The circular arc hull is a design for boat hulls created by Swedish engineer Fredrik Ljungström. In the 1930s and 1940s Ljungström designed and built sailboats, commonly called the Ljungström sailboat.
The frames, or ribs, of a circular arc hull all have the same radius. On Fredrik Ljungström's first models, frames were a cross-section (a single arc), but he soon realized that he needed a slightly narrower profile to cope with the sea. The result was that two arcs met at the bottom so that a slightly pointed bottom was created. The frames are tilted toward the mast so that the stern and bow lean while standing straight up.
Keel stock
Ljungström's yachts lack a traditional keel stock. The lower plank is twice as wide. Its curvature is a circular arc with its radius approximately equal to the length of the mast.
Planking
The table planks consist entirely of parallel ribs that begin and end at the rail. The bottom (longest) plank runs from stem to stern and the top two (shortest) are located amidships at the railing on the port and starboard sides of the boat.
Advantages
The circular arc hull's advantages are mainly in flow and manufacturing/engineering fields. Ljungström was an expert technical designer and knew that every surface and curvature change causes impaired flow. Constant radii worked the best. The consistent use of arcs in a hull shape provides maximum stiffness and strength, with which thinner skins can be used.
For boat builders, the circular arc hull has several advantages:
The planks are parallel planed ribs and need not be adapted to any keel stock.
All ribs have the same radius and can thus be glued into the same shape.[1] This reduces the effort in jig-building. When the planks are in place, the railing line can be cut.
The completed hull has relatively small surface area for its size, this reduced wetted area also reducing skin friction.[1] Moreover, there are no plank ends that suck water into the wood.
The circular arc hull is very well suited for so-called strip building, where the hull is built of thin, wooden slats as a distance material between fiberglass and epoxy.
Disadvantages
The circular arc hull, as a shallow, V-shaped hull, is not ideal for a rough sea as it does not cleave the waves. However, it can have a tendency to swage.
This lightweight construction has a large number of thin ribs and planks. Thus, there may be more movement within the hull than in sturdier designs.
References
^ ab"Roller Mast Takes the Sweat Out Of Sailing". Popular Science: 58–59. July 1951.
Sources
Fredrik Ljungström 1875-1964 inventor and inspirer, the son of Olle Ljungström, the Swedish National Association of Mechanical Engineers 1999, ISBN91-630-7639-X
Ljungström boat 75 years old, by Dr. Olle Ljungström, 2008, self-published.
External links
Info on Ljungström's boats (in Swedish)
March 22, 2023
circular, hull, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, books, scholar, jstor, july, 2013,. This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Circular arc hull news newspapers books scholar JSTOR July 2013 Learn how and when to remove this template message The circular arc hull is a design for boat hulls created by Swedish engineer Fredrik Ljungstrom In the 1930s and 1940s Ljungstrom designed and built sailboats commonly called the Ljungstrom sailboat Contents 1 Ribs 2 Keel stock 3 Planking 4 Advantages 5 Disadvantages 6 References 7 Sources 8 External linksRibs EditThe frames or ribs of a circular arc hull all have the same radius On Fredrik Ljungstrom s first models frames were a cross section a single arc but he soon realized that he needed a slightly narrower profile to cope with the sea The result was that two arcs met at the bottom so that a slightly pointed bottom was created The frames are tilted toward the mast so that the stern and bow lean while standing straight up Keel stock EditLjungstrom s yachts lack a traditional keel stock The lower plank is twice as wide Its curvature is a circular arc with its radius approximately equal to the length of the mast Planking EditThe table planks consist entirely of parallel ribs that begin and end at the rail The bottom longest plank runs from stem to stern and the top two shortest are located amidships at the railing on the port and starboard sides of the boat Advantages EditThe circular arc hull s advantages are mainly in flow and manufacturing engineering fields Ljungstrom was an expert technical designer and knew that every surface and curvature change causes impaired flow Constant radii worked the best The consistent use of arcs in a hull shape provides maximum stiffness and strength with which thinner skins can be used For boat builders the circular arc hull has several advantages The planks are parallel planed ribs and need not be adapted to any keel stock All ribs have the same radius and can thus be glued into the same shape 1 This reduces the effort in jig building When the planks are in place the railing line can be cut The completed hull has relatively small surface area for its size this reduced wetted area also reducing skin friction 1 Moreover there are no plank ends that suck water into the wood The circular arc hull is very well suited for so called strip building where the hull is built of thin wooden slats as a distance material between fiberglass and epoxy Disadvantages EditThe circular arc hull as a shallow V shaped hull is not ideal for a rough sea as it does not cleave the waves However it can have a tendency to swage This lightweight construction has a large number of thin ribs and planks Thus there may be more movement within the hull than in sturdier designs References Edit a b Roller Mast Takes the Sweat Out Of Sailing Popular Science 58 59 July 1951 Sources EditFredrik Ljungstrom 1875 1964 inventor and inspirer the son of Olle Ljungstrom the Swedish National Association of Mechanical Engineers 1999 ISBN 91 630 7639 X Ljungstrom boat 75 years old by Dr Olle Ljungstrom 2008 self published External links EditInfo on Ljungstrom s boats in Swedish Retrieved from https en wikipedia org w index php title Circular arc hull amp oldid 934368864, wikipedia, wiki, book, books, library,
