ADEQUACY OF MOORING 60 TO RESTRAIN PAVANA
86 In the light of the conclusions that I have reached, it is not strictly necessary to deal with the question of the adequacy of mooring number 60 as a mooring for Pavana. Nevertheless, that question was a substantial issue in the proceeding and it is appropriate that I express the conclusions that I would reach as to whether there was a breach of the secure mooring duty or a breach of a warranty implied by s 74(2) of the Trade Practices Act, if I had concluded that Holmeport owed the secure mooring duty or that a warranty was implied by s 74(2). The question, as I apprehend the contentions of the parties, is whether Holmeport took reasonable measures to ensure that Pavana's mooring was adequate to hold Pavana in conditions that could reasonably be expected in Rose Bay.
87 Mr and Mrs Ruaro alleged that Holmeport was in breach of the secure mooring duty and of the s 74(2) warranty in so far as Holmeport:
· failed to check the condition and adequacy of mooring number 60 for Pavana;
· failed to supply an adequate mooring block for Pavana to ensure that the mooring would not be dragged by Pavana;
· failed to ensure that mooring number 60 was adequate for the purpose of mooring Pavana so that it would not drag;
· failed to ensure that Pavana was allocated to a mooring that was appropriate for its use;
· caused Pavana to be moored to mooring number 60 when Holmeport knew or ought to have known that mooring number 60 would not be adequate to hold Pavana.
88 There is no accepted design or methodology for the design of swing moorings in Sydney Harbour. Components of mooring systems are assembled and installed by mooring contractors based on experience and judgment. However, Mr and Mrs Ruaro say that, even if there was no standard practice at the time for the laying of moorings or the allocation of moorings to boats, such a lack of a consistent industry practice is not a defence to their claims of breach of duty and breach of warranty.
89 Mr and Mrs Ruaro contend that Holmeport was under a duty to ensure, or alternatively, warranted, that the Pavana mooring was reasonably fit to withstand wind conditions more severe than the conditions that occurred on 24 August 2003. They conducted the proceeding on the basis that the issue was whether the mooring to which Pavana was attached ought to have been capable of holding her in weather conditions of a 50 year average recurrence interval. Average recurrence interval is a means of defining the frequency of an event. Thus, a 50 year average recurrence interval event is an event that is, on average, going to occur or be exceeded once in every 50 years.
90 Mr and Mrs Ruaro point to the evidence that conditions of the severity that was experienced in Rose Bay on 24 August 2003 occur, on average, much more frequently than once every 50 years. They say that, therefore, there was a breach of the secure mooring duty and of the s 74(2) warranty.
91 Holmeport, on the other hand, does not accept that an arbitrary criterion of a 50 year average recurrence interval is appropriate. It says that, in any event, mooring number 60 was adequate for Pavana and the conditions of 24 August 2003 were so exceptional that it ought not be held responsible for the failure of mooring number 60 to hold Pavana.
92 Mr and Mrs Ruaro rely on the evidence of Mr Gregory William Britton, a well qualified engineer, who is the principal of Patterson Britton & Partners Pty Ltd and who has 28 years experience in coastal maritime and environmental engineering. Mr Britton was asked to express his opinion as to whether mooring number 60 was, on 24 August 2003, reasonably adequate for a vessel of the dimensions, displacement, weight and design of Pavana. In his written opinion, Mr Britton said that, in order to assess the adequacy of mooring number 60, it was necessary to estimate its holding capacity as installed and the holding capacity that might reasonably have been provided in the circumstances.
93 Mr Britton said that the holding capacity of a mooring is a function of a range of factors, including the following:
· type of seabed;
· the weight of the anchoring mass; and
· the scope of the mooring line.
94 The seabed in the area of mooring number 60 in Rose Bay is sandy silt. Sand has a more consisting holding power than mud or silt. The weight of the anchoring mass of mooring number 60 was one tonne. Scope is the ratio of the length of total mooring line from the anchor block to the water surface, divided by the water depth. The total mooring line length of mooring number 60 was approximately 25 m, comprising 11 m of chain, 1 m of anti-chafe line and 13 m of silver rope. The water depth at the mooring at low tide was approximately 12 m. On that basis, the scope of the mooring line of mooring number 60 would have been 2:1. That is typical of the scope of moorings in Sydney Harbour.
95 The tendency for a mooring to drag is resisted by the frictional force between the sea bed and the anchoring mass, being the concrete blocks in the present case. That is dependent on the buoyant mass of the blocks, reduction in that weight due to the lift force and the coefficient of friction between the blocks and the sea bed. Concrete blocks having a mass in air of 1 tonne would have a buoyant mass of 0.6 tonnes. The lift force will depend upon the environmental conditions such as wind and wave effects. A typical coefficient of friction between concrete and sand is 0.5. Thus, the holding efficiency of concrete blocks would be expected to be less than half the combined weight of the concrete blocks.
96 In his written opinion, Mr Britton referred to Australian Standard AS4997-2005, entitled Guidelines for the Design of Maritime Structures (AS4997). AS4997 sets out guidelines for the design of structures in a marine environment and is intended to cover the design of near shore coastal and estuarine structures. It specifies the structures the design of which it is intended to cover, including berthing dolphins and floating berths. It does not mention swing moorings. While AS4997 was not published until 2005, a draft, in essentially the same terms, was circulated for public comment in 2002.
97 Section 5 of AS4997 is concerned with 'Design Actions'. Clause 5.1 provides that the design for ultimate strength, serviceability, stability and other relevant limit states for maritime structures should take into account the appropriate design actions, including wind actions, current and debris actions and wave actions. Clause 5.4 deals with "Wind Actions" and says that wind actions on vessels and floating structures may be designed using a wind pressure based on a 30 second gust rather than basic wind speeds due to 3 second gusts. The reason is that floating structures have a delayed response to wind loads.
98 Clause 5.5 of AS4997 deals with "Current Actions" and provides that the design strength of maritime structures should allow for the combined effects of tidal and river estuarine flood currents. Clause 5.9 deals with "Wave Actions" and clause 5.9.2 refers to "Design Wave Heights". Clause 5.9.2 provides that the design strength of maritime structures should allow for the highest wave likely to occur on the structure over the selected design life and an annual probability of exceedence based on the function category of the facility.
99 Table 5.4 of AS4997 shows the "Annual Probability of Exceedance of Design Wave Events" for structures of various design lives and function categories. It shows that the design working life of small craft facilities is 25 years and that the probability of exceedance of design wave events of structures presenting a low degree of hazard to life or property, being small craft facilities, is 1 in 50 years.
100 Section 6 of AS4997 is concerned with "Durability". Clause 6.1 provides that maritime structures are generally sited in very aggressive environments for normal structural materials and suggests that the design of maritime structures should include consideration of the requirements to withstand the aggressive environment while the structure remains serviceable. Clause 6.2.1, under the heading "Design Life", provides that, at the end of the design life, the structure should have adequate strength to resist ultimate loads and be serviceable, but may have reached a stage where further deterioration will result in inadequate structural capacity. Table 6.1, which follows that clause, specifies a design life of 25 years for small craft facilities.
101 In oral evidence, Mr Britton also referred to Marina Guidelines, published by the New South Wales Department of Public Works in 1987. Mr Britton said that the Marina Guidelines were superseded when AS4997 was introduced, such that AS4997 embodies some 20 years or so of practice in the relevant area. Mr Britton and his firm were involved in the preparation of the Marina Guidelines and in the preparation of AS4997.
102 The objectives of the Marina Guidelines were to identify the principal issues that should be considered by the proponents, designers and reviewers of marina proposals and to provide sound technical advice on design concepts for marinas. Section 5 of the Marina Guidelines deals with natural forces in the marine environment. Clause 5.1 states that wind and wave action can be the major cause of structural damage at a marina. Clause 5.3 provides that wind loads should be determined using a design wind pressure based on a "steady state" wind speed, rather than the speed of wind gusts, because the higher gust loads are seldom transmitted to the mooring system owing to the inertia of the boats and floatation units and the flexibility of mooring lines and piles. Clause 5.3 suggests that a mean return period of 50 years for the design wind is recommended.
103 Mr Britton said that the concept of an average recurrence interval is adopted quite regularly as a risk based approach to the design of small craft facilities. He said that it had certainly been adopted within the New South Wales Public Works Department and by other people who are involved in the design of marinas or small craft facilities generically.
104 In his written opinion, Mr Britton said that AS4997 "provides some guidance for the design event that might reasonably be adopted". He also said that, based on table 5.4 in AS4997, "it could be argued that an event having an average recurrence interval between 50 and 200 years should be adopted" [emphasis added]. In his oral evidence, Mr Britton said that the Marina Guidelines were generally accepted in New South Wales and that he regarded the reference to a return period of 50 years as confirming his opinion that it could be argued that an event having an average recurrence interval of at least 50 years should be adopted as the criterion for the holding capacity of a swing mooring.
105 Mr Britton expressed his opinion in oral evidence that there was not a lot of difference between the considerations that should be taken into account in relation to marinas, on the one hand, and swing moorings, on the other, in so far as they are both small craft facilities. He said that the consequence of failure in a marina is really no different from failure in a mooring: vessels will become adrift and may be damaged or may damage other vessels or other structures. Mr Britton said that he would not regard a vessel on a mooring as different in any significant way from a vessel on a marina berth, in terms of the consequences of something going wrong. He did not see the design of a swing mooring as being any different from the design philosophy used for marinas in determining wind loads. On that basis, he said that he would advise a client to adopt a 50 average recurrence interval as the relevant design event for a swing mooring.
106 Mr Britton explained that his reasoning process for that conclusion was that it is a balanced risk based judgment. He said that there is a certain likelihood of such an event occurring on average, once in every 50 years. If it does occur, the consequence could be substantial damage to the particular vessel, damage to other vessels and potential damage to life as a result of people trying to rescue vessels in such circumstances. He expressed the opinion that the standard to be adopted required a determination of the likelihood and consequences of failure.
107 In the course of cross-examination, Mr Britton accepted that what happens in relation to swing moorings on Sydney Harbour has really been based on local knowledge and information passed down, almost, from father to son. Mr Britton agreed that there are a number of well-known mooring industry families. He agreed that a great deal of experience had been built up by people involved in laying and servicing moorings, replacing moorings and in all activities involving moorings. He accepted that, in effect, there have been no designs or design standards that have been used in the mooring industry on Sydney Harbour.
108 Mr Britton was not aware of the use of the concept of average recurrence interval in relation to swing moorings. He said that swing moorings have not received a lot of regulation and there are very few industry standards in terms of their design. He said that, so far as he is aware, the concept of an average recurrence interval has not been written down in relation to swing moorings. In his experience, moorings are put in place by mooring contractors who have rules of thumb that they have developed over a number of years of experience, often handed down through family members. He explained that the rules of thumb depend upon size of vessel, water depth, and scope of mooring lines.
109 Mr Warwick J. Hood AO is a consulting naval architect and marine transport consultant. He has been in private practice for some 43 years. He has achieved great distinction as a naval architect and has appeared frequently to give evidence in litigation involving issues in which he has relevant training and experience.
110 In 1989, Mr Hood was a member of the Committee of Inquiry into Moorings for Recreational Craft in New South Wales, which examined all aspects of moorings including:
· the demand for moorings;
· typical mooring areas, such as Woodford Bay in the Lane Cove River and Rushcutters Bay in Sydney Harbour;
· typical mooring apparatus, including single swing, two point limited swing and trot mooring systems;
· typical loads on mooring apparatus.
Mr Hood was asked, in particular, to measure the loads on such systems.
111 Mr Hood conducted several tests designed to measure boats on mooring lines. Three moorings on which he conducted tests were located off Royal Sydney Yacht Squadron, at Kirribilli, and one was located in the Parramatta River at Putney. Each mooring block had a mass of 1 tonne. The three moorings at Royal Sydney Yacht Squadron, after an initial resistance of up to 1.2 tonnes, showed a resistance to dragging of between 0.9 and 1.1 tonnes. The mooring at Putney, which appeared to have sunk into mud, showed an initial resistance of about 1.2 tonnes and then showed a resistance of about 1 tonne. Mr Hood concluded that the steady dragging load in a mooring apparatus is approximately equal to the mass of its block, although the "break out" load is slightly higher.
112 In his written opinion Mr Hood said that, based on the specifications of the Pavana and the wind speeds recorded for 23 August 2004, mooring number 60 should have been adequate to hold Pavana without dragging. Accordingly, in his opinion, the reason for the failure of the mooring to hold Pavana was extreme and unusual weather, causing extreme pitching of Pavana.
113 Mr Hood observed that the winds on 24 August 2003 were predominantly from the north-west and that, while Holmeport's marina is itself protected from winds from the north-west by the high ground of Point Piper, mooring number 60 was located in such a position that it would have been subjected to the full force of the wind, because little protection is provided by the low land and buildings of Woollahra Point.
114 Mr Hood assumed that the wave action at the location of mooring number 60 was the result of the full force of the wind and a fetch of about 3 km to the north-west across the Harbour from the location of the mooring towards Cremorne. Fetch is the distance over which the wind blows in order to make waves. Mr Hood expressed his opinion that, assuming the wind speed was about 70 km per hour and the fetch was about 3 km in 12 metres of water, waves would have a height of about 0.76 m and a period of about 3 seconds at the location of mooring number 60. Mr Hood said that it is impossible to estimate accurately the effect that waves of that height and period would have on a vessel like Pavana without much more information than was available to him. However, having regard to his experience with yachts of similar size and configuration to Pavana, Mr Hood considered that it was possible that Pavana was pitching with considerable amplitude: the period of encounter with the waves could have been close to the natural period of pitch when the amplitude of pitch would have been increased because of resonance.
115 Mr Hood provided calculations concerning the effect of the wind speeds of 24 August 2003 on Pavana when attached to mooring number 60. The calculations assumed an area of Pavana that would be exposed to the wind, which Mr Hood referred to as the flat plate area. For a wind speed of 70 km per hour, the necessary flat plate area that would need to be exposed to the wind to develop a load of 1 tonne, the load necessary to drag Pavana's mooring, would be about 360 square feet. Since the beam of Pavana was 14.10 feet, the height of the "flat plate" would need to be 25.5 feet in order to produce a flat plate area of 360 square feet. Mr Hood considered that it was unlikely, from his limited knowledge of Pavana, that, with a beam of 14.10 feet, there would be sufficient height to create a flat plate of 360 square feet.
116 Allowing for a wind speed of 109 km per hour, the maximum gust speed between 5 pm and 5.30 pm, the flat plate area would need to be about 162 square feet. With a beam of 14.10 feet, the area exposed to the wind would need to be 11.5 feet high to achieve a load of 1 tonne. Mr Hood also considered that that was unlikely.
117 In the light of the calculations, Mr Hood concluded that mooring number 60 should have been adequate to hold a vessel of Pavana's specifications without dragging. It was for that reason that he concluded that the weather must have been so extreme and unusual as to cause extreme pitching of Pavana, thereby causing the mooring number 60 to drag.
118 Mr Peeters has, on behalf of Polaris, been responsible for the maintenance of approximately 20% of the 6,500 moorings in Sydney Harbour. Many of the moorings that he has serviced are swing moorings. In particular, he has serviced swing moorings located as follows:
· Sydney Amateurs Yacht Club, on the Cremorne side of Mosman Bay: all are a minimum of 1 tonne, although some are two 1 tonne blocks.
· Royal Prince Alfred Yacht Club, on Felix Bay, on the northern side of Point Piper: some are ˝ tonne moorings and some are 1 tonne moorings, having rather small boats on them.
· Cruising Yacht Club of Australia, in Rushcutters Bay: temporary moorings are laid at the time of the commencement of the Sydney/Hobart Yacht Race; they are 1 tonne blocks, although a few have two 1 tonne blocks.
· Royal Motor Yacht Club, next door to the Point Piper marina in Rose Bay. Mr Peeters first serviced them in 2000 and put down blocks of a minimum of 2 tonnes.
· Royal Australian Navy Sailing Association, in Rushcutters Bay: there are ˝ tonne and 1 tonne blocks.
· Balmoral Marina, in Middle Harbour, there are ˝ tonne and 1 tonne blocks.
· Double Bay Marina in Double Bay, the bay on the other side of Point Piper from Rose Bay has ˝ tonne and 1 tonne blocks.
119 Mr Peeters has also laid moorings for many private individuals in Sydney Harbour with a minimum of a 1 tonne block. Mr Peeters said that, in his experience, the material of construction of a vessel makes no difference to the mooring required. The important aspect is the "windage", which affects the force put against a vessel by wind. The windage is the area of a vessel that will be exposed to the wind. The greater the windage, the greater will be the force applied to the vessel by wind of a given velocity.
120 Mr Peeters explained that a schooner rigged yacht would not have as high a windage as the same sized motor boat or cruiser, with, for example, a big cabin. Mr Peeters prescribed a minimum of 2 tonnes for the moorings for Royal Motor Yacht Club in Rose Bay because all of the vessels moored there are cruisers: Royal Motor Yacht Club is a motor boat club and not a yacht club and all of the boats, regardless of their size and length, have a high windage.
121 Mr Peeters said that, apart from the moorings of the Royal Motor Yacht Club in Rose Bay, there were very few moorings with more than a single 1 tonne block. Mr Peeters said that he had experience of no more than three vessels of specifications similar to Pavana that were moored on swing moorings of two 1 tonne blocks. They were located in Rushcutters Bay and Parramatta River.
122 Mr Peeters has not given consideration to the concept of an average recurrence interval in determining the appropriate block for a given swing mooring. Rather, his experience is limited to placing such blocks as his client requested. That is to be expected, since Mr Peeters could never know the dimensions of a vessel that might thereafter be moored to one of the swing moorings that he laid.
123 Mr Peeters also gave oral evidence about the effect of suction on a mooring when it is being serviced. He explained that the force needed to break the suction and lift a concrete block from the sea bed normally exceeds the mass of the block. Force is exerted until the suction breaks, after which the block can be lifted. That is consistent with Mr Hood's experience concerning the break out load of a concrete block.
124 Mr Britton was an impressive witness and clearly a highly competent engineer. On the other hand, it is clear enough from his evidence that, prior to being asked to provide an opinion in relation to the incident of 24 August 2003, he had not previously turned his attention to design criteria for swing moorings. His expertise is in relation to the design of marinas and similar structures. The Marina Guidelines and AS4997 are concerned with the same structures.
125 A distinction can be drawn between marinas, on the one hand, and a swing mooring, on the other, in so far as the latter is a stand alone facility. On the other hand, a swing mooring must be adequate to restrain the vessel moored to it, at least in conditions that are such as might reasonably be expected in the location where the mooring is situated. If a mooring is not adequate to restrain a vessel, damage, not only to the vessel, but to other property, may follow. Further, it must be remembered that the criteria in AS4997 are based on a working life of small craft facilities, with which AS4997 is concerned, of 25 years. While Mr Britton, for the reasons outlined above, considered that it was reasonable to adopt the same criteria for swing moorings, there was no evidence as to the design working life of swing moorings.
126 I do not consider that failure to ensure that a particular mooring can withstand weather conditions that might occur more frequently than once every 50 years is necessarily the appropriate criterion for determining the standard of care required to avoid damage to property or to determine the fitness of a mooring for a particular vessel. Certainly, industry practice is not of itself the determinant. What is normally done is not necessarily not negligent or reasonably appropriate.
127 However, the difficulty with the one in 50 year criterion suggested by Mr Britton is that it is by no means clear, from the evidence, as to what weight of mooring block would be adequate to restrain a vessel of the dimensions of Pavana in weather conditions of the severity that occurs no more frequently than once every 50 years. There is certainly no industry criterion applicable in Sydney Harbour.
128 While Mr Britton is clearly an expert in his field, his opinions concerning swing moorings are hypothetical and argumentative. That is to say, in his written opinion, he expressed no opinion but simply said that AS4997 provides some guidance and that it could be argued that a 1 in 50 year event should be adopted.
129 The effect of ss 76 and 79 of the Evidence Act 1995 (Cth) is that evidence of an opinion will not be admissible to prove the existence of a fact about the existence of which the opinion was expressed unless the person who gives the opinion has specialised knowledge and the opinion given about the existence of a fact in issue is wholly or substantially based on that knowledge. While Mr Britton has a great deal of knowledge and experience in relation to maritime structures, he acknowledged that he has not really turned his mind to the question of swing moorings such as those in question in the present proceeding. Mr Britton's written opinion proceeded by way of analogy and, at best, did no more than advance a tentative argument. Even in his oral evidence, Mr Britton's opinion was one based on reasoning by analogy from his experience of maritime structures such as marinas, rather than any experience of the behaviour of swing moorings. While there was no objection to Mr Britton's opinion evidence on the basis that it did not satisfy s 79 of the Evidence Act, it may well have been rejected had there been an objection. Be that as it may, I have had regard to the opinion, but have discounted the weight to be given to it.
130 On the whole, the evidence as to the adequacy of mooring number 60 for Pavana is somewhat unsatisfactory. Both Mr Peeters and Mr Hood considered that the "windage" of a vessel was significant in determining whether a mooring was adequate to restrain the vessel in relevant conditions. Mr Hood's opinion is that, from the somewhat limited assumptions he made as to the windage of Pavana, a one tonne mooring ought to have been adequate to restrain it in the conditions that prevailed on 24 August 2003. He surmised, therefore, that there must have been highly unusual wave effects that resulted in extreme pitching of Pavana so as to cause it to drag mooring number 60.
131 There was no evidence that the combination of circumstances that led to the destruction of Seaquest were foreseeable. It may have been foreseeable that, if weather conditions that occur once every five to ten years prevailed, mooring number 60 may not be adequate to restrain Pavana from dragging the mooring. It would also be reasonably foreseeable that, if Pavana dragged its mooring, it may come into collision with another vessel in the vicinity. However, it appears to have been unusually bad luck that resulted in some part of Pavana or its mooring line cutting the mooring line of Seaquest, so as to allow Seaquest to become fully adrift and be blown to its destruction against the Roses Bay sea wall. Nevertheless, Holmeport did not contend that the damage that was actually occasioned to Seaquest was not reasonably foreseeable. Clearly enough, on the evidence, dragging of moorings is a risk that is known and is therefore foreseeable.
132 The winds recorded at Fort Denison and Wedding Cake West on 24 August 2003 were such as might be expected to occur at least once in every 5 or 10 years. On the other hand, the eye witness reports to which I have referred indicate that the weather conditions in Rose Bay on that day were fierce. The fact that Pavanna dragged its mooring for some 200 metres appears to me to be quite extraordinary. There was no evidence to suggest that anything other than exceptional conditions could have led to that occurrence. Mr Hood's evidence was directed to that very question. Further, the fact that seven or eight vessels were stranded on the sand in Double Bay, on the other side of Point Piper from Rose Bay, suggests exceptional conditions, although there was no evidence as to the size or other dimensions of those stranded vessels. When Mr Peeters lifted mooring number 60, he found that all of its components were intact. The conditions must have been particularly exceptional for Pavana to have dragged the mooring as far as it did.
133 Mr and Mrs Ruaro point to the suggestion made by Mr Peeters to Ms Kearney-Hayes that the outside moorings should be as heavy as possible and that two one tonne blocks should be put down. However, Mr Peeters was not expressing any view as to the adequacy of a mooring for any particular vessel. There was no vessel on mooring number 60 when Mr Peeters carried out his work and he did not no suggest that one tonne was insufficient for a vessel of the dimensions of Pavana. The observations made by Mr Peeters, therefore, must simply be regarded as referring to the fact that the outside moorings are preserved for the biggest vessels. It cannot be construed as a statement that the mooring blocks that were in place were inadequate for the particular vessels that were using them. There was no evidence, other than Mr Hood's, concerning a mooring that would be sufficient to restrain a vessel of Pavana's dimension.
134 I am not persuaded, on the balance of probability, that Holmeport did not take all reasonable measures to ensure that mooring number 60 was adequate for Pavana. Nor am I persuaded that the mooring to which Seaquest was attached was not reasonably fit for the purpose of mooring Seaquest. Accordingly, I would conclude that, if a warranty was implied by s 74(2), there was no breach of the warranty and that if Holmeport owed the secure mooring duty to Mr and Mrs Ruaro, there was no breach of that duty.