Ljungstrom rig

The Ljungstrom yacht Vingen 10. Foto: 2010.

Ljungstrom rig is the name for the sailing rig designed by Fredrik Ljungstrom with double main sails and rotating mast, but without boom, foresail, forestay and shroud. The early models of the Ljungstrom sailboat had a stern stay but this was omitted around 1945, before the model 12 (Vingen 12).

The Lj rig is competitive towards the competing rigs from that time when close hauled and full run but is lacking at beam reach and broad reach. Its main purpose and advantage is, however, safety and ease of handling.

History

The first LJ rig was developed by engineer Fredrik Ljungstrom to enhance safety at sea. The family had been close to severe accidents with the traditionally rigged Ebella, nowadays named Beatrice Aurore, when in hard weather the crew had to walk on deck to take in sail. Ljungström was against risking the safety of his crew and designed a boomless rig handled completely from the cockpit.

Components

Mast

The masten is made of glued clean wood, conical without stays and shroud. Boom, pole, gaff, spreader and such is completely omitted. The mast is supported by two ball bearings, one at the keel and one at the deck hole, and can thus rotate freely. The rotation is created using a wooden collar, with a V-shaped track, around the mast below deck. Around this collar an infinite rope sling runs through two blocks to a winch, powered by hand or an electric motor. In this way the sail is rolled onto the mast when less area is needed or when the sailing is finished. As a result of the conic mast, the clew will move up the less sail that exposed. As a result of the mast taper the clew will end up higher and higher the closer it is to the mast.

The mast is hollow, partly to reduce weight (up to 4.5% of a keelboat's displacement), and partly so that the halyard can run inside the mast, and therefore manufactured in two halves. At the top is a metal bracket with pulley for the halyard which then runs inside the mast and comes out below deck, where a pulley is located under the mast root. The mast foot is tapered so the mast stands firmly in the lower tapered ball bearing. In level with the deck the mast "bottleneck" where the upper ball bearing rests. By means of a bracket bolted to the deck upper surface the upper ball bearing is kept in place and thereby the mast is kept from being lifted from the lower layer.

Sail

A Ljungström rig usually has two, at the luff, stitched sails. In all winds except full run, these sails close together. In the unlikely event that one of the sails would rip the other still stands and the boat can safely reach harbor.

The Ljungström rig is often compared with a staysail with the big difference that the mast bends inversely to the forestay. This must be compensated for so that the luff is provided a belly which is <30% of the masthead deflection, about 2% of the luff length. Since the sail is hoisted throughout the season, it is appropriate that leach and foot consists of UV resistant fabric that covers the entire mast in furled state.

Sheeting

The two sails each have their own independent sheet. On previous models the blocks sat on the deck aft area but later improved forwarding with a pole which raised the sheeting point about one meter. Some models have a winch.

The greatness of the Ljungström rig, besides the simplicity and safety, is in the engineer's knowledge of fluid dynamics. The mast is rotated so that the sail rests on the mast at lee. This is to minimize turbulent flow on the leeward side of the mast and the propulsion force, which is so important, becomes almost undisturbed. This was totally new for that time and made a boat with Ljungström rig go higher towards the wind than its contemporary competitors. Today profiled master solves this partly but hardly more efficient. The real showpieces is however at full run where the two sails separate as butterfly wings and are sheeted on each side. similar to a spinnaker but no extra booms and guys needed.

Sources

"Fredrik Ljungström 1875–1964 – Inventor and inspirer", by the son Olle Ljungström, Svenska Mekanisters Riksförening 1999, ISBN 91-630-7639-X
"Ljungström boat 75 years" by Olle Ljungström 2008 (self-published)
"Roller Mast Takes the Sweat Out Of Sailing". Popular Science: 58–59. July 1951.

External links

Ljungstrom boats through the years – The unofficial web page for Ljungstrom Boats

Sails, spars and rigging

Rigs	Bermuda rig Cat rig Full rig Gaff rig Junk rig Ljungstrom rig Mast aft rig

Sail types	Asymmetrical spinnaker Junk sail Lugsail Parafoil Ringtail Spinnaker Turbosail Rotorsail Wingsail

Sails (sail plan)	Blooper Course Crab claw Driver Extra Fisherman Genoa Gennaker Jib Lateen Mainsail Moonraker Royal Skysail Screecher Spanker Spinnaker Spritsail Staysail Studding Topgallant Topsail Trysail Watersail

Sail anatomy and materials	Clew Foot Head Leech Luff Roach Tack Throat Peak Dacron Technora Kevlar Twaron

Spars	Boom Bowsprit Boomkin Dolphin striker a/k/a Martingale Pelican striker Fore-mast Gaff Jackstaff Jibboom Jigger-mast Jury rigging Main-mast Mast Mizzen-mast Truck Spinnaker pole Spreader Sprit Topmast Yard

Rigging components	Backstay Block Bobstay Boomkicker Braces Buntlines Chainplates Cleat Clevis pin Clewlines Cunningham Deadeye Downhaul Earing Fairlead Forestay Gasket Gooseneck Gunter Guy Halyard Kicker Lazy jack Outhaul Parrel beads Peak Preventer Ratlines Running rigging Shackle Spinnaker chute Standing rigging Sheet Shroud Stay mouse Stays Throat Topping lift Trapeze Traveller Turnbuckle Vang Windex

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