The resistance to capsize requirements in the Special Regulations provide more options for race Categories 3 to 7 and there is a calculator available to help.

Perusal of the Special Regulations Appendix B will show that options to demonstrate a boat’s resistance to capsize really opens up for Category 3 races and even more so for Categories 4 to 7. Two of the options that become available in these lower race categories are the Righting Moment Index (RMI) and Horizontal Stability Factor (HSF).

Each of these procedures involve practical tests and were originally put in the Special Regulations with small yachts, trailer sailers or sport boats in mind. The tests involve determining the weight required at a certain point on the mast to hold the mast at ‘horizontal athwartships’; onto its side. 

When pressed for a sensible answer, Jason Ruckert, owner of the pictured Thompson 7 Mr Magoo said “Surprised a few as to how stable a T7 really is when pulled down! And at any angle, they are a damn sexy boat!” Jason went on to astutely note “Cause if the Magoo wasn't self-righting, certain risks would be too much for us to handle!”

Owners of larger yachts will not find the pull-down tests quite so practical and should consider the use of the IRC or ORCi rating systems if wanting to pursue a measurement-based stability test.

For the RMI and HSF Template go to https://www.sailingresources.org.au/safety/equipment-auditing/
The Special Regulations can be read at https://www.sailingresources.org.au/safety/specialregs/

By Glen Stanaway https://www.sailing.org.au/about/ourstaff/.