During front crawl swimming, water is driven backwards with the limbs. Drag forces generated by the limbs are consequently used for forward propulsion. The hands are responsible for approximately 60% of the generated propulsive forces. Reaching a podium place in competitive swimming is dependent on differences in finishing times smaller than 0.5%. For this reason, investigating the effects of hand configuration on swimming performance is of interest. Configurable properties of the hand are the finger spreading and hand palm cupping. It is argued that a small finger spreading leads to a larger obstruction in the fluid flow compared to closed fingers, resulting in larger generated drag forces. Similarly, a small hand cupping is expected to increase the drag forces in analogy to the drag increase experienced by cupped disks. In this thesis, an experimental investigation is carried out to look into the effects of both finger spreading and hand cupping. Furthermore, CFD simulations are used for the abstract modelling of hands with finger spreading by use of slotted disks. 
Towing tank experiments in water are performed to investigate the effects of finger spreading for five full-scale arm models. The research showed that a small finger spreading of 5° can increase the drag coefficient of the hand with 1.7%, in comparison to closed fingers. Larger spreadings were found to influence the drag coefficient disadvantageously, where a 20° finger spreading reduced the drag with 1.5%. The found effects indicate that finishing times can be reduced with 0.3% by using 5° finger spreading instead of 20° spreading.
Wind tunnel experiments are used to look into the effects of hand cupping. Dynamic scaling based on the Reynolds number is used to account for the used air flow. Effects for five full-scale arm models with different hand cuppings were investigated, these have a 5° finger spreading which was found optimal from previous research. It appeared that small rotations around the longitudinal axis of the arm have large influences on the drag coefficient, where a maximum in drag was never found for the hand palm perpendicular to the flow, but with an abducted thumb opposing the flow. The research showed that 6% more drag is generated for a flat hand in comparison to the largest investigated hand cupping. This indicates that finishing times can be reduced with 0.8% by using a flat hand instead of a large hand cupping. 
In conclusion, the research found a hand configuration with 5° finger spreading and a flat hand palm optimal for maximizing drag forces. The found effects on finishing times indicate that using this hand configuration can play an important role in reaching podium places during front crawl swimming.

Rowing is a competitive sport where victory is determined by fine margins. In the past, the focus has been on optimizing the shell. Due to the increasing regulations placed on the shell design, the scope for manoeuvring in this area is greatly limited. This increases the necessity to focus on the less explored option of propulsion in rowing. The propulsion is caused by the momentum transfer from the rowers to the water with the help of oar blades. The design of these oar blades has also been extensively studied. However, knowledge on the effect of the air-water interface on the drag force on the oar blades is still lacking. Therefore, visualizing the flow around the oar blades will lead to better understanding of the flow structures, which would help in optimizing the drag force acting on the oar blades.

In the present study, a simplified scenario of a rectangular flat plate moving normally to its plane along a straight line and parallel to the free surface has been studied using hydrogen bubble visualization and Particle Image Velocimetry (PIV). Using a 4-axes industrial robot and a force/torque transducer, the effect of the air-water interface on the drag force on the plate has been studied at a Reynolds number, based on the longest edge of the plate, of 6×10⁴. The analysis of the drag force profiles at different plate depths led to the identification of a high drag case, which occurred at a plate depth h of 20 mm. The hydrogen bubble visualization indicated that in this specific case, the high drag was related to the formation of a compact wake behind the plate.

Hydrogen bubble visualizations were also performed at two other plate depths, h = 0 and h = 100 mm, to determine the effect of the air-water interface on the flow structures and ultimately on the drag force acting on the plate. The visualization of the deep water case (h = 100 mm) captured the formation of a vortex ring, which was found to have unique effects on the drag force. The presence of the air-water interface was found to significantly influence the drag force on the plate. Additionally, an extensive decomposition of the drag force profile showed a time-dependent added mass force and a decaying force acting on the plate.

Particle Image Velocimetry (PIV) measurements were carried out in the horizontal mid-plane of the plate. The tracking of the starting vortex and its disintegration has been identified using the swirling strength analysis. Finally, combining the hydrogen bubble visualization and PIV results, the formation and the development of the starting vortex was identified.