Sailboat Quilt Block Pattern

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How to Sew a Sailboat Quilt Block

The Sailboat quilt block is a charming nautical design built from half-square triangles. It’s a wonderful block for showcasing contrasting fabrics and creating a playful, graphic quilt.

Materials:

• Fabric in 3 colors: sky (background), sail, and water/hull
• Rotary cutter, cutting mat & ruler
• Sewing machine & thread
• Iron and ironing board

Instructions:

1. Cut your fabric pieces according to your chosen block size. You’ll need squares for the half-square triangle units (sail and sky), and rectangles or squares for the hull and water sections.
2. Make your half-square triangle units: pair sail fabric with sky fabric, right sides together. Draw a diagonal line on the wrong side of the lighter square, sew ¼" on each side of the line, then cut along the line. Press seams toward the darker fabric and trim to size.
3. Arrange all pieces following the sailboat layout — HST units and sky squares at the top forming the sail, hull and water pieces at the bottom.
4. Sew the pieces into rows using a ¼" seam allowance, pressing seams in alternating directions on each row.
5. Sew the rows together, matching seams carefully. Press the final seams.
6. Trim the block to your desired finished size, keeping all corners square.
7. Repeat to create as many Sailboat blocks as needed for your quilt.

Making Half-Square Triangles

This technique eliminates the need to directly manipulate the stretchy bias of the triangle. It uses two easy-to-cut squares to produce two half-square triangles.

On the back of the lighter fabric, draw a pencil line diagonally from corner to corner.

Stack a pair of light and dark squares right sides together. Sew a ¼" seam allowance on each side of the line.

You will end up with something like this:

Now cut along the diagonal line.

Press the seam to set it, then press toward the darkest fabric.

To trim to the exact size, line up the 45° diagonal on your ruler with the seam.

Then carefully trim your block with a rotary cutter.

How to Resize Quilt Blocks

The first step in modifying any quilt block is to decide on the finished size. You can base this on doubling a pattern, cutting it in half, or working with your available fabric.

Important: Always remove the seam allowance before doubling or tripling the size. For example, if your pattern calls for 3½" squares, subtract the seam allowances (½"), double the finished block size (3" → 6"), then add the seam allowance back (½"). You’ll end up cutting a 6½" piece of fabric.

Resizing Square Blocks

Add ½" to your desired finished block measurement. For a 4" finished square, cut a 4½" square of fabric.

Resizing Rectangular Blocks

Add ½" to both the length and width. To double a block that measures 3" × 4", cut a 6½" × 8½" rectangle of fabric.

Resizing Half-Square Triangle Blocks

Add ⅞" to the desired finished block size. For a 4" finished block, cut 4⅞" squares.

Resizing Quarter-Square Triangle Blocks

Add 1¼" to the desired finished block size. For a 4" finished block, cut your squares 5¼".