My first capsize and need for advice

It is possible to stay dry when capsizing a Mirror, but if you realise you're reacting too slowly to get over the top in time it's better not to try as that makes it more likely for the hull to turn upside down. It's also extremely hard to get back in after righting the boat if you're sailing alone - it's easy if you have a crew as you can help each other get in, but when you're sailing alone you need to add a piece of rope at the stern with a loop or rung on it to use as a step, and even using that is hard, requiring good technique which you'll only gain through experimentation and practice, so you need to do that in a safe place and with a rescue boat nearby. You could also experiment with a masthead float which may enable you to climb over the top even if you're slow, and then you can try getting back in as the boat comes back up, but that too takes practice as it whips upright suddenly and you have to react fast.

As "elbsegler" described, his boat was apparently totally turtled. I have also seen pictures of Mirrors totally upside down in regatta albums (World championships etc.) and am a bit puzzled. Shouldn't the gaff have enough buoyancy to at least slow down turtling considerably?
In the last 30 years, I capsized "Puffin" twice. On both occasions, she stayed on her side until we/I could right her. When I learned to sail, I was taught that one should try to pull the stern so that the bow faces into the wind before righting the boat. This means that once the sail is raised out of the water a bit, the wind actually helps you to right the boat. This tactic worked for me on both occasions. The first time it happened, my (then) 8-year old son was with me and his shoes, which were in the front stowage space on the side that was down in the water, didn't even get wet. I helped him to board the boat over the stern as she came up, which meant that a lot of water drained out of the transom holes. I then pulled myself up over the transom as well. We didn't have to bail too much water out after climbing aboard. I did lose my Greek fishing-boat skipper's cap in the process, though.
The second capsize, about 24 years later, is described on pages 15 and 16 of my 2012 cruise report http://mirrordiscussforum.org/documents/stories/jf2012english.pdf . I was wearing a padded sailing parka with the PFD over it at the time, so re-boarding was not so easy and I had to use my stern mooring line as a "stirrup" to get aboard. There was a bag with some clothes and other gear on the boat so she was heavier and had more water in the cockpit after being righted and quite a lot of water drained out of my jacket after I was back aboard. All the same, I only needed to bail less than a bucketful of water out (my on-board bucket is a ten-litre cheap plastic bucket).
@ Elbsegler: I think I'll try letting the boat lie on its side this year to see how much buoyancy the gaff provides and how much additional buoyancy is needed to prevent turtling.
OR has anyone else here already carried out such tests and can provide the answers here?

The gaff only floats with a tiny percentage above the surface, so it isn't going to stop the boat inverting - it must be the top of the mainsail that does that. I know a couple of people who found they could walk around on the mainsail of their Wayfarer during a capsize because the water held it up so well.

Come to thing of it, the centreline of a capsized Mirror is fairly high above the water surface, so only the upper end of the gaff would be in the water and the hollow mast almost completely clear of the water, so not contributing to stability. Dinghies without side floatation tanks would tend to float with the keel and mast almost at water level and remain stable if the mast has positive buoyancy.
After capsizing, I was too busy getting the boat righted to think about or observe these questions. Perhaps my boat stayed on its side fairly well because it was blowing fairly strongly on both occasions, so that there was probably a cushion of air trapped under the mainsail too.
Gernot H.

My capsize during the gybe may have been due to the slack boom kicker catching on the board, which I'd taken up almost all the way running downwind. After I was in the drink, I realised to my dismay that there was no board sticking out of the bottom and had to swim around the stern an push the board in (my CB has a very snug fit) before being able to hang onto it. I used the jibsheet to give me exra leverage (the boat being cat-rigged at the time). All this must have taken a few minutes, so the mast obviously had stayed fairly horizontal for a while.
Gernot H.