Every once in a while a weird little ship will catch my eye, and I have to tell you good people about it. , and today it’s the . There is a giant boom off the back of these ships that can lower an entire pressurized room to the bottom of a river. The room uses high air pressure to push all of the water out so a three-or-four person crew can hang out down there for a few hours. It’s mostly used to retrieve precious cargo from the bottom of the river without messy divers and cranes.

The crew can enter the arm while it is at the surface, wait for it to pressurize entirely, and lower the bell end of the boom to the bottom of the river – then the crew can simply walk down the stairs as millions of gallons of water flow over their heads. It’s a little bit like putting a drinking glass upside down into the dishwashing water and an air pocket sticks around in there. Nifty.

The Carl Straat has been in use since 1963, and as of 2021 Damen Shipyards had built the Archimedes to replace it. Both are truly wild machines. In the video below you can watch the crew track down and raise a lost ship anchor from the river bottom. According to the shipwrights that built her, the Archimedes has been used to do underwater maintenance, inspect the doors of transport locks, retrieve lost cargo, take river bottom samples, remove obstacles, and even uncover unexploded ordnance from World War II.

Most of the time these ships operate in waters around 13 to 25 feet deep, with a maximum depth of 32 feet. At these depths the crew don’t need to depressurize, as the ship really only requires one bar of pressure to keep the water out. That’s about 14.5 pounds per square inch, close to the maximum pressure humans can experience without experiencing adverse effects. The ‘divers’ don’t need a suit, but they might need to pop their ears and clear their sinuses. Regulations require that workers can’t spend more than three hours in the pressurized environment at a time, though.

Damen says the old Carl Straat is for sale if you wanted to sail it to Alaska for some coastal gold dredging operations. That might be a good move, as this would be the perfect ship for such a thing. Getting it there might prove prohibitively expensive, though.

If you’ve ever wanted to sleep on a river bed, this ship might actually be able to help you. Neat boat.