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**R&D JOINT ACTIVITIES OF NAVANTIA, CEHIPAR AND SISTEMAR**

In 1997 a strong co-operation among Astilleros Españoles, CEHIPAR and SISTEMAR started with the R&D project entitled "OPTIMIZATION OF SHIP PROPULSION BY MEANS OF INNOVATIVE SOLUTIONS INCLUDING TIP PLATED PROPELLERS" (1997-1999). At such time IZAR and NAVANTIA were not yet created.

The conclusions of these research activities were very positive for all the three partners. One of the goals obtained was to develop a procedure to extrapolate at full scale model test results with CLT propeller models. The necessary empirical know-how was deduced in such a way that nowadays CEHIPAR can extrapolate at full scale model test results with CLT propellers with the same degree of accuracy than in the extrapolation at full scale of model test results with conventional propellers.

The extrapolation procedure developed is almost the same than the ITTC’78 extrapolation procedure for conventional propellers but with the introduction of some special corrections on the scaling of the CLT propeller open water curves. The procedure was presented at The Motor Ship Conference 2005 (“Scale effects in model tests with CLT propellers”. 27th Motor Ship Marine Propulsion Conference. Bilbao, January 2005).

Another important goal of this R&D programme has been to stand out the scale effect existing in the epsilon coefficient, that defines the balance between the overpressure and underpressure forces acting on the blades of a CLT propeller.

At full scale the water flow is fully turbulent and there si not separation of the laminar boundary layer and hence the water leaves the cascade of profiles with direction tangent to the mean lines of the profile.

However, the laminar flow separation produced at mode field affects not only to the viscous forces acting on the blades (leading to higher CD values) but also to the pressure distribution on the blades and hence to the lift forces (leading to lower CL values).

Because of the above, scale effects not only on viscous forces but also on lift forces have to be taken into account to correct the influence of the laminar separation produced at mode field with CLT propellers.

Due to the higher CD values of model field and the lower CL values, the epsilon coefficient at model field is higher than at full scale and therefore the propeller open water efficiency is lower at model field than at full scale and furthermore, the cavitation performance at model field is worse than at full scale.

The above mentioned conclusions decided to IZAR to undertake further research, in order to clarify these results. Following this, a new R&D project has been carried out during 2001-2003 among IZAR, CEHIPAR and SISTEMAR.

The objectives of this project were as follows:

- To develop a new procedure to conduct cavitation test with CLT propellers, in order to assure that inside of cavitation tunnel a phenomenon similar to the one corresponding to full scale be developed.
- To study the advantages that may be derived from the use in the design of the CLT propellers of a new type of mean line developed by Sistemar, looking for a maximum increase of the momentum that the cascades of the propeller blades annular section gives to the water.
- To compare the pressure pulses induced on the hull by a conventional propeller with those induced by a standard CLT propeller and a new CLT propeller designed using the new mean line.

With the new type of mean line the following improvements were expected:

- To reduce the underpressure existing on the suction side of the CLT propellers/blades and also, to decrease even more the volume of sheet cavitation, and consequently the levels of hull pressure pulses.
- To increase the overpressure existing on the pressure side of the CLT propeller/blades. This would lead to an increase in the propeller open water efficiency of the actual CLT propellers.

With the aim to reach the above mentioned goals and once developed the procedure to conduct cavitation tests with CLT propellers, one model of conventional propeller and three models of alternative CLT propellers have been manufactured.

The performance at full scale of the basic model of CLT propeller is already known. With the four propeller models the following tests have been carried out:

- Propulsion and open water.
- Cavitation tests and simultaneous pressure pulses measurements.
- Three-dimensional measurements of water speed with a laser-doppler velocimeter in four axial positions (plans) with regard to each propeller tested. One axial position should be upstream of the propeller disk and the three remaining ones downstream of the propeller disk.

In figures 1 and 2 some examples of the results of the measurements of the axial components of the water speed are shown. They correspond respectively to one conventional and to one CLT propeller. The power delivered by both propellers and the respective rpm were the same.

Figure 2 corresponds to the speed measurements conducted with the model of the CLT propeller. It is observed that the velocities downstream of the propeller disk are higher than in the case of the conventional propeller. The diameter of the CLT propeller is 5% lower than the one corresponding to the conventional propeller, so, in the upper area of Figure 1 outwards of the CLT propeller diameter, the velocity of the conventional propeller is higher than the one given in figure 2.

**FIGURE 1**

**FIGURE 2**

The induced velocities by the CLT propeller downstream of the propeller disk are noticeably higher than those corresponding to the conventional propellers. Further analysis are needed, taken into account the differences in the areas of the propellers disks, but these results are in principle coherent with the assumptions of reaching a higher efficiency using CLT propeller in comparison with the one corresponding to the conventional propeller.