bound4blue

bound4blue is a Spanish wind-assisted propulsion company that develops the eSAIL, an autonomous suction sail. It has offices in Barcelona, Singapore, Suzhou and Shanghai and a registered address in Santa Cruz de Bezana, Cantabria.

The eSAIL is a rigid, wing-shaped sail with a suction fan that keeps the airflow attached to its surface. bound4blue says this produces six to seven times more lift than a conventional sail. An autonomous control system handles rotation, flap position and suction without crew input. There are three models: Model 1 (3.5 m wide, 16–20 m high) for general cargo and multipurpose ships, Model 2 (4.5 m, 22–26 m) for Handysize, MR, Panamax and ferries, and Model 3 (6 m, 21–36 m) for Aframax, Suezmax and VLCC tankers. Tilting is optional. The company claims fuel savings of up to 40% and payback in under five years.

eSAILs have been installed on vessels for Maersk Tankers, Klaveness (MV Baltazar), Odfjell and Marflet Marine, including four 22 m units on the chemical tanker Santiago I. bound4blue is expanding eSAIL production in China through regional partners. At SMM 2026 its eSAIL Model 3-24 received a Bureau Veritas design assessment.