Sky Archipelago in FTB Skies 2: Aero

Sky Archipelago is a terrain generation mod that adds a floating-islands world type for Minecraft 1.21.1. The project page says it currently only supports NeoForge for 1.21.1, because it was built towards Create Aeronautics airship gameplay. This pack includes version 1.3.6, and the mod has been in the pack since 1.0.3 or earlier.^[1][2]

It is not limited to sky worlds. The mod can also make ocean worlds with islands spread far apart, so the world you get is mostly down to how you configure it.^[1]

What you can configure

The project page lists these options as of the 1.0.0 release and says more configuration is planned for future updates. The sources here do not show what was added up to 1.3.6, so check your own config for anything newer.^[1][2]

• The project page lists island spawning density and the spacing of cluster islands as options, as of the 1.0.0 release.^[1]
• The project page lists an island sizing mode as of the 1.0.0 release: RANDOM rolls between a min and max for each island, while SPECIFIC lets you set small, medium and large sizes, each with its own min/max and percentage weight.^[1]
• The Y range islands can spawn in, plus low, mid and high bands with weights for where islands appear more or less often.^[1]
• The project page lists, as of the 1.0.0 release, a choice between ocean enabled or void enabled, with water or lava as the ocean block type.^[1]
• Island archetypes (Classic, Bowl/Crater and Terrace) that you can toggle and weight, and a toggle to relax structure spawning rules, since the mod has its own logic for placing structures on islands.^[1]

Presets

A preset is your whole configuration saved so you can share it. The mod has a dedicated preset menu to save, load and delete presets, and you can share them as plain JSON text. There are also OP-only commands to create, overwrite and export a preset.^[1]

The project page, written around the 1.0.0 release, says that for a dedicated server you set level-type to sky_archipelago:sky_islands in server.properties. After the server has run once, you paste your values into sky_archipelago-common.toml in the config folder. It says the Export Dedicated button or the in-game command /skyarchipelago preset export_dedicated can copy your preset for that. The sources here do not confirm whether these steps changed by 1.3.6.^[1][2]

Good news and a heads-up. Sky Archipelago is a world generation mod, not a content mod. It gives you sparse floating-island overworld generation with structure support validation, so your first steps here are about reading the world around you rather than crafting something.^[1][3]

Unverified The sources I was given for this mod include no in-pack recipes for its items and no quests, so there is no verified crafting order to show for it.

What the world looks like in this pack

The pack changed several of the mod's defaults to make the islands rarer and more spread out. Island density is islandDensity = 0.2 (the mod default is 0.4), and lower values mean larger sky gaps. Cluster spacing is clusterSpacing = 300 blocks (the mod default is 96). Expect long trips between islands.^[4]

Spacing mode is clusterSpacingMode = "CONSISTENT", which uses fixed spacing, so the cluster spacing value above is the one that applies. minClusterSpacing and maxClusterSpacing only matter in DYNAMIC mode.^[4]

Island sizes follow the random mode set in islandSizeMode, so each island rolls its radius between the minimum and maximum. In this pack that is minIslandRadius = 24 up to maxIslandRadius = 67 blocks.^[4]

All the island shapes can spawn: classicArchetypeEnabled, bowlCraterArchetypeEnabled, terraceArchetypeEnabled and crescentArchetypeEnabled are all true. Satellite and spire companion islands also generate around anchor islands, since clusterCompanionIslandsEnabled is true.^[4]

Island centers sit between minIslandY = 14 and maxIslandY = 261. The pack raised that top limit from the mod default of 170, so some islands float quite high.^[4]

The optional ocean layer is switched off here (oceanEnabled = false), so nothing fills in below the islands.^[4]

Where to change things

All the values above live in config/sky_archipelago-common.toml.^[4]

Unverified The pack also has a config/sky_archipelago-server.toml, but its contents are not shown in the sources here, so any server-side detail would be set in that file and is unverified.

Operators also get preset commands for creating, overwriting and exporting a world-generation preset, which is handy for sharing a setup. The mod's project page lists them under the /skyarchipelago command.^[1]

Sky Archipelago has no machines, multiblocks, power, fluids or item automation. It is a world generation mod, described as sparse floating-island overworld generation with structure support validation. So the mechanics you care about here are how islands are laid out, and how structures get placed on them.^[1][3]

Turning the world type on

The mod adds a Sky Island world type. On a server you select it by setting level-type to sky_archipelago:sky_islands in server.properties. After the server has run once, the settings live in the common config file, and the mod can export your current preset as pasteable text with an in-game command.^[1]

Clusters and density

Islands are placed per cluster cell. islandDensity is the chance that a cell becomes an island anchor, and lower values leave bigger gaps of sky. The pack sets it to 0.2, down from the mod default of 0.4.^[4]

Spacing between clusters is set by clusterSpacing, which the pack raised to 300 blocks from the default of 96. The pack uses the CONSISTENT spacing mode, which means fixed spacing. The DYNAMIC mode would instead pick a deterministic per-world spacing between minClusterSpacing (96) and maxClusterSpacing (115).^[4]

Small satellite and spire companion islands can also generate around the anchor islands, and the pack leaves clusterCompanionIslandsEnabled on.^[4]

Island size and shape

The pack runs islandSizeMode in RANDOM mode, so each island rolls a radius between minIslandRadius and maxIslandRadius. The pack lowered these to 24 and 67 blocks (defaults 30 and 75). Vertical thickness is capped at 140 blocks by maxIslandThicknessBlocks.^[4]

SPECIFIC mode switches to small, medium and large size bands, each with its own radius range and spawn weight. The pack has tuned those values too, but they only matter if you switch the mode.^[4]

• Small: radius 24 to 41, weight 0.34.^[4]
• Medium: radius 37 to 58, weight 0.33.^[4]
• Large: radius 34 to 50, weight 0.2.^[4]

The classic, bowl/crater, terrace and crescent island archetypes are all allowed to spawn. Their weights are classicArchetypeWeight, bowlCraterArchetypeWeight, terraceArchetypeWeight and crescentArchetypeWeight, and each is 1 in the pack.^[4]

terrainOverlapMode is VOID in the pack, which controls how overlapping island terrain columns are resolved. terrainReliefScale is 1, and higher values make rougher tops.^[4]

Height and what lies below

Island centers sit between minIslandY and maxIslandY. The pack sets these to 14 and 261, versus mod defaults of 20 and 170.^[4]

Within that range, islands fall into height bands. The dominant mid/high band has a weight of 0.75 (midHighBandWeight), the uncommon low band has 0.15 (lowBandWeight) and the rare very-high band has 0.1 (veryHighBandWeight).^[4]

Island interiors at or below Y 15 use deepslate, set by deepslateStartY (mod default 16).^[4]

The optional ocean layer under the islands is off in this pack (oceanEnabled is false). If it were enabled, it would fill with the block from oceanBlockType, which is water here, up to the level in oceanLevelY (0).^[4]

How structures are placed

Sky Archipelago brings its own structure placement and support rules, enabled in the pack through customStructureRulesEnabled. Structures are sorted into categories such as SKY, SMALL_GROUND, MEDIUM_GROUND, LARGE_GROUND, GROUND_VILLAGE, STRONGHOLD, UNDERGROUND and WATER. A category comes from an explicit override, or is inferred from words in the structure's path, for example sky, airship or floating for SKY.^[4]

For a normal structure, the mod samples a 5 by 5 grid under the footprint, scans 48 blocks down for support, and needs at least 0.6 of the samples supported. The settings are supportSampleGridSize, supportCheckDepth and supportThreshold. Sky structures have their own, looser thresholds.^[4]

• Smaller sky structures need 0.32 of samples supported, with a grounded-base ratio of 0.75 and at most a 1 block gap to terrain.^[4]
• Larger sky-surface structures need 0.42 supported, with a grounded-base ratio of 0.7 and at most a 1 block gap to terrain.^[4]
• The pack widened the search for smaller sky structures: 8 chunks outward (default 6), a 14 block local radius (default 10) and a 4 block step (default 8). Larger sky-surface structures use a 24 block local radius (default 16).^[4]
• Compatibility fallback placement is switched off for both small sky and surface sky structures.^[4]

The pack also overrides categories for several structures. For example, the vanilla pillager outpost is MEDIUM_GROUND, and a few Valhelsia structures are SMALL_GROUND. Airships, sky whale ships and the castle in the sky are whitelisted. Whitelisted structures skip normal support checks, but they still need an island nearby.^[4]

Server-side safety and performance

The server config keeps a crash shield on (structurePlacementCrashShieldEnabled), so one bad structure placement can't crash chunk generation. Structure placement is also serialized for compatibility with parallel worldgen mods such as C2ME (serializeStructurePlacementForParallelWorldgen).^[5]

The worldgen column cache has adaptive TTL tuning enabled. The pack raised the minimum TTL to 180 seconds, matching the 180 second maximum. The debug and metrics logging options are all switched off in the pack.^[5]

Most of what shapes your Sky Archipelago world lives in the common config file. The pack changes a good number of the mod's defaults there, so the world is sparser and a bit smaller-scaled than the mod would give you on its own. Here are the options you are most likely to care about.^[1][4]

Island density and spacing

• islandDensity is 0.2 in this pack (mod default 0.4). It is the chance that a cluster cell becomes an island anchor, and lower values create larger sky gaps.^[4]
• clusterSpacing is 300 blocks (mod default 96), so clusters sit much further apart.^[4]
• clusterSpacingMode is set to CONSISTENT, which uses the fixed spacing above. The pack also changes maxClusterSpacing to 115 (mod default 96), but that value is only used by the DYNAMIC mode, and minClusterSpacing stays at 96.^[4]

Island size

islandSizeMode is RANDOM, so every island rolls a radius between the global minimum and maximum. The pack lowers both: minIslandRadius is 24 (mod default 30) and maxIslandRadius is 67 (mod default 75).^[4]

The small, medium and large settings only apply if the mode is switched to SPECIFIC, but the pack has tuned them anyway:^[4]

• Small islands: radius smallIslandMinRadius 24 (default 30) to smallIslandMaxRadius 41 (default 42), weight smallIslandWeight 0.34 (default 0.28).^[4]
• Medium islands: minimum radius mediumIslandMinRadius 37 (default 43), weight mediumIslandWeight 0.33 (default 0.3). The maximum radius, mediumIslandMaxRadius, stays at 58.^[4]
• Large islands: radius largeIslandMinRadius 34 (default 50) to largeIslandMaxRadius 50 (default 75), weight largeIslandWeight 0.2 (default 0.42).^[4]

Height range

• minIslandY is 14 (mod default 20) and maxIslandY is 261 (mod default 170), so island centers can spread over a much taller band.^[4]
• deepslateStartY is 15 (mod default 16): island interior at or below this Y uses a deepslate substrate.^[4]

Structures on islands

The pack widens the search for spots to put smaller sky structures: smallSkyLocalSearchRadiusBlocks is 14 (default 10), smallSkyLocalSearchStepBlocks is 4 (default 8) and smallSkySearchRadiusChunks is 8 (default 6). Larger sky-surface structures get surfaceSkyLocalSearchRadiusBlocks at 24 (default 16).^[4]

skyStructureWhitelist lists structures that skip the normal support and grounding checks, though they still need a nearby island. In this pack it includes the shellbound_for_airship airships, the sky_whale_ship whale structures, the castle in the sky from mostructures and the Create Structures Arise pillager steampunk airship.^[4]

Things left off

oceanEnabled is false, so there is no ocean layer under the islands, and terrainOverlapMode is VOID. disableIslandsOverOceanBiomes is also false.^[4]

Server file

The server config has one pack change: adaptiveColumnCacheMinTtlSeconds is 180 seconds (mod default 15), which matches the maximum of 180, so the worldgen column cache TTL is effectively pinned there.^[5]

serializeStructurePlacementForParallelWorldgen stays true. It exists for compatibility with parallel worldgen mods such as C2ME, and the file says to disable it only for benchmarking or debugging. The debug and verbose log options are all off.^[5]

FTB Skies 2: Aero 1.10.0 ships Sky Archipelago 1.3.6, and the mod has been in the pack since Aero 1.0.3 or earlier. Here is what changed in the two most recent mod releases I have notes for.^[2]

Version 1.3.6 (the version in this pack)

The 1.3.6 changelog calls this the last set of fixes and changes before moving on to version 1.4 as the next release target.^[6]

• The ocean liquid type can now be any liquid type loaded in the modpack.^[6]
• Sky based structures can spawn anywhere. They were still tied to island-aware logic that was due to be removed after the 1.3.5 refactor but was missed.^[6]
• Strongholds spawn more frequently, by allowing smaller strongholds to spawn and through a few core changes that make spawning more likely.^[6]
• The per island structure category limits were removed in favour of a per structure ID limit that allows only 1 of each to spawn. The aim is to give other mods better chances to spawn structures and to avoid multiple small structures, which have higher chances to spawn.^[6]
• Terrain generation is improved, with a roughly 33% reduction in time taken per chunk. Biome and region caching also lets the mod reject early structures that would not be able to spawn in that biome anyway.^[6]
• The advanced menu UI was overhauled to make advanced configurations clearer and easier to adjust. The command /skyarchipelago preset current now shows the currently active template in a different colour.^[6]

Fixes in 1.3.6

• Sky based structures getting cut off by being too close to the world height limit is fixed. The structure is pushed down where possible.^[6]
• Fixed a game or server crash due to chunk generation during structure placement. It primarily affected jigsaw structures that trigger a chunk or block lookup during world generation before it was ready.^[6]
• Distant Horizons showing ghost structures that do not actually spawn is fixed. DH will not spawn structures, but traversing the terrain still invokes the structure placement itself.^[6]
• The preset menu supports GUI scale 4, where previously the button would exceed the screen boundaries.^[6]
• Partial fix for the AE2 Meteor crashing servers by taking too long to spawn. The odds of spawning are improved, but the fix is not perfect.^[6]

Version 1.3.5

The primary change was a refactor of how structures spawn. Instead of relocating a structure upon creation, the mod now provisions a source-chunk location and lets vanilla handle the rest more cleanly. The aim is less time spent on creating structures that fail, and more time spent finding a suitable host anchor island based on criteria, then spawning.^[7]

• Added a random mode to the island overlap logic.^[7]
• Dedicated servers can use the world type sky_archipelago as an alternative, to escape an issue found when using online dedicated service providers.^[7]
• Added the /skyarchipelago preset current command to check which preset is in use.^[7]
• The Deep Dark biome moves its Y location if an island is above where it would normally spawn, and Ancient Cities can spawn on top of islands where the deep dark biome exists.^[7]
• Underground structures can spawn with increasing quantity based on island size.^[7]
• Added concurrency support (C2ME and Distant Horizons).^[7]
• Strongholds no longer spawn a dedicated island. They now apply to islands made by the preset, going up or down on the Y level to ensure they are within an island by at least 80% coverage.^[7]
• Desert Pyramids, Ice spikes and Mansions no longer create massive pillars or columns going down.^[7]
• The Cartographer villager no longer freezes the server. Treasure maps now favour nearby structures or known placements, which avoids a search loop for something that does not exist yet. The changelog says a death-loop is still possible depending on structure mods and preset island sizing, but much less likely.^[7]
• Ice and Fire Community Edition dragon roosts and dragon nests work out of the box now, instead of sitting 8-10 blocks above the ground.^[7]

Unverified The 1.3.5 changelog available here is cut off, so there are likely more 1.3.5 changes than the ones listed above.

The 1.3.6 notes say the next release will be 1.4 and that it can take some time before it is ready.^[6]