Parametric roll

Parametric roll is an unpredictable phenomenon in which the ship starts to roll in head or stern seas. The roll angle can increase from a few degrees to over 30 degrees in only a few cycles.

This footage was filmed in a demonstration held in the Ship Laboratory of Aalto University School of Science and Technology on November 18th, 2010. The model, a RoPax vessel, encounters waves head-on. In the first part nothing happens, but as the wave frequency is adjusted so that the encounter frequency is roughly twice the natural roll frequency, parametric roll occurs. As the wave height is increased, the rolling becomes more violent.

It has been said that this is the phenomenon that caused the extreme rolling of the cruise ship Grand Voayger when it lost its propulsion in a storm.

Category:

Science & Technology

Tags:

• parametric
• roll
• resonance
• rolling
• ship
• ropax
• model
• basin
• wave
• towing
• tank
• aalto university
• aalto-yliopisto
• teknillinen korkeakoulu
• TKK
• grand
• voyager
• cruise
• storm
• cyclone
• valentina
• motions
• extreme
• rough
• sea
• heavy
• waves

[danielalonso23]

Mr Tupsumatu:

I´m triying to test a numerical model of the parametric roll and i need experimental values of this video and the drawings of the ship and his characteristic. (mass, inertia,etc.).

can you help?

Thanks.

[tupsumato]

@danielalonso23, unfortunately I am currently not in Finland, so I can not help with information regarding this experiment. However, best of luck with your research!

[danielalonso23]

I think this phenomenom only can happen if :

1) the body is no simetrical.(a box)

2) the lenght of the wave is less than the lenght of the body.

[tupsumato]

@danielalonso23, the hull is symmetric along the centerline, which is parallel to the direction of the waves.

[Triiiop]

I've experienced parametric rolls in the North Atlantic during a winter storm, very sudden, unexpected. Speed change will change the roll cycle in theory but it takes far too much time on a commercial ship. An immediate hard over 90 degree course change breaks the cycle much much faster. Watch officers must monitor wave period and ship roll period, a wave period 1 half of the ships rolling period creates a situation conducive to parametric rolls.

[tupsumato]

@Triiiop, I agree that changing the heading is much more effective than changing the speed - ships have so much momentum that I don't think anything but a crash stop would make a difference.

It's also nice to know that at least on some ships the crew pays attention to this phenomenon. I've made some trips on cargo ships and I've never noticed anyone doing anything like that. But then again, I've never experienced parametric roll either...

[danielalonso23]

@tupsumato Ok.Thanks for respond.

[tupsumato]

@danielalonso23, that's true. I might've misunderstood your first message.