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[Kate Wissen]

As I understood a fortifications are used as filters for water and magma. I used them at first to filter out magma from fire imps and such other threats, however the imp was washed right in with the magma. Thankfully it was already designed to be an obsidian farm. I figured the fortification failed because it was magma on a non-magma safe stone.

In my second use of them I had planned on eliminating migrants using a channel that I would flood with water and drain into a chasm. They arrived before I built the floodgate blocking the chasm, but I had a fortification in place to stop useful items from being washed into the chasm. However when the area was flooded the dwarves ran to the safest area, being next to the chasm, some drown, and surprisingly some fell into the chasm.

How effective are fortifications as filters for creatures in liquids in your experience? Does anyone use them like this?

[Qloos]

Bars and Grates are Superior.

[numerobis]

When a flow pushes something along, the flow can push said thing into vertical bars, fortifications, or wall grates.  Then the thing can walk out of that square -- for example, on the other side.  It's a known bug.

In the absence of flow, nothing can move through bars, grates, or fortifications.

[KoE]

I've been disappointed with the damn things as well. I typically tap into magma with the ingenious plan of 'carve fortification, run for dear life, savescum in the event of failure'. I once had a fort where I swear the little buggers actually thought the area under my forges was a room carved especially for them. They never actually bothered me, however.

And benoit just answered as I was posting. That makes sense (as much as any DF bug does), much appreciated, though that does mean the problem's not exactly solvable.

[numerobis]

The bug does not apply to floor grates, by the way: nothing gets washed through those.

[peekama]

I've been disappointed with the damn things as well. I typically tap into magma with the ingenious plan of 'carve fortification, run for dear life, savescum in the event of failure'. I once had a fort where I swear the little buggers actually thought the area under my forges was a room carved especially for them. They never actually bothered me, however.

And benoit just answered as I was posting. That makes sense (as much as any DF bug does), much appreciated, though that does mean the problem's not exactly solvable.

A bit off-topic, but there is a better way to tap into magma pipes.

You know how the walls of the pipe vary in diameter?
What you do is find a level with a small diameter of the pipe, and then look at the level below that.  There will most likely be an area where the bottom level will be larger, like this:

Spoiler (click to show/hide)

Code: [Select]

Level 1:
##############
#####~~~######
###~~~~~~#####
##~~~~~~~#####
###~~~~~~~####
####~~~~~#####
######~~~#####
#######~######
##############


Code: [Select]

Level 0:
#####~~#########
###~~~~~~~######
###~~~~~~~~#####
##~~~~~~~~~#####
###~~~~~~~~~####
####~~~~~~~#####
######~~~~~#####
#######~~~######
########~~######
########~#######
################


If you mine out a tunnel on the bottom layer like this:

Spoiler (click to show/hide)

Code: [Select]

Level 0:
#####~~#########
###~~~~~~~######
###~~~~~~~~#####
##~~~~~~~~~#####
###~~~~~~~~~####
####~~~~~~~#####
######~~~~~#####
#### ##~~~######
#### ###~~######
#### ###~#######
#### ###########


You can then channel out a space on the higher level like this:

Spoiler (click to show/hide)

Code: [Select]

Level 1:
##############
#####~~~######
###~~~~~~#####
##~~~~~~~#####
###~~~~~~~####
####~~~~~#####
#### #~~~#####
#######~######
##############


The hole that you channel will remove the wall on the lower level and give you a nice, safe flow.

[Grumman]

When a flow pushes something along, the flow can push said thing into vertical bars, fortifications, or wall grates.  Then the thing can walk out of that square -- for example, on the other side.  It's a known bug.

Would two layers of grates avoid this, or could the flow still push the imp from one occupied square into another?

[Shadowlord]

It might be worthwhile to try building a three-wide set of fortifications:

Where ~ is a water flow pushing to the left, and F is a fortification, and . is a chasm:
...FFF~~~

The flow on the right MIGHT only be able to push victims into the rightmost fortification, and they wouldn't fall into the cliff. Then again, it might not work that way - the flow might just push them all the way through all three fortifications... It's worth testing, at any rate.

[KoE]

I'm well aware there are better ways to handle magma-tapping, but sometimes the magma pipe just doesn't match what I'm wanting to do or I'm just damn lazy. That, or I have a dwarf I want to get rid of. Granted that's only when I get early immigrants thanks to my magma fetish, but eh.

I've only got the faintest idea of how magma flow works, but in the case of keeping fire imps out, it seems like a valid idea to have multiple fortifications like so (shamelessly stealing the above posters key, excepting tildes are magma and not water):
~~~F~~~F~~~F~~~

on the premise that any nasty magma critters would have to get washed into one and pick the 'correct' choice towards wherever you don't want them to be multiple times. Again I'm not sure how magma flow works once it all equalizes, so that may also just be delaying the inevitable since they can't move back. Just a thought.

[Cavalcadeofcats]

Shadowlord/Grumman's idea is much better than KoE's. Sorry, KoE.

[Osmosis Jones]

Honestly, I prefer KoE's idea. Think about it, if the flow that pushed the imp into the grate lasts for more than one tick, the imp can get pushed through multiple tiles.
KoE's increases the time taken to traverse the filter, hence increasing the likelihood the current will end, and the imp will be trapped.

Further, KoE's idea allows for safer extraction of the captured imps for fire turrets.

[Agent_Irons]

I propose a combination.

~~~FCCFCFFF.... (rest of fort)

a single fortification to keep out rifraff, some cage traps, more filters, cages, then triplewide fortifications.

My understand of the bug is that flows can push things onto the same square as fortifications, and then they can walk off onto an adjacent square, possibly on the other side. If the fortifications are two deep, then there's no walking into occupied squares. The safest, of course, is this.

~~~_
###.....
the magma flows through floor bars and down into the place where you want it to be. for forges, this means three levels for safe magma procurement( forge level, magma level, and above the two, channeling down for not lighting up your miner level.) and for the useful item catcher, means only two.

[KoE]

Yeah, it depends on how the flow interacts with the fortifications - I'd err on the side of it only going through one tile, which makes the most sense (if that's even a valid argument with DF). The cluster method is, barring some weird bug where they get pushed through multiple fortifications, a better one, excepting that with mine there is the possibility of extraction. Heck, Agent Irons is the best of both worlds, though I'm not sure you can retrieve cage traps from water or magma like that. I was thinking a hatch or something for the buggers to swim up through into a small chamber filled with traps.

I've been planning on designing a waterfall with a well-placed cave river in my most recent fort (about halfway up the mountain, whereas the bulk of my fort is dug in at ground level), so I can probably mess with the three-fortification hypothesis, assuming we're still making assumptions about it. It doesn't seem too likely it'll act unexpectedly, but then again, any excuse to drown some dwarves (or maybe kittens).

[_Acorn_]

Fire Turrets?

Will caged Fire Imps placed on the roof of your towers shoot fireballs at invaders or something?

[Soadreqm]

Do flows push things through floor grates? As far as I know, flows only happen horizontally, and gravity handles vertical drops. So the ultimate filter would be:

Code: [Select]

side view
-> flow direction ->

~~~OO   <- level z
OO#OO   <- floor between levels
OO~~~   <- level z-1

~ = water
O = wall/floor
# = floor grate
I think water pressure is slightly bugged right now, and the water wouldn't rise back to the original level without pumping. But if you have an extra level to spare, or power in some form, this should solve most of the related problems.