Boomilever 2027
What changed from the 2026 rules, what it does to the boomilever, and how we get to a new 2027 design.
Same challenge, same scoring
Most load that counts. Anything stronger is wasted wood.
Score is efficiency. Mass to 0.01 g is the first tiebreaker.
Bonus for touching the wall only above the 15 cm line.
Reach to the chain, centered within 2.5 cm.
Wall contact zone around the bolt. Any foot is 8 cm wide at most.
One piece, hung on the bolt. No tape, string, paper or coatings.
The loading block now starts above the bolt
Blue dashed: bolt centerline · Gray dashed: 15 and 20 cm lines
Shallower contact means bigger forces
15 cm contact depth · Bonus
20 cm contact depth · Base
Tension ≈ Load × L ÷ d
Compression ≈ Load × √(L² + d²) ÷ d
L = reach, d = contact depth below the bolt, Load = 15 kg. At 15 cm: 15 × 40.5 ÷ 15 = 40.5 kgf of tension.
Moving the foot up 5 cm adds about 33% to tension and 27% to compression. The compression member is also 2 cm shorter at bonus depth (43.2 vs 45.2 cm).
kgf means how heavy a force feels
1 kgf is about how hard a 1 kg object pulls down because of gravity.
- 15 kgfThe sand: one 15 kg bucket pulling down
- 40.5 kgfTension sticks: pulled like 2.7 buckets hanging from them
- 43.2 kgfCompression stick: pushed like 2.9 buckets standing on it
Why so much? Try a rope.
Steep rope: each hand pulls a little more than half the bag.
Flat rope: each hand pulls many times the bag.
A boomilever is a flat triangle: 40 cm out, only 15 cm down. Flat shapes multiply the load.
Keep how we build. Change the shape.
Our design: a plank box
Two solid side planks joined by cross members, plus a post and foot as needed. Re-proportioned for the 2027 wall.
Build habits
Match the two planks by density, flush joints, sparing glue, weighing every part.
Build sequence
Arms first, body jig, brace template on top and bottom only, offset zig-zags. The assembly jig changes.
Test loop
Same protocol: predict, film in slow motion, find the first break, log it, change one thing.
Bonus or base: expect bonus to win
Score advantage
At full load, bonus scores 20,000 g instead of 15,000 g: 20,000 ÷ mass vs. 15,000 ÷ mass.
Higher member forces
Bonus depth raises compression about 27% and tension about 33%. More force is not always more mass.
Break-even
If the base design weighs 7 g, bonus can weigh up to 9.3 g and still tie. Lighter than that, bonus wins.
Build one of each and compare mass and first breaks. Bonus could lose only in the tension arms and wall joint.
2027 Boomilever Event Supervisor Guide
Open the video on YouTube
Video on YouTube, opens in a new tab
Watch for
- How the wall, bolt, and contact lines are set up
- How supervisors check the block sits above the bolt
- How loading runs, and when it stops