Lloyds Clause 3.3 for boat 18m LwL

Discussion in 'Class Societies' started by Mitch1990, Oct 17, 2020.

  1. Mitch1990
    Joined: Feb 2020
    Posts: 71
    Likes: 1, Points: 6
    Location: Maine, USA

    Mitch1990 Junior Member

    Hi All,

    Please note this is a school assessment, not for a production vessel.

    I have been going in circles for a few days and do not know where to start on a midship structural analysis requires of the assessment. Unfortunately, in the previous assessment we got to determine the mission profile as the boat owner, i ended up with a 18m worlboat that can also coduct passenger transport. Now we must progress the design to include, seakeeping, midship structural analysis and maneouvering analysis.

    My design restrictions are not to exceed total length of 20m, not to exceed 1.5m draft, must hold 40 passengers (10 inside, 30 outisde). Must be able to conduct passenger transfers within 12nM of the coast, range of 400nM.

    I used the National Code for Commercial Vessels which is an Australian national standard as this is where the boat will operate. This standard defines 100% seating requirment and 0.85m2 per passenger, so I have used this as the governing constraint. The text I have is the marine engineering reference book by molland and I am using the volume limited design for a fast ferry where it provides starting ranges for Cb, B/L etc.

    My length Fr is 0.77 so i moved to a volume Fr of 1.8 and am looking at a semi-displacmemt or planing hull. I have developed a rough hull form that is hard chine and using a weight estimate conducted a resistance analysis using Mercier to better define my propulsion requirment which inturn refined my mass estimates.

    I believe I am now ready to start structural analysis. The NSCV refers to Lloyds clause 3.3 for structual analysis, however Lloyds is pretty clear that its not really applicable under 24m. I assume clause 3.3 is part 3 chapter 3.

    What should I do from here? I have conducted ABS scantlings before for 119m bulk carrier and we are expected to complete a midships structural analysis which I imagine for the purpose of the assignment includes a modulus of the section compared to a standard

    Thanks for any help

  2. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    I think your best option is to use the Lloyd's SSC rules and of course ISO 12215-5: 2019 is perfectly applicable to that boat.
    Let's see what the experts of this forum think.

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  3. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    Hi Mich,

    Well, if you have your weight estimate, this gives you your displacement, and if you have your hull lines (based upon this displacement), then you have a shape.
    Take the shape of the midships, and then this forms the basis for your midship section. Because you have spans..for the bottom frames, and spans, for the side frames, and spans, for the deck beam/frames.

    Since a midship section is based upon the shape of the hull...and then the inputs into Class rules, for the spans, which the input data required, notably length, displacement and speed.

    All Class rules can be used for structural design for vessels below 24m. The caveat is, they are not necessarily going to give scantlings that may be suitable. By that I mean, because these rules are intended for vessels between 24 -40/50m, any length below 24, is at the limit(s) of the formula that are appreciable, and hence the output, give "odd numbers" sometimes. Hence the caveat quoted above. It is not saying you can't use them, just that it may produce odd numbers and making you aware. Because you can apply for dispensation if you consider the output in error. And so you started a technical discussion with said Class rule to establish whether you can obtain a dispensation to the output. So from Class point of view, this adds time = cost. Cost they don't usually allow for, hence the caveat.
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