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How do you repel boarders? I frequently end up losing my crew to them.
Usual technique is to just vent them (with leveled up and/or manned doors). Just remove your crew and vent the room(s) the boarders are in.

Or fight them in your medbay.
If you have a medbay, try to fight them there, and vent the rest of the ship.
1) Restrict their movement. The doors subsystem may not seem important but it is vital for dealing with enemy boarding parties. Trying to kill enemies by evacuating their air is very difficult if they can just waltz into another room with air. One bar in doors will hardly slow down boarders at all. Two bars makes a big difference, they will still be able to eventually break through but it takes them a while. Three bars will usually pin them in place more than long enough to kill them. If you have a spare crewman you can get an extra door bar by moving a crewman into your doors control room. Note as a secondary bonus upgraded doors slow the spread of fires.

2) Suck out their air and suffocate them. Open one or more external doors as well as doors between the airlock room and the boarders' position. Eventually their room will go cross-hatched and they will start dying. It takes quite a while to kill boarders via suffocation, though, so expect them to do substantial damage before they die if they have access to vital rooms. If you are playing with advanced options remember Lanius don't need air.

3) Train anti-boarding crewmen. Mantis are best for this, with Rockmen second. Keep in mind these guys need experience to be fully effective, and they get it by actually killing something. If enemy boarders are suffocating in a no air zone or dying in a fire, let their health get nice and low but don't quite let them die, let them into a safe room then send in a killer to mop up and get an experience point for killing them.

4) Take advantage of Medbay. If your crewman and enemy boarders fight in your active Medbay, Medbay will heal your crew while they are fighting (Medbay never heals boarders). One bar of Medbay healing is often enough to offset incoming damage in a boarding fight. Two bars will usually heal faster than the damage comes in. Keep in mind this only works if Medbay is at least partially operational and powered.
My strategy is an easy one.

1- If the doors are not upgraded, then:
1a - if (amount of boarders is less or equal two) AND no mantis/rockman/crystal: send two crew to fight them.
- - - when two crew gets less then 1/3 of health send another 2, send the injured to medbay

1b - else: lock up everyone in medbay, vent all rooms except medbay and adjusting room - but leave control room with air and manned so long possible.

2- Else (If doors were upgraded to at least 1 level): quickly move one member - except from engine and control rooms - towards door room; then 1) shut down o2, then 2) vent half the ship around the boarders, then 3) immediately close all doors when they start to move.

This causes boarders being locked out inside large vacuumed section of ship with closed doors. The o2 is back once boarders are away, the crew has to endure.

If near the sun, then make sure shields are up.
Jumping away still with intruders inside is usually bad idea, as next spot often has aggressive enemy.

I consider anti-boarding drone waste of drone parts and useless, except unlocking special blue options.
Not all races are equal. If one-on-one-only fight is considered: Mantis beats anything; Rockman beat anything but Mantis; Crystal is better than human or slug. Engi and Zoltan are weaker (but for different reasons).

Trained, experienced fighters are better than untrained. Kills, including room level kills while boarding give combat experience points.
(Cheaty hint (assume transporter and med bay): Lanius, Crystals and even Rockman (theoretically possible but increasingly hard for others) can turbo train continuously demolishing autoscouts and letting them repair)

Try to create numerical superiority, if at all possible, and avoid being outnumbered if you can, fight 2 vs 1 or in large room 4 vs 2, your crewmen who not have brawl partner but are in same room will shoot at enemy and help a little that way.

Rotate your crew. In 2 vs 1 situation often is enough to swap brawler and shooter roles once. Else, you can send crew away or to heal in med bay and replace with fresh.

Fight in operational and powered medbay. Engi medbot dispersal can help a little (but mostly is waste of a slot a little).

Antiboarding drone is far from efficient investment mostly, but valid choice in situations with small Engi or Zoltan only crew.

Upgrade (and/or man) the doors. Open doors for them to let them where you want.

Suffocate enemies by venting rooms they in or most of the ship You can jump around with only few rooms actually having air at all (helps also against fire a lot).

Do crazy things, like drop fire bomb in your own, subsystem-less room. That's rarely sane, but can save you once per year.
Post edited December 24, 2016 by Enneagon