How to Add Numbers to a Sail

Have a new mainsail without numbers? An old mainsail with peeling numbers? How about a used mainsail that you bought and has the wrong numbers on it? You can easily replace or add professional-looking numbers to your mainsail without taking it to a sailmaker and I’ll describe how.

Before I continue, a bit of legal housekeeping. This post contains affiliate links. That means I receive a small commission if you make a purchase using those links. Those commissions help to pay the costs associated with running this site so that it stays free for everyone to enjoy. For a complete explanation of why I’m telling you this and how you can support this blog without paying more, please read my full disclosure.

Our friends at Sailrite offer precision cut sail numbers in two different fonts (including a digital font for dinghies) and four sizes, enough to fit the majority of recreational sailboats. The numbers are made of high-quality, black, self-adhesive sailcloth. All you need to do is peel and stick. (In case you’re wondering, I receive no compensation from Sailrite. I just like their products and services and think you will too.)

Alternatively, you can also cut your own numbers if you want to use a different font or color. I’ll describe how to do this in a future post about reproducing a class insignia. If you do that project yourself, you will have plenty of extra self-adhesive sailcloth material with which to make your own sail numbers.

Off with the old, on with the new

To replace old numbers, the process is simple:

  1. Use a pencil to draw light guidelines right on the sail along the sides or corners for each old numeral. The marks will erase easily when you’re done.
  2. Warm up the old numbers with a handheld hair dryer until the adhesive softens enough that you can carefully peel off the old numbers and remove all residue.
  3. Fold back the backing paper from one long edge of each new numeral. You want to expose just enough of the adhesive so that you can place the numeral without it sticking completely.
Start at one long edge

4. Place the exposed edge lightly in the same location as the old numeral. Be careful to not make any bubbles. If necessary, you can remove and reposition the numeral until it lays straight and flat.

5. Turn the unattached part of the numeral face down and with a piece of stiff cardboard or other material, press against the inside of the fold to unroll the backing paper from the rest of the numeral while you lightly press the newly exposed adhesive down onto the sail. You might find it easier to make the ends of curved strokes (like the 3 below) lay flat by peeling the backing paper off completely and tracing the rest of the numeral with your fingers .  If you do this right, you won’t get any wrinkles, bubbles, or distortion. The numerals 4, 6, 8, 9, and 0 can be tricky to get the closed parts of the numerals to lay flat. Take your time and reposition the numeral until you get it right.

Unroll the numbers from the backing paper to keep them straight and to prevent bubbles and creases

6. When you have all of the numerals where you want them, roll them firmly with a J roller if you have one. You can improvise one with a short length of dowel used like a rolling pin.

Roll the numbers firmly for a strong bond and no bubbles or creases

Numbering for the first time

To add new numbers for the first time, the process is a little more complicated because you don’t have the old numbers to work from. Instead, you will need to determine the correct size, location, spacing, and angle of the numbers yourself.

To choose the correct size numbers for your sailboat, first check what size is normally used for your class. Ask other owners or refer to the racing rules for the class or your local race authority. A good rule of thumb is 10″ or 12″ sail numbers for boats up to 22 feet on the waterline, 15″ numbers for boats up to 32 feet, and 18″ numbers for larger boats. For Catalina 22 owners, the latest class rules (October 2014) do not require sail numbers nor specify the size of numbers. Some local clubs adopt The Racing Rules of Sailing that are updated every four years by the World Sailing organization. The rules for sail numbers and class insignia can be found in Appendix G: Identification on Sails.

Unless specified in the rules that govern the races that you participate in, you can place the numbers anywhere you like but they are typically placed in the top 60% of the sail with the class insignia above the sail numbers. This ensures that the numbers will be visible even if the sail is reefed.

A good rule of thumb for the spacing between numerals is the width of one stroke of the font in which the numerals are made. For example, if the width of the vertical stroke of the number 1 is 1-1/2″ wide, space each number 1-1/2″ apart like shown in the picture below.

The goal of all these rules is so that a sailboat can be easily identified from a distance under most conditions.

Space numbers the same as the width of the number 1.

Here is how I applied numbers to a new Rolly Tasker mainsail that I recently purchased.

1. Determine where to place the numbers relative to the sail’s other features (seams, battens, reef points, class insignia, and draft stripe, if any). Avoid placing numbers over seams that can cause wrinkles and can cause the numbers to come loose over time. Choose a location where the numbers for each side of the sail will be vertically stacked over each other, not in the same location on each side. This makes the numbers easier to read when sunlight shines from behind the sail. A good choice is one number above a panel seam on one side of the sail and the other number below the same seam on the other side of the sail similar to the picture below. Since the seams are typically perpendicular to the leech, your numbers will automatically be at the right angle.

2. Use a pencil to draw a light guideline on the sail that will be the baseline for the sail number. Allow at least 1/2″ of space away from seams, etc. If you want the sail numbers to be horizontal relative to the boom, measure the same distance up from the foot of the sail to locate each end of the guideline. If you want the sail numbers to be angled perpendicular to the leech edge like shown above, use a panel seam as a reference or use a large framing square to draw the baseline. You can also use the old carpenter’s 3-4-5 trick to draw a perpendicular baseline. That is, a triangle with sides that are 3, 4, and 5 units long forms a 90 degree angle between the sides that are 3 and 4 units long. The units can be any measurement system: inches, feet, meters, and so on.

3. Draw a vertical guideline perpendicular to the baseline that you just drew to mark the edge of the number closest to the leech. Space the guideline one number width from the leech. For example, if the width of the number 0 is 8″, draw the guideline 8″ from the leech edge.

4. Draw additional guidelines to lay out each number one stroke width apart as shown above. On the port side of the sail, start with the numeral that is closest to the leech the (last numeral in the sail number) and work your way to the left or luff. On the starboard side of the sail, again start with the numeral that is closest to the leech (the first numeral in the sail number) and work your way to the right or luff.

The rest of the process (affixing the numbers) is the same as steps 3-6 as described above. Also refer to those pictures.


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