Trans RINA, Vol 153, Part B2, Intl J Small Craft Tech, 2011 Jul-Dec


requirements for an individual yacht will vary from those indicated in Figure 6.


100 110 120 130 140 150 160


60 70 80 90


5 1015 Length of Hull (m) 6.


Figure 6: Comparison of Minimum AVS Criteria CONCLUSIONS


The following conclusions can be drawn from the work described above:


(i) many yachts under 24m length are capable of being inverted by a breaking wave if the wave height is more than the yacht's beam.


(ii) it is therefore important that an offshore yacht should self-right


after an inversion, remaining inverted for more than (say) 5 minutes.


(iii) smaller yachts are more vulnerable because firstly their roll moment of inertia is less and secondly because the probability of meeting a wave large enough to cause capsize is much greater.


(iv) the presence of a mast, producing a higher roll moment of inertia, reduces the vulnerability to inversion, and improves the re-righting ability.


(v) re-righting ability is generally improved by a high angle of vanishing stability (AVS), but other factors mean that a 10° increase in AVS is not always accompanied by an improvement in capsize recovery time.


(vi) rapid re-righting after an inversion is probable if the AVS is more than about 140°.


(vii) beamy yachts are more vulnerable because their AVS is generally reduced, the boats are tripped by immersion of the lee side deck, and they are more stable when inverted.


(viii) in severe weather, the use of an appropriately designed drogue, towed from the stern, can very significantly reduce the probability of being rolled by breaking waves.


(ix) while various approximate formulae for estimating AVS have been proposed in the past, with the ready


©2011: The Royal Institution of Naval Architects B-101 4. 5. 6. 7. 8. 9. 10. without 2025


Wolfson US ISO


7.


availability of appropriate computer software it is considered that such methods have very limited application in the 21st century, and if used, should always err towards conservatism.


ACKNOWLEDGEMENTS


This paper presents little that is new, but principally summarises the work of others. The author therefore gratefully acknowledges the considerable contributions made by all those who have undertaken work in this field, in particular the authors of, and those referred to in, the references.


The author recognises that some valuable contributions to this subject may have been omitted from this overview, and offers his sincere apologies where this is so.


8. 1.


2. 3. REFERENCES


Forbes, Sir H.; Laing, Sir M.; Myatt, Lieut.Col. J., ‘1979 Fastnet Race Enquiry', Royal Yachting Association & Royal Ocean Racing Club, 1979.


Bruce, P. (editor), 'Heavy Weather Sailing' (fifth edition), Adlard Coles Nautical, 1999.


Claughton, A.; Handley, P., 'An Investigation into the Stability of Sailing Yachts in Large Breaking Waves', University of Southampton Ship Science Report No.15, January 1984.


Marchaj, C.A., 'Seaworthiness – the Forgotten Factor', Adlard Coles Ltd, 1986.


Joint USYRU/SNAME Committee, 'Safety from Capsizing -


Final Report of the USYRU and SNAME, June 1985.


Kirkman, K.L., Nagle, T.J., Salsich, J.O., 'Sailing Yacht Capsizing', Chesapeake Sailing Yacht Symposium, 1983.


Salsich, J.O., Zseleczky, J.J., 'Experimental studies of Capsizing in Breaking Waves', Ancient Interface XIII, 1983.


Jordan, D.J., 'What causes a boat to capsize?', Sail magazine, February 1982.


Jordan, D.J., 'Small boats and breaking waves', Sail magazine, December 1982.


Claughton, A.R., 'Report on Model Tests to Assess the Use of Drogues and Similar Devices to Prevent Yacht Capsize in Breaking Waves', University of Southampton Ship Science Report No. 35.


Directors',


AVS (deg)


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