Sail Number Digits

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For heavier sails, sticky-backed numbers work well.  For light sails, however, you need a different approach.  Typically, you need to ink your numbers on, using something like the pens sold for marking up overhead transparency films.  Make sure you buy the "permanent" waterproof variety, not the "water soluble" ones...!  To take the ink off in case of mistakes, acetone (nail varnish remover) works well.  For serious removal, try a solvent called MEK (methyl ethyl ketone) in a well-ventilated area and using rubber gloves.

You also need to be ready to add a "1" in front of your two-digit sail number in case another skipper at your event sports the same number as you.  Again, for heavier sails, sticking on a length of electrical tape or similar will do.  For lighter sails, it is not practical to ink on a "1" and then remove it afterwards -- it always leaves marks.  It is also not practical to use sticky-back Dacron or electrical tape, since the sail will distort and not set properly, and you run the risk of damage when you peel it off afterwards.  The answer seems to be to use some 3M "Spray Mount" repositionable photo adhesive.  This tip comes from Larry Robinson, who says to find some very light material such as the film covering used for model aeroplane wings and fuselages.  Cut to shape, and spray the repositionable adhesive on.  Leave to get tacky for 30 seconds, and then pop it onto your sails.  Peel 'em off after the event, and keep them safe by sticking them to a piece of plastic.  You can then use 'em again at the next event if you need to.

New rules 2002

The new 2002 rules, both for the IOM class and the RRS, take a completely new approach to sail numbers. A number of restrictions have been removed, only one new requirement has been added, and an easier set of specifications have been developed.  Appendix G of the RRS now deals with sail identification, not the ICAR, and for radio sailing Appendix G is modified by rule E6 of Appendix E.  Amongst other things, this approach now means that sail identification is an RRS issue, not a "measurement" issue, and your compliance with Appendix G as modified by E6 is now an issue that the Race Committee deals with at an event.

Recommended RRS E.6 revision

Keep an eye on the latest developments.  Appendix G as modified by Appendix E.6 is problematic in the 2002 RRS, and rule changes have become necessary.  ISAF-RSD have published a recommended change to E.6 on their Web site, and it is this that I describe below.

In summary, your sail numbers (and national letters, if any) should have a legibility "better than Helvetica".  Numbers must be between and 100mm and 110mm in height.  Their width, stroke, or radius of curvature is no longer specified.  Such numbers would typically result from a sans-serif font rendered at between 390 and 420 points in size.  The gap between adjacent digits or letters must be between 13mm and 23mm.  National letters must be capital letters, between 60mm and 70mm high (230 to 270 points).  Note that in order to obtain the right gap between numbers or letters, you will probably have to ensure that character spacing is set somewhat higher than the default value in your word processor, drawing package, or paint software. For the numbers, character spacing would be around 15%, and for the national letters around 25%, of the width of a space character.  The gap between numbers on opposite sides of the sail must be at least 60mm, and at least 40 mm for letters.  Remember that the starboard numbers or letters are placed higher than the port ones, remember that numbers and letters need to be all in the same colour, and remember to leave room for a "1" in front of your numbers.  If space is limited, there is a set procedure to follow according to E.6, and note that smaller digits are only permitted as an absolute last resort.  Numbers on the mainsail must be in the upper 75% of the sail, while the placement of numbers on the jib is not restricted.  National letters are to be below the mainsail numbers.  Finally, here is a simple test to check if your sail number in your favourite typeface is "clearer than Helvetica" -- make up your number in Helvetica, prop it next to your favourite, and then walk away until one of the numbers becomes unreadable.  It had better be the Helvetica number.... (You don't have Helvetica? Arial is pretty similar.)

The IOM insignia is a 50mm diameter black circle, with a central vertical white bar 10mm wide by 35mm high.

The "kerning" problem

The spacing between national letters should be between 13 mm and 23 mm, and our sailors in ITA have a potential difficulty with theirs.  If you think that the letters should have a "bounding box", and that the spacing between the letters should be measured as the space between the bounding boxes, you run into the "kerning" problem, as illustrated by the "T" and "A" in the first row.  The bounding boxes are 13 mm apart, but the letters themselves are over 30 mm apart -- outside the rules.


My unofficial suggestion is to forget about bounding boxes and to measure the gap between the letters (and digits) from their nearest points.  However, this is not a suggestion that receives universal support.  It seems that the exact meaning of the word "nearest" will have to be established via a request for an interpretation to ISAF itself.

Old rules 1995

The old rules used the ISAF RSD ICAR. The stroke width of each digit is 15mm, and each digit fits within a box that is 105mm high and 65mm wide. The ICAR specifications are, respectively, between 12 and 18; between 100 and 110; and between 60 and 70.

Digits to use

The digits below have been modelled on, but are by no means a copy of, the fine sticky-backed Dacron digits sold by SailsEtc, and they are fine for the 2002 rules as well as the 1995 rules.  What is "special" about them?  The loops in the "6" and "9" are slightly smaller than "normal", hopefully improving legibility.

To use these digits, right-click on each, and download (save) them on your computer. Using your favourite graphics package -- one that can open *.GIF files -- load up each digit and print it. If the printer doesn't give you the right size, then resize them until they fit into a 105mm x 65mm box, or blow up a photocopy. They have been saved as 90dpi images to minimise their size to an average of 1.5kb each; at 90 dpi, each digit fits inside a 372 x 230 pixels box.

The digit "7" looks a little odd. That is because there is an invisible white rectangle at its base to square off the down-stroke. It'll print just fine. If you'd like to play with the digits yourself, I can send you a Corel Draw ver.7 *.CDR file -- email me.

Instead of trying to remember these and other dimensions, the Three Rivers club site has a useful set of diagrams for sail numbering.  I expect the IOMICA Web site will soon have some guidelines as well.


2022 Lester Gilbert