This mod is an addon to Terrafirmacraft adds a few completely new items to aid in underwater exploration while trying to stay true to the feeling of that mod.

If you already played the newer versiosn of Terrafirma, you may notice that finding early game metals goes in mainly two ways:

You search the overworld for rare samples, and hope to get 10 or 20 to make a pickaxe and a saw or chisel;
You scour the riverbeds for ore deposits, which are much more common than the samples, but require you to constantly dive for a few seconds and come back up for air.

In order to make the second one more favorable, I decided to make a mod that allowed you to breathe underwater for just a bit longer, to scout for the deposits with more consistency. That ended up developing to this mod.

The first item you can build to help with underwater breathing is the Ceramic Blowpipe (used in TFC for glassblowing) by knapping and then firing it in a pit kiln. This item is not part of this mod, this mod just adds a new feature to it: holding it in your off hand while diving will allow you to dive in 2 blocks deep water while taking air from the surface.

All other items are made with brass or higher tiers of metals, and the helmets require the TFC glass lens to finish.

The Snorkel comes in brass, rose gold or sterling silver variants, and allows you to breathe up to 3 blocks deep, and frees your off-hand by being an helmet.

The Brass Diving Helmet is a much harder craft, but opens up the two last ways of breathing underwater:

By equipping it and holding a leather hose (made by knapping leather) on your off hand, you have the number of blocks you have of hose stack deep to explore in the water (up to 16/32 blocks). This hose tries to find air where it can, so even in underwater caves you can benefit from it! just make sure there is a pocket of air somewhere it can reach.
By equipping it and holding a Air tank in your off-hand, you have from 1 (with brass air tank) minute to up to 10 minutes (with blue/red steel air tanks) to breathe underwater. To refill the air tank, use it on a bellows (with the tank on your main hand /hotbar)