The risk methodology was first exercised and tuned with examples of weathertight doors in the as-built condition (section 4.1). The next step was the development of reconfiguration cases on several representative, and recent, designs. Summaries of the reconfiguration cases appear in section 4.2, and the full texts appear in Appendices B through D.
4.1 As built cases
Table 3 shows a sampling of the results applying the risk scoring methodology to doors serving passenger accommodation spaces on existing boats. All the particulars and scoring factors for each door appear, as well as the aggregate risk score. Descriptions of the existing door and the access solution indicated by the methodology appear in the rightmost column, for the purpose of comparison.
The risk methodology indicates solutions that are for the most part similar to the existing as-built doors, particularly those cases where alternate arrangements were approved in the inspection process. The exceptions are among the doors examined on larger and older vessels, the Subchapter H and K boats. In these cases, the risk-based solutions were less conservative than the as-built doors.
In the case of the Subchapter K overnight excursion boat, the main deck door giving access to the stern has a 6” high coaming in strict accordance with the regulations. The location and downflooding potential result in a moderate aggregate risk score of 8.0, indicating the need for protection from water ingress but allowing for an alternate design for improved access. The risk score is on the cusp between designated ranges for three different solutions. The conservative choice would be a weathertight door with a reduced height coaming, with sloped deck ramp (grated for drainage) and landing at sill height.
An “01 level” (one deck above the main deck) door on the same vessel scored quite low for risk (aggregate = 3.5). The indicated solution is nearly identical to the as-built door and both provide good access.
The 01 level door on the Subchapter K casino boat has a 6” high coaming, but scores for moderate risk only (aggregate = 7.0). The indicated solution is a weathertight door with no coaming and drainage/ water barrier protection. A more conservative option would be a door with reduced height coaming [50%] with sloped deck ramp (grated) and a level landing at the coaming height.
The doors examined for Subchapter K and T passenger-only catamaran ferries of recent construction had low to moderate aggregate risk scores. Notably, the indicated solutions were very similar to the as-built doors in all three cases.
Table 3. Risk scoring for as-built door examples
| Pathway || To & From | Purpose and use of door ([0 – 2]) | Door Location ([0 – 6]) | DF Potential ([0 – 6]) | Size of space doorway leads to ([0 - 2]) | Area of Operation multiplier | Total risk ([0-24]) | Existing Door and
Solution(s) |
| Subchapter K overnight excursion boat, weather deck | Passenger accomm. space | Passenger access to weather deck, alternate access not available (2) | Main deck, aft, facing stern; deck at door < 8’ above WL
(2) | Unprotected pathway to spaces below with 20’+ separation; Y < [2’]
(4) | Passage and passenger berths, less than 25% of main deck area (0) | Partially protected waters (1.0) | (2 + 2 + 4 + 0) * 1.0 = 8.0 | Existing door has 6” coaming. Indicated solutions are: 1) door with no coaming and protection for water; 2) door with removable regulation height coaming; or 3) reduced height coaming with sloped deck ramp (grated) and landing at sill height. 2 and 3 are the conservative choices. |
| Passenger accomm. space | Passenger access to weather deck, alternate access available (1) | 01 level, facing outboard, Pos. 1, less than 4’ from deck edge (1.5) | Protected pathway:20’+ separation; Y < [2’]
(1) | Passage and passenger berths, less than 25% of main deck area (0) |
Partially protected waters (1.0) | (1 + 1.5 + 1 + 0) * 1.0 = 3.5 | Existing sliding door has no coaming. Indicated solution is a weathertight door with no coaming. |
| Subchapter K casino boat, forward weather deck | Passenger accomm. space | Passenger access to weather deck, no alternate access available, closed in bad weather (1) | 01 level, facing forward, Pos. 1, more than 8’ above waterline (3) | Protected pathway: 20’+ separation; Y < [2’]
(2) | Gaming room, 30% - 50% of main deck area (1) | Partially protected waters (1.0) | (1 + 3 + 2 + 1) * 1.0 = 7.0 | Existing double doors have 6” coaming and nearby deck drain. Indicated solution is a weathertight door with no coaming and drainage/ water barrier protection.
|
| Subchapter H vehicle – passenger ferry, starboard weather deck | Passenger accomm. space | Passenger access to weather deck (1) | 02 level, facing outboard, within 4’ of deck edge (0) | No pathway to spaces below (0) | Passenger accomm. space, less than 25% of deck area (0) | Partially protected waters (1.0) | (1 + 0 + 0 + 0) * 1.0 = 1.0 | Existing door has 3” coaming with short ramps on either side. Indicated solution is a weathertight door with no coaming. |
| Subchapter K catamaran passenger ferry, starboard weather deck | Passenger accomm. space | Passenger access to weather deck (1) | Main deck aft, facing outboard, within 4’ of deck edge (1.5) | No pathway to spaces below (0) | Passenger accomm. space, more than 50% of main deck area (2) | Partially protected waters (1.0) | (1 + 1.5 + 0 + 2) * 1.0 = 4.5 | Existing sliding door has 1” coaming. Indicated solution is weathertight door with no coaming, with drainage or barrier protection. |
| Subchapter T catamaran passenger ferry, forward weather deck | Passenger accomm. space | Passenger embarkation, closed during operations (0) | Main deck Position 1, facing forward (6) | No pathway to spaces below (0) | Passenger accomm. space, more than 50% of main deck area (2) | Partially protected waters (1.0) | (0 + 6 + 0 + 2) * 1.0 = 8.0 | Existing double doors have no coaming with drainage in adjacent deck. Indicated solution is no coaming, with drainage or barrier protection. |
| Subchapter T catamaran passenger ferry, aft starboard weather deck | Passenger accomm. space | Passenger access to weather deck (1) | Main deck Position 2, facing outboard, within 4’ of shell (1.5) | No pathway to spaces below (0) | Passenger accomm. space, estimate more than 50% of main deck area (2) | Partially protected waters (1.0) | (1 + 1.5 + 0 + 2) * 1.0 = 4.5 | Existing sliding door has no coaming and protection of bulkheads forward. Indicated solution is weathertight door with no coaming, with drainage or barrier protection. |
4.2 Reconfiguration examples
Risk scoring tables appear for each case, but the door access solution is discussed in detail in the accompanying text rather than specified in the table (as was presented in 4.1).
4.2.1 Gladding – Hearn INCAT Designs, 35 meter long Subchapter T catamaran
This case study was to ascertain whether access through the forward doors for this bow-loading boat could be improved, possibly by the elimination of the coamings, on the basis of the risk management approach. The case was instructive because it uses a “type” boat design wherein a number of options for design and operation may be selected, allowing for examination of several scenarios involving design options and hypothetical consideration of operation in protected or partially protected waters. The design options were:
- The passenger deck may “float”, that is, be structurally separate from the catamaran hulls’ watertight envelope and no direct downflooding path, or may be integral with the hull tops.
- Embarkation access may be via the bow to the forward deckhouse doors, or via bulwark gates near the stern to the aft deckhouse doors.
The design specifies weathertight doors, whether facing forward for bow loading, or aft for stern loading. Doors are presumed to have 3” coamings (designed per Subchapter S watertight integrity regulations for vessels less than 100 GT).
Tables 4 and 5 summarize the analytical framework for characterizing the design technical risk factors associated with the location and use of weathertight doors. The tables show four scenarios each for the forward and aft doors. Moving from the leftmost column rightward, the cells first divide to indicate the deck construction options, and then divide again for service in “protected” versus “partially protected” waters.
Table 4. 35-meter catamaran, risk scoring for forward door options
| Pathway | To & From |
Purpose and use of door ([0 – 2])
Door Location ([0 – 9])
Downflooding Potential
Area of Operation multiplier
Total risk “R” ([0-24])
DF path ([0 – 6])
Size of space doorway leads to ([0 - 2])
Forward doors, port and starboard
Weather
||
passenger accomm. space
Embark-ation only, closed otherwise
(0.0)
Door sill less than [8 feet] above WL, facing forward in Position 2 (4.0)
Manholes only (1.0)
Passenger accomm. space, more than 50% of main deck area (2.0)
Protected waters (0.75)
(0 + 4 + 1 + 2) * 0.75 = 5.25
Partially protected waters (1.0)
(0 + 4 + 1 + 2) * 1.0 = 7.0
“Floating” deck, no DF pathway (0.0)
Protected waters (0.75)
(0 + 4 + 0 + 2) * 0.75 = 4.5
Partially protected waters (1.0)
(0 + 4 + 0 + 2) * 1.0 = 6.0
Based strictly upon the aggregate risk scores, the aft doors would appear to be the better choice for passenger access. The scores in both cases are low, however, and an accessible pathway via the bow doors would also be appropriate for the right combination of design features and operation. Note that access through the aft doors to the aft weather deck is required whether or not the embarkation pathway includes those doors.
Forward doors
In the bow loader configuration with forward embarkation doors, the choice of a “floating” deck would reduce the risk scores from 5.25 and 7.0 to 4.5 and 6.0, for service in protected and partially protected waters, respectively. The benefit of the floating deck for either service choice is modest and does not substantively change the outcome, because the downflooding risk from the closed manholes in the passenger cabin is low to start with.
With or without the floating deck, in protected water service, the solution would be a coaming-less weathertight door. The risk for this design could be further reduced with protective drainage features against water on deck. It may be appropriate to replace the weathertight door with coaming with an improved access doorway, for example, a weathertight door with a coaming of reduced height, and protective drainage.
Table 5. 35-meter catamaran, risk scoring for aft door options
| Pathway | To & From |
Purpose and use of door ([0 – 2])
Door Location ([0 – 9])
Downflooding Potential
Area of Operation multiplier
Total risk “R” ([0-24])
DF path ([0 – 6])
Size of space doorway leads to ([0 - 2])
Aft doors, port and starboard
Weather
||
PAX accomm. space
Embark-ation, and passenger access to weather deck during voyage
(1.0)
Door sill less than [8 feet] above WL, facing aft in Position 2 (1.0)
Manholes only (1.0)
PAX accomm. space, more than 50% of main deck area (2.0)
Protected waters (0.75)
(1 + 1 + 1 + 2) * 0.75 = 3.75
Partially protected waters (1.0)
(1 + 1 + 1 + 2) * 1.0 = 5.0
“Floating” deck, no DF pathway (0.0)
Protected waters (0.75)
(1 + 1 + 0 + 2) * 0.75 = 3.0
Partially protected waters (1.0)
(1 + 1 + 0 + 2) * 1.0 = 4.0
|
Aft doors
Use of the aft doors for access to the weather deck is required whichever embarkation path is chosen. The floating deck results in scores of 3.0 and 4.0 for the protected and partially protected waters. A coaming-less door would be appropriate in either case. For partially protected waters, the score of 4.0 is on the cusp and it might be appropriate to include protective drainage or a reduced height coaming with ADA-compliant short ramps on either side.
Without the floating deck, the aggregate risk scores rise slightly. Protective drainage or a reduced height coaming with short ramps and a landing would be appropriate for service in partially protected waters.
Discussion
It is evident that the door location and the large size of the accommodation space drive the aggregate risk score in all the scenarios, especially for the forward doors. The floating deck eliminates downflooding paths, but the benefit is modest because the only potential downflooding points in this case are bolted manhole covers leading to tanks and voids; the likelihood of any of those manholes being open during a voyage is slight. It turned out that the scoring bandwidth for all scenarios was relatively narrow at the low risk end of the range, but that there are several possible solutions.
This case shows there may be several design, operations, and economics decision points, of which mobility access is one. The operator and builder can consider accessible paths onboard in overall context of the desired operation for the boat (market served, waters served, and shoreside infrastructure and loading mode), and the added cost of mitigative safety features. An accessible pathway through either the forward or aft doors is feasible, given different design and operational choices.
4.2.2 Casco Bay Line monohull passenger only ferry, Subchapter K, 399 passengers, protected waters service
In this case, embarkation is via sliding weathertight doors on the main deck, port and starboard, forward (approximately 0.25L from the bow) at the deck edge. The doors have 3” coamings (per Subchapter S). The risk model exercise is to ascertain whether the coamings could be eliminated to improve embarkation access and simplify the design of the gangways from the shoreside piers.
Discussion
The embarkation doors, as designed, scored 4.5. The indication is that a weathertight door without coaming might be suitable. However, there would be no exterior drainage or water barrier protection available, given the deck edge location. The conservative approach would dictate retention of the coaming as structural protection and a strong gasketing surface against the unlikely event of waves impinging on the door.
Two possible reconfigurations would lower the risk score to below 4.0 and allow installation of a no coaming weathertight sliding door. First, the doors could remain in their forward position in a 48” recess, a protective bulkhead forward, and possibly a portable protective coaming at the deck edge while the door is closed. As shown in Table 6, the overall risk score would be 3.75 and the solution would be a sliding weathertight door with no coaming, with limited impact on the internal arrangement.
The second approach would be to move the doors aft to approximately amidships, resulting in a lowered aggregate risk score of 3.4 and a sliding coaming-less door. The internal space arrangement modification would be minimal. Bench space lost amidships would be regained forward at the former position of the door.
In this case, the two “downflooding” sub-factors, “distance to downflooding point” and “area of accommodation space”, work against each other. Long distances to the downflooding point are more common in large accommodation spaces. At first blush, it seems that rethinking this contradictory linkage is necessary. However, the space area metric also protects against large volumes of entrapped water, should the worst situation occur, that is, a failed door allowing ingress of large amounts of water from waves abeam or heavy spray.
Table 6. Subchapter K monohull ferry, risk scoring for embarkation door options
| Pathway | To & From |
Purpose and use of door ([0 – 2])
Door Location ([0 – 9])
Downflooding Potential
Area of Operation multiplier
Total risk “R” ([0-24])
DF path ([0 – 6])
Size of space doorway leads to ([0 - 3])
As defined configuration
Forward embarkation doors, port and starboard, as designed
PAX accomm. space
||
Weather
Embarkation only, closed otherwise
(0.0)
Less than [8 feet] above waterline, on deck edge, facing outboard in Position 1 (2.0 X 1.5 = 3.0)
Protected DF pathway: DF point at least [20 feet] from the door; Y < [2 feet]
(1.0)
More than 50% of main deck area (2.0)
Protected waters (0.75)
(0 + 3 + 1 + 2) * 0.75 = 4.5
Reconfigurations
Forward embarkation doors, port and starboard, recessed inboard
PAX accomm. space
||
Weather
Embarkation only, closed otherwise
(0.0)
Door sill less than [8 feet] above the main deck, inboard of deck edge, facing outboard in Position 1 (2.0)
Protected DF pathway; DF point at least [20 feet] from the door; Y < [2 feet]
(1.0)
More than 50% of main deck area (2.0)
Protected waters (0.75)
(0 + 2 + 1 + 2) * 0.75 = 3.75
Amidship embarkation doors, port and starboard, at deck edge
PAX accomm. space
||
Weather
Embarkation only, closed otherwise
(0.0)
Door sill less than [8 feet] above main deck, on deck edge, facing outboard in Position 2 (1.0 X 1.5 = 1.5)
Protected DF pathway; DF point at least [20 feet] from the door; Y < [2 feet]
(1.0)
More than 50% of main deck area (2.0)
Protected waters (0.75)
(0 + 1.5 + 1 + 2) * 0.75 = 3.4
4.2.3 Graul monohull dinner boat, Subchapter K, 127’ long, 368 passengers, protected or partially protected waters service
This is to ascertain whether the coamings could be eliminated or reduced on a risk management basis. The main deck passenger cabin has weathertight doors with 6” coamings, forward for weather deck access, and aft for embarkation and weather deck access. In this case, the reconfiguration will be to better protect downflooding points.
**Table 7. Subchapter K dinner boat, risk scoring for embarkation door options
**
| Pathway | To & From |
Purpose and use of door ([0 – 2])
Door Location ([0 – 9])
Downflooding Potential
Area of Operation multiplier
Total risk “R” ([0-24])
DF path ([0 – 6])
Size of space doorway leads to ([0 - 3])
As defined configuration
Forward weather deck door
PAX cabin
||
weather deck
Weather deck access and embark-ation
(1)
Door sill less than [8’] above WL, facing forward, in Position 2 (4)
Unprotected pathway, separation of DF point more than [20 feet] from the door, less than [2 feet] above the deck. (4)
More than 50% of main deck area (2)
Protected waters (0.75)
(1 + 4 + 4 + 2) * 0.75 = 11 * 0.75 =8.25
Partially protected waters (1.0)
11.0 * 1.0 = 11.0
Aft weather deck door
PAX cabin
||
weather deck
Ditto
(1)
Door sill less than [8’] above WL, facing aft, < 0.25L from stern, with struct. protection from water (1.33)
Ditto, except DF point is less than [20 feet] from the door
(6)
Ditto
(2)
Protected waters (0.75)
(1 + 1.33 + 6 + 2) * 0.75 = 10.3 * 0.75 = 7.75
Partially protected waters (1.0)
10.3 * 1.0 = 10.3
Reconfigurations
Forward weather deck door
Ditto above
Ditto above
(1)
Ditto above
(4)
Protected DF path, same horiz./vert. separations (1.0)
Ditto above
(2)
Protected (0.75)
6.0
Part. Prot. (1.0)
8.0
Aft weather deck door
Ditto above
Ditto above
(1)
Ditto above
(1.33)
Ditto (2.0)
Ditto above
(2)
Protected (0.75)
4.75
Part. Prot. (1.0)
6.3
The aggregate risk scores in Table 7 indicate that some form of weathertight protection is appropriate both for forward and aft doors, especially for partially protected waters service, for which the doors are designed. The deck arrangement precludes relocation or reconfiguration of the doors without serious impact. The reasonable approach is to examine reconfiguration of other risk elements, and the best accessible pathway.
The best way to reduce risk is better protection of the downflooding point. Replacing the non-weathertight door at the downflooding point with a weathertight door with a coaming would significantly reduce the risk. The downflooding path score for both the forward and aft doors would drop from 4 to 1 and from 6 to 2, respectively, as per Table 8.
Table 8. Downflooding paths, Graul dinner boat, revised scores
Note: Asterisk(*) used to highlight table provisions which apply to the dinner boat after reconfiguration
Risk scores for downflooding path
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
*Aft door: [2]
[1]
*Forward door: [1]
[0]
Unprotected
[6]
[4]
[4]
[2]
The aggregate risk scores for the aft door drop considerably, and a weathertight, accessible coaming-less door aft with a protective drainage arrangement appears to be appropriate for both protected waters and partially protected waters service.
The forward door has significantly lowered scores, but remains in need of protection against water entry. The conservative approach for safety might dictate retention of at least a reduced height (3”) coaming and designation of the aft door only as accessible for the mobility-impaired. This would provide the embarkation pathway and the accommodation of access to the weather deck. The fore deck would remain available to other passengers for embarkation and access during voyages. There would be benefit to the operator here as well in the reduction of the barrier for able-bodied passengers.
