Seahorse International Sailing
April 1999
As yacht designers we have a somewhat one sided view of the Sydney to Hobart Race. It revolves around one simple fact and that is the consistent effect of wind against current that creates sea states that are fundamentally unique in the world of established ocean races. When this combination is average it can and does break boats. When it is severe it is as vicious a sea state as you would ever hope to encounter. This simple fact means, in our minds, that designing for the Hobart is designing for the ultimate.
The fact that most Australian yachties (and a fair few overseas ones) aspire to do the Hobart and more than a few aspire to do a large number means only one thing. That is that the "average" offshore crew and boat essentially becomes progressively immunized to conditions that would be considered unacceptable for racing in other parts of the world. To confidently sail the Hobart on a regular basis means developing a capability to sail on a daily basis (SOPS races, BWPS races, etc.) in conditions that most people in other parts of the world would seriously think twice about. Our general skill level and temperament means that the typical offshore yacht that functions in this area must be tougher in every respect.
In light of the above our professional view of the 54th Sydney to Hobart revolves not so much around the all-important issues of seamanship / safety / equipment as it does around the integrity of the yachts. This relates to both their ability to survive the conditions intact as well as what will happen when that intact state is lost. Looking at the fleet as a whole the primary conclusion is positive. Boats were surviving horrendous vertical accelerations (some timed at over 4 seconds) with no loss of integrity. Keels all remained firmly attached, most rudders were fine and I am not aware of any modern boats that suffered major structural damage where that damage was not precipitated by a rig failure. All in all the standard catch phrase of "too light, too fragile" is misapplied in this instance. The scantling rules and their application by the industry seems to be working well. Given that we are in a self-policing environment this is to be applauded.
Where problems occurred they were often in the details. Mast gates, local deck reinforcement in way of high load fittings, reinforcement in the way of hatch cutouts - these are outside the view of most major scantling rules and fall into the realm of good engineering or good sense. That they are sometimes overlooked falls in to the general category of human failing as opposed to technical issue. The result of these failings is, of course, to expose the vessel to flooding . Combine this with a 250 kg mast with sail attached on the leeward side of the boat and a 60 knot wind pushing the boat onto it and you could only expect problems to occur.
Stability and more importantly the limit of positive stability (LPS) raises it head here once again. It has been a much debated issue in the IMS era but more from the point of view of those that want to go but can't due to a low LPS. I don't know of anyone who has bothered to read or understand the development of these stability limits which are documented under the heading Final Report of the Directors - Joint Committee on Safety From Capsizing, June 1985. The joint committee was the United States Yacht Racing Union and The Society of Naval Architects and Marine Engineers. The document is the result of testing and documentation to determine the mechanisms of yacht capsize and forms the basis of the IMS restrictions in this area. As well it is used in other areas such as the Whitbread/Volvo Race where the stability limit is 125 degrees or 10 degrees higher than for the Hobart. The prescribed amounts would mean that, in still water, the boat would obviously remain stable upside down. Where the values are made reasonable is in the consideration of the sea state that would actually cause a capsize. This same sea state, combined with an adequate LPS, will see the boat re-right itself in a reasonable amount of time. In the case of the 115 degree limit this is estimated to be around 3 minutes of inversion. Actual documentation from this last Hobart suggest that these values are not far off the mark though exact correlation should never be expected. It should also be noted that your certificate has a partner value for the LPS called the Stability Index. This was initiated to expand the LPS concept to include the probability of certain types of boats being more prone to capsize in spite of meeting the LPS requirement. Small, beamy and light are considered more prone that long, skinny and heavy. Despite ORC recommendations on this matter it has been largely dismissed probably because it keeps smaller boats out of Cat 1 races. It would be interesting to re-visit this matter in light of the new data derived from the Hobart.
The mast issue stands apart from all other areas in so much as the loss of the mast can lead to so many other problems. For all the available rules by which one can design a modern yacht there is nothing to guide or mandate the design of a mast. You can hire the best engineers and apply the most advanced methods but the final outcome is still only as good as the basic assumption of applied loads and the safety factors applied on top of those. This is up to the designer or mast engineer. They are unguided except by experience and standard practice. One of the few offshore races where some form of rule is applied is the Whitbread / Volvo Race where a total mass and tip weight (to determine CG) is applied. This is pretty simple and, in my experience, with the little sister version of this design, the Mt. Gay 30, it works pretty well.
The mast plays a more important role in the scheme when you look at its role in preventing capsize. This revolves around the concept of roll moment of inertia or rotational inertia. This loosely translates into a boats resistance to being rolled . Most of a boat's rotational inertia is supplied by the mast so, strange but true, a heavier mast will improve your resistance to capsize. Following from this is the fact that a dismasted vessel is much more vulnerable to rolling over and over. This points to two obvious conclusions regarding mast scantlings: heavier masts increase roll inertia and thus help resist capsize and secondly, increased scantlings assist in keeping the mast in the boat if in fact it does roll. Maybe it is time, after all these years, that we stop arguing about the weight of core material in a fittout and come up with something really useful - a working set of rig scantlings for racing and cruising yachts.
END
Scott Jutson
Jutson Yacht Design