ISAF OSR Cat_0 Self-righting sailboat?

Discussion in 'Stability' started by Joakem, Feb 11, 2016.

  1. Joakem
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    Joakem Junior Member

    It seems to be additional

    Thank you Stumble and PAR,
    Your thoughts are helpfull.
    If I read the "ISAF" regulation, than 3.04.3 seems to be aditional and independend from the previous paragraphs.
    Meaning that a category 0 boat also has to be self-rightening regardless of ISO, STIX, ORC, etc.

    From there I wonder if that is at all possible for a modern performance boat without resulting to:
    - canting keel (complex and expensive)
    - waterballast (a lot required)
    - a permanently open companionway (not nice)

    Does anyone know of any modern category 0 boat(s) that comply without the above mentioned tricks?

    Much apreciated
  2. PAR
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    PAR Yacht Designer/Builder

    The list of offshore racers that comply is pretty long. There's no tricks - they either comply or aren't certified for that category.

    A permanently open companionway is an absurdity, that can't be considered in an off shore yacht, Canting keels often are limited to certain classes and in itself isn't necessary for compliance and the same is true for water ballast.

    I believe, you're over thinking this requirement. Assuming a ISO 12217-2 cat A craft is designed and hits the minimums of IRC, ORC and/or STIX, you're good to go, as these insure reasonable stability, for the sea states they'll be expected to tolerate. 3.04.2B and 3.04.3 seem to me as the redundant definition for this class. Simply put, if you have a ORC rate of 120 or better, than you qualify. 3.04.3 seems to try to define what this might be, though rather vaguely.

    Maybe it would be better if you told us what you're trying to do.
  3. DCockey
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    DCockey Senior Member

    Section 3.04.3 applies only to Category 0. What events require Cat 0 compliance?

    After reading the relevant sections of the regulations I agree with Joakem's interpretation that the requirement of
    Mo0 3.04.3 Capable of self-righting from an inverted position with or without reasonable
    intervention from the crew and independent of the condition of the rig​
    is separate from the previous sections' requirements concerning stability.

    Section 3.04.3 does not say anything about AVS, GZ or STIX. It only says that the boat needs to be able to self-right from an inverted position with or without action by the crew. Positive stability at all angles of heel is one way to enable self-righting but not the only way. Other possible methods include:

    - Movable ballast such a canting keel or water tanks

    - Inflatable buoyancy bags. The condition that self righting needs to be independent of the condition of the rig appears to require that any such bags be deck mounted.

    - Tanks of sufficient volume on one side which can be flooded when inverted.
  4. Joakem
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    Joakem Junior Member

    No escape clause anymore!

    Hi PAR,

    Am toying for an idea for a deep-ocean cruiser/racer.
    Pretty much wat OSR category 0 is meant for.
    ISO STIX etc. provides a nice handle, but insurance wil want full OSR compliance
    In the very recent past the paragraph 3.04.4 that Stumble mentions was a clear "get-out-of-jail-card". But ISAF deleted that one, and 3.04.3 is very clear.
    It's a paragraph on its own, without ifs, buts, or maybe's.
    IF you accept that, than I am trying to find out what the simplest option is.

    Thanks David, saw your reaction after I submitted this post
    Last edited: Mar 22, 2016
  5. PAR
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    PAR Yacht Designer/Builder

    Define "toying for an idea" . . .
  6. Stumble
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    Stumble Senior Member

    As I understand it a boat must meet one of the 3.04 requirements, it doesn't have to meet all of them. So it must either the ISO requirements of 3.04.1, the stability calculations of 3.04.2, OR be able to self right without outside assistance. I don't think there is any requirement that a vessel must meet all of them.

    If I am wrong then the only way I can think of to meet the requirement is some form of movable ballast. Either water ballast or a canting keel. By definition if the boat is perfectly balanced keel up then the CB and CG are in a line and the vessel is stable in that position. Of course it may not have very much stability, but assuming no outside forces act on the vessel it will remain in that position permanently.

    Below is the GZ curve for the Pogo Open 40, notice the stability past the AVS. This boat is Cat 0 rated, but has water ballast. But note the positive stability past 128. Absent some outside force it will remain upside down even if it won't float with the keel strait up.

    Attached Files:

  7. Joakem
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    Joakem Junior Member

    Hello Stumble,
    Thanks for your reply.
    It is interesting for me to see a class 40 GZ curve.
    I guess that the big beam is compensated by the big draft, giving a fairly normal curve.
    May be interesting to see what happens with the tanks on one side filled, can it be that she is self-righting in that condition?
    Am now looking at previous version of OSR.
    That version version is more elaborate, with 8 paragraphs applicable to category 0, instead of 3. Maybe giving more opertunity for interpretation.
    Anyway, have just send a query to my national representitive from ISAF.
    I will report back to this thread, if anything usefull comes from that.
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