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Modern Windships; Phase 2
2. Project StrategyBackground
Strategy for Phase 2
Definitions
Background
At regular intervals during the last 30 years attempts to exploit the wind energy for reducing the fuel consumption of ships have been made, but because of low oil prices and the increasingly higher efficiency of modern diesel engines none of these attempts have proven economically profitable. The rising environmental consciousness in the latest years combined with the success story of the modern windmills has once again breathed new life into the ideas of developing a modern wind ship. With the findings from phase 1 of the project at hand a strategy for designing the modern WindShip was developed.
Strategy for Phase 2
For the design work in phase 2, Pelmatic Knud E. Hansen chose the following strategy:
1) Choice of rig design:
 | The difference between a traditional sailing ship and windships. |
| Traditional sailing ships. |
| Former ideas for a windship rig. |
| The rig design of the windship - phase 1. |
1.1) Brainstorming:
| CFD calculations of rig alternatives. |
| Wind tunnel tests of one or two of the alternatives. |
| Final choice of rig. |
2) Wind tunnel tests of above-water hull with rig.
3) Choice of under-water hull and propulsion devices.
4) Static force measurements of the windship’s hull in
towing tank (PMM tests).
5) Velocity prediction based on the results from the
wind tunnel tests of the above-water hull and the
static force measurements of the under-water hull.
6) Route simulation based on the results from the
velocity prediction and statistical wind data for 3
years on 6 routes world-wide.
7) Detailed rig design:
| Decision on design loads based on wind statistics. |
| Structural design and choice of materials. |
| FEM (finite element method) strength calculation and optimisation of the rig. |
| Detailed design of rig manoeuvring components. |
| Price and weight calculation. |
8) Economical feasibility study based on the route simulation results and the calculated rig price.
The strategy outlined above indicated the need to:
| Design a better rig system than the one obtained in phase 1, incorporating higher lift and less sail area. |
| Investigate the hull lines and appendages to get good manoeuvrability and low resistance. |
| Develop a Velocity Prediction Program (VPP) using the Planar Motion Mechanism tests (PMM) and wind tunnel measurements in order to predict ship speed depending of installed power, wind speed and wind direction. |
| Perform weather routing and calculate realistic data regarding fuel consumption on a specified route. |
| Make a commercial comparison on each chosen route with a conventional ship. |
| Visualise of the WindShip rig using 3D CAD systems. |
This strategy has removed many uncertain factors from the project, therefore the results in phase 2 are considered to be well founded, reliable and realistic.
Definitions
In the text of this report the following phrases and symbols have been used, see Figure 1 below:
Figure 1. Definitions used in the report.
The most often used English phrases can be found in Table 1 below.
The absolute wind |
= |
The direction of the wind in relation to the sea surface. |
The apparent wind |
= |
The direction of the wind in relation to the moving ship. |
Ship’s heading |
= |
The direction the ship’s centre line points. |
The leeway |
= |
The ship’s direction through the water. |
Drift angle |
= |
The angle between the ship’s heading and the leeway. |
The cord |
= |
A straight line from the leading edge of the sail or wing to the trailing edge. |
The angle of attack or angle of incidence |
= |
The angle between the cord of a sail or the centre line of a symmetrical steel mast and the apparent wind. |
Upwind |
= |
Sailing with the apparent wind from a forward direction. |
Reaching |
= |
Sailing with the wind from the side (about 90° to the ship’s centre line). |
Running |
= |
Sailing with the apparent wind from an afterward direction. |
Lift |
= |
The force generated by the sail or wing perpendicular to the apparent wind. |
Drag |
= |
The force generated by the sail or wing in the direction of the apparent wind. |
Stem |
= |
A fixed size mass (batch) loaded on product carriers, often 25-, 35- or 40.000 tonnes. |
HFO |
= |
Heavy Fuel Oil, heavy, cheap oil used at sea, high contents of pollutants. |
MDO |
= |
Marine Diesel Oil, lighter, more expensive oil used when in port, "cleaner". |
Table 1. English phrases, definition
The ship’s courses in relation to the apparent wind have been denoted as follows, see Figure 2:
Figure 2. Wind direction names.
The aerodynamic forces "lift" and "drag" have been defined as follows, see Figure 3:
Figure 3. Lift, drag etc,. definition of terms.
The lift and drag forces vary directly with the density of the air, the sail or wing area and the square of the wind’s speed. It is accordingly convenient to express these forces in terms of non-dimensional coefficients that are functions primarily of the attitude of the sail or wing.
The lift force "L" and the drag force "D" (in N) are given by the following expressions:
| L = ½ r V2 S CL | Equation 1 | |
| D = ½ r V2 S CD | Equation 2 |
Where:
| r | = |
density of the air (1.21 kg/m3 at 20°C and 1013 mbar) |
| V | = |
velocity of the air in m/s |
| S | = |
area of the sail or wing in m2 |
| CL | = |
lift coefficient |
| CD | = |
drag coefficient |
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