1. Energy Saving & Efficiency Feasibility Study SHIP AERODYNAMICS
Prepared for
2014 MARINE TECH KOREA

2. SHIP AERODYNAMICS Prepared by: Ernesto Valtorta Haiye Lou
Francesco Pacori
Thomas Clever
JM Lee
EV Consulting
Via Giulio Cesare 37
I Venegono Superiore VA (Italy)
Changwon (9/29 ~ 10/2/2014)

3. SHIP AERODYNAMICS INTRODUCTION
In recent years, in a climate of rising fuel costs and increased competitive pressure, the issue of energy efficiency has become the focus of attention as even a small amount of energy savings pays back in saved costs. This paper analyses the configuration of a typical transport vessel with the goal to assess the impact of aerodynamics on its overall energy efficiency.
These ships feature extended frontal surfaces with a low degree of aerodynamic streamlining. Due to the relatively low velocities in play, extensive and accurate studies to lower the aerodynamic drag have in the past seldom been judged necessary. Only in recent years some shipyards have begun to develop and produce vessels with shapes designed to increase aerodynamic efficiency. Refer to Figs. 1-4.

4. SHIP AERODYNAMICS SUMMARY
This work introduces the basic concepts underlying a correct aerodynamic dimensioning of the structure exposed to the winds of a large transport vessel. Included are indicative calculation criteria, and the levels of energy savings which can be attained by the introduction of a few modifications to the ship configuration.
The largest part of drag (~90%) seen by the ship in motion is attributable to the submerged part. For this reason we have included a few considerations pertaining to the submerged part. This could be the object of improvements through a limited set of modifications to reduce vortex and to improve the propeller efficiency. As an example, our team has recently collaborated in the development of racing ships (America Cup). Substantial improvements have resulted from the application of selected basic aerodynamic principles to the keel design.

5. SHIP AERODYNAMICS BASIC EVALUATION
The largest contribution to the vessels’ aerodynamic drag comes from the frontal surfaces which are mostly flat, lacking aerodynamic streamlining. By installing connectors to soften and round these shapes, the drag coefficient will be reduced while presenting an opportunity to create new volumes to be used for cargo or personnel.
Table 1 shows the geometry of these surfaces, an estimation of their respective drag coefficient and the computed power to overcome the aerodynamic resistance generated by these surfaces.
In order to estimate the total power required at cruise speed and the percentage pertaining to aerodynamics, we have assumed a net propeller efficiency of 0.55.
From this very preliminary analysis it can be seen that by implementing the described modifications, the power used to overcome aerodynamic drag can be reduced by about 50%.
As a consequence, the attainable net saving in energy is at a level of 2-4% for the typical ship.

6. SHIP AERODYNAMICS MODIFICATIONS TO THE FRONTAL AREA
As shown in the figures section, our draftsmen have imagined a few modifications, with varying degrees implementation difficulty. These are preliminary studies from designers who had been given latitude to propose their own solutions. Depending on the client’s wishes we are prepared to elaborate and finalize them.
DRAG INDUCING STRUCTURES ON THE OPEN DECK
Whenever possible, drag-inducing structures on the open deck should always be aerodynamically streamlined to avoid flat or complex surfaces orthogonal to wind direction. In the interest of a lower aerodynamic impact, even lifeboats should be placed advantageously in this respect, for example inside the frontal aerodynamic hood structure.

7. SHIP AERODYNAMICS
GENERAL CONSIDERATIONS We have carried out a sizeable study and analysis which has allowed us to evaluate and quantify the impact of the vessel configuration on some of its basic performance characteristics. Specifically, a hypothetical configuration with the navigation and quarter decks displaced to the bow would be worthwhile, bringing about more favorable stability conditions for navigation in crosswind situations; less rudder excursion to maintain course; higher degree of streamlining and thus a lower aerodynamic drag. An accurate study using more complex computation criteria has permitted to sufficiently validate the considerations emerging from the more simple analysis reported in the present document. With proper streamlining and covering modifications, the drag coefficient could be reduced by at least 50%, as detailed in figs. 5,6,7. With regard to the submerged part, we have found that it is not a common practice to analyze turbulence and hydrodynamic flow as it is customary in aerodynamics. We intend to assess the viability of the same type of cost-effective and easily installed modifications (ventral fins, vortex generators etc.) which promise an effective improvement to the submerged hull hydrodynamics.

8. SHIP AERODYNAMICS
BASIC CALCULATIONS
As reference and background to the study of ship hull resistance with modification proposals for energy savings, this appendix presents the basic principles and calculations governing ship hull resistance. We hope that this will help to clear any doubts which might arise.

9. SHIP AERODYNAMICS
Hull Resistance And Its Components Total hull resistance is defined as the force required to move a ship through calm water maintaining a certain speed. There are many factors that combine to form the total resistance force Rt acting on the hull, and they interact in rather complex ways. Assuming no interaction, the principal components of ship resistance are as follows: Friction resistance Rf, the energy required to overcome the friction and viscous effects of water acting on the hull Wave making resistance Rw, The energy required to create and maintain the ship’s characteristic bow and stern waves Vortex resistance Rv, The energy dissipated to create and maintain the vortices generated by the hull and its appendices. Air resistance Ra, the energy spent to maintain the emerged hull and the superstructure in motion in calm air. Thus we can write Rt = Rf+Rw+Rv+Ra Generally the two components Rw and Rv are combined to define the so called residual resistance Rr: Rr = Rw+Rv and therefore: Rt = Rf+Rr+Ra

10. SHIP AERODYNAMICS Determining Total Hull Resistance
Based on Froude’s hypothesis, which states that friction resistance and residual resistance are mutually independent, the friction resistance can be calculated with the following formula:
Rf = Cf · r · S · V2 (1)
Where
Cf = friction coefficient, found with empirical formulae
r = density of water
S = wetted surface
V = speed
In the formula, the wetted surface S has fundamental importance, the friction resistance being directly proportional to it. S can be calculated with good approximation by experimental formulae.
Alternatively, there are computer programs designed to calculate the exact value of S from the hull geometry derived from the construction drawings.

11. SHIP AERODYNAMICS Computing The Residual Resistance
Residual resistance being not easily calculated, it is obtained through model data from towing tank experimentation. In these experiments, a hull model is towed through the water at a given speed while the force Rt resisting the hull’s movement through the water is measured. The friction resistance Rf calculated with formula (1) is then subtracted from Rt resulting in the model’s residual resistance Rr. Model resistance data can then be scaled up to full-scale ship resistance using appropriate hypotheses and formulae.
The addition of friction resistance and computed residual resistance yields the total resistance of the clean (polished) hull. To derive the effective resistance, the resistance due to the hull rugosity (which increases friction), the air resistance and the resistance of appendices (obtained from empirical formulae) must be added.

12. SHIP AERODYNAMICS Determining the Installed Horsepower
Once the total ship resistance Rts is known, the effective horsepower is calculated with the relation
Pe=Rts * Vs
where Vs is the vessel’s design speed.
To determine the ship’s prime mover characteristics, we need to start from the effective horsepower and proceed to the installed horsepower, accounting for the different efficiencies of the propulsive organs involved:
• η0 = isolated propeller efficiency: in optimal project conditions, the propeller as propulsive organ will exhibit an efficiency of between 0.5 and 0.65
• ηh = hull efficiency: this takes into account the fact that the hull in motion will drag water with it, therefore the propeller will move at a different speed relative to the water as the ship.
• ηr = rotational efficiency: takes into account that the flow into the propeller is not regular, but perturbed by the presence of the hull.
• ηs = line shaft efficiency: takes into account the friction losses of bearings and reduction gear
Thus the delivered horsepower can be calculated from the relation
Pd = Pe/(ηo*ηh*ηr) = Pe/(ηd)
where ηd = propulsive efficiency
Shaft horsepower is calculated with the following relation:
Ps = Pd/ηs
Where ηs = mechanical efficiency of the line shaft
Ps is not yet the installed horsepower. Instead, Ps is usually increased by 10-15% to provide for a margin to be able to maintain the speed corresponding to the maximum continuous power in rough waters and “dirty” hull. Thus, brake horsepower and total propulsive efficiency ηpt obey the following relation:
ηpt = Pe/Pb

13. SHIP AERODYNAMICS Determining Air Resistance
In the following, we present a first approach to determining the resistance (distinguishing, where possible, resistance in water and resistance in air) of a number of livestock carrier vessels. Opportunities for reducing the resistance with the aim of energy savings will be examined and quantified.
Known quantities are the Normal Continuous Rating and the speed at that power level. After determining the propulsive thrust allowing for the various efficiency figures (which here have been best-estimated) we can proceed to estimate the air resistance with the current architecture. Then, we can evaluate the effect of simple variations and streamlining to the stern. The following figure shows how the ship superstructure has been partitioned into simple block shapes with the aim to ease the resistance determination.

14. SHIP AERODYNAMICS

15. SHIP AERODYNAMICS
In all cases, the resistance of the ship up to the upper deck remains as is, since we see no possibility of fruitful modifications. The only promising approach to reducing the thrust required to maintain the current speed is represented by streamlining operation to decks 2), 3) and 4).
The following resistance coefficients have been estimated for each single block:
Cd1 for the hull comprising upper deck and superstructures
Cd2 for the quarterdeck
Cd3 for the navigation deck
Cd4 for the equipment deck house (where present)
These will be used to obtain the total resistance to air (Ra) using the following formula:
Ra = (Cd1·S1+Cd2·S2+Cd3·S3+Cd4·S4)·ρ·Vs2 /2
Where
S1..4 = block frontal surface ρ = air density

16. SHIP AERODYNAMICS TYPICAL TRANSPORT SHIP
Normal continuous rating = Ps = KW ( 90%)
Speed = Vs = 19.5 kts = m/sec
η0 = 60 %
ηh = 95 %
ηr = 93 %
ηs = 97 %
ηd =
Thrust = -Rts = Ps·ηd/Vs = *10458* /(19.5*0,51444) = Kg
q = ρ·Vs2/2 = kg/m2
Block surfaces:
S1 = m2
S2 = m2
S3 = m2
S4 = m2
Estimated current Cd:
Cd1 = 1.45
Cd2 = 1.20
Cd3 = 1.35
Cd4 = 1.35
which bring Ra to:
Ra = (1.45· · · ·20.2) · = 5605 kg
Therefore equal to 10.3% of total resistance (thrust).

17. SHIP AERODYNAMICS Cd levels obtainable by suitable stern streamlining:
which would bring Ra to:
Ra = (1.30* * * *20.2)*6.289 = 4420 kg
Thus the total resistance Rts would be decreased by 2.2% with a savings of 227 KW.

18. Fig. 1 New generation ship
SHIP AERODYNAMICS
Fig. 1 New generation ship

19. Fig. 2a New generation ship
SHIP AERODYNAMICS
Fig. 2a New generation ship

20. Fig.2b New generation ship
SHIP AERODYNAMICS
Fig.2b New generation ship

21. Fig.3a New generation ship
SHIP AERODYNAMICS
Fig.3a New generation ship

22. Fig.3b New generation ship
SHIP AERODYNAMICS
Fig.3b New generation ship

23. Fig.4 New generation ship
SHIP AERODYNAMICS
Fig.4 New generation ship

24. Fig. 5 Modification proposals for a new configuration
SHIP AERODYNAMICS
Fig. 5 Modification proposals for a new configuration

25. Fig. 6 Futuristic design proposal
SHIP AERODYNAMICS
Fig. 6 Futuristic design proposal

26. Fig. 7a FINS IN FRONT OF THE PROPELLER
SHIP HIDRODYNAMICS
Fig. 7a FINS IN FRONT OF THE PROPELLER

27. SHIP HIDRODYNAMICS Fig. 7b FINS IN FRONT OF THE PROPELLER

28. SHIP AERODYNAMICS Fig. 8a NEW STX SHIP

29. SHIP AERODYNAMICS FIG. 8b NEW STX SHIP

30. SHIP AERODYNAMICS Fig. 9 Korean ship with good aerodynamic