Warship cannons influence on speed/direction I've been looking at great warships like the Iowa or equivalent ww2 warships, and I raised question.
This kind of war is pretty much only about strategic placements, accuracy and fire power. Hence the race to stack as many cannons as possible. Manage weight and size for manoeuverability vs fire power and range for example. And in the end it's all about having each ship perform it's specific role.
And with all that i was simply wondering if all the cannons would actually influence the ship's speed/heading each time they're fired. In one hand they're pretty massive, on the other hand the boat is pretty heavy and wide.
Would a 45 degree shot actually help the ship turn ? Or 180 give a small speed increase ? Would that be actually used to be more manoeuverable ? That would be pretty cool :o
I am sure there is some kind of influence, the ship won't obviously stay static, but I was wondering how much. Would it actually turn the ship say, 10 deg each time it fires or more something like 0.2. (For example). Anyway, my curiosity strikes again !
 A: To answer your questions,  would a 90 degree shot turn the ship, in theory yes, due to the conservation  of angular momentum law.  As long as the cannon was not exactly  amidships , in which case it would push, or more probably just cause a list, to port or starboard.
And would a 180 degree shot (aftwards) increase the speed of the ship, again, in theory yes, due to the conservation of linear momentum law. 
But in practice,  how much effect they would have depends on ratio of the momentum  of the ship (mass by velocity) versus the momentum of the shell, as well as other factors. The smaller this ratio,  which would be pretty small in the first place, unless the cannon were all fired simultaneously, the more difficult it would be to measure. 
You should think of having a go at this yourself. 
Lots of great physics in it. 
Variables : mass of ship, momentum of cannon shell, density of water, water viscosity etc. 
For an example of roughly the same idea, during WW2, propellor planes were sometimes  tied down and used as sideways thrusters, entering and/or leaving the dock area. The link below might tell you more and there might be a clip on YouTube. 
Turning a ship using aircraft engine thrust
The pilots hated  it though, as there was always the chance it would damage the plane engines through overheating.
