Updated:
Ocean Class Research Vessels:
Questions and Comments regarding the X-Craft
Over the past
few weeks, questions and comments regarding the X-Craft have been circulating.
These messages have been compiled and are provided below.
Please review the material below.
These questions/comments are being forwarded to the Navy and JJMA for
further consideration. Additional
questions and comments are welcome and can be sent to the UNOLS Office office@unols.org.
Additional
Information about the construction of the X-craft can be found on the Nichols
Bros. Boat Builders website at <http://www.nicholsboats.com/current_projects.htm>.
Letter
from RVOC:
DATE: October 29, 2004
TO: Dr. Peter Wiebe, Chair, UNOLS Council
Dr. Dave Hebert, Chair, FIC
Mike Prince, UNOLS Office
FROM: Tim Askew, Chair, RVOC
RE: RVOC input on X-Craft
The RVOC membership discussed the X-craft hull form as proposed by Admiral Cohen at the UNOLS annual meeting earlier in October. For the purposes of discussion, it is assumed that the R/V version of the X-craft would have a standard diesel propulsion plant giving a lower top-end speed and higher endurance. It is also assumed that arrangements details can be worked out as desired, such as adding an open aft deck section, location and number of permanent labs, location and number of portable mission modules (vans), and location/type of handling systems.
The UNOLS community will have to work with whatever hull form is decided on for thirty or more years. The following is a list of questions and concerns raised by the RVOC membership that we feel should be carefully addressed before any decision is made.
1. Experimental Hull Form: Concerns were raised about structural problems developing after delivery.
a. Has a finite element analysis been conducted?
b. Can the structural design meet commercial/ABS standards? Is the Alaska Ferry FAIRWEATHER classed?
c. Have insurance costs been addressed for an experimental craft?
2. Weight Sensitivity: It is assumed that the hull form is somewhere between a mono-hull and a SWATH with regard to weight sensitivity.
a. Because of mobilization needs in foreign ports, the vessel will need to carry several cruises worth of gear. Will this be possible?
b. What is real scientific payload after taking out fuel and other factors normally considered “payload” by the Navy?
c. How location sensitive is this hull form compared to a SWATH?
3. Station Keeping: Hull forms designed for speed normally don’t perform well on station, which is a significant part of an R/V’s mission requirement. The RVOC membership recommends the following:
a. Evaluate the Alaska Ferry FAIRWEATHER for station keeping ability. FAIRWEATER appears to be the only commercial X-craft in operation that is readily accessible, and an opportunity for field evaluations should be pursued. This vessel normally operates only on sheltered waters, so chartering it for a day offshore for trials in a significant sea state would be desirable.
b. Damping systems as proposed by Admiral Cohen tend to be complex and expensive. Are these realistic alternatives?
c. The user community for the R/V WALTON SMITH should be approached to evaluate pros and cons of the catamaran hull form for science ops in higher sea states. The captain and crew should be interviewed to see how they have overcome the unique vessel motions associated with catamarans. This may necessitate a rethinking of how to position an X-Craft type vessel to perform science operations – for example, working beam to the seas as opposed to the conventional stern/bow into the seas. The captain of the WATLTON SMITH should be included in any trials of the FAIRWEATHER so a meaningful comparison can be made.
4. Endurance: What is actual endurance with a conventional power plant? Specific mission scenarios from the Ocean Class SMR’s need to be compared to this endurance.
5. Necessity of High-Speed Hull Form: It has been shown time and again that science operations do not require high vessel speeds. It is apparent that federal funding constraints cannot support the cost associated with high speed transits – the only scenario where high speed might be desired. Because of these facts, there is a glaring disconnect between the proposed hull form and mission/cost constraints. It would seem imprudent to de-rate a high speed platform for the sake of having an innovative design.
6. Larger X-Craft: The JJMA presentation noted that it would take a 2400 ton version of the hull form to fully meet the Ocean Class SMR’s. Admiral Cohen stated that 1800 tons was the Navy target for an R/V. How close would this be in meeting the SMRs? It is understood that this would translate into no change in gross dimensions, but only that the hulls would get wider. How much wider, and how does this affect the hull efficiency and vessel motions?
7. Manning/Operating Costs: The JJMA presentation indicated a crew of 20-21 as opposed to the 11- 13 on the current UNOLS Intermediates. It is therefore assumed that the vessel will be USCG inspected with an operating cost closer to the current Global class. Manning requirements should be considered in detail.
8. Vessel Profile: The proposed X-Craft looks like military vessel with a rather “hostile” profile. Given the foreign waters this vessel would have to operate in, the look should be “softened” so it appears more like a benign research vessel.
Additional Questions/Comments from FIC,
Council and Ocean Class members:
SMR Comparison
Study – A
study comparing the capabilities of the compromise version of the x-craft
(~1800 tons) with the Ocean Class SMRs is requested.
General-Purpose
Oceanography Support - How
will the x-craft be used to support tradition oceanography day-to-day operations?
For example, how would one do a piston core, a CTD cast, launch/recover
and tow a towed vehicle, launch/recover an AUV or ROV, tow a MOCNESS net,
do a multi-core, perform a trace-metal bottle cast, deploy and recover a mooring,
and so on? Clearly articulated plans for carrying out
these science operations should be in place as early as process so that they
can be considered during the hull decision process.
Economic needs/use
analysis - How
much will it cost to maintain and operate versus traditional hull form, AND
what really is the benefit in terms of additional work performed in getting
between station occupations faster given that a lot of our observations are
now made underway (we rarely are engaged in pure "deadheading"). An "economic" needs/use analysis
is recommended.
Future Navy
Research Missions - To
what extent are future Navy research requirements not reflected in the many
'futures' documents and reports that the science community has generated over
the past 5 years? Considerable science
input to the SMRs came from scientists who have been active in ONR research
for many years. Is the vision of
future capabilities derived from that direct experience with modern (sometimes
'cutting-edge') technologies significantly different from the capabilities
needed to support future Navy research?
Stability at
High Speeds – There have
been reports that it is difficult to walk/move-about during high-speed transits
on the high-speed ferries. If this
is the case, it is very unlikely that the scientists can carry out sample
analysis between stations when transiting at high speeds due to this problem
and the lack of time (created by shorter transit times). Recommend an analysis of high-speed ferry transits,
which should include actual high-speed ferry ride.
Maintenance
Cost for Aluminum Hull – There
is concern that an aluminum hull ship requires more expensive, and specialized,
shipyard work to perform standard maintenance. Recommend a comparative analysis of maintenance
costs between an aluminum hull vessel with steel hull vessel (perhaps POINT
SUR and WESTERN FLYER).
High-speed
Underway Data - As the community
demands that more underway data be collected on transits (multibeam, ADCP,
and Met have been all cited recently by groups), high speeds can make these
instruments ineffective. Recommend
an analysis of system performance of science instrumentation when used at
high speeds.
Transit time, speed, and
Productivity Rates (email discussion)
–
Question (Bob Knox) - Do you know the origin of the
23% transit time figure that appeared in Frank's presentation re Oceans Class
hull form comparisons to UNOLS last month? The slide says that the 23% excludes "sonar survey at <
12 knots," but I'm wondering if it includes steaming and collecting ancillary
data while doing so – in which case some of that ancillary collection of,
e.g., multibeam data would be compromised by going at very high speed.
What does "productivity
rate" mean on that same slide?
Response (Freitag, John)
JJMA came up
with transit figures based on the mission scenarios in the
SMR document.
Personally I might take issue with some of the assumptions and might arrive
at different percentages but it is based on transit scenarios assuming no
survey taking place during transit, save possibly underway met and flow through
measurements, certainly no multibeam.
The "productivity
rate" refers to using the time gained as a reduction of overall mission
time and thus the percentage of "extra" mission work which can be
accomplished by a reduction of transit time.
Response (Dan Rolland)
Good questions - let's see if I can
explain what I did.
First of all, when the X craft is transiting
at high speeds (26 or 40 knots), it was assumed that minimal science would
take place - basically, just strap everybody and everything down and take
off for the next station. Your point
about lost ancillary science during the transit is a good one. Certainly, sonar survey would not be possible
because of sound speed limitations in deeper water and the increasing self-noise
from propulsors and hull wake. I
believe the T-AGS 60 ships are able to perform multibeam surveys up to 14
or 15 knots depending on the bottom type, water depth and sea state, but they
are a bit quieter than the global AGORs.
They also aren’t constrained as much by fuel cost considerations.
We haven't looked at X craft seakeeping characteristics at high speeds, so I don’t know what the ride quality would be like and how personnel might be impacted. Also, the X craft structural design may require that speed be restricted in higher sea states.
Now, on to the calculations:
The SMR-defined typical missions break
down as follows (this is copied out of Excel, hopefully readable):
So, 61 days out of 247 total at-sea
are transit. Then I threw in another
23 days for science party loading and unloading to get 270 total operating
days for the year.
61/270 gives 23 percent as the portion
of the operating year devoted to transit. Obviously, this assumes all ten of the missions occur in a typical
year. It's probably safe to assume
no one ever has a "typical" year.
The X craft reduces the total days to
complete the ten sample missions to 204 (when transiting at 40 knots) and
214 (when transiting at 26 knots).
When comparing productivity, I looked
just at mission days and didn't include any pierside days. That's the difference in the numbers. In retrospect, I should have been consistent
and included the pierside days – they have the effect of slightly reducing
the productivity gain. That would
bring the productivity of the 40-knot ship to 1.19 and the 26-knot ship to
1.14
The numbers compare as follows (again
copied out of Excel, hopefully readable):
Fuel Consumption:
As
far as fuel consumption goes, the 107,000 gallons is the per-day requirement
for the larger X craft (2400 tons) when running at 40 knots. The smaller one (1400 tons) requires about
54,000 gallons per day.
It is important to note that this exercise looked only at productivity gains of higher speeds and did not adjust the designs to accommodate the higher required fuel loads. So while the 40-knot transit speed improves productivity, in reality, the present designs can’t carry enough fuel to run at that speed very long. The mission profile for ONR’s X craft includes only about 5 hours at top speed and the rest at about 20 knots. 107,000 gallons of fuel is approximately 287 tons – which would last for only a couple of days at 40 knots. Even running at 26 knots requires about 23,000 GPD for the 1,400 ton X craft and 44,000 GPD for the 2,400 ton version.
The annual fuel cost calculation was done basically as you guessed. For each mission, the SMRs give number of days (or NM covered) in transit, survey, towing, or on-station modes. I calculated fuel consumption for each mode, multiplied by the number of days each, and summed up for the whole mission. Then I took an average per day fuel rate (assuming each mission has equal likelihood of occurring) and multiplied by 240 days of at-sea operation per year. Fuel cost was assumed at $1.75 per gallon.
So you get 19% greater production, but at 7 times the fuel cost. The X craft design certainly may be more efficient than a conventional ship at high speeds, but it still doesn’t eliminate the extremely high premium required to go fast.
Comment (Bob Knox)
Dan - thanks.
Very thorough and exact, as we've come to expect from you.
One of the key points is that in order to carry enough fuel to make
any significant use of the high-speed transit option, the ship would have
to be enormous/have enormous tanks. In
oceanographic work we seldom transit to a single-point work area, do our thing
there, then transit to the end port (and refueling).
More commonly a few work areas - or a whole transoceanic series of
work areas (stations) - comprise a cruise of a few weeks, so one would have
to carry "transit fuel" enough to move fast between all these areas/stations
for the speed advantage to be of practical use. Not very likely. I infer
that the military mission in mind for X-craft is more like the (oceanographically)
rare transit-single work site-transit-end model: a single "work"
site sandwiched between two high-speed transits.
Comment (Mike Prince)
All of this
discussion is leading me to think that there are certain circumstances when you
might use the very high speed, but they would most likely be much less than 23%
of an operating year.
There may be
a higher percentage of times when a somewhat increased speed would give you an
advantage, if you could do multi-beam or flow through/met surveys at the
planned speed.
What that
speed is and whether or not you need a high speed cat hull to achieve it are
open questions. We should try to be as
exact as Dan has tried to be, but I think we should evaluate the assumptions
more carefully before we agree on the final answers.
Comment (Bob Knox)
Good
point. Remember that certain kinds of
underway sampling - anemometer and ADCP - require ship heading accuracy, and
higher accuracy at higher ship speed, so that the ship speed does not get
aliased into (create an error in) the much smaller ocean current or wind vector
that you're trying to observe. Even
with today's 10-knot ships the heading accuracy issue is nontrivial, and at 40
knots it would be 4 times harder.