INDEX - TECHNOLOGYwww.islandbreath.org ID#0808-06
SUBJECT: STRUCTURAL DESIGN OF HSF
SOURCE: JUAN WILSON firstname.lastname@example.org
POSTED 9 APRIL 2008- 7:45am HST
Hawaii Superferry Structural Problems
image above: stern view of the Alakai in Mobile AL as published in HSF onboard Magazine Hahalua
Note: complexity of transom area where jets, Humphree devises and rudder intersect
by Juan Wilson 8 April 2008 Revision 5.0 080409
A WOLF IN SHEEP’S CLOTHING
The Hawaiian Superferry Alakai was built for the HSF Corporation by Austal USA in Mobile Alabama. This is a subsidiary of the Australian ship builder. The Alakai was one of two sister ships in a contract costing approximately $180 million dollars.
When Austal was first consulted to design a civilian ferry operation in Hawaii, they recommended a smaller ship than today’s Alakai. This was due to the fuel efficiency needed to make its operation profitable. Austal was over-ruled.
The Alakai is the largest all-aluminum hull built in the U.S. It has four ten-thousand horsepower diesel turbines to provide thrust. It is not unlike a high performance fighter jet in is configuration. It uses a similar structural premise:
Create a series of light metal frames and “skin” them with a thin metal sheets that produce a aerodynamic (or hydrodynamic) form. At the rear-end provide much turbine thrust as is possible, regardless of price, and train some pilots to keep these craft from crashing into things.
It is clear that the connection of this project to navel strategic planning negatively affected the ships implementation as a civilian ferry. But, the board of the Superferry corporation was stacked with Navy representatives, which includes its chairman, former Reagan Navy Secretary, John F Lehman. For the past three decades Lehman has pushed for a doubling the number of Navy vessels and creating a new kind of warship fleet in the process.
From the beginning the Hawaii Superferry’s core function has not been to be a profitable private ferryboat business. It is, in fact a working prototype of what Lehman has been dreaming about for a military Joint High Speed Vessel (JHSV). This explains why the partnership with the Army’s Stryker Brigade and Navy are an integral parts of the HSF planning. In the need to satisfy the Navy, Army and civilian specifications, the Superferry may have become badly compromised.
THE FLOATING BRICK
This has happened many times when a new weapons platform has had to fulfill too many promises. It certainly happened with the F-18 Fighter/Bomber which was laid at Lehman door. He knows something about getting something you don’t want shoved down your throat. In the fall 1982 Mary Ann McGivern wrote about the F-18 program in The St. Louis Economic Conversion Project (page 199 of (http://sdi.sagepub.com/cgi/pdf_extract/14/2/199):
“The plane was designed as a cheap compromise for the Navy and Marines each having their own air support (needs)... One gets the sense that the F-18 has been thrust upon the Navy... Secretary Lehman threatened to cancel the contract unless McDonnell-Douglas’ price went down instead of up... The Navy says the plane is not a good attack vehicle... it had too much roll, too much fuel consumption, too heavy, not enough cruise range, and troubles with the fuselage. McDonald-Douglas (The builder) says that a lot of the Navy's criticisms, including the current ones, are of factors that were never in the design specifications. Such a reasonable response will not make the Navy like the plane.”
The F-18 earned it enmity of the Navy and their complaints about it sounds a lot like a description of the Superferry JHSV. A “floating brick” instead a “flying brick”
Lehman and his Navy cronies went ahead designing their JHSV anyway. Austal did what it was told. For example, with a few tricks (like providing no on-board vehicle ramps) they got around the necessity of a DOT triggered EIS requirement
BLIND MEN FIND AN ELEPHANT
Austal used several individual computer software packages to engineer the form-factor, structure, performance and details of the vessel.
Some main components were:
Software Purpose Ship Constructor 3D modeling for production Workshop Structural Design Hull Speed Hull Resistance Strand7 Finite Element Analysis Ansys Finite Element Analysis MaxSurf Surface modeling HydroMax Hydrostatics Shipflow Computational fluid dynamics StarCD Computational fluid dynamics Comet Computational fluid dynamics SWAN Wave wash prediction MathCAD Formulas AutoCAD Drawing
It is clear that, as with most modern engineering programs, many design components have to be handled with separate computer software packages. “Virtual” ships have to be built and tested as theoretical models for each package. Integration between software packages may, or may not exist. When a single company provides specialized integration between two of its products, things often work smoothly. That would be the case with MaxSurf and HydroMax that are both provided by Marine Survey and Design Company to work with each other ineractively. This may not be the case with results of integration between Shipflow and Hydromax.
It is not dissimilar situation to several blind men coming across an elephant and each “seeing” a different beast based on that part of the elephant his hands have touched. Not only will they see different animals, but the blind men may never reach all parts of the elephant. As a result they could be very surprised when confronted with unknown features.
Individual software programs can have the same failure of observation. This is likely in complicated projects with many parts that are pushed to the limits on tight schedules.
ROCKET PROPELLED EGGSHELL
It is my opinion that too much stuff is going on in the narrow confines of the stern of each catamaran hull. The transom of each is penetrated with two wide diameter water-jet thrusters that swivel to steer the ship. There are also penetrations for hydraulically operated Humphree devices (steering brakes) as well as a penetration of the hull between the water jets for a rudder shaft.
This complexity of systems for steering the Superferry are to keep the large hull from slewing and fishtailing as it tears through the ocean. It is likely that a smaller ship operating a lower speed would have been able to use a simpler set of controls. Each of these steering device’s “violates” the integrity of the hull and will cause hot spots of stress when the ship is twisted, bent and shocked by a succession of massive waves that are found throughout the Hawaiian Islands during much of the year. Metal fatigues, yields and fails under such repetitive conditions. Misfortunes that have been publicly reported include:
The first failure were at the seams around the rudder post penetrations. These rudders were not so much used for steering as for stability through the water. Stress on the posts created cracks that allowed some water to enter the ferry's hull. This was how they realized there was a problem - leaks. The ship would have to go to dry dock for repairs.
More bad things began to happen. In the process of getting the Superferry to the dry dock it was run aground. A push by a tug would be needed to free it. The tug operator gave the Superferry a shove and was surprised to have caved in a twenty foot section of the hull. Too delicate.
The trouble was not over. Once in the dry dock facility the Superferry keel was blocked in preparation to support itself out of the water. Some of the blocking was not precisely line on on framing points and when the Superferry was raised out of the water its keel failed to support the ship’s own weight and portions of the hull failed.
Overall, the results of the design program made for a Superferry that was too big and too fragile a vessel. It has too much speed and fuel consumption for the routes it would sail. The Superferry was guaranteed never be profitable as a civilian ferry. But worse, it would never be robust enough to handle the open Pacific swells it would find itself plying.
And, sadly for Mr. Lehman, this Superferry will not meet the rigors of military duty. It is designed like an eggshell with a rocket engine. I’m sure there are many changes that will be made if Austal get the next JHSV design contract. They sure will have the advantage of having been paid to build a full scale working model and testing it on some guinea pigs who live out in the middle of nowhere.
Island Breath: Superferry Rudder Damage 02/05/08