But here's a thought: These mythical (for that is all they are) "collisions" and/or "explosions" are not claimed - as far as I understand, anyhow - to have occurred anywhere near the bow visor.
So, that being the case, the rather obvious question would be: exactly how/why would the bow visor have failed - especially in the manner in which the evidence shows it failed - if it happened after this "bomb"/"explosion" malarkey? After all, there's not really any credible mechanism for it to have failed either a) as a direct reaction to the "bomb"/"explosion", or b) as a reaction to the ship sinking. And, obviously, the odds on it coincidentally having failed in that tiny time window (relative to the age and history of the ship) is very close indeed to zero.
And yet..... all of the credible & reliable evidence, including structural/metallurgical analysis of the bow visor and bow ramp, points to the bow door having failed of its own volition owing to the combination of bad design/construction, poor maintenance, and the rough seas on the night of the sinking. And also, since the evidence shows that the bow visor and then the bow ramp failed in a specific manner, we know that the manner of their failure would have guaranteed a large volume/mass of seawater flooding the vehicle deck and fatally destabilising the ship. Oh and the manner of their failure is also entirely compatible with the passenger accounts of what they heard.