FASt - FEUP Autonomous Sailboat

The design

The FEUP sailboat was designed with a free boat design software (www.delftship.net). Initial design was inspired on the shape of high performance oceanic sailing yachts and has further counted with several opinions of experienced sailors and people in the business in boat building. The main dimensions (length and displacement) where determined after scaling down a typical Class40 sailboat, constraining the displacement to the 40Kg limit initially imposed by the Microtransat rules. The main views of the design are shown in the picture below.

FASt general dimensions:

Hull construction

The construction of the hull was done by a Portuguese kayak builder, located in Crestuma, north of Portugal (www.elio-kayaks.com). This builder has large experience in building high-performance and ultra-light competition kayaks in composite materials.

The initial positive model was build at FEUP, starting with plywood frames cut from the sections exported by the design software. The assembly of frames was covered with a rough layer of strip planking and fiberglass with polyester resin, followed by various iterations of filling and sanding to achieve a final smooth surface. This full scale model was then used to build a negative mould and, afterwards, the final hull.

The hull has been fabricated in sandwich of carbon fiber (outer layer), a low density honey comb core in the middle and a inner layer of fiberglass. This sandwich was pressed with vacuum during the cure of the epoxy resin. This is the same construction process used by Elio to build high-performance racing kayaks and resulted in a very stiff hull, weighing less than 5kg (without the deck).

The hull was then reinforced internally at the points subject to the major mechanical forces: the attachment of the keel, foot of mast and the points where the shrouds and stays fix to the hull. Two platforms placed at the bottom interior (front and middle) provide convenient space for mounting the electronic system and additional payload.

Foils

The long keel (1.20m plus 0.3m inside the hull) was built manually starting from a core of rigid polyurethane foam shaped to a NACA profile, then laminated in vacuum with several layers of carbon fiber. The rudders were made from a wood core covered by fiberglass, firmly attached to a stainless steel shaft.

Mast, boom and sails

The mast and boom were built from tubes of carbon fiber, used in competition paddles. The rail for the main sail was recovered from an old mast and attached to the tube. Shrouds and stays are made of conventional  stainless steel cable and the rest of the hardware is the same used in small dinghies.

The sails are being built by a Portuguese sail maker, located in Santa Cruz do Bispo, near Oporto (Velas Pires de Lima, www.velaspl.com). The first sails will be done with the same fabric of real size sails, but after tuning the boat a more resistant set will be necessary to withstand strong winds that are expected to be found during the transat.

Electronic control system

The electronic system is built around a microcomputer system implemented in a FPGA-based board (Suzaku SZ130). The computer runs a variant of the Linux operating system (uCLinux), offering a convenient development platform with important services like multitasking, file-system management and support of TCP/IP communications. The FPGA chip includes a RISC 32-bit central processor (Microblaze from XILINX) surrounded by a set of custom designed digital systems that implement the interfaces with sensors and actuators, and also some custom processing and control tasks. This allows the integration of almost all the custom digital electronics into a single chip and simplifies significantly the design of the control software, alleviating the processor from low-level interfacing and data processing tasks.

Sensors and actuators

FASt includes sensors to measure various parameters required for autonomous navigation: wind speed and direction, angular position of sails, temperature, speed, course, geographic position, roll, heading and pitch. The wind direction sensor was built from a commercial chip that measures the orientation of a permanent magnet placed near the chip's case (Austria Microsystems AS5040). The assembly with the chip was embedded in epoxy resin, making it completely water proof. The position of main sail's boom is measured with an identical device. All the other sensors are commercial modules: GPS (ublox), tilt compensated compass (Honeywell), 2-axis accelerometer and two 6-channel AD converters that provide information of the temperature inside and outside the hull, ambient light (some channels are free for future expansion).

The actuators are two standard RC servos that control independently the two rudders and a DC motor with position feedback to control the sail's sheet. A second DC motor may be later installed to implement a mechanism of reefing the sails (reducing the sail area) or deploy an additional fuller sail (gennaker) for downwind navigation.