Processes: Fagerdala Thiger Marine System

The Fagerdala Thiger construction system combines metal fabrication, steel or aluminium, with foams, fibres and resins to create a unique hybrid structure, effectively a monocoque. dag pike reports on this interesting Swedish initiative and its intended first creation, the steel/composite Thor 84.

Steel construction and high speeds are not usually seen in the same yacht specification, but that is all about to change. Fabrication is expected to start soon on a new fast motoryacht in Sweden that will not only boast speeds up to 45kt, which is not bad for any yacht with an LOA of 25.6m (85ft), but also a revolutionary steel-composite construction method, not to mention a rather interesting choice of engines. The yacht in question is the Thor 84.
This initiative is rooted at the Öregrund Shipyard, which dates back to the 19th century, but in more recent times has been building large catamaran ferries and superyachts. The yard is now under the control of Fagerdala Thiger Marine Systems AB, which up to now has been involved with the construction of boats, boat lifts and boat trailers under the brand name of Anytec. This new project marks a major diversification for the company.

Left: Designed by Ocke Mannerfelt, the Thor 84 features a long, low profile with a raised coachroof. The pilothouse has been raised above the coachroof only by its window height. At the stern there is a large sunpad and below there is a tender garage, unique in that its doors open sideways. Inside, the guest accommodation comprises three double staterooms and two double crew cabins. The lower lounge also has a breakfast bar counter with the enclosed galley and crew mess further aft. In the pilothouse, the helm area is separated forward from the top lounge. Two helm seats are provided facing a spread of electronic displays with the aft lounge area given over to a C-settee surrounding a table that can be used as an alternative dining area. Right: Fagerdala Thiger’s robotic cell at the Öregrund Shipyard in Sweden. US company Visions East originally developed the technology for simply fairing and painting superyachts, but this Swedish operation has taken it several stages further, making use of it to produce hybrid steel/composite monocoque boat structures.

Fagerdala Thiger Marine System Structural Breakdown

1. Panel/furnishing 2.Metal sheet 3.Visco-elastic adhesive 4.Fagerdala closed cell foam 5.Carbon fibre 6.Filler 7.Paint

Marketed as the Fagerdala Thiger Marine System, the revolutionary approach to vessel construction makes use of both metal fabrication and composite sandwich technology to form a hybrid structure. Moreover, at Öregrund much of the process is to be handled by a sophisticated robotic cell, which comprises two large robots that run on rails on either side of a large work area. These robots will mill, fill, fair and paint as required. And the cell can even change the robots’ tool heads automatically, so that they can be left to carry on working overnight if necessary.

As well as for constructing yacht structures, the Öregrund Shipyard plans to use its facility for the fairing and painting of large yachts. This should help to provide continuity of work for the yard and help to spread the cost of what is, after all, a considerable investment.
Supplied by Visions East, the subject of a feature in the October 2005 issue of European Boatbuilder, this installation is claimed to be the first of its kind anywhere in the world. It is essentially a joint-venture project between the yard and Visions East, which first developed its robotic system to fair and paint big yachts.

As already mentioned, the first yacht to be built using the Fagerdala Thiger Marine System is the company’s own Thor 84, which has a low sporty look based on a stepped deep-V hull. The company will market it as its own yacht model, as well as offer the whole process and its capabilities on a contract or licensing basis.

The first stage for the Thor 84 is to laser cut the steel plating using CAD/CAM technology. The steel will then be placed over a temporary plug-style inner frame, one produced flat-pack style from the same basic files used to cut the plates. Internal steel sub-assemblies — such as the engine beds — will be used to help support the plating during the fabrication process. The cut steel plates will be laid as flat sheets or with just single-plane curvature — all held in place prior to final welding either by simple tack welds or even magnets. The plug framing will allow enough room for technicians to get in and complete the necessary final welding.

It is said that the basic construction system will work just as well with aluminium and, should that be the case, there is even the possibility of using glued joints in the resultant structure, techniques already commonplace in the aerospace industry. Indeed, for production structures (which for this industry translates to boats built in meaningful volumes), welding or gluing operations could perhaps also be carried out by the robotic arms.

After the fabrication of what becomes a metal inner skin, the robots will be able to map the surface topographically; the data from which will be used as a basis for all subsequent processes. The system will also be able to prepare most of the surface by using a variety of grinding and sanding tools.

Back to the Thor 84, once the inner steel structure is complete, the whole exterior surface will be coated with a ‘visco-elastic’ adhesive, to which a layer of specially developed closed-cell foam will be applied. This semi-rigid foam will then be surface shaped using a suitable milling head attached to robotic arms — much the same process as CNC machining centers creating plug shapes out of foam blocks. This way relatively complex final hull and superstructure shapes can be created on top of relatively simple metal fabrications beneath.

Next comes a suitable composite skin over the foam, a thin layer of carbonfibre in the case of the Thor 84, but equally E-glass or some sort of regular glass reinforcement could be used with the system. The whole thing can then be vacuum-bagged and infused with resin.

This resultant sandwich construction will then combine both strength and rigidity without the need for any internal support structure — essentially a monocoque that gains the majority of its strength from the skin. It is an efficient structure in other ways too. The 25mm (1in)-thick PVC foam used in the ‘sandwich’ does not encourage noise transmission and offers good thermal insulation and no likelihood of condensation problems.

To complete the hull, filler and paint will be added to the outside and wood panels and furniture added to the inside. Because the hull surface has already been faired, the minimum of filler is said to be required, which helps to keep the overall weight of the structure to a minimum. The Thor 84 should end up displacing just 23 tonnes, but her low weight will not just be down to the construction of her hull and superstructure.

In the engine compartment, occupying much of the Thor 84’s 6.1m (20ft) maximum beam, there will be no fewer than five Volvo Penta diesels, 350hp D6 units hooked up to DuoProp sterndrives. This propulsion-package choice provides plenty of flexibility. For low-speed manoeuvring the two outer engines will provide excellent turning control. Then at speed the other engines can be switched in, depending on the speed requirements, and by using sterndrives the drive legs of the engines not in use can be flipped up out of the water so as not to create drag.

This novel choice of engines occupies very little space across the aft end of the hull, as the engines are coupled directly to the sterndrives. It also reduces the overall weight of the propulsion package and has a similar impact on costs, as the ‘mass-production’ of smaller engines allows a much keener price. Moreover, the combined effects of less weight in the vessel’s construction and in the propulsion choice impacts many other areas too — for instance, less fuel and less ground tackle need to be carried. Indeed, the fact that the Thor 84’s 45kt top speed will be achieved with 1,750hp is largely due to considerable weight savings.

When combined with automated hull painting and finishing systems, it is estimated that the manpower requirements for boat construction will be halved with the Fagerdala Thiger Marine System — despite the need for higher calibre and more expensive technicians. Even so, the cost savings are expected to be substantial and more than enough to justify the investment costs.

The robotic cell at the Öregrund Shipyard went into the yard in November 2004 and construction work on the first Thor 84 is expected to start soon.
For more on the Thor 84 or the Fagerdala Thiger Marine System, contact Percy Sundquist, marketing director, Fagerdala Thiger Marine Systems, Box 1164, 13 127 Nacka Strand, Sweden.
Tel: +46 818 20 10. Fax: +46 818 20 13. Email: percy.sundquist@fagerdalathiger.com
Website: www.fagerdalathiger.com

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