Fig 1. Breaking wave in front of the tested LCU at 12 knots

Fig 3. CFD result of a waterjet inlet, showing a large separation

Supported Vessel, and based on a design from Damen Shipyards and ESI, was considered. Resistance and propulsion tests (figure 2) up to almost 40 knots were performed, varying the weight distribution of the vessel. Results show that resistance really can be lowered dramatically at high speed, as soon as the breaking wave upfront has disappeared.

Fig. 2 model test of an air supported vessel at 37.5 knots

only blow its jet against the water instead of air.

Therefore, the alternative of increasing the brake power of the waterjet versions was considered. Because performance in sea state 3 is a critical requirement, added re- sistance tests in head waves were per- formed. These tests are important as the power demand climbs quite quickly be- cause of the increasing speed due to the breaking wave (figure 1), and because the

resistance is still difficult to predict in a quantitative way by calculation. After test- ing each alternative for three different draughts an evaluation matrix was given to the client as a basis for a decision. This clearly showed any gains in speed and ad- ditional costs for a particular design choice.

Air Supported Vessel The second track was looking at a completely new design with much higher speeds - up to 40 knots - for which a promising concept, named Air

CFD methods Model tests also showed that the waterjet inlet design requires careful attention in order to avoid air ventilation. But the design of the inlet can nowadays be evaluated in an early phase of the process with CFD methods. Figure 3 shows an example of the aforementioned mid-life upgrade evaluation. An advantage of this methodology is that both model and full-scale can be considered, as issues like flow separation can be different for both scales.

By a combination of model testing and calculations, MARIN was able to quantify and work out the pros and cons of different propulsors and LCU concepts, thereby supporting DMO on decisions concerning its LCU mid-life upgrade and long-term alternatives.

report 21

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