watertight bulkhead

Discussion in 'Boat Design' started by Pammie, May 28, 2018.

  1. Pammie
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    Pammie Senior Member

    @Ad Hoc: would it make sense to use a method that is not specific for the used hullform (width) and speed? If not: what method would you use to make it so?
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    A method for what...??
     
  3. TANSL
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    TANSL Senior Member

    All boats that intend to achieve the "CE" mark must comply with ISO standards for vessels of less than 24 m in length. These norms, more than 70 in total, are not anything, nor are they easy to understand. They are as technical as those of any Classification Society and are developed by highly qualified technical personnel and great practical experience. The fact of designing / building a ship according to the ISO does not mean that you are a " " small time "builds / designers" " but simply that you use the rules applicable to your ship.The roads used by the ISO standards are exactly the same as the followed by the CS Regulations, the only difference is that, due to the characteristics of the ships in question, the efforts caused by some cargo assumptions are not taken into account.
    A professional using ISO standards can be as important as the one who designs a high-speed catamaran. There is no reason to underestimate anyone.
     
  4. rxcomposite
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    rxcomposite Senior Member

    Tansl- From the ISO itself " Introduction-
    upload_2018-7-4_17-11-37.png

    Note we are talking about boats, not ships.
     
  5. Pammie
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    Pammie Senior Member

    @Ad Hoc: I meant using a monohull method (as in ISO 12215-5) for designing overall structural strength in a multihull.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Pammie

    You just need to be consistent and not cherry pick.

    Thus, Stick with LR or DNV-GL or ISO etc....don't attempt to pick the bits you like or are easy to understand. Mono or multi - apart from the global loads check (for multi), there shouldn't be too much difference, so long as you stick with one method.
     
  7. TANSL
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    TANSL Senior Member

    As I do not have the English version of ISO 12215-5, I have allowed myself to make a translation of a paragraph that appears on page 9: "For the complete scantling of the boat, this part of ISO 12215 should be used. in conjunction with part 6 for details, with part 7 for the multihulls, with part 8 for rudders and with part 9 for appendices and rigging points ".
    There is, without doubt, the "complete scantling", not of a base or a guide.
    From there, everyone who interprets what they like but is a verifiable fact that some administrations accept these standards as a tool to obtain the complete scantling of boats of length up to 24 m. Some of the ISO standards for small craft are accepted for commercial work boats (not recreational)
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    Pammie

    Just so you’re 100% clear.

    When any vessel is built for commercial purposes: car ferry, passenger ferry, workboat, tug, patrol boat etc, the designer and shipyard use Classification society rules. The client wishes to have their vessel designed and built to a known standard…Class rules…and also for the vessel to be inspected for adherence to said standard. Thus the designer and/or shipyard must use Class rules to demonstrate compliance.

    It is also the minimum, not maximum, the minimum necessary for any vessel to be Fit-for-Purpose. Depending upon the duty, area of operation and any unique feature I often design over the Class minimums, to ensure longevity of the structure. (This comes also from my large database of R&D I’ve done over 30years. The only problem with this is, if my designs are built at a yard that doesn’t communicate or listen to the advice/guidance I provide, things go wrong. C’est la vie…)

    Most Class rules start from 24m and up. You can ask Class for a vessel below 24m to be designed and built to their rules, but the minimums that must be complied with sometimes end up greater than one would otherwise expect – 6mm plate on a 10m boat for example. Simply because the formulae used tend to gives odd results at each end of the spectrum – Class know this, hence their general cut-off at below 24m. But Class are happy to comply for below 24m is you wish – just beware not all the results make sense.

    However for non-commercial until recently there has been no such common standard of compliance. (noted by endless sad accidents in the previous decades). One may simply say - it is for pleasure just a day at the beach etc – so what?

    Some Flag states have their own structural rules and stability rules etc, but in the ever expanding EU and its grip on EU regulations, this started to change. The European commission decide to adopt the ISO into EU law for general compliance.

    Thus, the EU decided to make a common standard of compliance for vessels that are not designed and/or built to any Classification standard. They wanted/needed a common standard and also introduced the CE mark for recognition of such.

    One is not forced to use ISO, but most designers and/or builders of small craft do not wish to go through the laborious task of reading Class rules and, more importantly, if they wish to sell their vessel after, it must come with the new CE mark that the EU directive brought in; since Class compliance is rather costly. Why pay high Class design approval fees simply for a small day run about RIB, for example.

    So, in general, ISO is for those not designing/building to Class as in the case of a ‘home build’ and need some guidance of what/where/how, or, those ‘home builds’ and now ‘others’ who are designing/building any kind of pleasure/leisure craft, but, no longer for personal use but for commercial purposes and need a means of obtaining a CE mark. So if you buy a small RIB for example, it will come with a CE mark and being a small run-about RIB it is not 100% necessary for Class design and build, as it would generally be cost prohibitive for small builds with tight margins, so, next easiest thing…ISO.

    I don’t use ISO as I find it inferior to Class rules, noting that 99% of my designs are built under Class rules anyway.
     
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  9. Pammie
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    Pammie Senior Member

    That makes it more clear! Ofcourse every method has it advantages and disadvantages. Main problems for non-professional designers is availability of class rules, understanding them (filling in the right numbers at the right spot) and indeed get a feeling or results are realistic for 2,5 x smaller boats.
    Still don't know but will make a decision in the coming days. And: will not be cherry-picking on results ;).
     
  10. Pammie
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    Pammie Senior Member

    OK, I decided to use ISO. Maybe not as good as another method but will be faster.

    <note: request removed; the way it was phrased seemed to invite violation of ISO copyright.>
     
  11. TANSL
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    TANSL Senior Member

    Copyright problems, I'm sorry.
    And, against other opinions, the ISO is as good as any other regulation for small boats. For some, it is the "appropriate" standard
     
  12. Boat Design Net Moderator
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    Boat Design Net Moderator Moderator

  13. Alik
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    Alik Senior Member

    Not exactly so. ISO12215 standard contains the engineering methods for local strength based on Savitsky-Brown, Allen-Jones and other theories, exactly same as all classification societies. The design loads are very similar, the methods for beams and plates are same, the methods for laminate stack analysis are the same as, say, LR. What is the difference? ISO has lower safety factors for composites (2.0 vs. 3.3), ISO is more flexible to certification of source materials, ISO has less prescribed structural details, as alternative, ISO also contains simplified calculation and testing methods for structural design, ISO does not talk much about global strength (which is understandable for small boats - not the case). I would say designer using ISO is usually proficient with class rules; the ISO12215 is not any simpler option!
     
  14. TANSL
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    TANSL Senior Member

    People have a tendency to despise what they do not know. After many, many years, working with the regulations of the CS, and around 12 years with ISO standards for small boats, at the moment, it is easier for me to work with the Rules of the CS than with the ISO 12215. Is anyone capable to understand and apply ISO 12215-6 well?.
    But this is just my opinion, of course.
     

  15. Alik
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    Alik Senior Member

    I always do this way: apply practical experience, common sense and engineering principles, and then look for justification in the Rules/Standards. It only works like this, because Rules (and surveyors) often tell You weird things.
     
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