Response: OIA2020.24
10 July 2020
To Brent Yardley
Via FYI.org – [email address]
Dear Brent
Official information request for information on the new ferries
I refer to your official information request 4 June 2020, and copied below -
…
with respect to the wake issue, how has it been determined that the new vessels
will produce less wake than the current ships? Given that the new vessels are
proposed to be twice the size this would appear to present a significant design
challenge. It would also appear to be a significant risk to the project and the
Marlborough Sounds environment if the ability to complete three return trips per day
is in jeopardy. Are there plans to verify real-world wake generation from these
vessels? is ISO 31000 being employed to manage risk in this regard? And can any
documentation concerning this aspect of the vessel design and performance please
be made available?
As you will be aware, the key component of the iRex project is to procure two new sister
ships which will be bigger, cleaner and more efficient that the current three ferries, with
modern propulsion technologies to improve manoeuvrability and reduce wake energies.
KiwiRail has commissioned the development of a concept design for inclusion as part of the
recent closed tender for supply of the new ships. The concept design will be the reference
for the shipyards designer to develop the actual design that will be built.
At the concept design stage, a number of functional/performance requirements are
considered/verified in order to ensure that the actual design of the new ships could meet or
exceed the set requirements.
The concept design includes the development of a hull form that, through a number of
design iterations, is optimised for efficient speed & power, seakeeping, manoeuvrability. This
includes the specification that ferries will be capable of three return voyages per day –
assisted by terminal design development to enable 60-minute turnaround times.
In our case another key performance requirement for the hull design is to comply with the
regulations on wave energy in the Marlborough Sound – Tory Channel and Queen Charlotte
Sound as per the Marlborough Sounds Resource Management Plan.
The design brief included the following requirements in relation to wave energy in the
Marlborough Sound:
• The new ships hull to be designed to meet the wave energy regulations in the
Marlborough Sounds Resource Management Plan.
• The new ships hull to generate equal or less wave energy of the existing consented
vessel Kaitaki in the Tory Channel and Queen Charlotte Sound.
• The wave energy to be calculated using one of the approved methods of calculation to
demonstrate compliance with the above-mentioned regulations.
• The wave energy methodology to be reviewed and approved by the Marlborough District
Council (MDC).
• The approved methodology to be complied with by the contracted shipyard to enable
KiwiRail to apply for resources consent for the actual hull designed and built by the
contracted shipyard.
The updated concept design, in relation to the wave energy compliance, was calculated by
computational model that uses the RANS (Reynolds Average Navier Stokes) computational
fluid dynamics (CFD). This is one of the calculation methods allowed by the Marlborough
Sounds Resource Management Plan
The results showed that the concept hull would generate less wave energy of the consented
vessel Kaitaki, with the optimisation of the principal dimensions of the concept vessel being
length at waterline, draught and beam was the reason for the result – more efficient hull form
than Kaitaki.
While the above point of a larger ship producing less wave energy than a smaller one (some
220 meters long compared to 180 meters) may be counter intuitive, it is possible by
optimising the principle dimensions, which have been refined during the design process with
the development of seven versions of the hull form.
The proposed methodology for calculating the wave energy on the new ships including
additional validation methods to CFD calculation were reviewed and agreed with the MDC.
The methodology is included in the RFP technical documentation; however, these
documents are currently withheld under Section 9 (2)(b)(ii) as the closed RFP process is
underway. More information on the concept designs will be made available when possible.
We trust this answers your query; however, any further questions please get in touch.
You have the right to seek an investigation and review by the Ombudsman of this decision.
Information about how to make a complaint is available at www.ombudsman.parliament.nz
or by calling free-phone 0800 802 602.
Yours sincerely
Dave Allard
Government Relations Advisor, KiwiRail
