Moffatt & Nichol, Theodore W. Bell, P.E.
Office of Technical and Information Services Architectural and Transportation Barriers Compliance Board 113 F Street NW Suite 100 Washington, DC 20004-1111
Re: Revised Draft Passenger Vessel Accessibility Guidelines and Supplementary Information (dated July 7, 2006)
Ladies and Gentlemen:
As a member of the Passenger Vessel Association, Moffatt & Nichol submits these comments on the Revised Draft Passenger Vessel Accessibility Guidelines and Supplementary Information (dated July 7, 2006). As background, I will explain that I am the practice leader for Moffatt & Nichol in the area of waterborne transit. A specialty area of this practice is the planning and design of ferry terminals and related waterfront facilities. In this role, I currently oversee Moffatt & Nichol’s engagements in the planning and design of fourteen ferry terminals --nine of which are located in the USA.
Previously, I directed Washington State Ferries’ Terminal Engineering Department and participated with other WSF staff in development of WSF’s ADA transition plan in the early 1990’s. I’ve worked on a multitude of ferry-related projects at thirty-two ferry terminals, again, primarily in the USA. Over the years I’ve become very familiar with the ADA issues affecting the design of ferry terminals and in particular, the interfaces between the ferry terminals landside facilities and the ferry vessel. My comments will focus on this interface.
First of all, I apologize for all of the technical detail. I realize it is a lot to wade through. This is an important subject to me. I’d be glad to answer any questions or explain further, or in person if that would be helpful.
Page 9 of 122, V208 Passenger Vessel Boarding – I believe the intent of the passenger vessel guidelines with respect to landside facilities is to address ADA accessibility issues for passenger vessels and not to address all general building code issues affecting landside facilities. I suggest the guidelines clarify that they are an overlay to locally accepted building code guidance --such as the International Building Code (IBC), or locally adopted building codes. Keep in mind that all landside facilities will go through some kind of building permit/approval process. The building permit/approval process will typically fall under the jurisdiction of the local building official, or in some cases the local port authority or the state department of transportation. The designer of the landside facility and the local jurisdiction official need to understand exactly what the passenger vessel guidelines cover and do not cover. An example of how this comes into play can be taken from the design issues associated with handrails. The Passenger Vessel Accessibility Guidelines address the requirements for a handrail, however they are silent on the requirements of the associated “guardrail” (the guardrail provides safety protection from a fall and codes such as the IBC define height, opening size and strength requirements for guardrails). The designer of a ferry terminal needs to put the two together in order to have a coherent design for a rail system.
Page 19 of 122, V104.1.2 Slopes – The draft guidelines state that all slopes are measured when the passenger vessel is in a static condition with a design trim and heel. I’m sure this definition is well intentioned. However from a practical standpoint, it is unclear and could easily result in an undesirable design for the gangway ramp portion of a passenger boarding system.
First of all, there are three types of slopes or conditions that typically come into play in the design of a gangway ramp for a passenger boarding system. (I’m not talking about fixed ramps, rather I am discussing below movable gangway ramps that rest on at least one floating body and move up and down with the vessel or a floating dock.) The three conditions are: 1) the slope of the gangway ramp between the landside facility and a floating dock (if a floating dock is employed); 2) the slope of the gangway ramp between the landside facility and the vessel; and 3) the slope of the gangway ramp between the floating dock and the vessel.
Addressing the first and second conditions, I don’t think it is the intent of the guidelines to indicate that the slope of the gangway ramp between land or a fixed pier and the floating dock or vessel be measured in a static condition. The slope of this type of ramp is affected by the tides; seasonal, weather-induced or manmade adjustments to the water levels on rivers and in lakes; and the pitch and roll of the floating dock or vessel. Due to these factors, the height of the deck of the float or vessel relative to the fixed point on land, where the ramp attaches, can vary by a few inches or many feet. The difference in height between the two affects the ramp’s slope. I think it is the intent of the statement on page 19 to only apply to the slope of a gangway ramp connecting the vessel with a fixed pier or floating dock. Further, I think it is the intent of the statement to only apply to the dynamics associated with the movement of the vessel. This in itself is problematic, as the “design trim and heel” of the vessel is not universally interpreted the same way by vessel designers and vessel operators. Is this the light boat trim or the heavy boat condition? Are we talking about trim conditions developed for theoretical stability calculations for the Coast Guard, or real life conditions of trim? Even if these questions can be answered, below I will discuss why I think it is not practical to measure slopes under static conditions. Additionally, I believe the passenger vessel accessibility
guidelines need to clearly address the slope of the gangway ramp under the conditions where it provides access directly from shore and is affected by the dynamics of tide, changes in water level and changes in vessel freeboard.
Even in the case of the statement on page 19 applying to gangway ramps connecting to the vessel, there are still problems with the draft guidance as written. First and foremost for purposes of safety, I think everyone would agree that the gangway ramp must be designed for the dynamic conditions it will experience. Regardless of what might be deemed as an acceptable slope from the view point of accessibility, the ramp must stay connected to the dock and the vessel during passenger boarding. The dynamic conditions encountered by a gangway ramp connected to the vessel include the yaw, pitch, roll, surge and sway of the vessel (see figure below) and also the yaw, pitch, roll, surge and sway of the floating dock (if a floating dock is employed as part of the passenger boarding system).
An additional dynamic that the gangway ramp designer must account for is that the vessel will change freeboard depending on its state of passenger loading and provisioning. If more than one class of vessel calls at the dock (as is commonly the case), additional freeboard variations will be introduced. The vessel freeboard might change by a few inches up to a few feet in some cases. Finally, if the ramp to the vessel connects to a fixed pier, then changes in tide or water level constitute a dynamic consideration for the ramp designer.
Given all of the dynamics, the designer often needs the gangway ramp to be deployed with some initial slope to allow for the relative movements between the structure the ramp is hinged to and the vessel. There are many types of ramp systems, but a common type rests the ramp directly on the vessel deck. For this type of ramp, the initial slope of the ramp is typically introduced in a downward direction to the vessel such that the gangway ramp can always lie on the vessel deck and not become high-centered on the vessel coaming.
To design the ramp, the designer would like to know the maximum slope that is acceptable from a safety standpoint and from the standpoint of accessibility. (Many passengers will walk across the ramp over its life and the designer will want to be able to show they followed accepted codes and standards in design of the ramp should there ever be a claim of injury.) The statement on page 19 of the draft guidelines that slopes are to be measured in the “static condition” becomes problematic to the designer. To determine the slope of the ramp, the designer begins with estimates of the relative movements between the structures or floating bodies at each end of the ramp. To determine the length of the ramp, the designer would like to know the maximum acceptable slope. For example, if the sum of the relative motions plus the change in vessel freeboard the ramp will face equaled (arbitrarily) one foot, and the designer used guidance on safe ramp slopes available in the International Building Code (IBC) or Uniform Building Code (UBC), the length of the ramp could be understood. The IBC and UBC set a maximum slope of a ramp as 1:8 for safety reasons. With a one foot height differential and a maximum slope of 1:8, the ramp would need to be at least 8 feet long. This was determined taking into account the dynamic conditions.
It is important to understand that the ramp in the example above will only be at the 1:8 slope momentarily and at the extreme dynamic condition. When the height differential is less between the ramp hinge point and the vessel, the slope will be flatter than 1:8. I think this is why the committee that drafted the passenger vessel accessibility guidelines introduced the statement on page 19. However, as written, I think the guidance goes too far and it leaves the designer with little to fall back on. A compromise might be that the slope for the gangway ramp be established as a maximum of 1:8 under dynamic conditions. In my experience, this would provide both a safe and accessible ramp under most conditions. I realize this is steeper than the 1:12 slope that has been long accepted in design of accessible facilities. However, it is a transient condition and for the most part, slopes would be closer to the 1:12 standard. Again, I am only proposing this for ramps that are moveable and provide the interface between floating bodies and shore. Fixed ramps located at landside facilities can generally be designed with 1:20 slopes or
1:12 if intermediate landings are provided.
Page 78 of 122, V413.2 Slope, Exception 4 – This exception needs to be written more clearly. I believe it is the intent of the exception to limit the length of a pier provided gangway. The first question, is that referring to a gangway attached to a fixed pier? Or does it also include a gangway between a fixed pier and a floating dock (that is part of a passenger boarding system)? How about a gangway from a floating dock to a vessel? I think the intent is for all of the above, but this should be clarified.
Exception 4 mentions the total length of a gangway run or series of gangway runs. If this total is at least 120 feet, then it states that section “V413.2 Slopes” does not apply. (I assume the intent of the exception is to refer to Section V413.2 and not Table V413.2.) First of all where does the gangway run begin? The overhead passenger walkway I designed at the Washington State Ferries ferry terminal at Edmonds, Washington in the mid-1990’s begins ramping up in the air from a location onshore several hundred feet away from the vessel (see photo).
The Edmonds passenger ramp climbs from the level of the shoreline to the level needed to access the passenger deck of the vessels. Since the ramp is well over 120 feet long (the movable portion at the vessel end on the left side of the photo is about 135 feet in itself), would fall under the exception and NOT need to comply with slope standards if designed today? I hope not.
I believe it is the intent of Exception 4 to set a reasonable upper limit on ramp length. I suspect the exceptions were developed as a way to get away from the economic justification clauses in prior drafts of the ADA guidelines for passenger vessels. Unfortunately, I don’t think the guidance is currently written clearly enough. There are two problems with the current language: 1) the language allows too many landside facilities to meet Exception 4. (It would be very common to have a series of runs equal a length of 120 feet – depending how the runs are measured); 2) the exception does not give guidance on what to do if the 120-foot rule is met. That is, it says the slope requirements in V413.2 shall not apply. So what does apply?
There are nuances to this whole issue of Exception 4 that I will not explain in detail. The exception is based on ramp length, but ramp slope for movable ramps (like those used to access the ferry or a floating dock) is not only a function of ramp length, but it is also a function of the elevation of the ramp hinge point. I won’t go into all of the details, but two ramps of the same length, can have dramatically different slopes depending on where the ramp hinge is set in elevation.
My recommendation is to get way from setting a maximum ramp length. It appears that the intent of the exception is to set limits on the size and expense of landside facilities. This is important because ferry operators have finite financial capabilities. It is also important because the shorelines are highly regulated and all shoreline structures receive intense scrutiny from the standpoint of environmental impacts. If the landside structures become too large, they also become too expensive and too difficult to permit.
From a practical standpoint, the need for a long ramp is almost always driven by a situation where a lot of tidal variation is prevalent. Many of the ferry projects I have been involved over the years included ramps in the 100 foot to 150 foot range. These ramps were developed in the absence of finalized federal guidance on ADA accessibility for passenger vessels and took into account the tides. I’ve found that ramps of this length are feasible from cost and environmental standpoints. I can understand setting an upper boundary. My recommendation would be to set a maximum ramp slope of 1:8 for pier provided movable ramps based on assessment of dynamic conditions such as tide. My belief is that ramps used by the public to board passenger vessels should not exceed a slope of 1:8 for safety reasons alone. I would then set a desirable guideline for slopes of pier provided movable ramps of 1:12 --again based on dynamic conditions. (Fixed ramps, including a series of runs of ramps, can easily be designed for 1:12 slopes with intermediate landings, or 1:20 slopes without intermediate landings.)
Thank you for the opportunity to comment on these draft guidelines. Feel free to contact me my phone at 206-622-0222, or by e-mail: tbell@moffattnichol.com if you have any questions.
Sincerely,
Theodore W. Bell, P.E.
MOFFATT & NICHOL
Director of Waterborne Transit
Associate Vice President
710 Second Avenue, Suite 720, Seattle, WA 98104, Phone: 206/622-0222