"I think I need a bigger board." Maybe. But before you spend the money, let's look at what a skimboard actually needs to stay on top of the water — because nine times out of ten, the board is fine and the physics are just being honest with you.
Planing is a speed contract
A skimboard doesn't float you. It planes — it skips across the surface the way a stone does, and like a stone, it only works above a certain speed. Below that threshold, the water stops behaving like a solid and starts behaving like soup. The board settles in, drag multiplies, and you grind to a stop in a couple of body lengths.
So when your board sinks, the first question isn't "is this board big enough?" It's "how much speed did I actually deliver to it?" And that speed gets decided in two places: the run and the mount.
A run at 70% effort feels fast when you're the one running. It isn't. Then a hesitant mount — that little pause between back foot and front foot — scrubs off another chunk. By the time you're standing, you may be carrying half the speed you think you are, and half isn't enough to keep a plane going. The board sinks because the contract wasn't met.
There's a location clause in the contract too: thin water. A glassy film over wet sand supports a plane beautifully. Step off into dead water — the still, deeper pocket where the surge has stalled — and even a fast rider bogs down. If your board sinks in the same spot every time, look at the water there before you look at your technique.
What the number says
The honest arbiter here is your speed at the drop — but relative to the water, not to your personal best on dry sand. Running out over a surge that's still pushing shoreward gives your board far more flow than the same run over water that's draining out, which is why identical-feeling runs plane on one wave and plow on the next. Fast enough to plane and still controlled enough to drop cleanly is the target; maximum sprint usually costs you the mount, and a blown mount wastes more glide than the extra speed bought. CoachVision reads your approach speed from a side-on clip in torso-lengths per second — useful for spotting whether you arrived with fuel or arrived flat, though it's measured from the footage, so compare it within a clip rather than between clips filmed differently.
If the number says you're arriving slow, great news: speed is trainable, and the board you own is probably fine.
The drill — Thin-Water Flatland Runs
Strip the problem to its essentials with Thin-Water Flatland Runs. Find a thin sheet of water with no waves — the film left on gently sloped sand is perfect. Then do full-speed run-drop-mount reps: sprint like you mean it, lay the board down flat, one step on, and see how far the glide carries you.
Do 15 runs. The glide length is your scoreboard. All the mechanics are in play — run, drop, mount — with none of the wave pressure, so every rep gives you clean feedback: more committed sprint, longer glide. When your flatland glides stretch out, you've proven the board planes just fine under real speed.
The board was never the ceiling. Your sprint is, and sprints improve every single week you work them.