Revision of ISO 12217 - Small craft - Stability & buoyancy

Discussion in 'Stability' started by Convenor 12217, Jan 18, 2013.

  1. gonzo
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    gonzo Senior Member

    meren: Do floating ball valves qualify the same as flaps?
     
  2. Guillermo
    Joined: Mar 2005
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    Guillermo Ingeniero Naval

    Most interesting discussion.

    We do regularly use ISO 12217 to assess boats manufactured by small boatyards, typically producing boats under 12 m. Most of them are in fact under 8 m length. We have assessed hundreds of such boats and I am not sure considering the people vcg to be at 10 cm above deck is a realistic move.

    When we assess small open recreational boats using a real test option, people during the test, if standing, tend to grab to whatever item is suitable, or then they tight a part of their body against a surface or fix point. Many times we reach listings in the range of 20º. Some of you probably know 12º is called "panic list" in passenger ships. And that's for a good reason.

    We also assess many small commercial fishing boats under Spain's specific rules and regulations for such vessels. Currently small open boats (which cannot have more than 7,5 m length and most of them are under 6 m) are nowadays asked to comply with ISO 12217 instead of the old spanish 1964 stability rule for boats under 20 GRT, which in my opinion used a demanding test quite simple to perform that has for many decades provided to thousands of small FVs a pretty satisfactory safety level.

    In commercial open FVs a real test option is in our country always chosen, because a detailed calculation assessment is too expensive for the average small FV owner (for this last option you need to have a trustable lines plan and accurately know the location of all CoGs, which I have found is almost an impossible task in real life). When assessing with a real test the crew is used as listing weight and, when standing, they always move from side to side within the crew area to positions tighting their knees or thighs against the lateral corridors.

    So, in my experience, 10 cm over deck makes not much sense.

    Also I would like to say ISO norms are quite complex for small boat manufacturers which produce very short series. But an excess of complexity seems to be the rule nowadays in our bureaucratic Europe.... ;)
     

  3. Alik
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    Alik Senior Member

    Fully agree. And this complexity has increased in last version of standard where only 2 load cases were studied.

    The amount of calculation work does not match the budget of desinging a small craft, and some cases they require to study are not the wors cases or not important. The calculation book we did recently for 48'powercat is about 140 pages, 6 load cases studied... It more cases than for commecial boat.

    The 2013 standard could have been done much better. I am preparing a paper which I intend to present at Damaged Ship conference in UK, where the subject would be reviewed in more detail.
     
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