Trans RINA, Vol 153, Part B2, Intl J Small Craft Tech, 2011 Jul-Dec RE-RIGHTING OF CAPSIZED MONOHULL OFFSHORE SAILING YACHTS – AN
OVERVIEW (DOI No: 10.3940/rina.ijsct.2011.b2.117) A G Blyth, A.G.Blyth & Associates, UK SUMMARY
The Fastnet offshore race of 1979 resulted in 15 fatalities and 24 yachts being abandoned as a result of hurricane force winds. Since then, the ability of an offshore yacht to recover from a total inversion or roll-over has been of great interest to the offshore yachting community. This paper provides an overview of the principal stability lessons learnt since the Fastnet Race Inquiry and an introduction to the subsequent experimental and theoretical investigations. The stability properties necessary to offer good prospects of a quick recovery are reviewed, and the current standards suggested for ensuring rapid re-righting are outlined.
NOMENCLATURE
AVS Angle of vanishing stability GZ Transverse righting lever IMS International Measurement System ISO International Organization for Standardization MCA UK Maritime & Coastguard Agency RORC Royal Ocean Racing Club RYA Royal Yachting Association SNAME Society of Engineers
Naval UK 1. United Kingdom
USYRU United States Yacht Racing Union VCG Vertical centre of gravity
INTRODUCTION
Offshore sailing yachts may experience very strong winds, which in turn generate large waves, which constitute a major hazard to the safety of these yachts. Prudent seamanship does not always permit such conditions to be avoided, and so it is important that the yachts are designed and built in a manner that offers a good prospect of survival.
Survival of both yacht and crew is greatly enhanced if the boat has characteristics that enable it to return to the upright condition after an inversion, even if in the process it has taken on water and perhaps lost the mast(s).
It self-righting
is therefore highly desirable that such vessels have characteristics
akin to those associated with specialised rescue lifeboats.
Historically, sailing yachts developed from working craft, which evolved over many decades. In the UK at least, such craft had relatively narrow, deep hulls, with significant ballast. However in the last fifty or so years, largely under the influence of the IOR rating rule, racing yachts have progressively become very much lighter, more beamy and having a very different hull-form. That this has not had a positive effect on their ultimate stability was not generally appreciated until the Fastnet Race of 1979.
usually
The RYA and the RORC immediately undertook a detailed study to ascertain the facts as far as possible [1]. The study was based on the 235 responses received to their comprehensive questionnaire.
A good overall description of the events of the 1979 Fastnet Race are given in chapter 17 of [2].
2.2 MAIN INQUIRY FINDINGS
The inquiry covered all aspects of the race organisation, weather, crew, equipment and rescue, but this paper will only focus on those related to the stability aspects of the yachts taking part.
Of the 235 yachts for which responses were received, 113 yachts (48%) were knocked down to the horizontal (B.1 knockdown), of which 73% occurred to yachts with a rating length of less than 29.0 feet.
For the same yachts, 77 (33%) experienced a knockdown to well beyond the horizontal (B.2 knockdown), of which 87% occurred to yachts with a rating length of less than 29.0 feet.
Clearly smaller boats are rather more vulnerable to such events.
This paper is intended to provide an introduction to this complex subject, and is far from exhaustive.
2. 2.1 Architects and Marine
1979 FASTNET RACE INTRODUCTION
In the early hours of 14 August 1979, 303 yachts were spread out over the course of the Fastnet Race from Cowes (UK) to the Fastnet Rock (Republic of Ireland) to finish in Plymouth (UK) when winds up to Beaufort Force 11 and associated waves up to about 13 metres high were encountered. Only 28% of the fleet managed to complete the course, 64% retired and 8% were abandoned. Fifteen crew members lost their lives.
©2011: The Royal Institution of Naval Architects
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