Trans RINA, Vol 152, Part A2, Intl J Maritime Eng, Apr-Jun 2010
especially if its aerodynamic design has been given little consideration.
Figures 18 and 19 show the trim angle and the draft of the transom for the planing hull and hybrid vehicle as predicted by the static stability model.
6. THEORETICAL OPTIMUM
Figure 17: Comparison of resistance to weight ratio for the planing hull and hybrid vehicle.
Both Figures 16 and 17 show the characteristic ‘hump drag’ for the hybrid vehicle. Above 30knots the total drag starts to reduce compared to the planing hull and by about 75 knots the maximum drag is reached. Where the planing hull drag increases constantly, the hybrid vehicle drag actually begins to diminish beyond 75knots. This is also the point where the aerodynamic lift becomes greater than the hydrodynamic lift, as is illustrated in Figure 15.
The previous results have shown that significant aerodynamic lift can be produced by a hybrid vehicle design, and that the total drag can be reduced by over 45%. However, the analysis was performed without any control over stability. It can be seen that the vehicle was not analyzed beyond 85knots and that at this point the vehicle trim angle was beginning to increase rapidly. The program evidently predicted that the vehicle would flip over at this point. As such, it would be essential to provide the final AAMV with control surfaces. This is perfectly logical and even simple planing hulls will often have control surfaces to determine the trim angle. Further research will focus on the dynamics of the AAMV with control surfaces.
The purpose of this section is to consider what may be achievable with control surfaces, and thus to identify the real potential of the AAMV concept. The AAMV will be compared to the theoretical results of Lazuskas shown in Figure 1 above,
from [4]. The vehicle
Lazuskas is the 1200tonne INCAT86, which is 76.41m long and 26m wide with a maximum draft of 3m. Versions of this ship are in use around the world and are capable of sustaining speeds of around 40knots. An estimated payload for ships of this
480tonnes. As discussed above, the INCAT is studied with various levels of aerostatic support to compare the benefit of cushion pressure at various speeds. However it was seen that a variable cushion pressure would allow a hybrid vehicle to out perform all of the individual designs proposed.
studied by
size would be
Figure 18: Trim angle in degrees for the planing hull and hybrid vehicle.
Figure 20: Optimum aerodynamic lift fraction as a percentage, shown against speed for a 1200 tonne vessel based on the INCAT.
Figure 19: Draft of the transom for the planing hull and hybrid vehicle.
A - 48
Figure 20 shows the estimated percent of aerodynamic lift which would follow the line of least resistance for a hybrid vehicle. The minimum and maximum markers show the upper and lower limits of cushion support at the given speed, which match Lazuskas’ minimum drag. The
©2010: The Royal Institution of Naval Architects
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