I.O.R "ton" ratings, 1/4 ton, 1/2 ton, 3/4 ton...

Discussion in 'Sailboats' started by sharpii2, Aug 20, 2022.

  1. sharpii2
    Joined: May 2004
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    sharpii2 Senior Member

    Here's a question that has stuck in my mind for some time.

    Just what did the IOR "ton" ratings really measure?

    I know that they were used so boats of the same "ton" rating could be raced as equals.

    It occurred to me that this rating measured the weight of the likely crew.

    A 1/4 ton rated boat would have maybe three crew on board. And if the standard assumed average weight of a crew member back then was taken as 150 lbs, then three of them would weigh 450 lbs, not including their carry on gear. This is very close to 1/4 ton.

    Am I out in the weeds on this.

    Or am I on to something.
  2. wet feet
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    wet feet Senior Member

    Way off.I'm afraid.It had a bit more to do with the existence of an older trophy One Ton Cup - Wikipedia https://en.wikipedia.org/wiki/One_Ton_Cup .None of which relates to the rather abstruse Thames tonnage that was the earlier reference for British designs.In their era the various categories of level raters probably had the best designers and sailors of keelboats engaged in very close racing.
  3. jehardiman
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    jehardiman Senior Member

    Yeah, it was all about a hitting a particular measurement, first as a class rule, then RORC, IOR, and IMS. So for a modern( 1965) One Ton first under RORC you had to hit 22 feet, then after 1971 under IOR it was 27.5 raised to 30.55 in 1983. After 1994 it went to IMS and VPP and then back to a rotating one design. Similailary, all the other tonners had to hit their own ratings, that is why IOR IIIa was such a cluster...so many boats changed rating overnight.

    From the ORC site;

  4. sharpii2
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    sharpii2 Senior Member


    And I thought I had a good narrative going.

    I figured that all of these boats used human ballast, so bigger boats would need more of it than smaller ones. And bigger boats would need bigger crews anyway.

    Having never raced (at least not officially), I presume that the definition of human ballast is any crew member who is not busy doing something else, while on watch.

    The math in my head created the seeds of my narrative. I figured a 1/4 ton boat would need a crew of three, and might end up with a crew as small as two, or as large as four.

    A 1/2 ton would need a crew of four to six. So, you add them up and throw in a bit of fuzzy math, and you end up with a crew weight of roughly 1/2 ton. And so on.


    It was fun while it lasted.
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