Digest | Zero USV 110 Kit-built hull Vessels today can be constructed from a flat-packed kit, in which the parts for the hull shape, frames, stringers, deck plating and shell plating are all cut from metal and stacked in a crate. “Back in the late 1990s, I worked with someone called Jim Moore, who came up with this system for producing selfjigging steel or aluminium kits, such that boats could be put together like a Lego kit,” Ratsey says. “The frames will largely feature positive tabs that come out, so that when you put the shell plating on it slots through. They will also have been cut with slots for inserting and holding the stringers, and all the other detailed holes and grooves you need are pre-cut, so that an Oceanus12 can be assembled and tag-welded together in a matter of days. “It really came about with the advent of advanced design software for visualising these sorts of components, as well as laser-cutting for precision, timeefficient metalwork of kit components. Laser machinery also lets us etch serial numbers on the frames, as well as other clever things, so you can really make quite a sophisticated kit.” Overseas manufacturing of Oceanus12 USVs can be arranged by simply sharing the design files with laser-equipped CNC houses for them to use in producing kits or by shipping the kits in containers. Snijtech in the Netherlands cuts, stacks and supplies the Oceanus12 kits (as well as sourcing the recycled aluminium they are made from) for Zero. “Snijtech’s leadership as a vessel kit manufacturer is one of the worst kept secrets in modern naval architecture,” Ratsey muses. “Basically, everyone is using Snijtech for their aluminium lasercut kits, and we can get kits fully cut and formed from the recycled aluminium, readied for assembly in Holland, and then delivered to the UK, all cheaper than buying aluminium in the UK, thanks to Snijtech’s volume, efficiency and know-how.” Monohull hydrodynamics Snijtech’s very large metal-forming and bending machinery has enabled the assembled Oceanus12’s shell plating to be made from large pieces of aluminium. Those feature soft, hydrodynamic curves rather than sharp corners across the boat’s length. “Getting a shipyard to do that costs a fortune, because they will have someone with a hammer slamming and bending metal manually, but doing it in a large machine with MDF templates means we can have some quite large sections bent and pre-formed, so the boats move efficiently and look good at a cost-effective price,” Ratsey says. Both software simulation and towing-tank tests of hull prototypes have gone into optimisation of the USV’s hydrodynamics, as have lessons from the Mayflower, despite it having a trimaran hull. “The build costs of a trimaran and other multihulls aren’t necessarily justified by the benefits,” Ratsey explains. “There’s some stability gained over a monohull in places, but with serious exceptions to that general rule. If you’re going over or down a wave, the trimaran can very easily and suddenly decide to do a hard left or right, possibly then capsizing.” Hence, a narrow, slender monohull became the preferred approach for Oceanus12, especially after simulating both hull types in the company’s trusted in-house software. As a result of the monohull’s efficiency and safety, at 6-7 knots, Oceanus12’s two 750 litre fuel tanks give a range of roughly 2500 miles (4023 km). If a survey speed of 3-4 knots is maintained, close to 1000 miles may be added to the range between refuelling stints. More fuel tanks can be added or mothership refuelling arranged if required. October/November 2024 | Uncrewed Systems Technology Due to the cost involved with GRP, the Oceanus12 today is an aluminium kit-built vessel; the kits cut and supplied by Snijtech in the Netherlands Snijtech’s machinery has enabled the Oceanus12’s shell plating to be made from large pieces of aluminium, featuring soft, hydrodynamic curves
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