submarine yacht - what would you do with it - well you would enjoy yachting - it will not be for everyone ... to give you a clearer answer here is the difference in a yachting day between submarine and surface boat.
First event of the day both the subber and the sailor row out to anchor place in a dinghi and board their vessels - the yacht is full of bird shit so the sailor starts with cleaning his deck - the deck of the subber is clean as the waves do this job. The yachty also has to perform a couple of repair jobs in mast, sails, lines due to UV light, wind, etc... Finally both open their hatches - the yachty gets a blast of 60 degree celsius hot air - stinky - product of heating of the teak deck from sunshine. The subber gets fresh cool air - product of a hull cooled by surrounding sea water. So the yachty stays on deck to wait for air circulation trough the hatches to make the interior of his ship bearable. The subber goes down trough the hatch in his "blue saloon" light comes in trough the viewports which with 50 cm diameter are bigger than windows you would find on a standard yacht so interior gets more light than you would have in the belly of a sailing yacht, as light goes trough water before it reaches the interior of the sub the effect is like in famous "gruta azul" in italia.
The yachtman may find things under deck a bit shaken, everything - on the floor, liquids spilled around, product of the last storm the yacht suffered on anchor place. The subber will find anything on its place even if things was not properly stored away at end of last trip. This is because the sub did not move in waves and if there are any movements they are very gently almost imperceptible.
Both vessels will leave anchorplace for a trip. While the yachtman has to store anything away before he passes the breakwater the subber leaves the coffee cup on the table even in rough weather. He will open a valve and take some 300 liter of water into the ballast tank so the water will cover the hatch and only thing above surface is a pair of snorkels. In this condition the boat runs with diesel engine. In a sailing yacht the noise level under deck when diesel is running may be very loud. Sound dampening is most of all a product of the weight of the walls - bad news for sailing yachts where the walls are made of light and thin material. - the subber is separated from the engine by a heavy concrete wall of 10cm so noise factor is much better. The sailor will enjoy sun, rain, wind, nature, the subber will get a view of the underwater world see fish. He might stop the diesel and close the snorkels to take up a few liter more of ballast water to dive down to the seaflor installing the boat a meter or two above the bottom in a neutral trim so currents will give a free underwater voyage making seafloor slowly pass in front of the viewports. You can stay down for hours without using battery power. At the end of the day the sailor will head for a secure port or anchor site running trough bad weather to make it before nightfall, risking his boat, depending on exact navigation. The subber will simply go asleep where he is - a save port is anywhere - just go to snorkel depth or lay the sub on sea floor during a quiet night sleep. After trip the clear up the ship is much easier on a sub- just close hatch drop anchor - ready - no spray hood, no storing away - a sailing yacht always must be prepared to stand the worst possible weather condition - alone on anchorplace - for a sub even on anchorplace weather is meaningless. ( concretesubmarine.com )
Cheers, Wl