"Then we probably shouldn't do that then. Hmmm...."
As the group struggled to make a plan, Francis decided to sit down and think. So the Gondola is heavily armoured and it's carrying precious cargo. Unless we do something incredibly loud and notorious, we likely aren't going to crack it open ourselves. Like Anne mentioned, the best way to open up the gondola is to draw out the guards, likely by making them want to escape the boat. She suggested we sink it by puncturing a few holes, but that hull is tough. What if we make them want to escape for other reasons?
Suddenly Francis grins.
Well the boat is made of iron, so it's bound to be pretty hot in there. What if we turn up the heat just a little bit. Set it on fire perhaps, turn it into an oven. That will get them running. But there's a problem with that, metal doesn't burn. Want to know what does though? Oil. We cover the boat in any kind of oil and just set it ablaze. That comes with its own problems though. Most of the oil would just slide off of the boat meaning that whatever was left wouldn't burn for very long. There's a crazy solution to that though, we fill the inside of the boat with oil. As for how you're going to get oil inside an impenetrable gondola.... hmmm
Aha! Of course, how did I not think of this sooner?! The drivers aren't going to be rowing this gondola blind, they're going to have to have some way of seeing where they're going. It could be either glass windows, which is unlikely since you can just smash those with a hammer, or small slits at the front that allow you to see through, kind of like in the visor of a knights helmet. We could pour in oil through the armour slits and then sneak a match through to light it up. Guards will flee for their lives, we take them out, and once the fire dies down, we steal the gondola.
Having finished with his thought process, Francis shares his plan with the group.
"Sorry for the wait everyone, but I think I've discovered a vulnerability in the gondola. The drivers inside must have some way to see the canal ahead of them, and I bet that it's going to be armour slits. As for how we can exploit this vulnerability, it's pretty simple. We take some sort of volatile substance, and then shove it inside through the slit. My personal recommendation would be lamp oil. If you pour in a gallon of lamp oil and then sneak in a lit match, the inside of the boat will be set ablaze and the guards will flee for their lives. That's when we strike. We subdue the guards while they're fleeing and once the fire dies down, we take the gondola for ourselves."
After looking at the facial expressions of the rest of the crew, Francis adds:
"If burning the gondola makes you feel uncomfortable, then don't worry. I'm fairly certain that simply telling the guards that their boat is filled with flammable lamp oil and then threatening to light a match will make them come out."
And then also adds:
"What do you think? Is there anything I may have overlooked?"