# Parametric Rolling Part 2

Doesn’t look like the One Apus was case of parametric rolling - so thought a new thread was in order.

It pays to be wary of the site Marine Insight. The quality varies.

For example in the article about Parametric Rolling the Marine Insight post says this:

The difference is that “Parametric Rolling” is a type of movement that is experienced only on Container Ships .

That’s just flat out wrong.

An older thread on parametric rolling here:

Case mentioned in above article is the APL China - Oct 1998. Parametric rolling was not understood by the maritime community at the time.

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http://www.maths.lth.se/matstat/staff/georg/HuaPalmquistLindgrenSTAB2006.pdf

Between February 1 and 4, 2004, the PCTC AIDA experienced head sea parametric rolling at
five different occasions, which was recorded by an onboard operational decision support system.

Greatly detailed articles beyond my understanding! Does any other ship-type use the hull shape of the container ships?

Those characteristics turn up whenever speed / length is more important than dwt / build cost, while deck space is valuable. This doesn’t apply to a lot of big boats, though. KC mentioned PCTCs, which seems logical. The other example that springs to mind is aircraft carriers; does anyone know if they’re prone to parametric rolling?

Indeed, this sentence is indicative of someone who doesn’t really get the whole object through water thing:

Good post from Old Salt Blog. Rick Spilman is: “a writer, a sailor, a naval architect, a student of maritime history, a videographer and a multimedia designer,”

Some good links at Spilman’s post.

Technical but more understandable than the more academic articles.

Current Status of the 2nd Generation of Intact Stability: Investigation of the Pure Loss of Stability and Parametric Roll Mode

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Here is the story of the APL China

A ship heels, when the transverse weights/buoyancy forces are off the center line, CL. An inclining experiment in still water to decide the KG of a ship is one example. You move a known weight at CL to the side and the ship heels a certain angle due a heeling moment applied. It doesn’t roll. When you move the weight back to CL, the angle of heel becomes 0 again. Similar heeling, that can be thought of as rolling, may occur in a swell (ocean interface water/air is wavy) passed at 45°, when the buoyancy forces P&S become uneven, e.g. the bow flare is immersed more on one side, while the stern is immersed more on the other side and a heeling/yawing moment due to uneven buoyancy above/below waterline will develop – the ship heels and yaws. The sudden heel can be >40°, which some people call parametric (?) rolling. The ship may also yaw (twist, change course) >10° at the same time. Anyone who has been at sea has experienced it. Only way to avoid it is to slow down and/or change course. It is called good seaman ship!

Please disregard the terminology and pay attention to the footage.

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That’s a pretty dramatic example, heightened by the choice of HeroApproachesPiratesThroughStorm.mp3

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Maybe the crew has headphones at sea and listens to trash rock to pass the time?

It’s a demonstration where the parameters are selected to produce the worst possible case. Nonetheless, the rolling angles increase within a few cycles. Can imagine such phenomenon coming as a surprise to the crew.

Not just a surprise. A big sea boarding from ahead or a series of synchronous rolls from a quartering sea might come unexpectedly but at least it’s easy to see and understand what’s happening. Parametric rolling can be both unexpected and inexplicable.

The master of the APL China said it was as if the devil had sized the ship.

From Outside Online Monsterwellen

A seasoned mariner from India who’d been captaining container ships for 15 years, Guard was an exceptionally expert witness, France said. In a deposition lasting three of the six days that the China spent in Seattle, Guard reconstructed the voyage day by day, then, as the time of the disaster neared, hour by hour, then minute by minute, corroborating his testimony with entries in the logbook. While that testimony isn’t in the public record, one very telling quote from it is. Just before the containers began to fall, the ship had suddenly become “uncontrollable,” Guard testified, “as if there were a devil in it.”

The (wave tank) experiment proved that if Parvez Guard had done everything he’d been trained to do, if he’d heaved to and decelerated and the engines had not yet failed, the accident still would have occurred. And ironically, if Guard had not done what he’d been trained to do if he’d maintained his speed, for instance disaster might never have struck.

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