Section 3 Drag coefficients for pontoons

3.1.1 The nature of the forces on floating bodies is considerably complex and not fully understood. In theory, the forces depend on factors such as speed of flow, area normal to the flow, total wetted area, roughness, detailed form or shape, and the proximity of the seabed or other boundaries and bodies. In practice, simplifications are made when describing forces.

3.2.1 Towing tests on wall-sided boxes have also been performed and results are reproduced in Table 9.3.1 Typical current drag coefficients for wall-sided boxes.

3.3.1 There are very little data on forces or coefficients for floating structures such as barges and pontoons. However, towing tests on barges have been performed, and graphs of typical drag coefficients are reproduced in Figure 9.3.1 Longitudinal drag coefficient for rectangular pontoon in deep water, Figure 9.3.2 Transverse drag coefficient for rectangular pontoon in deep water, Figure 9.3.3 Longitudinal drag coefficient at various water depths for rectangular pontoon with current head on, Figure 9.3.4 Transverse drag coefficient at various water depths for rectangular pontoon with current beam on.

3.3.2 The coefficients in Figure 9.3.1 Longitudinal drag coefficient for rectangular pontoon in deep water and Figure 9.3.2 Transverse drag coefficient for rectangular pontoon in deep water and Table 9.3.1 Typical current drag coefficients for wall-sided boxes apply when the water is deep (depth/draught ≥ 5). The coefficients in Figure 9.3.3 Longitudinal drag coefficient at various water depths for rectangular pontoon with current head on and Figure 9.3.4 Transverse drag coefficient at various water depths for rectangular pontoon with current beam on apply in shallow water.

The following equations should be used when applying the coefficients given in Figure 9.3.1 Longitudinal drag coefficient for rectangular pontoon in deep water, Figure 9.3.2 Transverse drag coefficient for rectangular pontoon in deep water, Figure 9.3.3 Longitudinal drag coefficient at various water depths for rectangular pontoon with current head on, Figure 9.3.4 Transverse drag coefficient at various water depths for rectangular pontoon with current beam on.