Q:

In Skyfall, what happened in the boat on the way to the island?

In Skyfall, after leaving the floating casino in Macau, Sévérine gets on board a boat.  Bond gets on board too and they have an amicable scene in the shower.  The boat is shown going out to sea.
Then, the ship is approaching the deserted island where the villain Raoul Silva is hiding out.  Bond and Sévérine are both restrained with their hands tied behind their backs, and there are a number of thugs on deck with automatic weapons.
Did I blink and miss something?  When were Bond and Sévérine taken prisoner?  I don't remember any fight scene on the boat.  Was she used as bait?  Was she being forced to go to the island in the first place?  If she was going to be taken prisoner, why didn't she warn Bond?  (Well, I guess she did sort of, in the casino she told him he would be killed shortly.)

A:

You must understand that Sévérine was under the complete authority and control of Raoul Silva. Everything she did or was doing was on Silva's command. Silva wanted Bond on the barren island and Sévérine was to be the bait. Though she tries her best to warn Bond of the danger involved and makes her reluctance shown. But Bond being Bond and having his own plans, follows her to Silva.
The only thing to notice is that Sévérine already considers herself dead and has no expectation of being freed from Silva's slavery. But fear of Silva [1] and hope [2] that Bond just might be her savior, brings her to do what she did.
[1]

Sévérine: What do you know about fear? 
James Bond: All there is.  
Sévérine: Well not like this. Not like him.

[2]

The scene where Sévérine says that her bodyguards are going to kill
  Bond right after
    she leaves, she asks Bond if he'll be able to kill Raoul Silva(something on these lines, dont remember the exact quote).

A:

If I recall correctly, as the boat is approaching the island, Bond and Severine are standing at the front of the boat, looking at the island. They are NOT tied up yet. 
Severine gets cold feet and says something like "we still could turn around." But Bond knows that Silva is expecting him, and Bond knowingly says something like "no, it's too late" -- just as the shot widens to show the ship's crew slowly approaching Bond and Severine with their guns drawn.
So the crew took Bond and Severine prisoner just before reaching the island. 

