Adaptive Mould Technology: Building without a mould - better and cheaper?
How do you build a ship in the best possible way? This question is almost as old as the invention of the dugout. But now there is another exciting answer when it comes to composite hulls, including those made of GRP or CFRP. And this is how it works: foam parts are heated and bent and twisted over a movable mould in such a way that these foam sheets are joined together to form a fuselage.
Glued together in an auxiliary frame, they form the moulding part. The workers then laminate a few layers of resin and hardener on the inside of these panels, after which the deck is placed on top. The boat is then turned, resin, glass, filler and varnish are added to the outside, and the hull and deck are finished. Sounds simple, because an expensive mould is not required for this method. Is this the big hit in modern GRP boat building?
The answer here, as so often, is: it depends. A brief digression into series boatbuilding: in order to make the hull and deck very smooth and shiny on the outside, gelcoat is applied in a mould that is as smooth as it is flat. The smooth surface of the negative mould determines the surface quality of the hull.
Conventional moulds are very expensive for small series and one-offs
The gelcoat evens out the unevenness of the laminate. This means that the fuselage can be rough on the inside and smooth on the outside. This production method is cost-effective at first glance, as it does not require any further labour-intensive optimisation of the surface quality of the fuselage after moulding. The gelcoat is smooth on the outside thanks to the mould. However, this requires a very flat and precise mould. And these moulds are expensive to produce.
So expensive that a shipyard has to ask itself over how many hulls it will probably spread the cost of the moulds for the hull and deck. If you calculate with too few units, the proportion per ship becomes too high and the price becomes unattractive on the market. If you take on more units than are ultimately sold, the shipyard pays more, as the costs for the moulds are not recouped. A difficult trade-off. This construction method becomes downright nonsensical if only a small series or even a single ship from this mould is ever sold. Then the small series or the one-off hull becomes too expensive. Production in one mould is ruled out in this case.
"We then built one-offs or small series over a moulded frame. Foam strips were glued to this. This was followed by sanding, filling and finally laminating. But that had some disadvantages," reports Paul Dijkstra. He is the owner of Dijkstra Composites in Uitwellingerga, Friesland.
The advantages of the Adaptive Mould Technology
His shipyard specialises in one-offs and small series made of composite and is now producing ships using the new construction method for the first time. The main disadvantage of the previous method is that the sanding and filling process results in uneven hulls. No one can handle the sanding equipment with such precision that the hull sides are exactly identical. In addition, according to the shipyard boss, it is absurd to apply foam first only to sand it away again straight afterwards, as this creates a lot of waste.
The moulded foam panels are much more precise, there are no deviations from the final shape, less filler is needed and less sanding is required. It's all simply more efficient. "And we throw away less because we work directly in the final mould. The moulding frame consists of significantly less wood. That's why there's not so much waste. So the whole thing is also sustainable," says the shipyard boss.
And there is another advantage: "We used to build over an upside-down moulded frame. When the hull was finished, it first had to be turned. Today it works the other way round. The interior laminate, including the strongback and bulkheads, is inserted into the foam panels, which are glued together. Then the deck goes on first," explains the enterprising Frisian and adds: "The whole ship is already very stable when it is turned. This ensures much better dimensional accuracy during construction. All we then have to do is apply the outer layer of laminate, fill and paint. Then the hull is finished."
The disadvantages of the technology
Of course, the construction method also has disadvantages. For example, the production of a 15-metre hull can take several months. The hull and deck of a Bavaria 46 are laminated in one day. The process is of course much more complex than large-scale production. However, if you calculate the mould costs for a small series, the new production process can still be worthwhile. And it is flexible: "Of course, we can discuss and implement customisations with each owner," says Dijkstra. A winch platform further forward? No problem. A longer cabin superstructure? Feasible. Other hull openings for an alternative drive? Any time! Of course, this is not possible in large-scale production. It should be clear that a lead time of several weeks is more expensive than that for a mass-produced hull that is laminated in one day. Nevertheless, the new process is certainly more favourable than the conventional construction method using a moulded frame.
This magic is made possible by a company called Curveworks. The Dutch company has a flexible mould that can be changed with the help of a computer, known as Adaptive Mould Technology. The Corecell foam is heated to a good 100 degrees Celsius and then moulded. This allows 3D moulds to be created that only have a few limitations. One of these is the radii. They have to be at least 250 millimetres, the foam cannot take any less. Chinese cannot therefore be bent. Incidentally, Curveworks also manufactures elements with laminate already applied on the outside and inside. The company Adapa, for example, which built the system for Curveworks and has various boat projects as well as various architectural solutions as references, offers comparable services.
Will the new construction method revolutionise boatbuilding? Perhaps. "From an identical quantity of around five, it is worth building in the same mould as before, as it saves on sanding and filling," says Dijkstra. But if individualisation is a megatrend in society, as researchers have been predicting for decades, then the new production method is the answer. Have your own hull built? Realise your personal preferences and dimensions? Even in small quantities? What was previously only possible in aluminium or as wood epoxy or foam epoxy using moulds is now much easier. On pre-moulded foam or even entire hull elements including laminate. This is innovative and could well turn the world of one-offs and small series upside down. Even the professional is surprised: "It worked much better than I expected," says a delighted Paul Dijkstra.
"More precise, cheaper, better"
Mr Dijkstra, what are the advantages of the new construction method?
Oh, there are a few. Firstly, we produce the final hull mould directly, and we no longer build moulds that are thrown away afterwards, which means less waste. So we are much closer to the finished ship right from the start.
And the mould accuracy does not depend on the skills of the employees, but on the CAD data. And they are always accurate!
Are there any other advantages?
Yes, because the deck is already on when turning, everything stays in shape during the process.
Otherwise this was always such a critical moment, as the hull is as limp as a lamb's tail without the deck and strongback. And the film for the vacuum when injecting the resin can be sealed much better on the large panels than on a hull glued from foam strips.
Is the manufacturing process also cheaper?
Yes, compared to the conventional way. I don't want to say that it costs half as much, but it does save a few steps.
Is the process suitable for large-scale production?
No. We can't work with gelcoat. To get a smooth hull, you have to fill, sand and paint. A hull takes a few months, depending on the size. It's much quicker from the negative mould. I would say that from a series of five boats, a conventional mould is worthwhile.
Have you patented the construction method?
No. Maybe I should have done that. But I'm a boat builder, not so much a businessman. Customers come to me because they want a good boat. I want it to stay that way.
