Those balls will roll around unless you put something under them from stop rolling.
Also, whats keeping the cannons in place once they fire. They have a levy system that rolls the cannon back for reloading and forward for firing. Also, how do they move them in and out if one becomes broken?
You have a great base, but it needs a lot more detail to flesh the area out and make it more believable.
Take a look at the interior of the HMS Victory for reference.