Maniakes Rafts

Kardian Strategoi Bardas Maniakes once had a problem. The senate had given him an army, a couple cannons, and told him to go take the city of Potomas back from filthy barbarians. For any other city, this would be no problem. Set up the cannons after breakfast, pound down the gate, have lunch at the cute cafe by the city hall. But this city, Potomas, was named for the fact that it sat on an island in the middle of a river that was just wide enough that cannon fire was usually spent by the time it reached the walls. Nobody was quite certain how the barbarians had seized the city in the last war,some fifty years ago. But, here they were, and Maniakes wasn't allowed home until he had liberated Potomas once and for all.
So what was a homesick strategoi to do? Bring the cannons closer of course. "Requisitioning" some pleasure barges and their accompanying waterpigsfrom local estates, Maniakes loaded them with cannons and set sail for the city. At eight in the morning, just after breakfast, the cannons opened fire.
The results were... mixed. The defenders, taken aback by the sheer ludicrousness of the display, could do nothing as modern weaponry ripped through centuries old stonework. A single volley was all it took to bring down a vast section of wall. But, the waterpigs who had found themselves suddenly drafted the day before were just as surprised. Twenty cannons and their crews were dumped in the current as panic took the poor animals. Maniakes still managed to get his landing force across, but without artillery support, they missed their lunch reservations and had to settle for dinner at the hip new restaurant.
Though disappointed with the portion size, the idea of waterborne artillery stuck with Maniakes and he spent the next decade tinkering with the idea. When Laerug tried to invade, Maniakes' fleet was ready. He sailed it right up the Krag River and blew apart the walls of Lumbale. He might have gone all the way to the capital too, if the Laerug hadn't unveiled their own fleet. Turns out, observers had seen his stunt at Potomas and seen its potential as well. What followed was the first ever hippopotamus-drawn-raft-mounted cannon duel. Maniakes managed to once more squeeze out a victory, but he'd taken heavy losses. A peace treaty was signed before he was given a chance to innovate further.
But Maniakes had already achieved immortality. Not only as an inspired national hero, but his design for the rafts became standardized and as more and more nations adopted the siege engine, his name was invariably attached. No army these days is willing to march without a fleet of maniakes covering their riverside.

Propulsion

Two specially trained waterpigs per raft.

Weapons & Armament

A cannon bored to fire twelve-pounders, mounted on a swivel.

Armor and defense

Excess powder is kept in an armored locker. Everything else onboard is encased in a thick composite made from luck and prayers.

Communication Tools & Systems

Long range communication is accomplished most quickly and reliably by semaphore, but some commanders prefer trumpets or bullhorns. A "runner" on the back of a race pig is another common option.

Additional & auxiliary systems

A barge carrying extra shot is often employed for longer engagements.

Nickname

Big Pig Rigs

Motto

"Thunder On The River"

Rarity

Just a fact of modern warfare at this point.

Speed

Depends on the pigs but averages about fifteen mph in calm waters.

Complement / Crew

2-3 cannoneers and 1 driver

Cargo & Passenger Capacity

Room for the crew to work, a keg of powder, and 20-30 twelve-pounders