I'll just say this and get it over with before we start: cannons are scary. They make very loud noises and shoot very heavy projectiles that can do a lot of damage. If you don't know what you're doing or you're not careful or both they can hurt their operator pretty badly, too. And those are just the modern versions.
In the days of iron men and wooden ships and lit fuses next to black powder, things were even worse. Even on large frigates or men-of-war that had separate gun decks, working the big guns was not only hazardous but tight. Sometimes there was no more than 20 inches of space to support the recoil and guns were positioned as close together as two feet. Each gun needed at least a four man crew. Hot, sweaty, deafening and dangerous. Ah, the good old days.
On a pirate or privateer things were even tighter. The guns were smaller of course. Most pirate ships carried nothing larger than a ten or twelve pound gun while a navy ship of the line might carry thirty-twos (remember, the weight of the ball is what is being spoken of here; a ten pound gun could weigh upwards of a thousand pounds). The ships were smaller too, however. Sloops, schooners and brigs displacing no more than two to three hundred tons would quickly succumb to what was called "hogging" if too many guns of too large a size were place on her. A ship hogs when she begins to bow upward out of the water at her center known as the waist, her stern and bow bending down like the two ends of a banana. Once this happens the ship is ruined and ships are pretty dear, mate.
Even when things seemed relatively "normal" with regard to the great guns, there was always the potential for something to quite literally snap. Generally speaking guns were lashed down in place with what was known as gun tackle. These ropes kept the cannon, which were all by necessity on wheels, from ranging the deck like chickens. When in use, one large rope - the breeching rope - secured the cannon to the side of the ship to keep it from over reaching its allotted space during the angry recoil, one of the most precarious points in the firing process. A cannon that slipped or broke its breeching rope was said to "jump the track" where upon it became a "loose cannon". A thousand pounds of metal now free to roll with the pitch and yawl of a ship at sea while highly combustible black powder was on deck with lit slow match. One of the most unsafe of countless unsafe situations at sea.
The risk of crush injury or outright explosion was always eminent and more than one sailor over his grog ration has paid the price. Pirates in particular, who didn't ration their liquor, were wounded by their own cannon. Most pirate articles included payouts specifically to men injured and unable to continue a voyage. Some even had provisions for widows.
Mind your breeching ropes, Brethren. They should be in top form at all times. Just in case you need to work those great guns you'll want to stay on track. And then some.