## 6 Description of the Developed Design
### Navi Group  
The Active Propulsion Component to be used has two modes: one to generate thrust and drive the SailREC System forward, and one for regeneration. In the latter mode, the propeller will work as a generator and deliver electricity to the power bus. This component will be optimised for the regeneration mode. The Wind Turbine Subsystem will be used as a Passive Propulsion Component. The thrust acting on the wind turbine is used to move the SailREC System. This subsystem will primarily provide propulsion in order to improve energy efficiency.  
For the Anti-Wind Force Subsystem, a combination of four symmetrical keels is used to fully compensate for the thrust on the wind turbine in the direction of the undisturbed wind, preventing the wind from turning the system away from the wind and allowing a small curve radius. The arrangement of the keels, as presented in Figure 11, is inspired by the wing arrangement of a typical aeroplane.  
Each of the two rear keels has a rudder attached to steer the SailREC System. This makes up the Control Surfaces Subsystem.  
The Buoyancy Component of the Floatation Subsystem consists of several hollow bodies. Most of the buoyancy is generated by two long, fully submerged bodies that are connected to the main platform via struts. Floodable sections allow the system to be trimmed, the draught to be adjusted, or the payload to be increased. Only a small fraction of buoyancy is provided by multiple smaller bodies that are also connected to the same struts but are positioned between the main deck and the fully submerged bodies. This arrangement will minimise the area of the Floatation Subsystem that is exposed to waves. To dimension the Buoyancy Component, the total mass of the SailREC System needs to be compensated for by the mass of water displaced. Considering the masses of all subsystems and components as listed in Table 3--with reserving 200 t for additional equipment and assuming the structural mass to be 40% of the system mass as done by [PERSON] et al. (2018)--a system mass of 1553 t is obtained. The displaced water volume, however, is increased by 20% to account for the floodable sections, resulting in a total of 1864 m\({}^{3}\). By assuming a length of the long, fully submerged bodies of 70.2 m--this length excludes the cone of the buoyancy bodies in the front section (cf. Figure 11), which, however, is considered in Table 3 for the overall system length by adding 2 m--which is 60% of the rotor diameter, the diameter of the buoyancy bodies (the smaller buoyancy bodies' volume is neglected at this stage of development) is about 4.1 m. The catamaran-style arrangement of the buoyancy bodies makes up the Counter Torque Component. While the two large, fully submerged buoyancy bodies located 70.2 m apart (given as the distance between the centres of the considered buoyancy bodies; thus, the cylinder radius needs to be added twice to obtain the overall width of the system, as provided with 74.3 m in Table 3) provide static torque countering, they do not generate additional buoyancy in dynamic situations, such as when the system rolls. This, however, is provided by the multiple smaller buoyancy bodies.