The foredeck and bowsprit are uncomfortable places to work when the wind and waves become rough. However, the staysail attached to a steel cable does not come down by itself when you release the halyard. Especially not when the wind picks up and the sail flaps with great force. Then someone has to go to the foredeck to pull the sail down by hand. On larger ships, special lines – downhauls – are used to pull the sail down.
On yachts, people have started to replace the steel cable with a rotating rod to which the sail is attached. A simple mechanism allows the staysail to be rolled up onto the rod by pulling on a line. This invention is commonly known as a ‘furling jib’ or ‘furling reef’. Experiments with such systems were already being conducted in England over 100 years ago. But it was only with the introduction of modern materials – stainless steel rails and plastics – that the furling jib became suitable for mass production, especially on cruising yachts. Electric and hydraulic systems are now also available for use on large sailing ships.
Furling jib on the Swiss 28-metre research vessel ‘Forel’. Pulling on the sheet unrolls the sail and the line at the foot of the system is wound onto the drum. Pulling on this line rolls the sail back onto the rotating rod, which serves as a stay.
Three-masted barque for people with disabilities
Sailors are constantly working on optimising their ships. And so the roller-furling jib idea was soon put to use for other sails as well. On the ships of the English Jubilee Sailing Trust, the Lord Nelson and the Tenacious, not only are the headsails equipped with the roller-furling mechanism, but also the square sails, which can be rolled up. The ships were built to enable people with disabilities to enjoy active sailing trips. In addition to aids such as wheelchair lifts between decks and a talking compass for the blind, the roller reefing mechanism means that no one has to be sent up the masts to furl the sails.
The Teancious in harbour with its sails rolled up.
Dyna rig (so far) for billionaire yachts
With the Dyna rig, too, the sails are rolled up in the hollow carbon mast. These sails are pulled into their working position in rails embedded in the arched yards – or rolled up again when stowed. As this creates a continuous sail area, the Dyna-Rigg uses the wind much more efficiently than traditional square sails. The yards are firmly connected to the carbon fibre mast, which rotates as a whole.
The Dyna-Rigg was developed in Germany back in the 1960s. To allow the mast to rotate freely, the shrouds have to be omitted. Wilhelm Prölss, who invented the system, therefore proposed a three-legged mast, made of steel at the time. However, this construction is too heavy. That is why the idea of the Dyna rig was only taken up when carbon became available as a lighter material that is strong enough to absorb the forces of the sails as a single freestanding mast. As with the furling jib, the Dyna rig is an idea that can only be implemented once the appropriate materials are available. High-tech is expensive. So far, the Dyna rig has been used on two billionaire yachts. The Dutch design office Dykstra has developed plans for a cargo ship with a Dyna rig, but this has not yet been built.
The 88-metre-long billionaire's yacht Maltese Falcon with Dyia rig. This was originally developed for cargo ships, but was only built once expensive high-tech materials for the free-standing masts became available.
A single person can operate the entire rig at the touch of a button. Sensors also ensure that the sails are always automatically adjusted to the optimum position. However, this automation means that the yacht is dependent on a power supply: electrically operated winches pull the sails into position and roll them up again. The motors that turn the masts into the correct position also rely on electricity. There must be no blackouts. Blackouts on ships are not an everyday occurrence. However, on the 289-metre-long container ship ‘Dali’, a single faulty cable connection was enough to knock out all systems in a chain reaction. The result: a destroyed bridge in Baltimore and six drowned workers who were carrying out maintenance work on the bridge.
‘Like any wind propulsion system, the DynaRig relies on a power supply,’ confirms Rudy Jurg, sales manager at Southern Spars. Among other things, the company manufactures the DynaRig for Greenpeace's Rainbow Warrior IV in Poland. "Precautions have been taken to operate the system manually if necessary. Although the total sail area is large, each sail is relatively small, so the loads are very manageable if manual furling is required.‘ This has never been necessary on the yachts ’Maltese Falcon‘ and ’Black Pearl‘ to date. Together, they have covered over 400,000 nautical miles – ’mostly under sail alone". On the Maltese Falcon, the sails have been set and taken down 15,000 times. In addition, most ships have several electrical backup systems: engines, generators, batteries and an emergency power supply.
No muscle power, no teamwork when tacking, no commands to coordinate the choreography of a manoeuvre, just a few buttons: high-tech sailing with the Dyna rig.
Jurg explains that these rigs are equipped with fibre optic load monitoring devices. ‘The sensors provide real-time data to the bridge and warn the captain when the material load reaches a specified limit.’ He describes the free-standing masts as ‘inherently much safer than conventional rigging when designed, engineered and built to specification’. Furthermore, carbon fibre is not subject to the same material fatigue as aluminium or steel.
The Indosail rig for cargo ships
The Indosail rig takes a completely different approach. Originally developed for Indonesia, it consists of commercially available, existing components. No expensive high-tech materials like those used for luxury yachts. And nothing needs to be invented and tested as a prototype first. This reduces construction costs. Overall, the Indosail rig is a further development of the gaff schooner.
The core of the idea here is also the furling system. The sail is rolled up onto a furling pole along the mast. The boom and gaff are aligned horizontally parallel to each other and connected to the cams by a trailing strap. This line keeps the rectangular space between the mast, boom and gaff taut at the rear, within which the sail is set, reefed or stowed like a curtain using lines that can all be operated via winches on deck.
The sail itself has a specially reinforced leech. In high wind pressure, it takes the load from the trailing strap, which comes loose. This tells the person at the helm that it is time to reef. Sensors can even be used to install an automatic reefing system. Reefing is done horizontally by partially rolling the sail onto the roller-furling bar.
The system is designed for several masts of equal height, as the gaff also has a sheet that is led over the top of the rear mast. A triangular Bermuda sail, which can also be rolled up, is used on the rear mast, and a roller-furling jib is used in front of the front mast.
Design principle of the Indosail rig.
Aerodynamic advantage: As with the Dynarigg, the Indo sail creates a continuous surface from bottom to top.
As with many traditional gaff rigs, the rectangular shape at the top, where the real wind is stronger, provides a lot of sail area. Since the gaff also has a sheet, the angle of attack to the wind can be controlled over the entire length of the sail.
Economic advantage: The rig is designed so that all sailing manoeuvres, such as setting and striking, can be performed either manually or automatically. Since everything can be operated at the touch of a button from the helm, a relatively small crew is required. And one more thing: ‘We encourage anybody who likes the idea to use it!’ writes Peter Schenzle, an engineer from Hamburg and one of the main inventors of the concept, on his website. So no patent, and therefore no licence fees to cover development costs.
First experiences on the Maruta Jaya 900
The Indosail rig saw its first use on the schooner “Maruta Jaya 900”. This sailed between the Indonesian islands from 1993 to 2012 and transported relief supplies to the regions devastated by the tsunami in 2004. Its loading capacity was 900 tonnes. The ship sank in 2012. ‘After the tsunami relief effort off Sumatra, it was probably left in the anchorage without any tasks or maintenance. So it probably rusted through,’ suspects its Hamburg-based designer Peter Schenzle. One reason for the neglect: during a change of regime, the Indonesian Minister of Research, who pursued the vision of emission-free shipping, was dismissed.
The University of Emden/Leer compiled the experiences with a view to the new construction for the Marshall Islands. ‘Despite of exceeding all expectation regarding sail performance, several aspects of rig and vessel-design proved to be difficult and led to later changes in design and especially in construction of the system.’ Among other things, criticism was levelled at the quality of the sailcloth, the design of the rudder and the fact that components were used that were available in Indonesia but were not ocean-proof and therefore quickly suffered corrosion damage (Vahs et al., 2021).
The Indosail rig was first developed for the 63-metre Maruta Jaya 900 – a rigging system that is as easy to operate as possible, without expensive high-tech elements, for supply ships in countries in the Global South.
Image: Vahs et al., 2021
A critical point in the overall concept is the gaff. With traditional gaff rigging, this is lowered when the sail is taken down. With the Indosail rig, it remains up. There, it is difficult to control in rough seas and light winds and is difficult to reach for technical checks and any repairs.
Greenpeace captain: sceptical about automation
Next, the Indosail rig was used on the Greenpeace ship Rainbow Warrior II and the expedition ship Syscomp-1. Both were conversions from former motor vessels to sailing ships. Manual winches were installed for the sheets on the Rainbow Warrior II, and electric winches on the Syscomp-1.
Peter Willcox, a Greenpeace stalwart, sailed on both ships. He was captain of the first Rainbow Warrior when it was sunk by French secret service agents using bombs in the port of Auckland, killing one person. And he was captain of the Arctic Sunrise when Putin's Russia imprisoned the entire crew for two months and threatened them with 15 years in prison for protesting against oil drilling in the ecologically sensitive Arctic Sea.
The Rainbow Warrior II initially sailed with an Indosail rig. In the picture, all sails are reefed, i.e. partially rolled up. Greenpeace later replaced the Indosails with Bermuda sails (as on the aft mast), which, according to Captain Peter Willcox, worsened the sailing characteristics.
Willcox's technical explanations and opinions on individual components are best read in the original (Vahs et al. 2021 / Willcox n.d.). His criticism of Greenpeace's decision to replace the Indosail sails with triangular Bermuda sails shows how convinced he is of the Indosail design: ‘The second Rainbow Warrior was very successful until approximately 1994, when Greenpeace, in a move caused from pure ignorance took the gaffs off the boat. I sailed the boat in 1995, and was so disgusted that I never sailed on the boat again. ’
He also warns against too much automation: ‘I agree that it is important for the helmsman to be able to control the sheets from the helm. I do not believe that the sails should be set or furled from the helm. A big aid in set or furling the sails is your ears. Sail fabric or lines coming under strain can be heard often before it is seen.(...) Make the crew go out to the base of the mast. ‘
He also shows no enthusiasm for semi-automatic steering systems. "It is the same as letting your GPS talk directly to your auto-pilot. It takes the operator too far out of the program. Make the mates aware of what is going on, and make them adjust the sails. Nor would I use a fully automated system. What could go wrong? Adjusting sails to the optimum wind angle does not require a computer."
With all his years of experience, Willcox believes it is important for the crew to know what is going on in the rig and to develop a feel for it. This comes from daily handling of the sails. On the other hand, he acknowledges: ‘Simple operation leads to higher percentage of usage for the wind propulsion system as compared to the manual handling aboard traditionally rigged vessels and also compared to the partly manually controlled Rainbow Warriour II.’ Willcox writes that he was able to sail a 52-metre ship like the Syscomp-1 with a crew of only three people due to the higher level of mechanisation (motor winches for the sheets). On the 55-metre-long Rainbow Warrior II, on the other hand, at least six people were needed for gybing and tacking.
References
National Transportation Safety Board (2025): Contact of Containership Dali with Francis Scott Key Bridge and Subsequent Bridge Collapse, Patapsco River. Baltimore, Maryland, March 26, 2024, DCA24MM031, https://www.ntsb.gov/investigations/Documents/Board%20Summary%20Contact%20of%20Containership%20Dali%20with%20Francis%20Scott%20Key%20Bridge.pdf
Peter Schenzle (o.J.): A Modern Multi-Mast Gaff Schooner. The INDOSAIL Utility Sailing Rig. http://indosailrig.com/assets/files/INDOSAIL-UtilityX-2.pdf
Michael Vahs, Siegfried Wagner, Sascha Strasser (2021): The INDOSAIL-Wind Propulsion System. Review regarding the INDOSAIL wind propulsion system aboard Maruta-Jaya, Rainbow-Warrior-II and Syscomp-I/Sedna-IV in preparation of renewed implementations. University of Applied Sciences Emden/Leer, with support from Peter Schenzle and Capt. Peter Willcox
Peter Willcox (o.J.): On the Ease of Handling an Indosail Vessel. http://indosailrig.com/handling.html