The 7-10-7 Rule: Perfect Spars Without Math

The 7-10-7 Rule — An Old Boatbuilder’s Trick for Perfectly Rounding a Spar In this episode of Nomad Boatbuilding, I share a simple geometric method that replaces repetitive math when shaping spars by hand. Some people think wooden boat building requires complicated calculations. That can be true when designing boats — but building them is another story. In practice, geometry is often far more useful than math. The 7-10-7 rule is a straightforward way to divide the face of a square into proportional sections (7 units, 10 units, 7 units — 24 in total). By removing the corners at those marks, we quickly create an accurate octagon. Repeat the process and we move from square to octagon to 16 sides… and eventually to a smooth, round spar. In this video I cover: • How the 7-10-7 rule works • Why imperial rulers make scaling easy • Turning square stock into an octagon • Moving from 8 sides to 16 sides • Using (and making) a spar gauge • Applying the method to tapered spars • Why geometry beats repetitive calculation • Using the same principle for moldings, banjo necks, plugs, and even walking sticks This method works for squares, rectangles, trapezoids, and tapered spars. It’s one of those core pieces of traditional boatbuilding knowledge that makes shaping round forms efficient, accurate, and satisfying. 🌐 Website: https://www.nomadboatbuilding.com 📸 Instagram: https://www.instagram.com/nomadboatbuilding 🛠 Support these videos on Patreon: https://www.patreon.com/nomadboatbuilding If you value traditional boatbuilding knowledge and want to help keep these videos coming, consider supporting the channel on Patreon. ⏱ Chapters: 00:00 Introduction — What Is the 7-10-7 Rule? 00:43 Geometry vs Math in Boatbuilding 01:01 Turning Square Stock into an Octagon 01:24 How the 7-10-7 Division Works 03:56 Demonstration on a 6x6 Cross Section 06:24 From Octagon to 16 Sides 08:08 Applying the Rule to Rectangles & Trapezoids 11:17 Using the Rule on a Tapered Spar 12:37 Spar Gauges Explained 14:41 Imperial vs Metric Scaling 16:08 Making an Octagonal Plug for a Hollow Mast 17:38 Planing to the Lines by Hand 18:50 A Simple Tape Trick for Divisions 20:19 Beyond Boatbuilding — Banjos & Walking Sticks 21:14 Why This Method Works So Well #woodenboat #boatbuilding #sparbuilding #woodworking #handtools #traditionalcraft #geometry #DIYwoodworking #NomadBoatBuilding #MarkReuten