The April, 1986 issue of the SUBMARINE REVIEW carried an important article “The Submarine Tanker.” The article sets the stage for what, hopefully, will be a serious and continued dialogue on this subject in the REVIEW.
Since the 1956-1970 time period, during which the General Dynamics work referred to by Pisces was going on, there have been occasional papers dealing with the commercial petroleum cargo capabilities of such submarines. Not mentioned in the Pisces article, however, was a 1980 GD conceptual design study for an Arctic liquifie~ natural gas (LNG) submarine tanker or 140,000 m cargo capacity. This is equivalent to 58,000 deadweight tons of the liquid gas cargo — carried in six cryogenic tanks. The 12-knot non-nuclear version or this LNG submarine tanker would have a displacement of aqa,ooo tons. The ratio, thus, between payload and displacement would be 1:14.4. In a nuclear propelled 15 knot version, the ratio for a 59,000 dwt LNG tanker would be 1:11.9 . But neither seem practical for making money, since they must compete in the BTU market with other carriers or more cost effective fuels — like oil, gasoline, naptha, methanol. Moreover the LNG submarine tanker would have little or no naval utility carrying this specialized fuel in cryogenic tanks. Figure 1 shows the GD steam turbine powered LNG submarine tanker design, which would use liquid oxygen (LOX) for the oxidizer and LNG boiloff for the fuel in a steam boiler plant.
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There have been other designs developed for submarine tankers. They are readily available to the serious student of the art of the submarine tanker. This means that one can readily learn a good deal more about the subject without the strictures of classification. In the April, 1986 issue of the SUBMARINE REVIEW the Editor makes note as to the matter of secrecy inhibiting innovation in the submarine technology field. However. in the submarine tanker field there is a significant amount of open literature. But none of the work has been sponsored by the Navy.
Work on LNG submarine tankers by the Maritime Administration moreover is now facing extinction due to Gramm-Rudman. Under this condition it becomes increasingly important for the Navy to “pick up the baton” of the submarine technology effort in the United States.
In 1974, MarAd sponsored a study of Arctic crude oil submarine transportation systems. The form of propulsion power was specified by MarAd as a 120,000 hp Consolidated Nuclear Steam Generator, driving steam turbines — the naval architectural design of the submarine thus conforming to this surface ship type nuclear power plant. The steam generator design required a 65-foot tall cylindrical pressure containment vessel with hemispherical heads. This necessitated that the engine room portion of the submarine be housed in horizontal cylindrical pressure hull of 85 outsidediameter.Thataccountsforthe substantialhulldiametersectionshown amidships, in Figure 2. With 120,000 hp, the 278,000 dwt submarine would be capable of 20 knots.
The dwt payload to displacement ratio is only 5 –which is quite good. However, the central pressure hull, in being sized to accommo-date the surface ship type of reactor, skewed the economics of the system by as much as 30%, from .
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At the conclusion of that study, an extension of the study to carry out a redesign of the submarine tanker was proposed. A redesign was looked at based on two loop-type nuclear reactors, housed in the port and starboard pressure hulls. This would eliminate the necessity for a central large diameter pressure hull section. The twin reactor arrangement would also provide backup power for a worst-case scenario of a single reactor breakdown under the Arctic icecap.
In 1982, the Department of Energy sponsored a study of a fuel cell propelled submarine tanker system. This study was performed by Arctic Enterprises Inc. . The study was based on carrying Prudhoe Bay natural gas energy in the form of methanol. The presently reinjected solution natural gas, which is produced along with the oil, would be made into 450,000 barrels per day of methanol, to be carried to the U.S. East Coast via an Arctic Ocean route under the icecap, in six 165,000 dwt submarine tankers. This submarine tanker design was also capable of carrying crude oil. When carrying 165,000 dwt of methanol it would displace 262,000 tons. This configuration was based on liquid oxygen and methanol fuel, fuel cell power and twin screw electric drive. The ratio would be 1:1.59. See Figure 3. At 165,000 dwt the percent of potential cargo weight allocated to liquid oxygen is 1.7J, to the methanol used in propulsion 2.1J and to the tankage required for these two consumables another o.BJ — only 4.6% of the deadweight tonnage.
The rationale for the use of the fuel cell propulsion is persuasive. The 20 Megawatt power plant of this design consists of four 5 MG modules providing suitable backup capability. Compared to the roughly 33J conversion efficiency of a steam turbine system, the phosphoric acid fuel cell power plant on methanol and liquid oxygen has a conversion efficiency of 55%.
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More recent work on molten carbonate fuel cells using diesel fuel could raise the conversion efficiency to 65J or more. It is the electro-chemical nature or this direct energy conversion which outclasses the heat engines which are inherently Carnot Cycle-limited in their energy conversion.
The needs or the Navy tor inoreased survivability or its fuel oil tankers, the fleet resupply or aviation gas to carriers, and the prepositioning or fuels. strongly suggests the use of tanker systems that are not visible on the ocean surface by surveillance satellites. Carrier task force underway replenishment with probe and drogue fuel transfer systems was alluded to in the Pisces paper. However it was indicated that the perennial Navy “limited budget” was used as the turndown reason in the early 1970s. This is still the condition today, 15 years later, even though the threat to naval surface tankers has dramatically increased in the intervening years — as ocean surveillance has improved and anti-shipping submarine fleets have grown.
The naval logistic fuel support submarine tanker need not be nuclear propelled. Fuel cell technology has advanced in the last 15 years. The cargo deadweight fraction which needs to be devoted to fuel, onboard oxydizer and tankage is entirely reasonable. The argument that fuel cell propelled Navy submarine tankers would somehow be charged against a budget assigned to “a 100 submarine nuclear powered fleet” is a non sequitur .
Navy evaluation of the fuel oell propelled submarine tanker for carrier task force jet fuel underway replenishment is timely. Many of the SUBMARINE REVIEW’s readers no doubt still oonsider the surface fleet as rivals. Here is one case where the submarine-surface fleet relationship can be strengthened and become complementary. There is more to submarining than just SSN and SSBN operations.