Superferry Rudder Problems - New Data

 

The following effort is based on the problems with the Superferry’s “auxiliary” rudders  first came to light on Jan. 30, 2008.  From that time on, there have been confusing and conflicting news stories.  The following analysis is an attempt to reduce the confusion.  It is based partly on data from the Austal web site.


For starters, Austal is a huge ship building company.  Most of its facilities are in Australia and Tasmania.   The newest facility - which built the Superferry - is in Alabama.


I did a quick count on the Austal web site and came up with about 30 different models of vehicle-passenger fast ferries, 48 models of passenger-only fast ferries, a few military vessels and even a few cruise ships.  That’s a lot vessels.


Probably all Austal fast ferries incorporate jet drives.


I was surprised to find that about 7 of the vehicle-passenger ferries include rudders.   Figure 1 below shows rudders from one or two of these ferries.  They may be identical or similar to the “auxiliary” rudders on the Superferry.   I assume that the other 23 vehicle-passenger ferries get by with only interceptors.

Figure 1:  Rudders on Austal Fast Ferries

On many (perhaps all) of Austal fast ferries, steering has been controlled at low speeds by water jets and at high speeds by “interceptors”.  (Interceptors are discussed under Superferry Rudder (?) Problems).   My impression is that, at least in recent years, Austal did not feel that rudders were necessary for it’s fast ferries because “interceptors” were quite adequate.   Then, for reasons that I have not looked into, Austal decided to add rudders to some of it’s ferries to assist the interceptors in high speed steering. Hence they were called “auxiliary rudders”.


The two rudders on the left side of Figure 1 appear to be rather close together which suggests to me that they are under the same pontoon.  However, it could be an optical illusion.  If the camera was far from the vessel and the picture was taken through a zoom lens, the rudders would appear to be a lot closer together than they actually are.

Auxiliary Rudder

Figure 2: Back end of Hawaii Superferry

Figure 2 is a cross section of the back end of the Superferry.  It includes a rudder which has the same shape as the rudders in Figures 1 and 2.  This is the so-called “auxiliary” rudder which has caused the Superfery’s recent rudder problems.


So, in view of these problems, why have we not heard about rudder problems with Austal’s other fast ferries??  A few possibilities follow.


1. Rougher waters in Hawaii leading to higher stress on critical parts.

2. No publicity for rudder problems with other Austal fast ferries.

3. Better rudder design and workmanship on fast ferries built in Australia compared to the Alabama-built Superferry.

4. Pilot or computer error:  The Superferry has both interceptors and auxiliary rudders.  Both appear to have the same function which is to control high speed steering.  Maybe the pilot or the complex computerized steering system got confused by this redundancy and the auxiliary rudders ended up doing most of the work which increased the stress on the auxiliary rudder posts (more on this below).

5.  Maybe an auxiliary rudder on the Superferry hit a whale.


We have been getting lots of bad information from HSF representatives about the rudder problem.   so it is hard to get an accurate picture.   However, I think the following explanation is consistent with news stories and with HSF’s less confusing statements.








The crude diagram above shows side and end-on views of a rudder and rudder post which resemble the auxiliary rudder on the Superferry. The rudder post extends upwards thru a hole in the hull. The diagram includes a gasket around the rudder post to permit the post to rotate in the hole. Any unbalanced force on the rudder will put stress on the rudder post. This will tend to tilt the rudder post and put a torque on the hull of the pontoon where the rudder post passes through. The end-on view at the right of the diagram shows an exaggerated view of the tilted rudder pole. The jagged lines represent stress cracks in the hull. Whenever the rudder is being used to turn the vessel, there will be an unbalanced force on the rudder as indicated by the arrow. This is normal. However, if the hull is poorly designed and/or constructed, it may not be able to withstand the torque produced by the rudder post. The gasket will be damaged first and then the hull will start to give way. An unbalanced force on the rudder could also occur in high seas when the vessel is rolling or pitching and the rear of the vessel comes crashing down into the water. However, the details are way beyond my ability to understand. The important point is that any unbalanced force on the rudder will cause a torque on the hull at the point where the rudder post passes through. However, damage would only occur if design and/or construction criteria did not take realistic operating conditions into account. This includes the operation of the Ferry in high seas. It would probably not include the possibility of the ferry hitting a whale. In the present case, HSF representatives stated that the Superferry’s rudder problem was discovered when water was observed which had flowed upwards into the hull from “hairline cracks”. This sounds suspicious because, by definition, “hairline cracks” are extremely small and water would flow through them very slowly. It might even be normal for a little water to flow upwards through the gasket. My guess is that the cracks were larger than “hairline” when they were discovered and that HSF representatives were trying to minimize the seriousness of the problem. The term “surface crack was also used in some news stories. So what is a surface crack?? How deep does it go?? If it is really only on the surface, water would not flow through it. So, again, do the statements about “hairline cracks” and “surface cracks” sound suspicious?? Anyhow, in an e-mail probably dated Feb. 4, I wrote: “Rudders would always stick down into the water and would add to the vessel’s drag – reducing the ferries already poor fuel mileage. To minimize this effect, it would be reasonable to make the rudder and supporting posts as thin as thought practical. Thus, if the rudder should strike a whale, it might easily crack. In fact, an auxiliary rudder could be one of the weakest underwater parts of the Superferry.” Part of my statement above is wrong. When I wrote it, I had only limited information and I assumed there was more than one post supporting the auxiliary rudder – in which case the supporting posts could be fairly thin. But in the case of the Superferry, the rudder post was clearly very strong and the rudder itself did not crack. As discussed above, the weak part was the hull around the hole that the rudder post passed through. This is shown on the sketch on the right side of Figure 3. But the ao-called”“hairline cracks” did not stop the Superferry people. They made plans to repair the cracks and their plans were quickly approved by both the coast Guard and Germanischer Loyd which is a firm that companies like HSF hire to make their vessels run better. Also, to quote from the Maui News story of Feb. 2, “Joe Almony, Superferry’s director of maintenance and engineering, said he was following best practices to make the Alakai “as good as new.” So HSF proceeded to try to repair the cracks which HSF thought would take only a few days. But it was not that easy. “It’s been frustrating,” Garibaldi said but divers making repairs 10 feet underwater have faced a difficult task” It turned out to be more than frustrating. They just plain failed – so they removed the auxiliary rudders and plugged up the holes in the hulls. In a Honolulu Star-Bulletin story of Feb. 9, Terry O’Halloran was quoted as saying that “the rudders, which are used to improve passenger comfort and fuel efficiency, were removed for an interim repair but that the Superferry found that without them the ride suffered”. So was it really safe to remove part of the steering system and then travel between Honolulu and Maui?? Was water still creeping through the “hairline cracks”?? And what did it mean to say that the ride suffered?? The small number of passengers on the Superferry have already suffered a lot from rough rides – so what’s a little more suffering? My guess is that the Coast Guard approved the patch-up repair job – but can the Coast Guard’s judgment be trusted?? i would like to think that it can. But on the other hand consider the following quote taken from a KGMB story of Jan. 30 and attributed to the Coast Guard. “The Coast Guard said the trouble is with the rudder post, which houses the rudder and is controlled by jet drives that help stabilize the Alakai” What kind of gobbledegook is this?? Did the Coast Guard really say that?? Does the rudder post really house the rudder?? Is the rudder post really controlled by the jet drives?? Ridiculous!! It would be sad if the Coat Guard were actually responsible for the above quote At least someone spelled “Alakai” right. In any case, the Superferry was scheduled to go into dry dock on Feb.13 to make another try to repair the “hairline cracks” and make the Superferry “as good as new”. Will HSF get the Coast Guard or the State of Hawaii to pay for using the dry dock facilities?? More importantly, will the military lose interest in buying or leasing the trouble-prone Superferry or a similar vessel built by Austal?? Will another company get the big contract that John Lehman is hoping for?? Links to all other pages in this web site are listed at the top of this page

Figure 3:  Rudder and Rudder Post - Side View and End-on Views

stress cracks