As the name of the thread says, is it possible to add more small artillery to ships? Usually when I look on wikipedia I see that most ships have a very small amount of ,cannons" ,so I was wondering would it be possible to simply add 100-155mm cannons or howitzers on bigger navy ships? I don’t mean the huge,huge cannons that are more than 200mm, but smaller ones like for example the soviet d-30 or d-20, they weigh around 2500-3500kg (and that’s including tires and parts you wouldn’t need here), so like a car, they aren’t light, but I don’t think that it would be a problem putting them on huge ships, the only problem I see is maybe the fact that boats move and that it would be less precise than on ground…
You could certainly do this. Look at any WWII ship.
Why would you want to, though? What are you trying to accomplish?
Corrected spelling in title.
Colibri
General Questions Moderator
One problem is going to be that the boats are already designed to handle X weight and now you’re adding more. So if you take out 2000 pounds of stuff, you could probably add a 2000 pound gun.
Number two is going to be balance. Guns are pretty compact - their weight isn’t exactly distributed around the ship. So maybe you’re going to need to add reinforced deck plating too, or a counterweight on the other side of the ship. Well, that’s some additional added weight.
Number three is the recoil and its effects. If you’re just putting some nasty looking stuff on your boat to sail into harbors to do a little “gunboat diplomacy” and leave the real fighting to someone else, you’re probably ok. But when you fire that thing, are you going to tip the ship over?
Don’t forget that the ammo has a lot of weight, too. Those fancy guns don’t do anything useful if you don’t have anything to put in them.
You also have to keep in mind that these ships are designed for specific purposes. They don’t just sail around on their own and get into scraps. They function in groups. Sure, you could add cannons all over a large aircraft carrier, but why? The carrier isn’t going to be the guy slogging it out on the surface. That job goes to the destroyers and frigates, and those guys got plenty of guns for what they do.
Firing solutions on a moving/rolling ship are much diffenent than standard artilary will be able to accomplish unless we are talking point blank shooting.
.and we can throw on that ammo takes a lot of volume. Mounting a new gun adds weight and takes volume for the gun, space around the gun to enable moving it to aim, maintenance access to all components of the gun, and things like transport mechanisms to move ammo to the gun. The you look at potentially more crew to serve the gun during operation if it’s manned. That crew needs to eat, sleep, defecate, bathe, etc. That all pushes volume and weight constraints
All that’s in an era when missiles dominated guns in the race to take up weight and volume because they offered longer range lethality against naval surface targets. Even the venerable Iowa class lost guns when it was reactivated in the 1980s to make space for missiles. It’s not that more guns couldn’t be added but a matter of more guns being less useful in modern surface combat.
I was just wondering, my knowledge on anything related to boats is minimal, but I think that for example it was important during ww2, now there are missiles and stuff, but most boats today still don’t have a lot of offensive weapons and artillery could be useful to attack targets that are on a coast, for example in the Ukrainian scenario Ukrainians could use it to attack Novoazovsk which is under DNR control or DNR (if they had a ship like that) would be able to attack targets in Mariupol,etc.
OK, first off, warships are not “boats.” 
Secondly, the idea that modern warships “don’t have a lot of offensive weapons” is completely wrong. A modern U.S. warship is positively lethal. For example, an Arleigh Burke-class destroyer carries a 90-cell or 96-cell vertical launch system of missiles. The visible weapon (a 5-inch gun) is almost an afterthought.
In a conflict between a WWII-type ship and a modern warship, the WWII-ship (though bristling with guns) would never even get a chance to get with within range of the modern ship before it was sunk by missiles.
OK, you want to do shore bombardment. While this is possible, the main problem with this is that a 5-inch gun has an effective range of about 13 nautical miles. For a ship to get this close to shore, it has to put itself within range of return fire from shore, and modern warships are not armored like WWII-type ships.
It’s generally more effective for the ship to launch a Tomahawk with a 900 nautical mile range that you can target through someone’s window. With that range, the warship never has to expose itself to return fire from shore.
(There is some room for disagreement on this, which is one reason why many fought to keep the Iowa-class battleships in commission. These vessels, however, with their 16-inch guns, are a whole different animal than the small guns referenced in your OP. For one, their range was over 20 nautical miles, which is over-the-horizon. For another, the shells weighed over 2,000 pounds. In any event, the battleships were ultimately deemed too expensive and manpower-intensive to keep in commission.)
In the pre-dreadnought era, some Naval tacticians thought that “smothering” a target with lots of medium and small shells was the way to go (destroying the unarmored portions of a ship, as well as breaking morale).
Typically speaking, while small guns have a good rate of fire, their accuracy drops off faster (compared to the “heavy” guns) as the range increases.
In the dreadnought era, bigger guns meant better accuracy at longer ranges, as well as the power needed to punch through a foot of steel armor.
Nowadays, no one builds armored ships like they used to, so smaller guns may be a viable solution again. 
Edit: In light of what robby said: You build your ship for a specific mission. If you want it to be multi-tasking, that takes up more weight & space (& money). You want long range bombardment? Try aircraft or missiles, instead. Hunting Somali priates? The 3 to 5 inch naval gun is fine.
How many cannons do you want? Currently commissioned warship mounting over 100 artillery pieces ranging from 110mm to 155mm.
I immediately thought the OP was asking about mounting as large an artillery piece on an actual boat as possible, to which I then thought that you could probably fit a pretty large recoilless gun on one.
In WWII most of the guns added to ships were of the AA type.
For bombardment missiles and bombs would be a better way to go.
And you needed a whole forest of them because at the best you may have some rounds with an early version of a proximity fuse, but you mostly had dumb rounds so you had to lay a thick flak cloud at the far end of the range, or close in actually hit the target. Those ships made during late WW2 that stayed in service the next three decades, when they got their upgrades in the 50s and early 60s they got more of their guns removed, to be replaced by rocket/missile launchers and helo pads. Naval architects all over the world, East and West, went for the reduction in gun firepower as the technology progressed, too, so it’s not like someone’s biding his time before ravaging the seas with his mighty fleet of Cleveland-class cruisers.
Just a quick note. …
The 5" gun on the front of a WWII destroyer fired a couple rounds per minute and they landed withing a couple hundred yards of where aimed.
The 5" gun on a new destroyer looks the same to noobs like us. It fires 40 rounds a minute and they all hit within a handful of yards of where aimed.
And the improved aiming systems means we’re now aiming at where the target really is, not where the old ratty systems approximated it to be.
Net, net, there’s a lot more combat effectiveness is something that looks from a distance very much like its thoroughly antique 75 year-old predecessor.