FRP Class Rules

Discussion in 'Class Societies' started by ABoatGuy, Sep 12, 2011.

  1. ABoatGuy
    Joined: Aug 2004
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    ABoatGuy Member

    I'm quite familiar with the ABS FRP rules and have been asked to take a look at BV, DNV & Lloyds for a new build. (The prospective owner had a disagreement with a surveyor on an annual on a previous build so he is shopping around).

    Does anyone have a good grasp on how an FRP hull will come out based on the various class rules, all else being equal. The vessel is sandwich topsides, solid bottom, semi-displacement. I'm not looking for numbers, just a general idea (i.e., all things being equal an FRP hull built to Class rule X will be heavier, lighter, stiffer etc. to satisfy minimum requirements). Don't worry guys I'm not designing to minimums - it will just give an easy comparison point. I will certainly get into the rules before making any decisions - just tapping resources at this point for a quick thought. :)

  2. tunnels

    tunnels Previous Member

    What was the disagreement about????? . surveyors are on the whole very agreeable and helpfull people , have never had any kind of disagreements ever and have delt with Surveyors for the past ????? years and beyond !.
    The owner is Shopping around why and for what ?? The serveyor is only doing his job and not there to agree with what ever the owner thinks should be done . You are there to build boats to what on the plans that have been stamped and approved by the company the serveyor comes from . If you deviate from what there just because the owner said !! you are in the hot seat !! Me i always build better than what written and been approved .
  3. ABoatGuy
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    ABoatGuy Member

    Clarification - I think you missed the point. The point of the post was to ask a simple question regarding the hull scantlings one would arrive at using different classification societies not berate surveyors. I have no problem with surveyors, ABS or otherwise and never said I did. I have found them to be helpful as well. I don't know where your idea came from that I intended to deviate from anything. I was not involved in the "problem" and really no nothing about it. Maybe read the post twice before flaming.
  4. nemo
    Joined: Apr 2002
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    nemo Naval Architect

    Hi, ABS rules are quite old and not very "advanced". I think that with DNV you would be able to save some weight because they can keep into account the plies orientation, etc.
    I have extensive experience with Lloyd's aluminium and steel vessels, but not on fiberglass. Generally, the LR scantlings are usually slightly heavier than the ABS one. If you tell them you want to change from ABS to Lloyd's, they may be willing to do a free preliminary assessment, they made it for me once.
    I know that RINA was developing a new set of FRP rules, which derives directly from the classic laminate theory, so calculations would probably be more accurate, but I don't know how far they've gone.

    Re the surveyors: I think they're just human being, some are less "client oriented" than others, but this is more related to the person rather than the register.
  5. tunnels

    tunnels Previous Member

    Its a attitude problem !!

    I was in charge of a department making all and everything for the internal structure of a 147 foot super yacht .
    This took in everything tanks, floors ,carbon girders ,Beams, ring frames ,collision and water tight bulkheades, wall panels alsorts of strange shapes made in one piece , after they were told it was impossible . you name it we made it ,
    When i started i was told everything revolved round DNV regulations and was to be done by the book !!!.
    So i went a couple of steps ahead and set the bar higher for all my guys to follow in a very short time the Surveyor could see we were pulling out all the stops and had put there book on the shelf .
    While the rest of the factory quivered at the thought of the insector coming to point his finger we just carried on same as always and most times they never even came near our department .
    They set there guide lines ,so we set our own guide lines higher and all the guys in a very short time refused to lower there standards to Dnv specs . Its an attatude thing !!,if every one works together and helps and assists with everythingproblems dont exist . In 2 years we never had one single failure everything exceeded there specs and the QA INSPECTOR recorded everything methodicly to 0 percent no pluses or minuses . Samples we were told to make specially to go away to be tested were just off cuts of existing panels and always exceeded the DNV specs .
    Its a minimum guide line to follow so think beyond what they want how can you improve what they aske for . dont be smart and try to cheat and hide things it your *** that on the line . If the owner wants things changed let him sort it with the surveyor and get it signed twice and stamped with APPROVA;
  6. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Not 100% sure what you mean by "..will come out..." :confused:

    I recenty designed a hull to those exact requirements using DNV. Simple!
  7. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    Some of the issues with class compliance in a FRP boat will be the structural fire protection plan. A and B rated bulkheads and decks on an FRP boat can be a challenge with very limited ways to comply.

  8. cracker
    Joined: Sep 2011
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    cracker NA

    Without knowing the size, it is nigh on impossible to comment. For smaller boats LR SSC really penalises with its impact skin thickness minimums. SO, as a very general statement, I would say that LR will give a heavier (small) boat. However, if you can talk to LR and get them to do specific approvals to reduce minimum skin thicknesses, problem goes away.
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  9. DavidJ
    Joined: Jun 2004
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    DavidJ Senior Member

    Nemo is completely correct. The ABS rules are old and out of date and in my experience they result in a much heavier vessel than the DNV rules. They are however much easier to use. I have some experience with the Lloyds rules but not enough to confidently compare them. They are similar to DNV.

    I have a fair bit of experience with both the DNV rules as well as ABS. On one project (110' motor yacht) we had done 90%+ of the structural design to the DNV rules when the shipyard decided that they actually wanted to go with ABS. This package involved over 30 separate structure drawings including detail drawings and computer models involving hundreds of hours. We were obviously not interested in started again from scratch. I recalculated all major members using the ABS rules and found it very frustrating when I started finding requirements for deeper members throughout. A different company was producing the interior design and having to tell them that they now had an inch (or whatever) less headroom throughout would not have been a pleasant prospect. We decided to submit first principal calculations to support our existing DNV scantlings for major members and this was accepted by ABS without any complaints.

    Incidentally around this time I spoke to a friend I went to school with who works for ABS and found out that he was in the process of rewriting the ABS rules for composite yachts. He was told to use the DNV and Lloyd's rules for comparison. He agreed with me that he was finding the existing ABS rules to result in much heavier boats than the others. He asked his boss if he could lower the requirements and was told no. Perhaps that will change before they are eventually released but for the moment it appears ABS still plans to continue as they have. (but at least they won't be crappy photocopied documents)
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  10. ABoatGuy
    Joined: Aug 2004
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    ABoatGuy Member

    Thanks David, Nemo. That's the sort of info I was after. I probably stated the question poorly.
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