The Elements of Boat Strength: For Builders, Designers, and Owners

Discussion in 'Boat Design' started by wardd, Oct 24, 2009.

  1. Paul Kotzebue

    Paul Kotzebue Previous Member

    Daniel,

    I don't think the ISO standards for keel attachment have been adopted yet. Designers have been relying on the ABS guide for offshore racing yachts for keel attachment standards. Following the standards does require some engineering knowledge and skill. It's not just a matter of plugging in numbers.

    The boats I'm aware of that have lost their keels and the cause has been investigated, the Cynthia Woods and Hooligan, did not meet the ABS guidelines. There was loss of life in both instances. This tells me it is important to have engineering standards for boats and they need to be followed. The problem may be more with those who use the standards than with those who create them.

    You mentioned using Lloyd's scantling rules. Lloyd's 1979 rules for yachts and small craft is an excellent source for scantlings of traditionally built sailing yachts. It is still accepted by the USCG for passenger vessels.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    ISO, section 11.9 Structural Support for Sailing Craft Ballast Keel
     
  3. TeddyDiver
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    TeddyDiver Gollywobbler

    Keels are still under evaluation by ISO I believe..
     
  4. Alik
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    Alik Senior Member

    Part of ISO12215 standard for sailing boat keels attachment is not in force yet.
     
  5. MikeJohns
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    MikeJohns Senior Member


    The 1986 ABS scantlings for GRP construction were inadeqaute and lead to the detachment of a keel and two deaths that I know of.
    They were revamped in 1994. Following a coroners inqust.

    How did that occur when the engineering is relatively simple? LLoys register was criticised for being overly strong at the same time these lethal designs were being knocked out under ABS. The word at the time was that ABS was too weak but it took deaths to get them to change.

    Current ABS rules appear to be quite inadeqaute for their assesment of small boat fore-deck loads in heavy weather. So now they dopped the whole scantling and everyone is supposed to migrate, either to Lloyds register or G.Lloyds or BV or ISO but ISO is a compromise so I'd stick with one of the others if you don't check your own engineering.

    How many pre-1994 boats were built with fin keels to ABS and are falling apart?

    Dave Gerrs scantlings should be more than adeqaute in this regard but even reasonable scantling rules can be screwed up by non-engineering background designers , witness the Maxfun 35 debacle and death when the designer confused the keel bolt Ultimate Tensile with yield as well as other very poor errors.

    Most NAME types will check the structural side of the design for a few hundred dollars. Many boat designers use engineers to do this, some like Ted Brewer employed engineers in his design office.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Mike
    I can't say for 100% certainty, but I have a few friends who are yacht designers that use ABS constantly, almost exclusively. The reason why they have been using ABS for many years, since the 80s, is a you point out
    "..ABS scantlings for GRP construction were inadeqaute.."..in other words, lightly built. Light structure = cheaper...ie less material costs.

    "...LLoys register was criticised for being overly strong at the same time these lethal designs were being knocked out under ABS.."
    Correct, as this was their reply to me, whenever i mentioned LR or even DNV as an alternative to ABS, that they are "over built". Hence the preference for ABS. They also said ABS rules were 'easier' to use too.

    I've only recently used ABS, first time for 20 years. It was on a 51m steel patrol boat. Oddly enough, the scantlings are far far higher than LR and DNV...most odd. Too much 'over engineering'....
     
  7. MikeJohns
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    MikeJohns Senior Member

    John
    The ABS I was reffering too was for offshore racing yachts known as ABS ORY while you would be using the commercial rules which are very robust and are fully supported.

    I should have added that to properly comply with any rule the design should be submitted and approved which acts as a design review.

    The problem with pleasure boats is that the construction is only regulated if they are to be used commercially. For private use anything goes and it's buyer beware, in this regard the RCD is a step in the right direction.

    DNV is very well supported around the world too , I forgot to mention them, they even have an office here.
     
  8. Paul Kotzebue

    Paul Kotzebue Previous Member

    Which boats were these? I'm not defending ABS, but I am interested to know which boats had keel failures that met ABS ORY.

    How do you know this?

    Who?
     
  9. MikeJohns
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    MikeJohns Senior Member

    Paul

    It concerns me that many people including both surveyors and designers in the USA are quite ignorant of this.

    I'll try and dig one of the coroners reports for you. I don't now how old you are but it was all well documented when ORY was beefed up signigicantly in scantlings by way of the keel for GRP boats.

    Everyone should check the hull thickness in this area of pre 1994 GRP boats built to ABS 1986 minimums. Of even more concern is people using scantling programs and nice old bound books they have been given which are not up to date.

    All scantling rules are a bare minimum and designers used to be more conservative, many had engineering training and they used scantling guides as starters for weights and still engineered the hull or copied another robust design. The need to shave every bit of shavable mass lead to the minimums being adopted and scantling societies are not infallable although they get there in the end by a process of constant rule revision.

    How do I know Dave Gerr's scantlings should be adequate?

    I don't, it's just an opinion I formed, as I said I read his book after checking someones design based on his scantlings and I thought he erred on the heavy side but you would still always check against a current class society guide.

    If you want your design checked you'll need to ask around but since you are in Ca and I'm in Tasmania it's probably of no use for me to give you NAMES. I'd suggest that any independant will do a structural check of frame moduli spacing and skin thickness against one of the rules they have a spreadsheet or scantling program set up for. When we did it we sent them a spreadsheet form which they filled in then we checked the scantlings, looked over the construction drawings and signed off.

    You'll get the same service (Plan approval) from any of your local societies and their design surveyors are often independant and may be prepared to check against another rule for you.
     
  10. Paul Kotzebue

    Paul Kotzebue Previous Member

    Mike,

    As a registered professional engineer in California and Washington, I'm one of the few yacht designers in the U.S. who can legally offer engineering services to the public. One of the things I do for a living is to review scantlings of small craft for submittal to the USCG or classification societies. It usually costs more than a few hundred dollars. I'm just curious who the "NAME types" are that will "check the structural side of the design for a few hundred dollars". I don't think there are any in the U.S.

    I'm capable of checking my own designs, but thanks for the suggestions.
     
  11. MikeJohns
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    MikeJohns Senior Member

    Paul
    What license do you hold? And anyone can be a 'yacht designer' of course.

    Surely every and any suitably licensed engineer can do this legally.
    I do see some dubious claims in the US where someone claims to be a PE 'yacht designer' and they are licensed for example as a civil (non structural) engineer. Not even mechanical.

    I know several mechanical engineers who offer design assistence to boat designers. Maybe you have just never had the need to search for such a service.

    I just wonder why it should cost so much to review a boat design if it is from a designer who has already done the work particulalry if it's to a standard that you are familiar with and have computerised. I usually find the scantlings are fine but the errors are in omissions of things like not achieving required end fixity one way or another.

    Bit if you are talking a cutting edge FEA study not to any standard... yes I do that too but then its several thousand dollars. But I don't go there to check scantling compliance.

    But I'm really curious if you are a PE and also a yacht designer how come you are not aware that the eralier ORY was deficient ? If you ever see a GRP keelboat built to ABS before the 1994 the first thing you should ask is whether the laminate is sufficient in the way of the keel. There was a big public info campaign here and lots of boats had laminates added to strengthen the hull.

    But it would be more fun to talk about engineering.
     
  12. frank smith
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    frank smith Senior Member

    How is it that these boats were produced . Surly they had the science to spec.
    the laminate schedule at the time . Is it that the engineering at the time did not take into acount certain factors , or were they not tested enough?
    How much is a result of economizing in construction ?

    As this may be of interest to others besides myself , would it be possible to post location for info on keel attachment failures.
     
  13. Alik
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    Alik Senior Member

    Even with rules, correct interpretations and engineering experience helps to make right decisions. In case of ABS - they are developed for high-quality construction, no allowance is given to reduced properties of laminates. In ISO12215 there is an allowance, unless particular laminate test data is used.

    Question: does anyone have a link to LR's special craft software, including structural? Would like to buy.
     
  14. MikeJohns
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    MikeJohns Senior Member



    No it was just an oversight, I'm not sure that some of the people at ABS were ever all that happy with ORY.

    To properly put the dates on things:

    The 1986 ABS ORY had inadequate hull shell thickness to prevent shear failure at the keel attachment backing plates. This was corrected in the 1994 version.

    The coroners recommendation (Australi) following a fatal keel separation was that all light displacement boats built to pre 1994 ABS ORY should be contacted with a view to checking the laminate schedule and where appropriate upgrading to the 1994 requirement.


     

  15. ancient kayaker
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    ancient kayaker aka Terry Haines

    Since keel separation is dramatic, easily recognizable, and a localized failure it catches the attention.

    I'm not sure if it is a particularly common cause of loss of life and property, but I would find that surprizing. It seems a much simpler matter than most other aspects of boat design. The static and dynamic loads are accessible to analysis. The material characteristics are known, manufacturing variables are controllable by inspection, and material degradation with age and use can be determined with tests.

    And yet, even discounting individual cases of boats that are not built to design, it is not the rare phenomenom that it should be. Is it simply a question of racing craft being built and operated to -or beyond- the limits, or does it also plague commercial and recreational craft to a significant degree?

    As a retired engineeer, some posts in this thread leave an impression of a cookbook approach to boat design similar to the build-to-code approach used for housing construction. That is not necessarily a bad thing except there is a lack of confidence being expressed in the various standards. Perhaps I am naive, but I was expecting something closer to aircraft design practice.
     
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