Kettlecrest dev diary: how the river surge works

Nothing in Kettlecrest has an engine. Ottilie the otter races in a copper kettle with a wooden spoon for a paddle, and her friends float in half a pumpkin, an upturned umbrella and a cast-iron bathtub. The speed comes from the river: every summer the Big Melt sends great rolling surges down the Long River, and the game is about being in the right place when one arrives. Here is how we built that surge.

A timetable, not a dice roll

Surges are not random. The first one is already rolling behind the start rope when a race begins and reaches the pack about four seconds in. After that a new surge comes roughly every sixteen seconds, give or take a second and a half, in sets of three like waves on a beach: a smaller one, a big one, then one in between.

Each new surge rises out of the water behind the last boat, so it never pops up under anyone, and no more than three are on the river at once. Just before one reaches you, a band of foam appears along the bottom of the screen.

Ottilie in her copper kettle among other boats on an icy river, a line of foam across the water just ahead and a fading band of foam along the bottom edge of the screen — Four seconds in, the first surge has just rolled under the pack. Its foaming crest is right ahead, and two rivals are already riding it.

The river shapes the wave

A surge travels about a quarter faster than any boat can paddle. Its speed depends only on where it is on the river, so one surge can never catch up with another.

Its height depends on the riverbed. In a narrow canyon a surge stands tall and steep; across a wide, slow pool it flattens into a ripple nobody can ride, then gathers itself again below. Meltwater Mile, the first run of the game, has both: about a third of the way down, an ice canyon where surges stand tallest, and just below it a melt pool where they go flat.

Finding the sweet spot

On the front of every surge you can ride, a few metres ahead of the foaming crest, the water sparkles with warm glints: the sweet spot. Steer into it as the surge arrives and it picks you up, kettle and all. It does not always follow the fast water round a bend: on Meltwater Mile it often sits mid-river or even on the inside, so trust the glints.

We changed two things here along the way. The glints alone showed up under your boat too late to act on, so now a surge coming up behind you draws a faint shimmering band ahead of you, showing where to sit before it gets there. And the sweet spot used to jump a little where two stretches of river met, which could throw a boat off even when it sat just right, so we smoothed it along the whole river.

One more rule keeps things fair: one surge, one ride. Every boat can ride each surge once.

Ottilie’s kettle and a newt in a walnut shell riding one surge round a bend on a glacier river, a crayfish in a straw hat beside them on the left, warm glints on the water under the kettle, a picnic blanket over a gravel bar on the left — Two boats ride one surge round the elbow bend, and a rival has just dropped in beside them. The warm glints under the kettle are the sweet spot.

Drop now, or ride to the canyon?

Riding already carries you past everyone paddling, and the drop-in adds a burst on top. Press the wave button (Space on a keyboard) and your boat shoots down the front of the wave with a burst of speed. The burst depends on how steep the surge is at that moment and how close to the middle of the sweet spot you sit. Drop dead centre on a steep surge and the game calls it a Clean drop.

So every ride is a small decision: take a sure drop now, or hold on until the canyon where the surge stands tall. Meanwhile the ring round the wave button counts down your ride, heavier boats lean on you and a rival lines up a Splash Pump. Picnic baskets ride the surge too, just outside the sweet spot, so you have to lean to the edge to grab one. We first put them further out, and the lean kept throwing boats off the surge, so we pulled them in.

Ottilie’s kettle shooting forward in a burst of spray inside the ice canyon, with the words Clean drop! above the river — Dropped in dead centre on a tall surge in the ice canyon: a Clean drop.

Why the surge never picks on the leader

A surge can pick up every boat it overtakes and set them down together, which keeps the pack tight and the lead changing hands. The boats at the back meet each surge first, and the leader rides the same surge when it arrives. Nothing on the river picks on anyone: every surge starts behind the last boat and rolls on to the leader, and baskets and the gulls’ prizes are the same for the leader and the tail.

You can see it all coming. The winding strip at the top of the screen is the river, every boat is a little face on it, and every surge is a curl of foam sliding down it towards you.

Every boat sits on a crest its own way

At the Jetty you pick a hero, and each boat rides a little differently. Fennel the capybara’s half pumpkin sits deep: a wider sweet spot, a softer drop. Juno the kingfisher chick’s upturned umbrella sits light: a narrower spot, a sharper drop. Ottilie’s kettle sits in between, and Brogan the hippo blacksmith brings a bathtub that shoves like a boulder.

New to racing, or playing with a younger rider? Turn on Steady Crest in the settings for a wider sweet spot, a drop made for you and a brighter crest line on the water.

Picking Ottilie the otter and her copper kettle at the jetty, beside a red boathouse — Pick a hero, pick a boat.

Meltwater Mile is free to race in early access at kettlecrest.com, on a computer, tablet or phone. More about the game is on its Kettlecrest page.

How the river surge works