I'm talking about the icebreakers they are more than likely faster and stronger than their sail boat friends.
Yes they were made to get past the ice in Northrend but these things have a lot more potential than just that. Why does the Alliance not give them the overhaul they gave their current navy boats?
Yes it doesn't have as much cannon space as the other ones but they're still faster. Yes they have metal on them which makes them slower but...so does the current Alliance battleship
Now combine these two designs and add some more metal and you've got a massive death machine. Add some mortars on the deck to shell the Horde while they're out of cannon range and you're golden.
I personally think the Alliance(Blizzard) could have done better at giving the Alliance kick-ass war technology. I do like our airships and the fact that they don't get blown up everytime they make an appearance.
So to recap:
Current naval ship design + icebreaker influence(The steam engine being the biggest) + see through windows + mortars + a crap ton of cannons.