In conclusion the performance advantage showed by the slender model yachts does not seem to have been as great when scaled up to full size. A possible reason for this could be down to the sailors as the full size tests were carried out in a computer so the yachts were always sailed with the same level of skill, while the models are sailed by people with various levels of experience and therefore skill. Another reason for the loss in performance could be down to the performance in waves, as the V.P.P being used was unable to model this condition accurately. If this was taken into consideration, the performance advantage of the slender model yachts may appear when scaled up to full size. It does seem however that the slender hull form exhibits more desirable motions with respect to roll and capsize risk. The nose diving problem is an interesting area as it did not seem to be as big a problem as was previously thought. Whether this would be a problem on the full size yachts of this type is unknown, but model tests seem to indicate it should not be a problem, the only way to establish if this would be a problem would be to carry out tests on full size super slender yachts, but since this would require large amounts of money and time it has not been possible. The low beam does seem to be a problem, although by increasing the overall length the yacht, it may be easier to work with from the point of design. It does seem possible to design and build a yacht measuring in at around 15.24m - 18.29m with the low beam as long as the designer is careful with the internal layout. The longer yacht at around 40m - 50m may be possible but with the low knowledge of structural loads on such a vessel, it may have problems which are unseen at the design stage. The choice of rig also seems to be a compromise between speed and ease of handling.


The final conclusion is that the super slender yachts do have advantages over their wider counterparts, but whether these advantages are enough to warrant a change in the development path it is unknown. The problem that would face this hull form seems to be the one mentioned at the very beginning of the project, that many people are against change, and some will even go to great lengths to ensure it does not happen. The decision as in most things is left to the designer who must decide whether to be radical and experiment, or as it is sometimes put "to go with the flow". Also with the increase in complexity of rating rules, the yacht designs are becoming more alike each year, and therefore the designers are being forced to experiment less and less. It is only in classes such as the Open 50 and Open 60 that the designer is free to experiment with new ideas.


There are some aspects of the project which could be followed up in further research in this area, such as accurate model tests to clarify the V.P.P results in areas such as performance with various rigs and also performance in waves. It is highly likely that the performance in waves is a major contributor to the yachts performance, and could account for the loss in performance between model and full size.




The project was started in June of 1996, and the information regarding the slender model yachts was taken from around this time. Information regarding full size yachts has been an ongoing study. The purpose of this section is to provide information on the latest developments in both fields at this point in time, May 1997.

Figure 5.1, Hulls used in 1997 1 metre world championships


In the area of model development a very interesting path has been taken by some of the designers of the International one metre class of model racing yacht. In the 1997 World Championships held in New Zealand in February, the hull designs being used were of the T52 Design shown in Figure 5.1. The design is a double wide skiff i.e. very wide skimmer dish hull form. This design took six of the top ten places with 1st 3rd 4th 6th 8th and 10th with the only slender yacht finishing 9th . This change in the development path is interesting, unfortunately the Marblehead World Championships have not taken place at this date so it is unclear if they too have followed the same path. The performance of these skiff yachts did seem to be quite good but it was found that they would get out of shape easily, meaning that they would broach easily in strong winds. This may indicate that the models are starting to copy the full size yachts such as the Open 60 designs with their very large beam.


In the field of full size racing yachts there has also been a slight change in the development in the Whitbread 60 class. Most of these yachts are designed by Bruce Farr, and some of the yachts designed for the 1997-98 race have had their waterline beam reduced to improve light air performance. It is unclear how slender these yachts have become but it could indicate a possible change in thinking by the designers. Early results from sailing trial of these yachts have shown good performance with speeds of 20 knots when planing in 25 knot winds.


In conclusion it seems that the two areas, models and full size, have both switched development paths. Whether this is an indication of the types of racing yachts that are going to be seen from now on, only time will tell.






[1] Aero-Hydrodynamics of Sailing, A. Marchaj 1979

[2] The History of Yachting, Douglas Phillips-Birt 1974

[3] Seaworthiness. The forgotten factor, A. Marchaj 1986

[4] Principles of Yacht Design, Lars Larsson, Rolf E Eliasson 1996

[5] Sailing Yacht Performance in Calm Water and Waves, J. Gerritsma, J. A. Keuning, A. Versluis. The Eleventh Chesapeake sailing yacht symposium.

[6] Predicting the speed of Sailing Yachts, Peter van Oossanen. SNAME Transactions Vol. 101, 1993

[7] Sailing Yacht Design - A New Appreciation of a Fine Art Richard T. Miller, Karl L. Kirkman SNAME Transactions Vol. XXX, 19XX




Model Ships. Vic Smeed 1979

Sailing Theory and Practice. C. A. Marchaj 1982

An Assessment of the progress in yacht design through an examination of model yacht characteristics Andrew Claughton, Ian Howlett, Roger Stollery The Eight Chesapeake Sailing Yacht Symposium



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Yachting World. October 1994

Yachting World. February 1997

Yachting World. May 1997

Marine Modelling. November 1990

Marine Modelling. December 1991

Marine Modelling. April 1992

Marine Modelling. October 1992

Marine Modelling. January 1994

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Marine Modelling. May 1996

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Model Boats. February 1992

Model Boats. June 1992

Model Boats. December 1992

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Copyright 1998 Anthony York