Presented as another entry in the JackPoint website/blog, and tagged with the warning to beware of icebergs, here is an eclectic discussion of all manner of things in and under the water.
First up, a discourse on The Reality of Sea Travel. Whilst people and goods are often transported by air, the sea is still used extensively, particularly for the transportation of bulky goods and for recreational purposes. The vessels used have developed, and submarines are no longer merely military playthings but used commercially, but sea traffic is by and large unchanged in its general nature.One thing to bear in mind is that watercraft can be leading, if not bleeding, edge or they can be archaic... and that these tech levels can combine in a single craft - consider a sailboat with the latest navigational and communications gear, for example.
This leads on to the real meat of the work: a catalogue of vessels that your 'Runners might encounter, even wish to acquire, when their activities take them to sea. First up, the Suzuki Watersport, a jetski. It's easy to imagine waterborne 'Runners scooting around on these, mounting inshore attacks or making good a watery escape... or even cavorting on a day off. As well as a nice image and game statistics, each craft's entry is accompanied by atmospheric comments about their use and abuse, adding to the alternate reality of the setting. Other craft follow thick and fast. The GMC Wavecutter, another small pleasure craft. The Mitsubishi Water Home, for vacations or even a mobile hideout. A classic - if updated - speedboat, the Zemlya-Poltava Swordsman. Several more such 'light raider' type craft follow, so you can have some variety in your next waterborne chase scene, rather than be limited to everyone operating identical craft because that's all that you have details for!
Then under the water with a recreational minisub (I want one!) and larger submersibles designed for transportation and other uses. They're said to be popular with pirates too, an interesting and plausible development from the classic anti-shipping submarine warfare of the mid- to late-20th century. For those who like their leisure to be relaxing, there are some sailboats as well as luxury cruisers (with a note that scantily-clad members of the fairer sex do not come as standard, whatever you might think from the advertisments!).
It's not all small craft, though. There is a cruise ship - perhaps that next bodyguard (or extraction) job might involve accompanying your principal as he enjoys a cruise. Surface and submarine freighters and even a frigate too, even if that is more likely to belong to port security (be it governmental or corporate). More exotic things like an amphibious 'diver transport' and several drone craft designed for underwater inspection and repair, which are easily repurposed to more nefarious uses. There is only one thing you can do with a torpedo or an anti-ship missile, but if that's what you want to do, these are in here as well.
If you ever suspect that your 'Runs will involve water, this is worth a look at. Even without the assorted commentary to provide ideas, just reading through the various vessels spawns plenty of ideas, and the commentary embeds each craft firmly into the Shadowrun setting.