Actually you can totally swim in plate. A suit of armor weighs about 50 or 60 pounds, which is less than the weight carried by a modern soldier. The reason why 18th century sailors didn't use it is because by the 18th century, gunpowder had rendered metal armor obsolete.
Similarly, climbing and running would barely be restricted, especially when you consider that the ones wearing the armor in the first place would train for it.
Neither are the plates unwieldy; you'd have full range of motion available to you.

This is clearly not an argument either of us are going to win...

I believe that properly made and fitted plate mail is rather mobile, but mass produced/secondhand make wouldn't fit proper and would limit mobility understandably- but even then, not too horribly negatively.

Plate mail is also, for the most part, capable of sustaining black powder rifle shots-- to the torso, at least. Not many, but one shot wouldn't penetrate fully. It'd crush the armor in and likely kill them anyway, but the armor could be fixed up good as new rather easily-

But this is neither here nor there xD

The Fated Fallen said
This is clearly not an argument either of us are going to win...

That's because it's already been won by history.

Also, phoenix, a single rifle shot wouldn't completely crush the armor. If it didn't penetrate, it would only leave a dent to some degree. It might crack a rib.

I use exaggerations often, sorry! I forget that tone is often lost through text ^~^

As long as we're talking about tech, an 18th century level of firearms technology and production would mean that full plate had been phased out, most swords and pole arms were gone; we'd passed the medieval combat you associate with sword and sorcery by literally centuries.

Most combat was done via rows of riflemen, firing in succession, then taking land by charging with their bayonets. Officers would receive cavalry, and there'd also be teams for cannons.

Also there's no reason to use magic with this level of gun technology. Why would you try and cast a weak fireball that might kill you when you could just shoot a gun that won't kill you?
Why would you bother using magic at all when it would probably kill you if you do anything wizards are normally useful for?

Whoops; disregard that last post. I was thinking of an entirely different game.

1) Nobody wore plate armour in the 18th century, you know what else happened in the 18th century? The American revolution. Saying sailors in the 18th century didn't wear plate armour is like saying "Humans don't have tails." 18th century is not medieval times at all, everybody used gunpowder
2) Nobody in plate armour trains to climb or swim. Knights often went on horseback or in heavy units where they wouldn't need to do either of those. The peasants would storm the walls while the knights stole the glory. That isn't any sort of contrived opinion that's what happened.
3) The plates are very unwieldy. You can't move anywhere near as freely as someone without. Even just the padding would make it really hard to swim (and yes they had significant padding that was very absorbent). Imagine fighting in a body fitting sleeping bag (as an extreme example). The reason this padding was there was to stop the plates from scraping skin off as the user moved.
4) Because the armour was so bulky training wasn't about climbing or swimming, training was about stamina and learning to fight in a fridge, not dance in one as you claim. Keeping up your strength in combat while realising how to use your armour as a second shield, not about providing yourself with mobility
5) You may consider this nit-picking, but saying 'Wouldn't slow you down at all' is an exaggeration in itself so don't complain at Phoenix. Any weight will slow you down to some extent
6) Saying magic is obselete when compared to a gun is foolish. Bear in mind it depends on what lore you are using but not all ideas of magic are weak fireballs, the reason gunpowder may still have ruled out magic is because it is easier to learn and thus can be mass deployed.
And not all lore follows that casting a spell can kill you, and muskets certainly can misfire disfiguring and blinding the user for life
Not to mention magic is not restricted to fireballs, there is also healing and protection, illusion. All warfare is based on deception

And you posted that last comment before I posted, so disregard some of my points I put if you want

I'm not saying it would be impossible to swim in plate, just you would be a rare man (or lady) indeed to be able to do it, and certainly not for any length of time

This is not an argument either of us will win. You have made your mind up long ago, as have I. Attempt to change either of our minds is futile and I have not the energy nor the will to proceed, I suggest you duck out of this one as well otherwise we'll hate each other to the end of time

Also a musket into the plate could still easily cause internal bleeding, something they couldn't treat very well in medieval times (just like everything in medieval times)

Also I am just spamming the chat message after message in a list of things people won't read

:)

It's only 50 or so pounds. Modern military forces train to swim with heavier weights on their back, instead of being distributed evenly. A man wearing armor can fight with dexterity equal to an unarmored foe.

For reference, this video has a clip showing a man sprinting in an accurate recreation of 15th century plate.
http://youtu.be/NqC_squo6X4?t=34m29s
Immediately afterwards, it shows a short video of two knights fighting on foot with polearms, further demonstrating the speed and mobility available.

The Fated Fallen said
This is not an argument either of us will win. You have made your mind up long ago, as have I. Attempt to change either of our minds is futile and I have not the energy nor the will to proceed, I suggest you duck out of this one as well otherwise we'll hate each other to the end of time

An inability to agree does not mean an answer does not exist.

I never disputed them being able to run, not at the same speed but still able to happily run. You could tell, however, that he still doesn't run entirely normally, but that is not the dispute I am making

Ever seen an un-armoured person fight? The knights there were not as dexterous, most obviously you saw him stumble as he was hit, and he was slow to turn back. When at the very start one of them strikes fully with his poleaxe it takes him a good second to wind back to ready.
Notice their large, exaggerated movements? That is not a normal fighting style. Their fighting style is based on the idea of counter attacking, because without their deftness they are unable to quickly respond by jumping back into a guard, as they would most likely lose balance on the uneven terrain and fall over due to the extra weight. As both combatants realise this it becomes much more intimate, relying on grapples to bait their opponent out into an attack, over extending and countering. This last point about grappling however could be attributed to their use of long weapons as well, but no historian worth their salt believes a single factor is important above all others

I can attest to what incrediblebee States, in the army I have been made to swim with most of my battle gear on, I've tread water without using my arms and dived to the bottom and resurfaced. It's damn difficult, but definitely possible.

(Bloody hell here come the number points again. I really don't like doing this you know guys...)
Vietmyke;
1) Humans today are both taller and stronger than humans back then. Both things that can really help with swimming
2) Back then I still believe it would be a rare person indeed who can swim in plate. As for keep themselves afloat was probably quite possible... for a while. But between the exertion needed, the far slower speed due to lack of manoeuvrability and the padding slowly getting soaked and heavier (which there was a lot of as I keep moaning on about) there is no way they could maintain it for any period of time more than 10 minutes, 20 at best.

Summarised:
Humans today are stronger and taller, better at swimming
Even if they could swim for a little bit back then, they couldn't maintain it for all that long. Want to swim through a river in plate being a medieval person fine, but get knocked into the sea you are as good as dead unless there are others to immediately help you.

Swimming perfectly fine in plate is a misguided opinion, because you aren't just going around in metal and it is very awkward to move in (despite what our good friend IncredibleBee attests to)

Even if you believe that you would have freedom of movement in a suit of plate, it is far from the perfect shape to be swimming in, the human body is quite aqua-dynamic, armour is not

I think, for the sake of balance, we should say plate is super heavy and restrictive. Of course, back then sheet metal was hyper expensive, but suprisingly mobile. William the Conker could somersault onto his horse in full armour, for example.
One idea is half-plate. Not as expensive, not as heavy, but not as protective.
But the last thing I want is to be stuck in a swordfight with some nob whose as agile and evasive in full armour as I am in a shirt and funny hat. Witchunters don't wear much physical armour, you know.

EDIT: I know the problem! Plate armour is fine, but because it was so expensive, in the 15th centurt people began to make "Munition" armour, which was cheap and protective, but bulky, unwieldly and heavy.
There needs to a distinction between "normal" plate armour and "munition" plate armour.

I preached a while back about stopping this argument while it was still in birth, I once again restate my case. There can be no winners in this argument, we have both made up our minds.

Can we move onto more fun things now?

Yeah. Like the magic system.