Scantlings methodology for recreational boats

Discussion in 'Class Societies' started by TANSL, Dec 21, 2013.

  1. rxcomposite
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    rxcomposite Senior Member

    It does appears so but if you take a deeper look, LR and ISO have something very much in common. The plate analysis is very similar except that ISO has the "expanded version" (ISO Table H2 and H4) while LR has the "bells and whistles". Another thing that is frequently overlooked is the ply angle deviation from the stress direction. ISO has this formula, so does LR and BV. Very important but often overlooked.
     
  2. daiquiri
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    daiquiri Engineering and Design

    Anyways folks (AH and RX), it appears that you are discussing vessels above 24 meters, since you're talking about Class rules.

    For recreational vessels up to 24 m the reference is the ISO, and Class societies tend to deal no more with small recreational ships.

    All this to say that what you say is correct, within the range of the applicability of the respective rules.

    Cheers
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Er..quite right, my apologise for the incorrect deviation into isotropic global structures, well spotted :D

    See, told you I don't use composite rules much and need a bit more time than ally structures to refresh my memory :)
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    Not for me.

    I don't as a rule use ISO. I designed an 18m composite catamaran to DNV Class rules several years ago. A college of mine is currently doing several composite boats, all to LR and all under 24m.

    As I noted before, it really depends upon the "measure" of competency and thus compliance that one is demonstrating to the Flag state.
     
  5. rxcomposite
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    rxcomposite Senior Member

    Hahaha. No apologies needed. LR rules are so dispersed you have to hunt them down. Confusing sometimes. Could also be a typo error. My second rule set is so full of errors that LR has to issue corrections nearly a chapter thick. I know there is mention of global stiffness but in another chapter. Was just too lazy to look it up.:D
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Agreed...a mess.

    Mind you DNV still uses the 50m cut-off, unlike LR as you rightly pointed out use 40m :p

    I keep telling LR to make them easier....as I'm on their tech committee....slow progress :eek:
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Why??

    If the object is to learn, then no need. Whilst the threads title and your opening post is specific as such, deviation, if all relevant should be welcomed, especially if knowledge is shared, in whatever form. That is the object of such forums...yes?
     
  8. TANSL
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    TANSL Senior Member

    I will continue learning from you, of course. But what interested me was the methodology in the calculation, rather than a discussion of what the rules say different. and who knows more about each standard. This is another argument, also very interesting, but it's another discussion.
    Thanks again, sincerely.
     
  9. daiquiri
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    daiquiri Engineering and Design

    Now this can be an interesting digression, AH. :)
    I guess you are referring to the DNV 2.21: https://exchange.dnv.com/publishing/stdcert/2010-04/Standard2-21.pdf

    If you recall, we have recently had two discussions concerning ISO and class rules, this one: http://www.boatdesign.net/forums/boat-design/elements-boat-strength-49168.html and this one: http://www.boatdesign.net/forums/diesel-engines/stainless-fuel-lines-prohibited-49094.html

    There you have talked about the difference between class and flag rules, and it stands. But the fact remains that in order to be commercialised in the EU, a recreational vessel has to comply to the RCD (94/25 EC) - which adopts ISO as reference. No ISO means no commercialization of the vessel in the EU. So, the logic requires that any class rule which covers the field of recreational craft necessarily needs to be at least equally demanding as the relevant ISO technical standard. Otherwise, a vessel designed to a class rule less demanding than the ISO could not satisfy the RCD. Please correct me if I am wrong on this.

    Now, I am reading the C300 section (page 71) of that DNV rule, which concerns the fuel piping. It does not ban the use of stainess piping for the fuel lines. But the ISO 10088 excludes the stainless fuel lines, as we have seen in that other thread! So, at least in the C300 section, the DNV rule is less demanding and hence not compliant to ISO. The apparently obvious conclusion should be that a vessel whose fuel lines were designed to DNV will not satisfy the RCD. :eek:

    Since I do not find very probable that DNV would create a set of rules which go against the RCD, how to interpret this apparent incongruence between the two?

    Cheers
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    D

    I’m not overly familiar with RCD rules, as it is not my field, I design commercial vessel which are 99% to Class not pleasure/RCD vessels. However the RCD code when relating to structure states:

    3.INTEGRITYANDSTRUCTURALREQUIREMENTS
    3.1.Structure
    The choice and combination of materials and its construction shall ensure that the craft is strong enough in all respects. Special attention shall be paid to the design category according to section1, and the manufacturer’s maximum recommended load in accordance with section 3.6.


    I see no mention of ISO.

    I think the confusion comes in when looking at The InLand Waters Small Passenger Boat Code. This is where ISO 12215 is cited for structural design. But as noted this code only applies to “..This Code is intended to apply to vessels operating commercially with a skipper or crew, and which only carry passengers….”.

    Thus I think, for whatever reason, there has been a blurring and an assumption that pleasure craft/recreational craft must use ISO. But the RCD code does not state this, only small commercial vessels, which many prefer not to use Class rules, owing to cost implications of plan approval and extra costs and delays for the builder. So in the absence of structural dwgs to Class approved rules (see my previous note above) what standard can be applied??...only available one, is ISO.

    As to the invariance. Commercial vessels are subject to inspections and other mandatory regulations which are generally not applicable to pleasure boats. As such what may be acceptable on a commercial vessel simply because of constant attention by a well trained crew and part of the QA system would not be considered applicable to a pleasure boat that may be used for just a “few days” or “weeks” per year. Thus one could infer that such variances are solely for “safety” since regular maintenance and inspections by independent authorities (to allow their PO’s) does not occur on pleasure/recreational vessels.

    I should add that several years ago I designed a "pleasure vessel" for a client. I submitted a structural report to MCA based upon Class rules, not ISO rules; since I am very conversant with Class rules unlike ISO rules. It was accepted. Ergo, section 3.1 as i read it, does not mean one must use ISO, as it is not mentioned. The design category in Section 1 was simply transferred to the equivalent Class notion, and that was it, done.
     
  11. TANSL
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    TANSL Senior Member

    I would draw attention to the title of this thread: "Scantlings methodology for recreational boats", everything else, in my opinion, is to mix apples and oranges.
    Few years ago among the few existing regulations was the DnV Rules for boats under 15 m. It was very simple to implement and very comfortable. Currently, in my opinion, this regulation is obsolete and even on the website of DnV-GL, it is difficult to find.
    One of the things that today is much emphasis on the calculation becomes inhomogeneous materials. I believe that, today, all the regulations require, for non homogeneous materials, an analysis of the loads in the different layers of a laminate. This is not called for in the old regulations. In this, as in many other things, and fortunately, we have gained a lot in rigor.
    Anything wrong with what I said, please tell me what. Thank you.
     
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  12. daiquiri
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    daiquiri Engineering and Design

    Hi Ignacio,

    Did you check the link to the DNV Rule 2.21 in my previous post? It is a DNV rule for design of small craft (<24m), "mainly for commercial craft, but also recreational craft outside scope of EU directives" (page 9, item A101).

    It makes me wonder what does the latter phrase mean? That where other EU rules exist (ISO?) they should be applied, or what?
     
  13. TANSL
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    TANSL Senior Member

    I'm not refuting what you say at all. What I wanted to express is that even the rules of the CS may vary and some rules that were in place 25 years ago, today they are not. I meant that some concepts that years ago were used for calculation are not admitted today, or vice versa. I know nothing about the DNV Rule 2.21. only say that the rule DnV had for boats under 15 m, in my opinion, does not apply today.
    Based on this, going back to the spirit of my thread, if calculating the midship of a pleasure boat you have to do an analysis of the various layers, I see difficult that can be done in a few minutes. If we compare this method with another, just dividing two numbers we get the thickness of the plate, of course the latter is much faster, but it's like comparing apples and oranges.
    On the other hand, I think the boats built and sold in Europe, as you say, have no choice but to comply with the ISO. There is another aspect to consider perhaps, is whether the construction is in series or is it a single vessel. Maybe there requirements, especially the inspection and certification of construction, are different.
    Cheers
     
  14. Alik
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    Alik Senior Member

    It is a fact that all European societies switched towards ISO for pleasure craft below 24m. But some of them still keep their own rules for small craft covering pleasure boats.

    DNV 2.21 'Craft' Rules cover small commercial craft and to some extent to pleasure craft.

    GL has the Rules for boats and yachts below 24m that covers pleasure boats as well. (Should be noted that design loads in GL are taken from ISO12215-5).

    The choice is by designer and customer. We use 'small craft rules' of classification societies for patrol, passenger, fishing, workboats and other craft. And we use ISO for pleasure craft; this is primary option for craft below 24m and I do not remember we ever used anything else. Also, in some jurisdictions such as Australia, South Africa, etc. ISO are officially accepted for small commercial boats.
     

  15. TeddyDiver
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    TeddyDiver Gollywobbler

    Actually it's quite acceptable to calculate structures based on loads, no necessity for ISO compliance in that regard..
     
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