Michelin Inflatable Sail.

[DJE]

Looks easy to reef - just pull the plug out! Will it catch on?

Michelin develops giant inflatable sails

Yachty bit is about one minute in to this video.

 

[Paulg25]

Looks easy to reef - just pull the plug out! Will it catch on?

Michelin develops giant inflatable sails

Yachty bit is about one minute in to this video.

Depends on price and payback time (fuel saved).
Looks like a good idea.

 

[LONG_KEELER]

Looks good for bulk carriers but may be difficult for container ships perhaps.

 

[mjcoon]

Buoyancy could be useful in extremis, too... ;-)