Question: In [Triangle](http://www.imdb.com/title/tt1187064/), at the start when Jess arrives at the boat for the "first" time, is this the start of the continuation of the ending scene?

It's known that the cruise ship and any surroundings after leaving it is in a time loop.

Though Jess remembers the ship and tells Greg, she makes no indication that she is in the time loop. So yes, the movie was meant to confuse the user. But seeing that, according to the number of dead Sallys on board, the time loop occurs more than 20 times.

So, the first time she entered the loop, the storm sent her into an alternate reality with the never-ending time loop? Is this what the movie was showing? I noticed there is a deadly Jess that was not really in the foreground that got shot in the head, and stabs Sally and Downey in one of the rooms. I cannot really place where she falls into the picture seeing that one of the previous Jess instances killed that Jess instead of letting her jump overboard.

So is there a separate timeline/reality?

Answer: 
I agree that we enter the loop during its Nth playthrough. However, I do not think we are following the same Jess all the way through -- there is a moment when the film seems to judder and jump back several frames -- I think this represents several more playthroughs of the exact same moment thus we have jumped forward 2 or 3 Jess'. Remember, these are not rewinds but replays starting a frame or two behind.

PS, I am reading really annoying theories that there is a third killer, a masked man. This theory is based on a blooper -- you can see "masked Jess" hairy arm near the cuff, i.e. the stunt man when he throws the shot gun. This same theory holds that the third masked killer disappears but it is explicitly shown that this is really masked Jess who works out unmasked-Jess' attempt to distract her by throwing a valve. Consequently, she runs ahead of unmasked Jess and waits to ambush her.

It is a supernatural punishment loop of some kind for killing her son -- whether it's murder or manslaughter we will never know.
Not the way I remember it. The way I see it Jess is in a kind of purgatory, as the end of the movie shows her as an abusive mother. She's trapped in the time loop, but seems to be gradually changing things. Perhaps when she has righted all her wrongs she can be free?