I finally pulled together a quick comparison of what "long" and "short" blades actually mean for bifins. Across the usual depth fin brands there is a pretty clear split between competition-length blades and travel/pool blades.
I wanted to see how a simple cantilever beam model matches what happens with freediving fins. The idea is that a fin blade is essentially a thin rectangular beam clamped at the footpocket and loaded at the tip by the force of the water.
I finally pulled together a quick reference for how tip load ("hardness") and bending profile play together on long freediving blades. The clearest explanation I have found so far comes from this breakdown: ▶️ Blade stiffness explained.
After mapping out bifins, I want to gather materials and design notes for building a monofin blade. This will be a bit more complex than bifins because monofins need more lateral stability and usually use internal reinforcements.
Now that I’ve mapped out the foot pockets, I want to gather everything I need for actually building a short carbon bifin blade. This is basically my BOM (bill of materials) plus a few notes on layering and finishing.