Trans RINA, Vol 152, Part B1, Intl J Small Craft Tech, 2010 Jan-Jun 1.1 1.08 1.06 1.04 1.02 1 11. ACKNOWLEDGEMENTS 0.98 0.96 0.94
0 15304560 7590 βT [°]
105 120 135
Figure 10: Boat speed difference for four VT from VPP calculations using the ‘power’, ’reef and flat’ and ‘twist and ease’ models
9. CONCLUSIONS
Based on the concept of the ‘reef and flat’ trim parameter model the extended ‘twist and ease’ model has been developed and implemented. Instead of modelling the de- powering as reefing and flattening of the sails the new model describes the de-powering as twisting and easing of the sails. The comparison to wind tunnel tests shows that the ‘twist and ease’ model describes the changes in CL, CD and zCoE due to de-powering more accurately and the predicted boat speed is within ± 1% compared to the under prediction of up to 4% with the ‘reef and flat’ model. The new model requires three additional input parameters which have been obtained analytically from aerodynamic principles and are independent of the rig characteristics such as size, aspect ratio and efficiency. The parameter values are therefore universally applicable so that it provides a feasible alternative to the ‘reef and flat’ model.
10. FUTURE WORK AND IMPROVMENTS
The scope of this work is to develop the ‘twist and ease’ model. The additional input parameters are independent of the rig characteristics and can be derived analytically. To fulfil the scope of the project to develop an improved generic de-powering model, which does not require yacht specific de-powering input data, the analytical values have been used for the comparison.
In future work the input parameter values could be obtained from experimental or numerical data to further improve the accuracy of the model. Research by Fossati
©2010: The Royal Institution of Naval Architects
The authors thank all their colleagues at The University of Auckland who contributed to this work, especially Dr. Angelo Tempia for his earlier work on this topic and David Le Pelley. Special thanks also to Dr. Karsten Hochkrich of FutureShip GmbH for his continual cooperation and support.
12. REFERENCES
1. Kerwin, J.E., "A Velocity Prediction Program for Ocean Racing Yachts
revised to February 1978".
Technical Report (Report No. 78-11), Massachusetts Institute of Technology, Cambridge, 1978.
2. Hazen, G.S., "A Model of Sail Aerodynamics for Diverse Rig Types". New England Sailing Yacht Symposium. SNAME, Lew London, Connecticut, 1980.
3. Campbell, I.M.C., "The Performance of Offwind Sails Obtained from Wind Tunnel Tests". The Modern Yacht Conference. RINA, Portsmouth, 1998.
4. Ranzenbach, R. and Teeters, J., "Enhanced De- powering Model Performance Yacht Auckland, 2002.
for Offwind Sails". High Design Conference. RINA,
5. Hansen, H., Jackson, P.S. and Hochkirch, K., "Real- Time Velocity Prediction Program for Wind Tunnel Testing of Sailing Yachts". The Modern Yacht Conference. RINA, Southampton, 2003.
6. Hansen, H., Richards, P.J. and Jackson, P.S., "Enhanced Wind Tunnel and Full-Scale Sail Force Comparison". The 18th Chesapeake Sailing Yacht Symposium. SNAME, Annapolis, 2007.
7. Fossati, F., Muggiasca, S. and Viola, I.M., "An Investigation of Aerodynamic Force Modelling for IMS Rule Using Wind Tunnel Techniques". The 19th International HISWA Symposium on Yacht Design and Yacht
Construction. HISWA Association, Amsterdam, 2006.
8. Jackson, P.S., "An Improved Upwind Sail Model for VPPs". The
15th Chesapeake Sailing Symposium. SNAME, Annapolis, 2001.
9. Poor, C.L., 'A Description of the New International Rating System'. In Publications of the United States Yacht Racing Union, USYRU, 1986.
Yacht
VT=4m/s reef & flat VT=6m/s reef & flat VT=8m/s reef & flat VT=10m/s reef & flat VT=4m/s twist & ease VT=6m/s twist & ease VT=8m/s twist & ease VT=10m/s twist & ease
et al. [7] on the effect of mainsail roach and jib overlap indicates that the de-powering behaviour does not change significantly with mainsail roach and jib
overlap.
Nonetheless the applicability of the ‘twist and ease’ model and the input parameter values for different sail plans should be investigated.
The two stage reefing model introduced by Claughton et al. [14] and briefly described in section 6 could be combined with the ‘twist and ease’ model to give the most realistic description
of de-powering sails by
considering the reduction in sail area and sail shape changes.
B-19
VS /VS (power) [-]
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60