of Marine Inspection (OCMI) in the relevant Captain of the Port (COTP) zone.

Most importantly for the aim of this study, the CFR defines “exposed”, “partially protected”, and “protected” waters, for the purpose of applying the stability criteria and regulations to H, K, and T boats. These terms describe the sheltered versus exposed nature of the waters, that is, the severity of waves and swells likely to be encountered therein, as well as the proximity to safe refuge of vessels operating therein. The OCMI has the authority to designate waters as seen fit to account for local conditions. Many of the stability regulations vary in application depending upon the waters plied, for example, the specified “wind heel” load that the vessel must sustain. Included among these are the “Watertight Integrity” regulations, which regulate openings in the hull and superstructure, including weathertight doors; these are discussed in detail below.

The Coast Guard conducts a regulatory stability assessment for each inspected passenger vessel, the result of which is the stability letter issued to the owner. This letter identifies the type of waters (e.g., “partially protected”) upon which the vessel may operate, given its design and stability characteristics, as well as any loading restrictions deemed appropriate. The stability letter is generally not posted onboard in public view. An example of this document appears in Appendix A.

The Coast Guard also issues a certificate of inspection (COI) for each inspected passenger vessel. The COI addresses many safety aspects including manning and certification of crew, and stability, and specifies operations in well defined areas, including “rivers”, “limited coastwise”, “coastwise”, “Great Lakes”, “lakes, bays, and sounds”, and “oceans”. The COI is posted on board by regulation and is the document that the traveling public are most likely to see. Again, the COTP has discretion to re-designate any area in his zone based on environmental conditions and safety considerations. The COTP can also impose limitations or grant extensions of operating routes based upon stability criteria and unique construction or operating characteristics of the vessel (Coast Guard Marine Safety Manual). An example of the COI also appears in Appendix A.

These two operating area designations are not linked in the regulations. Table 2-1 provides a general guideline as to how they match up in practice. There is a correlation in a general sense only, e.g., the stability designation “partially protected” to COI designation “limited coastwise”, or “exposed” to “oceans”. It is important for the reader to keep in mind that the COTP can alter this correlation depending on local conditions and the design and construction of the individual boat. It should be held foremost that designations for stability purposes are what matter for the purposes of this study. Watertight integrity regulations for Subchapter H passenger vessels
Subchapter H passenger vessels are the largest sized regulated class and are generally subject to the most stringent structures and stability requirements, in both Subchapter H and Subchapter S (“Stability”). Subchapter H specifies plan approval for a wide array of hull structure drawings and annual inspection of watertight doors and subdivision bulkheads. Subchapter S addresses “Watertight integrity above the margin line in a vessel 100 gross tons or more” (46 CFR 171.122), by specifying weathertight closures and coamings for “each opening in an exposed weather deck”. The interpretation is that those openings include only hatches, and not doors into superstructure on the weather decks. The reason for this omission is not clear, although Coast Guard experts felt that such doors would generally be higher above the waterline (and less likely to be exposed to boarding waves) and that the relatively large size of H vessels would preclude a safety problem due to wind driven rain or spray1. H vessels subject to the International Load Line Convention would have to meet superstructure and deckhouse door coaming requirements. These, however, are vessels operating in international waters only and would not include most of the Subchapter H vessels currently documented in the United States.

Table 2-1
Coast Guard Designations of “Waters”


Designation of Waters for Purposes of Stability Regulations


Exposed waters

Partially protected waters

Protected waters


Waters more than 20 nautical miles from harbor of safe refuge; applies on Great Lakes from Oct. 1 to April 15.

Waters not more than 20 nautical miles from harbor of safe refuge; applies on Great Lakes from April 16 to September 30.

Sheltered waters with no special hazards, e.g., rivers, harbors, and lakes.



Puget Sound

Boston Harbor, New York Harbor

Roughly Corresponding COI Designations

Oceans – any route more than 20 nautical miles offshore.

Limited coastwise – any route not more than 20 nautical miles from a harbor of safe refuge.

Lakes, Bays, and Sounds – route on same.

Coastwise – any route not more than 20 nautical miles offshore on oceans, gulfs, and seas.

Coastwise – as designated by OCMI

Rivers – route on same.

Great Lakes – includes St. Lawrence River, from Oct. 1 to April 15.

Great Lakes, from April 16 to September 30. Watertight integrity regulations for Subchapter K and T passenger vessels
The watertight integrity regulations addressing weathertight doors are identical for Subchapter K and T boats (46 CFR 116.1160 and 179.360, respectively). The relevant citations for weathertight doors in Subchapters K and T are identical and read as follows:


“(d) A weathertight door must be provided for each opening located in a deckhouse or companionway. Permanent watertight coamings must be provided as follows:

  1. “On a vessel on an exposed or partially protected route, a watertight coaming with a height of at least 150 mm (6 inches) must be provided under each weathertight door in a cockpit or a well, or on the main deck of a flush deck vessel.
  2. “On a vessel on a protected route, a watertight coaming with a height of at least 75 mm (3 inches) must be provided under each weathertight door in a cockpit or a well.
  3. “The height of a watertight coaming for a hinged watertight door need only be sufficient to accommodate the door.”


A cockpit or well, as described in sub-paragraph (a), is an area of deck set below the weather deck, with the same weather-tightness requirement for all its boundaries. They are given special mention because of the potential for water to become entrapped therein and the necessity to prevent downflooding through doors giving access to spaces below. Cockpits and wells are uncommon on the whole in the inspected passenger vessels fleet, and are usually found on passenger sailing boats. A flush deck denotes continuity of the weather deck from bow to stern at the upper limit of the hull sides.

The paragraph allowing substitution of a watertight door with no required coaming height provision is 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 situations2.

Subchapter S “Stability” considerations
Discussions with naval architects and Coast Guard personnel revealed some redundancy and confusion arising from the watertight integrity and coaming provisions of Subchapter S, also part of the Coast Guard’s Title 46 regulations. Subchapter S addresses coamings among many stability matters, and applies to all vessels less than 100 gross tons, not just passenger vessels. The design of a small passenger boat requires attention to both Subchapter S and Subchapter T or K. The regulations are sometimes clear in the matter of integrating those requirements (see following paragraph), but are not so with regard to coamings.

One example of clear guidance is that Subchapters K and T explicitly cite Subchapter S intact stability standards (that is, the vessel’s ability to stay upright under loading from wind, waves, passenger movement, etc.) for passenger boats with particular physical or operational characteristics. Subpart C of Subchapter T (parts 178.310 – 178.340) specifies compliance with four separate parts of Subchapter S for vessels more than 19.8 meters in length, carrying more than 12 passengers on an international voyage, and having more than one accommodation deck above the bulkhead deck. The point here is not to discuss the technical fine points of these particular provisions, but to illustrate how clearly in one instance Subchapter T guides the user.

The redundancy and differences between Subchapter K or T and S citations for weathertight doors and coamings is not specifically addressed in either Subchapter K or T. The relevant citation for weathertight doors and coamings in Subchapter S (part 171.124 “Watertight integrity above the margin line in a vessel less than 100 gross tons”) is similar, but not identical, to those in Subchapters K and T (shown in the first paragraph of, and reads as follows:


“(d) A weathertight door with permanent watertight coamings that comply with the height requirements in table 171.124(d) must be provided for each opening located in a deckhouse or companionway that –

(1) “Gives access in to the hull; and

(2) “Is located in –

(i) A cockpit;
(ii) A well; or
(iii) An exposed location on a flush deck vessel.

“(e) If an opening in a location specified in paragraph (d) of this section is provided with a watertight door, he height of the watertight coaming need only be sufficient to accommodate the door.”


There are several subtle differences in the definitions and interpretations of locations onboard where coamings are required. The Coast Guard itself has occasional problems in applying these provisions, as illustrated by an internal memorandum from the Headquarters Office of Design and Engineering Standards on the definition of “weather deck” for the purpose of applying the weathertight door provision3. The following points summarize the comparison of and difficulties among the relevant parts of the three subchapters:

In summary, the terms of reference in the weathertight door and coaming regulations in these three subchapters can be confusing and subject to various interpretations for particular boats by both industry and the Coast Guard. Subchapter S requires more interpretation by the naval architect and will in some cases be more stringent for passenger boats operating on protected waters; that is, a door’s “exposed” location and/or proximity to a downflooding path might be interpreted to require a 3” coaming where Subchapters T and K require none. T and K are prescriptive in nature and may in some cases be more stringent for boats on exposed and partially protected routes. T and K could require a 6” coaming in a location where interpretation of Subchapter S would not.

Diligent naval architects and regulatory personnel seek safe and reasonable designs based on technical knowledge and experience. They must consider the owner/operator’s intended use of the vessel and the will apply the regulations and their own best practice methods as appropriate.

The case studies in Chapter 3 herein include a sampling of anecdotal information on safety “equivalencies” to these regulations granted based on design particulars. The philosophy and safety precepts evident in Subchapters K, T, and S will be brought forward into the Phase 2 work of finding safe, accessible solutions for weathertight doors. Watertight integrity regulations for Subchapter C passenger vessels
Subchapter C covers “uninspected vessels“, as described above. Such boats are subject to the construction and flotation requirements that apply to all uninspected boats, but the regulations in Subchapter C are limited to Parts 24–26, which include lifesaving and fire prevention and extinguishing equipment. Those under 100 gross tons include many “open deck” boats without the type of doors addressed herein. Weathertight doors are in any case not required for Subchapter C boats that have deckhouses with doors. “Good marine practice”
The term “good marine practice” describes commonly accepted marine design and construction methods in addition to the requirements of the CFR. Coast Guard regulations describe minimally acceptable features that can be and are often exceeded by the naval architect and the shipyard.

Good marine practice is in no way a universal standard, but varies by service, region, design operating conditions, and even preferences of the owner and the shipyard. In the case of doorway coamings, it is not uncommon to find them on vessels where the service and operations do not require them. It is possible that good “accessible” design practice can change this particular element, with improved awareness by designers and operators.

2.1.2 Hazards and Risks Hazards associated with stability
The hazard addressed by the watertight integrity regulations, and the coaming regulations in particular, is water ingress and downflooding. Protracted exposure to waves and ingress of water, even in incrementally small amounts, can degrade the vessel from an “intact stability” to a “damage stability” situation. A brief explanation of the concepts of intact stability and damage stability is first in order.

Stability in both modes is the ability of the vessel to remain upright while sustaining applied loads. These loads can be external (e.g., waves, wind, water on deck) and internal (weight shifts such as passenger crowding, movements of liquid or solid cargoes). The vessel’s weight and buoyancy distributions determine its stability characteristics. The ultimate stability hazard is capsize, a fast moving event with the potential to cause devastating loss of life. Prevention of capsize is the aim of the stability regulations. Lesser hazards are associated with non-capsize scenarios in which the vessel’s response to external loading can cause discomfort or injury to passengers, particularly those unused to marine travel. The naval architect addresses these hazards, and they are not covered by the regulations.

Intact stability addresses situations when the vessel is operating in the undamaged, normally loaded condition. The latter descriptor may be one of several conditions that must be checked by the naval architect; examples include 1) full load departure and 2) return with partially full fuel tanks.

Damage stability applies in abnormal conditions when water has entered the vessel following events such as groundings, collisions, and ingress of water due to storm conditions. Domestic and international damage stability regulations are most stringent for passenger vessels as compared to other types, but the reader must bear in mind that the stability and safety of a vessel in this state has been seriously degraded. Regulations and risk
The Coast Guard now sees safety as a risk management process. Risk is the product of an event’s probability and its consequences. The consequences of ingress and downflooding are always serious, that is, the degradation of vessel’s stability. The potential consequences of the capsizing of a passenger vessel – tens or hundreds of lives lost – are unacceptable; therefore, the regulations are intended to minimize as much as possible the probability of that event. The coaming regulations are one element of watertight integrity requirements meant to reduce the probability of significant ingress of water.

This explains why the regulations are tied to definitions of exposure and protection that include a consideration of time, that is, proximity to a safe harbor. In protected waters, sea conditions are less likely to cause significant water on deck, and the proximity of land and emergency services assets further reduces risk, should flooding occur. In exposed or partially protected waters, water on deck and the conditions for downflooding are more likely and “safe harbor” is likely to be at greater distance. The regulations are more stringent in such cases because the likelihood of water on deck is higher and more time is needed to get to safe refuge.

2.1.3 “Equivalents” and “Special consideration”
The CFR allows for review and approval of engineering and design proposals, in both Subchapters K and T, from any regulations, based upon an equivalency of safety. “Equivalents”, described in 46 CFR 114.540 and 175.540 for K and T boats, respectively, allow for the Commandant to “approve any arrangement, fitting, appliance, apparatus, equipment, calculation, information, or test, which provides a level of safety equivalent to that established by specific provisions of this subchapter”. The applicant is required to submit such requests to the Coast Guard Marine Safety Center (a Headquarters unit located in Washington, DC) via the local cognizant OCMI. All such proposals are evaluated strictly on a case-by-case basis.

The “Equivalents” regulations also allow for the Commandant to accept compliance by a high speed craft with the provisions of the International Maritime Organization (IMO) “Code of Safety for High Speed Craft” as an equivalent to compliance with applicable requirements of the relevant subchapter. These requests are also submitted to the Marine Safety Center via the cognizant OCMI. The IMO Code does not specify coamings, but addresses doors in a general way, as follows:

“2.2.4 The means of closing openings in the boundaries of weathertight structures should be such as to maintain weathertight integrity in all operational conditions.”

“Special considerations”, described in 46 CFR 114.550 and 175.550 for K and T boats, respectively, empower the OCMI to “give special consideration to authorizing departures from the specific requirements when unusual circumstances or arrangements warrant such departures and an equivalent level of safety is provided”. The equivalent arrangement in these cases pertains only within the particular COTP zone under the OCMI’s cognizance and is for particular circumstances of a vessel’s design or operations. A special consideration request may in fact be for a particular voyage or event, for example, a boat approved for “oceans” service carrying extra passengers for an event (e.g., a fireworks display) in protected waters, with the appropriate added precautions such as sufficient lifesaving equipment.

Discussions with Coast Guard personnel reveal that there would be several factors to consider in an assessment of safety equivalency for doors without coamings, which are the following:

2.2 ADAAG and Advisory Committee Recommendations
The Americans with Disabilities Act of 1990 (ADA) applies to most passenger vessels. Yet, as of October 2004, no ADA standards or guidelines have been promulgated which specifically address passenger vessel access. However, the ADA Accessibility Guidelines for Buildings and Facilities (ADAAG) does exist and is found in the Appendix to 36 CFR Part 1191. Per ADAAG, the essentials of accessible doorway design are the following:

In 1998, the Access Board established a 21-member Federal advisory committee to provide recommendations to assist the Board in developing passenger vessel accessibility guidelines. The committee included disability organizations, industry trade groups, State and local government agencies, and passenger vessel operators. The Passenger Vessel Access Advisory Committee (PVAAC) submitted a final report "Recommendations for Accessibility Guidelines for Passenger Vessels" in December 2000. The report mainly addressed Subchapter H and K vessels, with one chapter devoted to certain Subchapter T and C issues. Door specifications for both H and K vessels followed those from ADAAG very closely, with the important exception that PVAAC recognized the conflict between access and safety inherent in the weathertight door coaming regulations.

The Committee developed solutions only for ramping over the coamings, including the double ramp and single ramp methods (see Figure 2-1). Both methods modified a number of ADAAG door requirements to allow coamings and some degree of access to co-exist.

Figure 2-1
PVAAC Coaming and Ramp Solutions

Figure 2-1 (a) shows a single ramp with a landing 48 inches (1220 mm) long. If the height (x) is 3 inches or less, the slope may be 1:4 max, between 3 to 6 inches, the slope may be 1:6 max; above 6 up to 9 inches, the slope may be 1:8 max; over 9 inches the slope is 1:12 max. Figure (b) shows a double ramp with a 1:12 slope max if no landing is provided; door must be automatic.

The PVAAC report did not include solutions eliminating coamings from weathertight doors, but in their meetings the Committee noted that ADAAG complying door designs could be developed which also provide an equivalent level of vessel protection as the coamings. The only specific design discussed by PVAAC involved having two doors in series, with the required separation and the operational requirement that one door always be closed.

The PVAAC report specified, without explanation or elaboration, the following for H and K boats:

206.5.3 Weather Deck Access. Where the main deck of a passenger vessel is greater than 3,000 square feet (280 m2) at least one exterior door on each accessible weather deck shall comply with 404.2.5 (maximum threshold height of ½”) and shall be located on an accessible route that provides access between the weather deck and the interior of the passenger vessel, except where prohibited by an administrative authority having jurisdiction.”

The minutes of PVAAC meetings and subsequent discussions with members indicate that the reasons for this specification may be that larger vessels would have doors higher above the water the waterline and that small amounts of ingress from rain and spray could be sustained (similar to the Coast Guard’s interpretation of H boat weather deck closure requirements). The size may also allow better opportunities for placing a single accessible door in a low risk location, relative to water and wind.

2.3 Current Practice in the U.S. Passenger Vessels Fleet
The vast majority of publicly available passenger boats in the ferry and excursion trades operating on a regularly scheduled “common carrier” basis are T and K vessels. The age of boats in this fleet ranges up to 100 years, and the majority of those are conventional monohulls predating the ADA of 1990.

Access onto these boats follows, nearly without exception, the safety regulations in Title 46 of the CFR. Weather doors have coamings as specified for boats operating in partially protected and exposed waters. Many other boats have the coamings as a matter of good marine practice, even when the operating area may not require it. Operators and crews are solicitous of passengers’ needs in general and of the access needs of disabled people in particular. It has been common practice for crew members to assist passengers in wheelchairs onto the vessels, especially where traditional marine design elements, such as coamings, prevent independent access.

Passengers on K and T boats commonly use weathertight doors for entry into the accommodation area, because the embarkation deck is usually the “main” deck. Interior doors commonly have no coamings. Doors to the weather on decks above the main deck may have coamings, although this is a matter of the designer’s preference rather than the regulatory requirements. Passengers very seldom encounter watertight doors, as those doors are found below the main deck in watertight subdivision bulkheads between working spaces like the engine room.