Why do you think containers are lashed down? They just sit there and in bad weather some of them fall off, this happens all the time.

Their sail might provide some lift, true, but they also apply rotation and shearing forces around the (double) container like a lever.

There are at least a few that are lashed on some ships.

Containers don't just sit there- they are secured, with a combination of lashing rods and twistlocks that connect the bottom of the container to the deck or the container it is resting on. In fact, there are computer programs which tell the crew exactly how this needs to be done. They do sometimes fall off in bad weather, this is due to failure of the lashings.

See here [0]: "The MAIB’s preliminary assessment found that [the ship]’s violent pitching and ploughing into the heavy seas resulted in a rapid loss of speed and heading control, which exposed the deck cargo to green sea forces capable of overwhelming the maximum loading of the container securing arrangements... corrosion to the vessel’s deck cargo securing arrangements may have contributed to the scale of the loss."

Or here [1]: "At 0800, the ship sailed from Xiamen with 6,466 containers on board... At about 1000, the bosun and four deck crew mustered at the forward end of the weather deck and began a post-departure inspection of the deck cargo securing arrangements... they checked that the manual twistlocks, connecting the first tier of containers to the hatch covers, were locked, and ensured that the container lashing rods were correctly tensioned. With over 12,000 twistlocks and 3000 lashings to inspect, the checks continued all day"

[0]:https://www.gov.uk/maib-reports/loss-of-34-containers-overbo...

[1]: https://www.gov.uk/maib-reports/loss-of-cargo-containers-ove...

Okay I must have misunderstood this when I worked at Zodiac maritime. The lashings do not look strong enough to support a sail: https://www.marineinsight.com/wp-content/uploads/2019/03/Imp...

I think they must have said they stay put is under weight and the lashings just keep them from slipping? Who knows, I'm definitely wrong here.

I was under the impression that their double wide container rig would be at deck level and lashed down to the vessel; not stacked on top of other containers. This is the only way they could control the vertical height of the retracted sail for going under bridges, etc.

Love how this idea has energized HN.

When sails provide lift, that is forward motion, not vertical.