Well, he could be a great swimmer as far as we know?

I didn't find this annoying at all (mostly 'cause I was more annoyed at other things). I don't know if I'd call it a "deus ex machina," but if nothing else to me, it was a little confusing, but nothing else. Besides, I actually like the idea a bit that we don't really get an explanation why it happened or how.

But wasn't Dark Island like 20 yards away from Ramandu's Island when Lilliandil first showed it to them? It looks like Eustace could have easily swam from there.

but wasn't Dark Island like 20 yards away from Ramandu's Island when Lilliandil first showed it to them? It looks like Eustace could have easily swam from there

.

It was closer to a few miles.

I didn't mind the teleporting from the undragoning to Ramandu's Island since I'm sure Aslan wouldn't leave him on a sandbar to die, while his friends are torn apart by imaginary monsters and nightmares
The Teleporting from RI to the DI was kind of weird but Aslan could do it if he wanted to

Well, Eustace can't swim in the books...
Anyhow, I found it really annoying. There was no explanation for him being in all those places. It seemed like the scriptwriters got tired and just said, "Oh, to make everything better we'll make Eustace pop up here, and then he can fall into the water right here so he's back with everyone."
I appreciate clear explanations!!!!

It didn't make sense at all to me. I wonder if there might be some deleted scenes?

I didn't mind it when he was teleported to Ramandu's Island, because that was plausible as Aslan helping them, but I was really confused when he suddenly turned up in the water next to the ship. That was a seriously long way for someone to swim in a few minutes.

It was incredibly annoying, but I only just noticed it now with the reminder of it. In both my viewings I think there were other things that bothered me a lot more.

However, I don't think Deus Ex Machina is a bad device. Just often an ill-used one.

I didn't think of anything about the "teleporting" the first and the second time I watched. Though I don't find it annoying but I find it weird once I gave it a thought, especially when Eustace being in the water out of nowhere.

Well, actually I don't really care about it.

I found the first teleportation strange, but as for the second, I had always assumed that Eustace had swum to Dark Island from Ramandu's Island. I found it extremely annoying that the filmmakers would so soon forget that they placed the two islands quite a few miles apart from each other. Quite seriously I thought it was a mistake until my sister told me that it didn't bother her and that she just assumed that Aslan had placed him there in the water. That statement changed my entire opinion of the scene, making it at least plausable that Eusatce could be there.

I don't think that the filmmakers are breaking any rules. After all, what are the Narnian books about if not portals connecting two faraway places?
Besides, in the book of VDT, after Aslan undragons Eustace he suddenly finds himself near the camp with the others, and so Eustace wonders if it was all a dream. Evidently Lewis himself was not against having Aslan teleport Eustace after the undragoning, so I'm not going to get uptight if the filmmakers want to do the same thing.

This was discussed somewhat in the "Undragoning" thread....
viewtopic.php?f=25&t=2283&p=122438#p122438

I liked that Eustace just appeared in the water. I didn't care how he got there and since it appeared to be the shortcut way of showing him spiritually reborn (via water) I loved that he ended up where he did with Reep leaping in beside him to keep him company. I do not believe that he swam there and that he pretty much reappeared by Aslan's power where he was supposed to as much as the people who were sacrificed to the green mist reappeared where they were supposed to....which was near the water of the Dawn Treader....very convenient for reunions.

Well, Eustace can't swim in the books...

Slightly off-topic BTW, your comment about Eustace's swimming makes me think of the painting scene....at times during that scene when Will Poulter's shown diving towards the surface I thought...."hmm...maybe Eustace really can swim" ...and then when he first surfaces near the DT he looks like he needs rescuing...a bit inconsistent... It maybe would have been better if he caused Lucy to go down with him in panic like he did in the book.

Actually in the movie I don't think he's drowning. He says "I'm going back to England" and then it looks like he is attempting to dive underwater to find England again. The Telmarine stops him from diving though.

I actually didn't notice that Eustace was jumping around from place to place at first. I was too preoccupied with other annoying things.
Once I did notice, I did find it annoying, but like I said, I was so worried about other things, that this seemed like a minor problem in comparison.

I wasn't bothered by Eustace popping up in different places at all. Even though it wasn't exactly like it, it reminded me of a scene in the Lord of the Rings The Return of the King. In this scene Frodo is outside the tunnel of Shelob when all of a sudden he ends up in a forest with Galadriel for a moment. Again I know that it is not the same thing but that is what it reminded me of and therefor I was not bothered by this.
And wasn't the Dawn Treader already sailing away from the Dark Island when they found Eustace in the water? Perhaps it wasn't that far away from Ramandu's Island.

to me, I saw it as more of Aslan's doing than anything. it was Aslan who came in when the adventurers need was dire and he transformed Eustace back into a boy. then he sent Eustace to Ramundu's Island to complete the task of laying down the swords in order to save the Dawn Treader's crew.
then Aslan sent him back to the ship once the task was complete.

just my two cents.....