New Tanker Concept?

The new vessel will need to consist of two distinct parts: the "tractor" unit which is built strong enough to withstand the pressure differentials, and, the container unit which will be allowed to self pressure regulate, so, a standard dracone might do. Clearly you would need a simple but reliable way of controlling the buoyancy of the container unit. Making the two parts so that they can disengage could be an additional advantage. Making the container part in multiple sections may also score points for convenience and risk management.

This is a great idea but I see one problem. If he plans to ship oil, the density of oil is so much lighter than sea water that the ballast needed to make neutral would require massive steel, rocks or something to make it sink. I understand that large modern tankers the level of the oil inside is much higher than the waterline of the vessel. In a large vessel I bet the difference between fresh water and seawater densities would make it buoyant!

I can't think of any liquids that are shipped in large tankers that have a density higher than seawater (or close enough) to make them neutrally buoyant.

It may work for many solids, alumina, ore, coal, rocks, sand...

Looking for a good answer here!!

Frank Herbert wrote a novel called The Dragon in the Sea (aka Under Pressure) regarding this same concept. As a plot device, it seemed to work pretty well. In the real world, results may vary. Still, worth a read to see how he "solved" some of the technical problems.

You beat me to it. Good book, although I agree the engineering was glossed over. That's normal for good SF, though.

Commercial use eh? Well, one of the Columbian drug cartel tried it a few years back, in 2000. It seems they hired Russian submarine designers who were out of work who fabricated a 100 foot sub in a wareshouse about 7500 feet up in the Andes mountains. The plan was to truck the sections down the mountain on trucks and put them together; the nearest port was 210 miles away. The USDA said the sub could transport 200 tons of cocaine to a location off the coast of the US and be offloaded. An American had rented the warehouse and would not explain the sound of hammering and the hissing of torches that sometimes went around the clock. Several years earlier, the drug cartel had tried to purchase a Soviet submarine from corrupt Russian officials using a go-between in the US. I wonder how many have not been found. This may be the only commercial use of submarine that I've ever heard of, other than the tourist things.

They are still in use...http://edition.cnn.com/2008/CRIME/03/20/drug.subs/

"Although the vessels were once viewed as a quirky sideshow in the drug war, they are becoming faster, more seaworthy, and capable of carrying bigger loads of drugs than earlier models, according to those charged with catching them."

The article includes video from the U.S. Coast Guard intercepting a semi-submersible vessel.

I am unfortunately well aware of the cartels' use of semi-submersibles. Just last week we busted two with over 14 tons onboard. In fact, there is legislation before Congress right now about the use of SPSSs. But self-propelled semi-submersibles would not work for this concept, as they would still have the same problems with the ice that regular deep draft surface ships do. And this also raises another question: If commercial shipping (as well as the illegal drug trafficking) moved to full-submersibles, would the Coast Guard be forced to stand up a Subsurface fleet as well?

There are additional reasons why this could make sense, not just in an icebreaking environment. The Trieste, which went to the bottom of the Mariana's Trench, looked somewhat like a dirigible with an oil-filled envelope. The reason is that liquids compress only slightly with pressure. If the oil tanks of the submarine tanker were filled with oil to approximately 100%, then there would be far less compression on the container part of the hull. This means that the vessel could be built much more cheaply, and can have shapes besides cylinders like those used for conventional submarines, whose cargo require large amounts of open space. On a return trip, the tanks would need to be filled with seawater (this can be done by having a bladder from seawater inside the tank so that the two do not mix and so the seawater does not corrode the hull). In response to carrying oil underwater, there are some grades of oil that are heavier than water. However, many grades of oil are only slightly less dense than water, so all it would require is some seawater ballasting to sink the vessel. The tractor portion of the hull (also having the living spaces) would need reinforcement like conventional manned submarines to operate at the underwater pressures. At depth, the propeller does not cavitate as much as at the surface, and the propeller has higher efficiency. Provided the navigation and logistics for these could be figured out, these vessels could be much safer than surface tankers in that they avoid the long-period waves and issues with the hull being slammed by waves. The submarine aspect also gives the operators another degree of freedom to navigate and avoid collision while maneuvering in the open ocean. Grounding is certainly an issue, as well as pulling into port for dry-dock, and connecting with offshore oil stations. For this I propose that the tractor portion split off of the container portion for dry-docking, and the container portion is serviced at sea. Since vessels become more economically efficient as they get larger, and since these vessels are not limited as surface tankers are on the open ocean, they could be made to extreme dimensions.

A separate recent thread here concerned unmanned submersibles that used temperature differences (thermoclines) as a propellant force. Oil and wax were the heat transfer media. I suppose this would also affect an oil-filled "subarge", as would currents, and possibly even haloclines, but navigation techniques could likely compensate for all that.

Staying on course would be de rigeur, of course, to avoid grounding, noted iceberg positions, and counter-flow shipping. I don't see why deadheading back with seawater only as a ballast would be necessary, other goods could also be transported (although not as readily if not in liquid form).

I imagine the sausage shape is efficient enough for a subarge, although whales are only slightly similar, so some design tweaking might help. But the size could indeed be scandalously large.

This would be a very specific vessel. One of the major selling points for this being practical as a submarine is that the container portion could actually be optimized for much smaller pressure concentrations. The vessel could be so structurally light that it should not operate without a full liquid load or at the surface for any length of time. A vessel with large amounts of air in the container portion would be subjected to much higher static loading while submerged than a surface vessel, and would have many of the same limitations as a conventional submarine. Perhaps there is a product liquid that may be used on the return trip. I am envisioning a liquid being pumped into the bladder inside the tank, thus offloading the oil at the same rate. One benefit of this is that the entire vessel will not need to adjust ballast and can remain submerged with minimal stress on the hull while loading/offloading. Another drawback is that solid loads take much longer to onload/offload and would be difficult to store in a compartment which has liquid residue and "toxic gas" hazards associated with it.

All points made are granted, I'm not saying it wouldn't be more difficult, but sometimes it might be worth the effort. Suppose you have two (or more) layers of whatever the hull is made of. One layer is filled with crude or refined oil inside the other. When unloaded, it retracts to one end. The open space could be refilled with another liquid product, or maybe a slurry of mineral ore with water. Possibly even a flowable dry particulate cargo like wheat. That way the return trip would also be profitable. Limitations, sure, but maybe enough value to figure how to overcome them.