Refine design of hullforms for high speed surface water crafts
Frazer-Nash has developed unique capabilities in hydrodynamics and CFD applied to the marine sector
Boat operators are continuously seeking ways to travel at ever increasing speeds (sometimes in severe sea states) whilst reducing operating costs. With this in mind, Frazer-Nash were asked to provide design recommendations to our client on how to improve the speed and efficiency of their high speed craft.
Our highly experienced marine engineers already knew that the ship’s hullform directly influences the speed, fuel consumption and behaviour of the boat, whilst its structure keeps it robust and sturdy (and is also where the manufacturing costs go). The key challenge was to balance sea keeping (how smoothly the boat travels over or through the waves) with low resistance and high stability – whilst maintaining a steady platform upon which crew can work effectively.
We began by developing a Computational Fluid Dynamic (CFD) model of the boat on which to apply data captured early in the design stage. This enabled us to assess the smooth water resistance of the hull form, and to select the powerplant and propulsion system, and estimate the size of the required fuel tanks.
We were also able to simulate how wash affected the vessel, and how it could be better managed in terms of hullform, craft speed and trim. We then analysed the same performance in rough water, simulating the irregular characteristics of the sea surface over many wave peaks. We discovered that the motion of the hull on the proposed ship’s design could potentially impose unacceptable accelerations on the crew, causing nausea, fatigue or even injury. Using “HydroDyna” (our unique numerical code), we demonstrated to the naval architects and designers:
- An understanding of allowable speeds in various sea states
- The design and production of a sprung crew seat to counteract the motion
- The placement of operators’ stations in the boat to reduce the occurrence of sea sickness
Applying the same software technology, we then quantified the pressure loading on the hull at high speed in severe sea states, and applied the impact pressures to a Finite Element (FE) model of the full hull and internal structure to analyse effects on structural strength. This method has in the past highlighted regions that experience loads in excess of standard empirical design best practices and are not easily found by conventional methods.
Incorporating this capability into the design of a high speed craft greatly improved our client’s understanding of performance at an early stage in the development process. Whilst greatly improving performance, this also reduced the likelihood for a redesign later on in the programme.