Gerrard:

Taking two of the strong healing potions and one of the water breathing ones, Gerrard says, "Many thanks, these will help greatly."  Pulling out his insulated swim shirt from his magical bag of holding, he asks, "Do you have any insulated clothing like this that might help my companions?"

He also asks, "Do you have anything that will shed light a fair distance underwater?  I expect it to be dark, and the options I have are short distance only."

As he waits for the others to get ready (and finish the long rest), Gerrard asks about the diving suit and the line, thinking that perhaps they should at least take it down with them so it could be used as a way to get pulled up if things go sideways.  He arranges with Korrin a simple system of strong pulls in a pattern that will transmit simple requests, like "more slack/deeper", "hold position", and "less slack/shallower".

"There is a strong arcane light attached to the diving bell," replies Korrin, "but it is not removable from the bell, which is tethered to the ship. The bell is also equipped with a powerful harpoon, but it is loaded with only a single projectile. This ship, of course, can defend itself should danger approach here." 

"You can communicate with the ship through the speaking tube, as long as you remain in the bell. There is no diving suit. The bell is dry, seats two people. Should you flood the bell or attempt to leave the bell, communication will end, as will your air supply."

"Should the bell become tangled or compromised, it can be easily jettisoned from either end."

"The cold is intense, and unnatural. Warm clothes do not seem to help. And the water is deep - some 300 feet here."

Kellen

An involuntary shiver runs through Kellen as Korrin talks about the unnatural cold. He thinks for a moment, then snaps his fingers. Give me an hour...ish. I have an idea.

Kellen goes back to his cabin, returning with a dingy looking spellbook that was a little dog eared and frayed. He thumbs to a page, and lays it down, slowly performing a series of complicated hand motions and muttering unintelligible words under his breath. After an hour or so, he gets up and looks over the side of the boat. An octopus is floating at the surface, tentacles undulating as it bobbed in the water. There, we can use him. I summoned him from the Fey, and he'll be able to see and breathe down there and shouldn't be too bothered by the cold. I'll be able to see and hear through him as well...as long as he doesn't get too far away, anyway. Kellen shrugs. At least, I'm pretty sure I can. I don't do this too much...these things are a little too smart for my liking. Kinda creepy.

Another hour passes as you continue to prepare for whatever lies ahead. Kellen's new octopus friend surfaces momentarily outside your small porthole. 

(Would you like to rest, eat, and prepare a little longer so that everyone may benefit from a Long Rest?)

(There are four greater healing and two water breathing potions unclaimed. Who wants which?)

(Presuming you intend to descend soon, how else do you want to prepare? And how do you intend on descending? Does anyone plan to descend via the diving bell?)

(Yes to the long rest.  Gerrard also plunges his head into some water to see if he can breathe water still, or if his strange condition does not confer that benefit.  He does not plan to be inside the diving bell).

Kellen

Kellen grabs one of the potions of healing for his bag, and peers into the diving bell. I can see what the creature sees from in here...how safe is it again?

You continue to take your time in rest and quiet preparation. The sun rises in a mostly clear sky – an unusual, and somewhat unnerving sight. Everyone may receive the benefits of a Long Rest. It is becoming mid-morning. (There are three greater healing and two water-breathing potions unclaimed. Any more takers?)

Ever refilling his bucket, Gerrard lowers his face into it and tries to breathe it in. He finds it extremely frustrating, as he can remember the comfortable feeling of water filling his lungs, but he cannot seem to be able to extract what he needs from it. He longs to be back in the ocean. For now, he cannot breathe water. Yet.

Kellen examines the diving bell, affixed to the stern of the vessel. It has a large coil of double cable – evidently a tether and breathing/communication tube – together with a hand-operated air pump bolted to the ship's deck. The interior is simple and comfort-free. Two metal seats, a small porthole, and the mechanism for aiming and firing a barbed harpoon affixed somewhere underneath. It has very limited navigation or maneuverability – just some very simple hand-cranked propellers to turn or slightly adjust the position of the bell. There is a hatch that can be opened underwater by first flooding the bell, but there is no airlock. It looks very cramped and uncomfortable, but well engineered.

"Oh it's safe," explains Korrin. "But that didn't stop the last diver from vanishing down there. She left the bell and did not return. Her remains came to the surface some hours later, riddled with knife wounds and frostbite."

Gerrard:

”Right, we should get going,” says Gerrard, quaffing one of the water breathing potions.  “I can hold onto any potions you guys don’t want to carry,” he adds, taking the remainder of the potions once Kellen and Kei have had their chance.

”Master Kellen, Master Kei, are we ready to proceed?” he asks.  Turning to Korrin, he adds, “Remember the codes we worked on.  They will be important if we lose communication through the diving bell.”

Kei 

Hmmm. Very generous of our benefactor. He keeps his snarky comment to himself as he gathers 2 healing and one water breathing potions. "Thanks" he says bluntly as he stashes them away in his pack.

"We won't get any more rested than now, so may as well go for it. I'll ride down in the bell." With that statement he heads to the contraption; "How do we get into this thing?"

Kellen

Mildly disturbed that the others weren't disturbed by the phrases "riddled with knife wounds and frostbite", Kellen shakes his head and climbs into the bell. Just get in here and sit down...you'll need to man the harpoon. I'll be otherwise indisposed. Kellen closes his eyes and relaxes on the hard metal, telepathically moving his senses over to the octopus.

Gerrard:

"That puts me as outside-the-bell guide," says Gerrard, eyeing the cramped confines of the bell and the lack of a third seat.  Making sure his insulated swim shirt is secure under his Mariner's Armor, he waits to climb on top of the bell and hold onto the tether once the other two are securely ensconced within. 

'Ready when you guys are," he says, missing Boko, Peri, and Thwack.

Kei and Kellen climb into the cramped bell. It feels gloomy and suffocating, like a coffin built for two. The narrow porthole looks out into murky water, revealing little. The controls are limited, and simple. Korrin closes the hatch above you.

Captain Edrik steps out onto the deck to wish you well. Kei and Kellen can hear his tinny, distant voice echoing through the speaking tube. "Be careful down there. We'll be ready here for whatever you might scare out of that wreck."

Lowering himself into the relaxing embrace of the cold, salty ocean, Gerrard can see little below him. But oh, the sea feels good. Two schools of glittering fish swarm the waters nearby.

Kellen's octopus, scouting ahead, begins to make out the scene some 300 feet below:

The rotting skeleton of a war galley’s stern looms up from the dark, nearly colorless ocean bottom, devoid of vegetation. The sinking ship evidently broke in half during its descent, its bow section gone missing but its stern plunged backward into the seafloor like a spike. The sandy bed around the wreckage is scattered with partially buried bones and debris. 

Once you're ready, Korrin detaches the diving bell and begins to lower it with a small winch bolted to the deck of the Gloom’s Wake...

Gerrard:

Holding onto the line with one hand and standing on the diving bell, Gerrard draws his rapier as they submerge, using its light to illuminate their way.

You feel the cold shortly after dropping below the surface. It feels as though a giant door has opened: an icy draft passes right through you in a single wave, affecting Gerrard in the water and Kei and Kellen in the bell indiscriminately. Kellen's octopus freezes solid and sinks, lifelessly, into the gloom. 

Everyone:
• Make a DC 16 Constitution saving throw, taking 20 cold damage on a failed save, or half as much damage on a successful one.
• Also everyone:  Make a DC 16 Charisma saving throw. 

Gerrard:

As he feels the icy cold wash over him, Gerrard is surprised that the ocean around him isn’t frozen solid.  Just something else he doesn’t understand about magic, it would seem.

Constitution Save:  24

Charisma Save:  21

Kellen

Losing his contact with the octopus, Kellen sits up suddenly, and then feels the cold seeping through the walls of the bell.

Con save: 17

Charisma save: 19

What the hell is making it so cold down here? 

Kei 

"Well this thing offers little protection" complains Kei of the diving bell as the cold tears through him.

CON save 14

CHA save 16

The bell stops just feet from the bottom. Its light shines weakly through the cold sea onto the wreck, surrounded by bleached bones and debris. The schools of fish that swarmed in the waters above are conspicuously absent. Everything here is dead.

Numerous breaches in the hull and openings on the rowing decks appear to allow entry into the ruined ship. Alternatively, one could swim down into the stern’s interior from the top of the ship, where the bow is missing. With some maneuvering, the bell might fit through the latter as well, although you would have to take care to avoid getting tangled. (Kellen has some proficiency in maneuvering watercraft, although he has never piloted anything underwater before...)

Gerrard:

Swimming around to the viewport, Gerrard mimes an offer to help guide the diving bell into the large hole for further descent.

The bell can be rotated and made to perform small lateral movements mechanically using controls inside. For larger lateral movements, as would be required to drop the bell into the cavity formed by the missing bow of the wreck, coordination may be performed with the ship above, using the speaking tube. Having an outside diver like Gerrard to guide the bell would certainly help. It's not a large wreck, leaving little room for error in fitting the bell inside.

The site remains unnaturally cold, completely devoid of life, and perfectly still.