“Just a silly millimeter longer”  Measurement Blog

Chris Bolton

Anybody remember that Chesterfield cigarettes ad (NOT Benson and Hedges; it was in response to their 100 mm cig that Chesterfield introduced their 101)?  Yeah, I’m old.  Anyway, thought that would make a good title for this blog, because we care about silly millimeters.

Open class measurement rules can be very tricky and very precise, but given the recent (and everlasting) issues with maintaining true One Design” classes worldwide (see Laser and Etchells), I think we have it easy.

For the first discussion on this blog, let’s cover the new Classic rule on curved boards.  First, let me note that this is still a trial rule.  Even though the vote was successful that contained this wording, there are still several steps that must take place before it becomes Class law (not that I expect anything to change).  Second, I will note that the new Measure’s Guidelines have not been published, which are very important to how this rule will be interpreted.  As a quick aside, if anyone has comments on suggested changes or improvements to the current guidelines (which are available on the International Class website) please send them to Bailey or myself.

Several of the measurement rules don't match what most of us would consider to be proper english nautical/aeronautical usage, or are not easily understood as such.  The new trial rule says in part “or the radius of the chord of the leading edge is to be a constant curve of not less than 1.190m”.  I agree that using "chord", i.e., the fore-to-aft width of the board, in this context, is confusing.  However, if you consider ALL of the chords from top to bottom, and pick the leading edge of those chords, maybe it makes a little more sense.  In any event, this change was specifically put in place to move the measurement point from the trailing edge to the leading edge, and in so doing, now allows asymmetric and twisted boards.

The way they will be measured, at this point in time, is that the leading edge of the board will be laid on a curve of that min. radius, and if the leading edge conforms to the radius line, or is behind it on the ends (i.e., larger radius), it is legal.  The amount of twist in the trailing edge is open (as far as I know, right now).  The "continuous curve" would then apply to the whole length (or span) of the board, but only against the leading edge. I would check this by laying the board, leading edge down, on a piece of cardboard, and drawing a line as close to the leading edge as I could.  If you then slide the board up and down this curve, it should follow this track.  Any significant deviation from the track indicates a non-uniform curve.  Experiment at home :-)  Pictures below.

The question has been raised as to whether the vintage F1 curved boards seen at the North Americans in 2019 would pass.  I have been told that their twist was on the leading edge.   However, note this part of the new rule:

• All boats measured prior to 1st March 2019 shall comply with : “Trial Rules” 1, 4 & 5 and have daggerboards restricted to either a straight or constant curve axis. · All boats measured from 1st March 2019 shall comply with : “Trial Rules” 1, 2, 3, 4 & 5

Since we measured those AFTER March 2019, they do not comply with the new rule (if they do have leading edge twist).  If they were measured BEFORE March 2019, they do not comply because they weren’t a constant curve J

 I plan to play with my boards soon to see how easy this is to implement. The thinner trailing edge is clearly easier to line up than the thicker leading edge.   I have an idea that a small carpenters triangle could be used to get a nice straight edge to check against, and IF the board had a constant thickness, you could easily match that to the min radius curve. 

Attached are some pictures that may be of assistance.

Place the board, leading edge down, on your measuring surface, which has a minimum rdius line already drawn on it.  Do the ends of the board stay on the min radius line, or od they stay outside of it (on the convex side)?  If so, the board is not less than min raius, and is legal.

If one or both ends fall inside (the concave side) of the line, it is at less than the min radius, and is therefore illegal.

If the board doesn’t conform exactly to the min radiius line, place the board on a measuring surface, which hopefuly is not the same as your critical minimum radius devcie.  Draw a line along the whole length of the board as close to the leading edge as you can.

Slide the board up and down this new line; if the leading edge does not stay on that line, it is not a constant curve, it does not meet the rule.