# Help with Roll in stern quartering seas

Discussion in 'Stability' started by Rian199, May 10, 2016.

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### Rian199Junior Member

Hi, I am a Naval Architect student doing a project on Roll and Heave accelerations in an irregular seaway. I've done a simulation on MaxSurf Motions using the wave scatter data and vessel model provided. Now there seems to be maximum roll in a stern quartering seaway around 30-40 degrees. Now I've done some research of my own, trying to find papers justifying this phenomenon, but I can't quite rap my head around the concept. Is there anyone who could help explain this to me? I feel like I sort off get it but I'm finding hard to express it in a way I can present it? See my results attached.

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### jehardimanSenior Member

Stern-quartering is always worst for real hull ship shapes in fully developed seas. Think about what causes rolling, a difference in the water surface on each side of the ship. So it is easy to see when you have a short crested sea from the beam (090. Wave angle is defined as the angle between the wave heading and the ship heading so 000 = waves from astern, 180 = waves from ahead). When the distance between the crests is twice the beam, then one side of the ship is on the crest and the other is in the through generating a maximum rolling moment.

For stern quartering it is a function of required fullness aft and narrow entry forward as the wave crest overtakes the vessel. Because the vessel is making headway, there is a significant length of time where the stern is on the crest and the bow is in the trough. Note that the length of a deep water 7 second wave is ~250 ft (76 m) and is traveling at ~37 ft/sec (21 knts). So its overtaking speed in your example is ~5 knots and the along ship distance between crest and trough is ~53m. If that is a 50m fishing boat in a 2m sea you have a serious problem.

Go read the first 4 chapters in Dynamics of Marine Vehicles by Bhattacharyya. Good explanation of the problem and some basic worked examples.

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### kaptcatbJunior Member

You can check following paper and other papers from same authors -
Development of Second Generation Intact Stability Criteria, by Belenky , Bassler and Spyrou.