This block is a bit trickier to sew accurately and is best done by using pins to match the seam line beginnings and ends. Accuracy is very important with this block and fudge factor does not apply here. Make sure the edges of your triangle blocks meet as shown in the photo to ensure an even outer edge of your 5" x 10" (plus seam allowances) block.
"Ocean Currents" features batiks on front and back with cotton batting and simple machine quilting. To draft a block for this quilt, simply draw a 5" x 10" rectangle, then draw a line through opposite corners. Add seam allowances to all sides of the half triangle.