Tuesday, February 5, 2008

HI Superferry: One more about the "Rudder"

From Greg, a knowledgeable mariner:

"What is at stake here is the "deck slamming" capabilities of the vessel at various speeds and wave heights. Marine architects model this. USCG reviews their models and either agrees, modifies or rejects. No real world testing is done on ship design, only hypothetical, especially in the special cruise market. Most passenger vessels are ‘one-offs,’ unique and never tested before. Sure they are built on some form of a platform or hull that has (perhaps) limited history, but it is not until operation can the flaws be detected. What is likely to happen to HSF, is USCG will review engineering calculations, speeds, etc., and place new operational limitations on it. We know O’Halloran disclosed a 19’ wave height “no sail” condition by USCG. Given the current failings of the vessel, they are likely to review and revise this."

Juan Wilson has another good article on this with an indirect Coast Guard source:

POSTED: 5 FEBRUARY 2008 - 9:45am HST
USCG says Auxiliary Rudders Damaged


by Juan Wilson on 5 February 2008

I just got a phone call from Tim Rysdale, of Wailua. He was one of those arrested back in August in the aftermath of the Superferry's attempt to land on Kauai.

Tim's family has always been a supporter of the United States Coast Guard. He maintains friends in the service, despite his disfavor with the USCG coming under the wing of Homeland Security Department.

A friend of Tim's active in the USCG, and in a position to know, has told him that the Superferry uses an new prototype of auxiliary rudder, in addition to other steering mechanisms.
This is in addition to the control surfaces and Humphree devices mentioned as possible "rudders" in previous speculation.

As I understood Tim's description, these rudders are hydraulically rotated through sleeved posts that enter the ship through the aluminum hull. Stress on the posts created cracks that allowed some water to enter the ferry's hull.

With my limited knowledge of ship design, and structural metals, I would maintain that this represents an engineering flaw that has resulted in at least a minor structural failing of the hull.
Yes the Superferry is running again. I'll bet that the next ferry Austal builds will have some re-engineering on the structure of the auxiliary rudders before the boat is ready for sea trials.

George Peabody HSF Video
by Juan Wilson on 4 February 2008

George Peabody, of the Molokai-Advertiser News, sent us this portion of a video he shot of the Superferry Alakai passing by Molokai a week ago, before the "rudder" damage was detected.

George has a dial-up internet connection and therefore sent only a small resolution portion of the video. A longer higher resolution version may soon be available. Note, this is the source of the video shown on KGMB-9 TV.

The pitching bow of the Alakai deck in the swell appears to pass through more than 30 vertical feet of movement. Certainly enough to throw passengers of their feet if not holding themselves securely to the ship. I'm not quite clear how or if vehicles are secured on board. I have traveled on large Nantucket vehicle ferries and they do not secure cars and trucks. Could get dicey in a pacific Ocean winter swell.

There must have been tremendous stress on any of the control surfaces deployed and active.
End article.

And another edited evaluation from Lee Tepley, Ph.D.:

Was the Superferry rudder damage caused by a collision...??‏
From: Lee Tepley

Was the Superferry rudder damage caused by a collision...?? Feel free to circulate.

In an e-mail dated Feb. 2, I made the point that, for earlier Austal fast ferries, an important Austal official had stated that steering at low speeds was controlled by the 4 water jets. At high speeds (above about 25 knots), steering was controlled by Interceptors. In that e-mail (and also on my website), I questioned whether the Superferry even had rudders.

However, yesterday I found the following sentence on the Austal web site: “Austal first developed and implemented the interceptor, and the system now also incorporates sophisticated primary and auxiliary steering systems.”

The last part of the above sentence implies that significant changes were made in the steering systems of the Superferry compared to earlier Austal fast ferries. It implies that Austal was not satisfied with the performance of it’s interceptors which had previously controlled steering at high speed – so it added “sophisticated primary and auxiliary steering systems” which probably included rudders.

This seems to be related to the recent rudder damage to the Superferry. In fact, Superferry officials stated that the damage was related to “the auxiliary rudder which is involved with steering”.

In addition, the Coast Guard supposedly said that “the trouble is with the rudder post which houses the rudder and is controlled by jet drives that help stabilize the Alakai."

The above Coast Guard statement does not seem to make sense but is at least consistent with the idea that the damage was related to the new steering systems.

This suggests that the Superferry may have serious structural problems which did not arise with earlier Austal fast ferries. This seems ironic. I have felt for some time, that HSF could care less about earning money as a commercial operation and that the proposed 2nd daily trip to Maui was only to establish operational reliability with the idea of impressing the military. Joan Conrow has done a great job.... Go to http://www.honoluluweekly.com/. Then read Joan’s story on U.S.S. Superferry.

Anyhow, it now seems that the Superferry is anything but reliable – which may not impress the military - and it may be hard to blame it’s problems all on bad weather.

The structural problems could have been caused by poor design, metal fatigue, etc. They could have also been caused by a protruding rudder or it’s support elements striking an underwater object....

First, lets compare the operation of rudders and interceptors:

1. Interceptors would probably be mounted behind the transom and would only be lowered into the water a short distance (maybe only a few inches) when turning was involved. Vessel drag would be increased for only a short time. It is hard to see how any part of an interceptor could be damaged by striking an underwater object.

2. 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 [an object], it might easily crack. In fact, an auxiliary rudder could be one of the weakest underwater parts of the Superferry....


I was talking with a couple of knowledgeable people and when the HSF goes over large waves and then slams back down into the water, esp. with high seas and slamming into water between the two catamaran hulls, that that has the potential to do this type of damage. So an object none other than water being slammed into repeatedly after falling off of 20+ foot waves may in fact be the culprit. On a given transit wind waves may be reported to be something like 15 ft., but invariably there will be some rogue waves and sets out there in the channels that are much more than the reported wind wave heights.

Aloha, Brad

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