3D-printed hard tops: weight, lead time and what changes compared with fibreglass

The hard top is the part shipyards and owners ask us for most often, and the one that best shows the difference between large-format 3D printing and fibreglass. The reason is simple: almost every hard top is a one-off. It replaces a canvas bimini, it has to match that boat’s cabin, it often has to work around an existing rollbar. In fibreglass a one-off pays for the whole plug and mould; in 3D printing there is no mould.

How a fibreglass hard top is made, and what it really costs

To laminate a hard top you first need a plug (the positive, milled from foam or wood and faired by hand) and then a mould (the negative, laminated over the plug). Only then can the actual part be laminated. For a one-off, plug and mould are used once and then take up space in the yard or go to waste. That is weeks of manual work and material that never ends up on the boat. It is why, for a 7.5 m fisherman, the plug and mould would have cost more than the hard top itself.

How we do it

1. Survey and design. We start from the designer’s 3D model or, if the boat already exists, from a 3D scan on board. The part is designed for printing: split into segments that suit the robot and the truck, with joints and assembly references built in.
2. Robotic printing. The robot lays down reinforced thermoplastic in thin walls with no infill. Stiffness comes from geometry, patented hollow ribs and iso-grid structures where needed, not from extra material.
3. Assembly and lamination. The segments are joined on a CNC-cut jig and laminated with glass or carbon fibre, by us or at the yard. From then on the part is a composite like any other: fairing, painting, installation.

The numbers from five installed hard tops

Boat	Size	Weight of the printed part	Printing hours
Aquasport 245 fisherman (7.5 m)	250 × 60–47 cm, h 130 cm	24 kg	20
Oceanis 43 sailing yacht	400 × 180 cm	55 kg	40
50’ motor yacht with rollbar	480 × 200 cm	75 kg	70
55’ motor yacht	650 × 270 cm	80 kg	100
13 m RIB, one-off hard top	815 × 320 cm	60 kg	80

Printing hours are machine hours, not working days of a crew: the robot also prints overnight. The Aquasport hard top was delivered and fitted about 90 working days after the order.

Weight: what changes up high

A hard top sits in the worst place on the boat for the centre of gravity. The printed part is light because the structure is hollow and the walls are 2–3 mm thick; the final weight depends on the lamination the yard chooses, but it stays well below an equivalent cored fibreglass part. Less weight up high means a more stable boat, less roll and an installation done by two people and a light crane instead of a crew.

Lead time: weeks instead of months

With no plug and no mould, time goes straight from design to part. For the 13 m RIB hard top documented in our study with Politecnico di Milano, production was twice as fast as milling. The advantage grows with complexity: curved shapes, undercuts and hollow cable runs are free in printing, while in a mould they are paid for in labour hours.

Cost: what you do not pay for

We do not publish price lists, because every hard top is different: size, number of segments, level of finish and who does the lamination all change the quote. What can be said in general is what disappears from the bill: the plug, the mould, their disposal, most of the hours of manual fairing, and the shipping cost of a heavy, bulky part (the segments travel on a standard truck). For a one-off the result is almost always in favour of printing; for a run of dozens of identical parts the mould becomes competitive again, and we say so.

The questions we always get

Is it strong enough? The hollow-rib structures were bend-tested against balsa sandwich panels and are installed on boats that have been sailing for seasons; a printed RIB windscreen did 150 hours at 28 knots with no damage.

Can it be painted and repaired? Yes. After lamination the part is treated like any composite: filler, primer, paint or gelcoat, and repairs are the same as for fibreglass.

What about the sun? Thermoplastics need UV protection: lamination and painting do exactly that, as on traditional parts.

How big can it be? Printed segments reach several metres and are assembled: the largest hard top in the table measures 8.15 × 3.2 m.

If you have a hard top to build, send us the 3D model or photos of the boat: we reply with a segmentation proposal, an estimated weight and a lead time.