Superferry Rudder (?) Problems

 
Introduction: I first wrote this page on Feb. 2, 2008. I wrote this introductory paragraph 7 days later. During the interim I came upon important data from the Austal web site. I now understand the Superferry steering system a lot better than I did before. Also, I now understand why and how the so-called “auxiliary rudders” are the cause of the Superferry’s recent rudder problems. Rather than make major changes on this web page to correct errors due to my not adequately understanding the problem, I decided to write a new web page called “Superferry Rudder Problems - New data”. However, I will add comments to “Update” this page. So how serious is the Superferry rudder crack problem – and does the Superferry even have rudders?? Update: Yes!! The problem is serious and the Superferry does have so-called “Auxiliary Rudders”. The following comment about the “Auxiliary Rudders” was taken from Larry Geller’s Blog of Jan. 31, 2008 in a discussion about the rudder cracks on the Superferry: “Superferry officials declined on camera interviews, but said the vessel's two auxiliary rudders are rarely used. They said the rudders serve to make only slight course adjustments. The Superferry's four jet drives in the rear of the ship serve as the primary steering mechanisms, they said.” The above comment is totally misleading and is in contrast to what follows below in Larry Geller’s blog where it is stated that “interceptors” control the vessel’s steering at speeds greater than 25 knots. So what are “interceptors”?? -- and are they the same as rudders?? Update: No! interceptors are not the same as the “Auxiliary Rudders”. It is not clear if interceptors control the Superferry’s high-speed steering - or whether the interceptors and Auxiliary rudders work together. New subject: What is the “Seastate TMax high Speed Steering system”. In Juan Wilson’s blog of about Jan. 31, 2008, Juan pointed out - “It is my understanding that the Seastate software is used by all the new Austal multi-hulled passenger-vehicle ferries”. Right!!– and, apparently, on some Austal ferries that are not so new. So what is the Seastate software?? It is part of a computerized system which is supposed to steer and stabilize Austal fast ferries. Part of the software is called “the Seastate Tmax high speed steering system”. It was first used on the Austal “Highspeed 2” ferry. (See Figure 1). Also on the “Highspeed 4” ferry. Also on Austal’s “Euroferrys Pacifica” which is a lot like the Superferry. The Seastate TMax system was probably also used on the Superferry – although changes may have been made along the way. Superferry_Rudder_Problems_-_New_Data.htmlshapeimage_2_link_0

Figure 1:  First Austal fast ferry using the Seastate TMAX system

The TMax system is integrated with a motion control system comprising T-foils forward and interceptors at the transom of each hull.  So how do I know this??  It is from a statement in Figure 2 below from Seastate’s General Manager  .

Figure 2:  Statement from Seastates General Manager.

The key point in the above statement is that the TMax steering system switches   on at speeds above about 25 knots. Steering is then controlled by the interceptors. At lower speeds steering is controlled by the water jets which can pivot. In fact, at very low speeds the Superferry can make very sharp turns as shown in Figure 3 below.

Figure 3:  Austal fast ferries making sharp turns at low speeds

Juan Wilson’s story includes a picture of T foils from an unidentified ferry.  It also includes a diagram (copied in Figure 4 below) of a “Motion Control system Monitor” which shows 4 Interceptors at the transom, 2 roll fins about mid-ship and a forward T foil.  They all have sensors which probably go to a control panel at which wondrous things must be done to keep the vessel stable  - That is, if anything this complex can be made to work by a computer or a real live human.  No wonder the Superferry often seems so unstable that the passengers all get sick.





Figure 5: Four Humphree interceptors mounted on the transom of a monohull

The Interceptors are fairly simple devices.  My guess is that the Superferry has one or two of them mounted near the outputs of the 4 water jets.  To turn the vessel, the interceptors on one pontoon are lowered a short distance into the water which increases the drag on that side of the vessel – so it turns in the direction of increased drag. An obvious advantage of this type of steering  is that, in contrast to conventional rudders,  the interceptors are only lowered a short distance below the bottom of the transom and, therefore, are much less likely to strike an underwater object - like a whale. 


But “interceptors” are not the same as rudders.  Does the Superferry also have conventional rudders??   And when Superferry officials refer to rudder damage, does this really mean damage to one of the interceptors??  And when they stated that  “the rudders serve to make only slight course adjustments” were they dead wrong or just trying to minimize a serious problem?? Does HSF know the difference between a “rudder” and an “interceptor”??  I have no idea.


Update:  it is now clear that HSF did know the difference.  Initially, I was puzzled because I had found no data on the Austal Website referring to any type of  rudder.   A few days ago I finally found such data.  Then things started to fit together.  I now may even almost understand the rudder problem.  Go to the page called “Superferry rudder Problems - New data.

I suspect that the “Motion Control system Monitor” shown above is for an Austal trimaran rather than for the Superferry because it includes a sensor in the center - so the Superferry would employ a slightly simpler version.   Note that the above diagram shows 4 interceptors at the transom.  However, there is no indication of rudders near the transom that might also be involved in motion control.


Anyhow,  what are these “interceptors” referred to by Seastate’s general manager??  Are they the same as the “rudders” that the Superferry officials said were damaged??


Update:  No!!  They are completely different and, in contrast to the “auxiliary rudders, they are probably very difficult to damage.


Juan Wilson came up with a PDF file about “Humphree Interceptors”.  I came up with 2 additional PDF files which may be a bit easier to understand. (All PDF files available on request.) They even include pictures of Humphree Interceptors.  Figure 5 below shows 4 Humphree Interceptors on the transom of a monohull just above the water line.  It seems likely that similar interceptors are used by the Superferry.

Figure 4:  Diagram of Motion Control system Monitor

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