OpenFront Ports — 300 Tiles Is the Hinge

Trade income is an S-curve in the distance between ports, and the inflection sits exactly at 300. Distance 200 pays 13,557. Distance 400 pays 91,443 — doubling the distance nearly septuples the income.

So port placement has exactly one principle: as far apart as possible. Far from each other, and pointed at distant countries.

Income by distance

Gold per trade ship:

Broken into segments, it is obvious where the value lives:

Everything happens between 200 and 400. Past 400 the curve flattens hard — going all the way to 600 adds only 15% over 400.

Five practical rules

1. Never build ports side by side. A distance-50 route pays 2,541. A 125,000 port needs fifty ships to pay for itself.

2. Aim for 400. 300 is barely half the maximum; 400 is about 80% of it. Take a safe 400 over a risky 600.

3. Reach different bodies of water. A port only trades across water connected to its own tile. If no sea route exists between two ports, they simply cannot trade. Along a long coastline, splitting your ports across different seas widens the pool of partners.

⚠️ Beware the lake port. Any shoreline is buildable, including an inland lake or a river that never reaches the sea. Such a port has zero possible partners and will never launch a single trade ship — and nothing on screen tells you so.

“Move ports inland so a SAM can protect them” circulates as advice. SAMs defend a location; there is no notion of guarding a particular building, and a coastal port inside the radius is covered exactly the same. With a 15-tile minimum structure spacing against a 70-tile minimum SAM radius, coastal versus inland makes no difference at all. You gain nothing and risk the partner pool.

4. A port’s level also raises how often others pick it. When someone else’s trade ship chooses a destination, each candidate port is entered into the draw once per level. But a level-3 port and three level-1 ports hold the same share of that draw — so this does not overturn the spread rule below. Equal total levels attract equal incoming traffic; only outgoing ships favour spreading.

⚠️ Your own ports never trade with each other. Candidate partners are drawn only from other players’ ports, so building several of your own creates no traffic between them. Trains are the opposite: a train stopping at your own city still pays 10,000 gold. Sea trade has no such self case.

5. Spread rather than stack. “Upgrade one port to level 10” circulates as advice. The code says otherwise: a port launches at most one ship per check, whatever its level. A level-10 port makes ten attempts inside one check but stops at the first success, so the rest are wasted.

A level-10 port produces 6.9× what a level-1 port does — but ten level-1 ports get ten separate checks, so 10×. Both routes cost exactly 7,875,000 gold, since the price exponent counts total levels.

Levels 2–3 are still efficient when you have no more coastline to build on. Going to 10 is not. And a nuke deletes a structure whole regardless of level, so one bomb erases the entire stacked investment.

→ Factories work the same way — one station dispatches at most one train per check. The same arithmetic is in Factory and Rail Income.

The trap — ports and factories share a counter

This catches almost everyone.

Build three ports and your first factory is already priced as the fourth building (1,000,000). It works in the other direction too.

The formula is min(1,000,000, 2ⁿ × 125,000), where n counts ports and factories combined. Expanding ports without a plan makes the switch to a factory economy brutally expensive.

The building cost calculator accounts for the shared counter.

Port level raises how often trade ships spawn, not what they pay. Gold per ship depends only on distance.

Trade pays your partner too

When a trade ship arrives, both sides get gold. Building a port also funds your neighbor’s growth.

Two consequences:

• Trading with a weak neighbor feeds them. If you are going to eat them anyway, eat them
• Trading with a strong neighbor is how you keep pace. If you cannot beat them, stay attached

Attacking cuts trade for 5 minutes

Any player you exchange attacks with has trade suspended with you for 5 minutes.

If you have leaned on port income, one border skirmish costs more than it looks. A single 90,000 trade ship route, cut for five minutes, is several cities’ worth of gold.

Choosing your fights is your economy. Leave trade partners alone and expand in directions where you have no route.

Warships and shipping lanes

Ports are also the prerequisite for warships.

• Warship patrol range is 100 tiles
• Trade ships caught by an enemy warship are captured
• Transport boats also launch from ports; sinking means total loss of troops aboard

If your trade route crosses an enemy patrol zone, the income may never arrive. When siting a port, look at whose waters the route crosses.

Where ports sit in your build

More

• Trade ship calculator — income by distance
• Building cost calculator — shared port/factory counter
• All Six Buildings — including factory rail income
• What Happens When You Betray an Alliance? — trade loss versus betrayal gain