Explosive experts: could you blow up a ship like this?

What is the typical thickness and hardness of the steel in the hull of these ship types? Most likely a shaped charge warhead will easily breach the hull. But then the distance between the outer hull and the LNG tanks will dissipate the shaped charge jet. And the warhead on a boat of that type does not have the momentum or rocket motor with any unused fuel of your typical anti ship missile that would overcome the distance issue.

So now let's say that the outer hull is breached majorly, and serious structural damage occurs to the immediate surrounding compartments and the closest LNG sphere. Once one sphere is breached, will the LNG escape and go back to a gaseous state where it becomes flammable again? 

That looked like a Stinger on the bow, which would have a fragmentation warhead, not shaped charge.  It also looked like the main charge on the boat went off about 8' from the side of the hull.  I imagine the blast would have damaged the hull, but I doubt it would have ignited the cargo.

Would a flash-bang grenade under a gas tank blow up a car?

I'm far from an expert in either case, just opining.

During WWI the British air force thought a single fighter would easy shoot down a Zepplin using tracer ammo, but they where unseccessful with each attack.   Turned out that it took several airplanes to damage enough gas bags that the Zepplin could no longer stay airborne or the vapor/air ratio was finally met to set the ship on fire.  It took a lot of work of several fighters to bring one down, like lions bringing down a water buffalo.

I'd approach analyzing this scene with a skeptical mind, because it's a scene from a movie, and one that had political overtones, at that.  The production team might have worried more about how spectacular it was, than whether it was 100% accurate.

My initial thought was that it's just a complete load of movie tosh, but;

Substantial damage caused to USS Cole in Aden & the nearly new super tanker MV Linburg by similar means has me wondering (the MV Linburgs inner hull was breached);

Right... tankers are not armored warships, so they will take some damage. But I doubt the charge that would be hand carried to such a fishing boat would not be likely to cause a catastrophic loss. Certainly not one apocalyptic blast. Think of the "tanker war" portion of the Iran/Iraq war of the 1980s. The anti ship missiles used then which would have far better penetration and after blast effects due to any unused rocket motor fuel igniting ruptured fuel tanks would not instantaneously take down such a vessel.

stikpusher

What is the typical thickness and hardness of the steel in the hull of these ship types? Most likely a shaped charge warhead will easily breach the hull. But then the distance between the outer hull and the LNG tanks will dissipate the shaped charge jet. And the warhead on a boat of that type does not have the momentum or rocket motor with any unused fuel of your typical anti ship missile that would overcome the distance issue.

So now let's say that the outer hull is breached majorly, and serious structural damage occurs to the immediate surrounding compartments and the closest LNG sphere. Once one sphere is breached, will the LNG escape and go back to a gaseous state where it becomes flammable again?

The thickness of a hull is typically 1" and I think the sphere is similar. Don't know about the hardes but it is certainly not meant to be an armor protection a la military. If the liquid is released in the athmosphere, it will become gas, but as you know, the mixture of gas and O2 has to be just the right proportion. Also, the hull's side is often double, so now we have 3 layers that have to be penetrated.

So, the more I think of it, the more Hollywood it is

There you have it. It's Hollywood and not a documentary. Compare the actual footage of the USS Arizona explosion at Pearl Harbor to the CGI version of that in the film "Pearl Harbor". Shall we say artistic license? It's all about the wow factor.