I was recently called a terrible engineer, which kind of pissed me off. So I started thinking, what could I have done differently that would have kept us alive and made everyone happy? I'll start by explaining my general strategy for repairing as main engi.
First thing you probably tell a new engi is that mallet is for repairs and spanner is for rebuilds. But what if the hull is only taking light damage? A mallet often results in a lot of overhealing and a hefty cooldown, which is kind of wasteful. It can give you time to run around and whack other components with the mallet, but doing so can cause you to lose a large amount of armor before it can be repaired again. In those cases, sitting on the hull and whacking it with a spanner can let you survive significantly longer. I'll explain with a purely hypothetical situation.
Say you have 270 armor and you are taking 30dps. After 9 secs, the armor will break and the hull will be exposed. If you wait 7 or 8 seconds and hit it with a mallet, you bring the armor back up to about 270, which will then break 9 seconds later. Total armor uptime is now ~16secs. Now if you try healing with the spanner initially (which heals 20hp/s), you effectively reduce the incoming dps to 10. After about 22 seconds, the armor will drop enough where you can get the full effect of the mallet (which is more efficient at 25hp/s), which will bring it back to about 270. 9 secs later, the armor will break, resulting in a total armor uptime of ~31 secs, which is nearly double the amount of time it would have stayed up if you'd just used the mallet.
In actual combat, the incoming dps varies significantly, but it usually buys at least 5-15 seconds of armor uptime. It's especially effective against gatlings and flak that chip away at the armor relatively slowly (as opposed to bursting it down). However, all the time you're sitting there on the hull, you're not doing anything else. On the Spire, Goldfish, and Pyramidion, that's not much of a problem. On a Spire, you're not really doing much else. On a Goldfish, armor is still low enough that your captain will love you for keeping them alive longer, and the other engi can handle most other things himself since he's not doing much else anyway. On a Pyramidion, it's still really useful since the balloon isn't your responsibility and the hull has enough armor that you can still run back to hit the engines when necessary once you're no longer using the spanner. Even on a Squid, you can usually buy an extra second here and there between rebuilds.
The decision is a little harder to make on a Junker or Galleon. Since main engi is responsible for both hull and balloon, and pulling the gungineer off a gun results in a significant loss of dps, you have to choose between keeping the hull alive a few more seconds or keeping the balloon up a few more seconds. However, the Junker and Galleon have a lot more armor than most other ships and the balloon tends to be the primary responsibility of the main engi, so the extra few seconds of armor uptime tend to go less appreciated on those ships. But when both armor and balloon are dropping, i tend to prioritize hull.
The primary thing to take away from this is that every second you can afford to delay using the mallet, you're keeping the armor up an additional second. It's also important to note that it's better to use the mallet a little early than a little late, because burst damage could ruin your world.
Back to my story, both the armor and balloon on the Junker were taking heavy damage, so I decided to buy as much time for the hull and let the balloon pop. This upset the captain because all he saw was me camping the hull for several seconds, followed by the armor breaking while I was still standing there. There was also the problem of how I couldn't make a round trip between hull and balloon during the mallet's repair cooldown. No matter how I tried I couldn't manage to do it. It was weird because I knew I'd managed to make the round trip before, but couldn't manage it in that match. I just tried it again a few seconds ago in the Sandbox and managed it in 7 seconds. Really weird. Potential bug maybe?
So because I couldn't keep both hull and balloon up, I prioritized the hull. When I tried to do both, we died faster, resulting in him calling me terrible and ragequitting after the match. I could have done better to communicate what I was doing and letting the other engi know to help with the balloon, so that was bad on me, but is there anything in my strategy above that you see is glaringly awful? Am I prioritizing hull armor too much?