COPYRIGHT Tim Lovett © July 2004
A ramp would be an advantage for floor-to-floor access, during construction and thoughout the voyage. If it was used for a horse drawn cart, the slope must be kept to a minimum. But a ramp that is too gentle in slope consumes floorspace.
Modern wheelchair access slopes are too gentle for this situation. Assuming a comfortable but noticeable 10% slope, the 4.5m floor-to-floor height would require 45m of ramp - roughly across the ark twice. That's a lot of ramp.
One option might be a circular ramp set within a semi-circular bow/stern. The bow shape resembles a barrel and forms a pressure vessel structure. If the bow of the ark needs to be pointed then perhaps this could represent the stern. If the bow only needs to be blunt ended (from a sea-keeping perspective) then a barrel shape is a better pressure vessel anyway - especially when cross-laminated.
At 25m diameter, a semi-circular path gives almost 40m, which is not far off a 10% ramp slope. This less than the building code limit of 1:8 (Ref 2), but we are on a ship. Handrails would be required, along with a non-slip surface and perhaps indentations or a grid to allow horse hoofs to get a good grip.
The alternative would be a ramp with landings running across the ark. But this cuts out a lot of floor timber and interferes with corridors. Running longitudinally would require the severing of transverse structural members that hold the hull walls apart against the pressure of the sea. There is also a longitudinal limit of 7m between 'bulkhead' frames, which would turn the walkway into a multi-turn zigzag. A mid vessel solution doesn't look easy.
To save walking the people could use stairs. Several staircases and ladders could be fitted throughout the ark to gain quick access to another deck. This means a ramp location at one end of the vessel is not such an access problem, the ramps would only be used for the bigger things.
1. Recommendations for Accessibility Guidelines for Passenger Vessels: Final Report http://www.access-board.gov/pvaac/commrept/
Chapter 1. 403.3 Slope. The running slope of walking surfaces shall not be steeper than 1:20. The cross slope of walking surfaces shall not be steeper than 1:20.
|1. Recommended Ramp Slope http://www.hazardcontrol.com/rampfalls.html
The least possible slope should be used for any ramp. According to the Human Factors Design Handbook (Woodson, 1981), where space allows, a ramp slope of 1:20 or a 5 percent slope (2.86 degrees) is recommended. When the slope becomes greater, it is very taxing for most wheelchair users to "pull the hill." Thus this upper limit is a preferred slope guideline for all ramps. Although healthy, non-handicapped individuals can negotiate fairly steep (high slip resistant surfaced industrial) ramps up to 15 degrees (27 percent slope or a slope of 1:3.7), the main criteria for designing most ramps should be based on the needs of the average user, including the elderly and the disabled. While recommending a maximum ramp slope of 1:20 or 2.86 percent, this reference states that no (public) ramp should exceed about 8 percent slope (1:12 slope or 4.76 degrees) under any circumstances.
ANSI A117.1-1986 recommends that the least possible slope be used for any ramp, limiting the maximum slope of a ramp to 1:12 (1 inch rise for every 12 inches of run), equaling a percent slope of 8.33 (the decimal equivalent of slope times 100 equals percent slope) or an incline of 4.7 degrees (arc-tangent of slope equals degrees).
The Standard Building Code (1988) and the Uniform Building Code (1988) also require that ramps for the physically handicapped not exceed a slope of 1:12 (4.7 degrees), and do not allow any ramp to exceed 1:8 (7.1 degrees).
The Life Safety Code allows some classes of ramps
to have a slope as steep as 1:8 (7.1 degrees). Both the Life Safety
Code and the National Safety Council recommend that ramp slopes do not
exceed 7 degrees.