52 Digest | SeaTrac SP-48 USV sections would break first. Most of the changes, as Boeschenstein recounts, relate to fasteners, seals and keel design (for easier launch and recovery, and compatibility with underwater sensors). Structure and layout The SP-48 is a somewhat flat monohull at 42 cm draft, with considerable subsystems packed in defined areas across the hull for a SWaP-optimised platform. Atop is a mast for antennas and sensing instruments, besides six solar panels and a plethora of hatches for accessing subsystems below deck. “Under the bow hatch we have a main electronics enclosure; under the next hatch along the USV’s length we have our battery assembly, with the moon pool right behind that; and then we have a larger hatch, which we call the payload hatch behind,” Boeschenstein says. “That has different options for mounting equipment. You can put in different kinds of plates and brackets to support instruments of varying sizes up to about 4 ft long and 2 ft wide. Behind the payload hatch are the propulsion and steering assemblies, which are accessible via a stern hatch.” The boat is constructed broadly from three pieces: a hull piece bonds to a deck piece, with a separate moon-pool piece bonding within those at roughly the centre. All three are largely made from pieces of fibreglass composite with foam core material. Hull-part manufacturing is largely outsourced to a strategic partner, with assembly performed in-house; a process that includes SeaTrac’s engineers cutting hatch holes, mounting fasteners, and installing subsystems as required before the hull and deck get adhesivebonded together. “It took a long time to narrow down to the contract manufacturers for our fibreglass composite parts we use, but we’re now very happy with their consistency. The exact same hull and deck pieces get delivered every time, even when we’re scaling up or down our orders, and our people in our workshop are able to get them prepped and rigged very quickly into a fully assembled unit each time without any surprises,” Boeschenstein says. “The whole assembly process for a single SP-48 can be completed from start to finish in just under four weeks if we push ourselves, and we’ve always placed a lot of emphasis on being able to do that reliably and consistently. “Buddy and Jigger put a lot of work into organising and optimising our production process plans, our jigs and fixtures, our tools, our training processes and other key inputs to make sure that when we’re building a USV in one part of the workshop there is no-one left with just a tape measure, trying to figure out where they’re meant to put a hole.” Instead, the team’s fixtures are designed to be laid down on hull pieces, and those then register where a feature is meant to be, such that holes and hatches get cut into the exact same spot and dimensions every time, with no misreading of tape measures and no wrong measurements or other manufacturing errors. Solar electric boat The solar-panel cells are made from a standard, widely available, high-efficiency crystalline silicon. The full panels are custom-built with a total panel rating of 816 W at 1 kW/m² solar generation. That power runs from the six panels into the battery in parallel (so that if one is shaded, the others continue to function) via SeaTrac’s power-management system, built with customised charging boards. The battery is monitored via SeaTrac’s own in-house developed BMS, which controls the charging and discharging rates. The batteries are engineered for a 39 V nominal voltage (with the 39 V supply ports interconnecting seamlessly with the battery bus). Floatage above or below that nominal level is minimised by virtue of the pack being composed of lithium iron phosphate cells – one of the more stable cathode chemistries. “As one of the safer chemistries, it may have a slightly lower energy density than some others used in uncrewed systems, but it doesn’t quite suffer the same certification or clearance issues that higher energy, more unstable chemistries do,” Boeschenstein explains. “That means it’s easier to get it shipped, moved by truck or approved for bringing it into some kind of base, so choosing that battery composition was a very conscious choice.” December/January 2025 | Uncrewed Systems Technology The USV is largely constructed from three pieces of fibreglass composite sandwiching foam core material, which comes from a contract manufacturer that SeaTrac prizes for its consistency
RkJQdWJsaXNoZXIy MjI2Mzk4