Rationale for selection of
the design vessel.
Statement of Problem.
The Feasibility Report for Savannah Harbor channel deepening indicated that a
container vessel with the characteristics of the Regina Maersk would most likely be the
largest vessel ever expected to call at Savannah in the foreseeable future. That vessel
would be used as the “design vessel.” Although the Feasibility Report is dated
1998, the economic portion of the analysis was completed in 1997 and was based on 1995 and
1996 information. Since that time, the world container vessel fleet has grown in size and
number beyond anything predicted in 1996. The question now raised is whether a larger
design vessel should be used to ensure the channel can accommodate more of the larger
vessels now coming into service and expected to come into service in the foreseeable
future.
Background.
Appendix B of the Corps of Engineers Engineering Manual (EM) 1110-2-1613 describes the design vessel as,
“A hypothetical or real ship with dimensions of the largest vessels that a navigation
project is designed to accommodate.” It appears that this is a draft EM and has not
been finalized since its original publication in 1994. The version it would replace is a
1982 version that does not address design vessel determinations.
Engineer Regulation ER
1110-2-1404, Hydraulic Design of Deep-Draft Navigation Projects, paragraph 6.c. states,
“The study plan proceeds on the basis of alternate design fleets represented by a
design vessel.” It says further that selection of the design vessel is a joint
responsibility of engineering and planning disciplines, i.e., considering a combination of
safety, economic efficiency, reliability, economic justification, and environmental and
social impacts.
Earlier in the Economic
Working Group process, a proposed methodology was developed and agreed to. The methodology
was based on the Corps regulations and discussions with the Corps and at the EWG meetings.
In applying that methodology, it was found that the way in which economic information was
presented in the Economic Appendix of the Feasibility Report precluded a direct
application of the methodology developed. That is, the information in the Feasibility
Report relative to the design vessel characteristics could not be updated through a direct
comparison of information available prior to the Feasibility Report with information
obtained subsequent to the report.
At a subsequent EWG
meeting, it was decided to abandon the previously approved methodology and to develop an
analytic paper for the design vessel based on a qualitative analysis. The qualitative
analysis would include consideration of factors influencing a decision to retain a design
vessel with the characteristics of the Regina Maersk or to use a design vessel with
different characteristics.
Analysis of
qualitative factors.
1. Vessels on order.
The proposed design vessel in the feasibility report would have the characteristics of the
Regina Maersk, with a length of ___ feet, a beam width of ___ feet, and draft of 47.5
feet. A vessel with these characteristics would most likely be handled in a channel 48
feet deep, depending on results of ship simulation model studies yet to be done. In
addition, data from current vessels on order indicate that vessels exceeding 9000 teus are
being designed with drafts of less than 48 feet. Thus, based on this information, it is
likely that a channel depth of 48 feet would be able to handle almost all vessels in the
world fleet for the foreseeable future. With respect to the vessel beam and length, the
largest mega-ship now on order, 9000 teus, has a design beam width of about 150 feet and
length of 1083 feet. However, several ships with 6600 to 7000 teus have design beams of
140 feet and lengths of 1140 feet.
2. Environmental
Effects. Because of significant concerns about potential environmental impacts of
a deeper channel, the authorization was made subject to very stringent environmental
conditions. Increasing the size of the design vessel and thus triggering consideration of
a potentially deeper channel would have at least two serious environmental concerns.
First, the existing environmental concerns would be increased in intensity and presumably
be more difficult to mitigate. Second, a deeper draft design vessel with a deeper channel
would work against current federal mitigation requirements for sequential mitigation of
first avoiding impacts, second minimizing impacts, then only as a last effort,
compensating for impacts.
3. Cost. A
larger design vessel leading to a deeper channel would increase the project cost. Assuming
ultimate approval of a project, the project costs would be shared between GPA and the
federal government. There is an abundance of evidence that neither partner has unlimited
funds. A cost increase would likely work against the priority this project might receive
in state and federal funding decision processes. Competition for state and federal funding
is keen. As a result, project costs must be kept to the minimum amount absolutely
necessary to provide an effective channel. While the impact on costs of a deeper channel
would be very significant, a design vessel with broader beam and greater length would not
have nearly as much proportionate cost impact.
4. Future world fleet.
Larger vessels now being designed to accommodate growth in world container shipping are
being designed longer and wider with little increase in draft. It is entirely likely that
a channel designed to accommodate a vessel of 48-foot draft would be sufficient for the
vast majority of the world fleet for the foreseeable future. It may be necessary to
increase the length and beam of the proposed design vessel, but not the depth. Table 1
shows design characteristics of vessels now on order in the world fleet.
5. Other
considerations. Current marine design technology results in newer larger vessels
having better handling characteristics that many older smaller vessels. Thus, the limiting
condition for handling vessels in the channel may be the maneuverability of some older
vessels with shallower drafts but with less sensitive handling characteristics than the
more modern vessels. That is, the limiting channel safety design factor may not be the
largest vessels expected to call. It may be older vessels that are more difficult to
handle. This issue will be resolved through consultation with harbor pilots.
Conclusion.
This analysis indicates
that use of a design vessel with a draft of 47.5 feet is sufficient for the objectives of
the project. All the factors evaluated indicate that a 48-foot channel is sufficient for
the foreseeable future. In addition to increasing the project cost substantially, a deeper
draft design vessel leading to a deeper channel would also increase environmental impacts
and potentially work against successful resolution of current environmental concerns, and
would be in excess of the vast majority of the currently anticipated world fleet needs.
There may be some
justification for increasing the width and/or length of the design vessel. The need for a
design of greater beam or length will be determined by a closer examination of world fleet
trends with respect to vessels being constructed and planned for the foreseeable future.
At the present time, from the preliminary vessel data in Table 1, it appears that a design
beam width of 140 to 150 feet and a length of 1100 to 1150 feet would accommodate almost
all the likely world fleet for the foreseeable future. More thorough data now being
developed will be used to confirm or modify these data.
Table
1. New Container Ships
*data in feet
| Shipbuilder/Ship Name |
TEUs |
Draft |
Beam Width |
Length |
Source |
| AP Moller |
7060 |
47.6 |
140.4 |
1138 |
AAPA Advisory |
| Arafura Sea |
n/a |
45 |
n/a |
798 |
AAPA Advisory |
| Caroline Maersk |
6600 |
47.6 |
141 |
1139 |
AAPA Advisory |
| Carsten Maersk |
6600 |
47.6 |
141 |
1138 |
AAPA Advisory |
| Evergreen/Ever Ulysses |
5364 |
41.7 |
131 |
935 |
AAPA Advisory |
| Evergreen/Ever Uranus |
5364 |
41.7 |
131 |
935 |
AAPA Advisory |
| LT Usodimare |
5364 |
41.7 |
131 |
935 |
AAPA Advisory |
| Samsung |
8800 |
42.5 |
n/a |
1000 |
JOC |
| Samsung |
9000 |
47.6 |
150 |
1083 |
AAPA Advisory |
| Sea Land NY |
6250 |
n/a |
131 |
965 |
AAPA Advisory |
| USNS Seay |
n/a |
34 |
106 |
950 |
AAPA Advisory |