ORC Worlds fleet ITC analysis

Here is a preliminary parametric study made to evaluate performance of ORC rating system 4 July 2011.

For the two days of inshore racing at the ORCi World Champsionship that concluded a week ago in Cres, International Technical Committee (ITC) Chairman Alessandro Nazareth was on hand to observe the fleet and the racing.


He has made some preliminary observations based on some parametric analyses of the top half finishing designs in Class A and Class B, looking at the following non-dimensional parameters: LVR; Sqrt(UP SA) / VOL^0.33; Sqrt(DWN SA) / VOL^0.33; UP SA / WS; DWN SA / WS; DRAFT / IMS L; and RM /DEF RM.

A summary of the observations Nazareth has made of Class A are as follows:

All the top-finishing boats (Aniene TP52, Calipso IV Cookson 50, Airis GP42, Enfant Terrible Farr 40, Altair 3 Felci 50, Marina Kastela GS 56) have all their non-dimensional parameters on the more powerful side, meaning that the winning boats have very powerful characteristics.

They are the longer and lighter boats, they have greater sail area compared to displacement and wetted surface, and they have deeper keels and so are stiffer.

The only design that has smaller ratios but is still among the top-scoring boats is the very well sailed Man GS 4205R, a 'boxy boat' with a conventional bulb-less keel, but the quasi-sistership Bohemia Express has changed their keel into adding a T bulb and thus has a higher RM.

My very quick conclusion is that older 'boxy' boats can survive because their narrow shape still helps them on up-and-down courses, but that the power of being light or with more sail area is allowing the more 'modern' designs to be competitive with them on corrected time, and often to beat them, even on windward-leeward courses. Perhaps if there were more wind we would have seen this effect even more pronounced on the offshore races.

Class B
It is interesting to note that the Class B designs are composed completely of less powered boats. For the LVR ratio, only 5 boats have more than 5.5, a value smaller than for Class A.

Some top boats (Scugnizza, Rewind, Italia 10.98) are on the lighter (5.7) side but the NM37, Comet 38, GS40, X37 are among the top boats as well but are averaging values of 5.3-5.4.

For UP SA/VOL only very few reach the minimum of group A (5.0) and they are the lighter ones (like Scugnizza) and those GS40's with overlapping jibs. The NM37, X37 and Comet 38 have average values (4.7) of the larger group.

For UPSA/WS only the two GS40's with genoas reach the minimum of Class A (3.0), with the remaining having very low sail areas compared to WS.

Downwind in the top boats only Scugnizza, Scricca and the X-35 have sail areas in the average of Class A (both in SA/VOL and SA/WS).

Looking at RM/DEF RM, very few are above 1.0, which means that very few have stabilities higher than what ORC is estimating. Only the Comet 38 and Salona 34 has stability in the range of the TP52, GP42 and Cookson 50. This characteristic of the NM 38 may account for the favorable upwind speed of the NM 38.

This is a preliminary analysis, with a more in-depth study being prepared for the next ORC column in Seahorse magazine.

Other ITC news is that a Working Group studying Residual Resistance is meeting in Delft over 16-18 July to examine how to improve this algorithm in the ORC VPP.

For more information and parametric plots that accompany this analysis, and for more information about ORC rules, rating systems and events, visit www.orc.org.