Terminating a ferry is well within the capabilities of the jihadists, much simpler than thermite.
Thermite is pretty simple to make. Its just hard to ignite. Sparklers can do it. Once lit, it could easily burn through 2 decks and the hull of a loaded ferry.
Just my honest guess...but at any one time between Seattle and Vancouver...there are at least four ferries out on the water. It would be interesting for some amateur Jihad group to sink all four ferries at the same time. Around rush-hour...at 5pm...you might even get a dozen ferries in the region...out on the water at the same time. This would make major news throughout the Pacific coast and probably make huge issues for months while awaiting new ferries (they aren’t built every week, you know). I’m sure some Islamic characters from Vancouver are behind this episode. If you walked around their neighborhoods with the pictures...someone would eventually point out the guy in question.