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.

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

stress cracks