Is a polymer base coating, developed to reduce aerodynamic drag, applicable for use on the hulls of submarines?
In 1983, a fluorocarbon-base liquid, developed by Fluorocarbon Technologies Inc., was sprayed on the aerodynamic surfaces of the Hawker Sea Fury and the F-51 Mustang aircraft competing in the National Air Races in Nevada. The Sea Fury’s maximum airspeed was increased 25 mph over its normal maximum speed of 320 mph. The Mustang’s airspeed improved 11 mph from a top speed of 383 mph. The Sea Fury set a new course record as did the Mustang, but the Mustang also won the Gold Unlimited prize. The drag reduction noted in these aircraft was substantial.
The coating used on these aircraft was essentially hydrophobic and resistant to foreign debris attachment. And, the sub-surface penetration of the fluorocarbon material significantly prevented corrosion and oxidation.
A next step, using this polymer paint on marine craft, then followed. A wide variety of power and sailing craft were coated below their waterlines. Their drag reduction was even more dramatic. A Bristol 42 Trawler got an increase of 2 knots of speed over the trawler’s normal speed of 8.5 knots at 1200 rpm. A Hatteras 47 reduced its normal fuel consumption by 9J during a 7000 n.m. cruise. And, a one-ton yacht increased its powered speed from 6.1 to 6.7 knots over a measured course.
Several smallcraft were observed for their marine growth. The yacht JUVENTUS, a Gulfstar 50, was in the water for 27 months without appreciable fouling and this included no barnacle growth. Other yachts, so coated, were rapidly cleaned on their marine railways by merely a hosing down. It was thus evident that the anti-fouling qualities of this paint were good, while there was a minimum loss of coating over a period of more than a year, resulting in no appreciable increase in fuel consumption.
Several types of metal-hulled craft showed a good anti-corrosion effect. Coated stainless steel, cold roll steel, aluminum and copper all proved corrosion free in a 4 week test of this coating.
When its applicability to submarines was questioned, an attempt was made to acquire towingtank drag resistance empirical data on coated models. However, no U.S. tanks appeared willing to conduct such tests. They feared that the antifouling nature of such paints would be likely to foul the water of their test tanks — just like the environmentalists who protest the use of toxic marine paints. Hence, eventually, a towing tank was found which would conduct tests on fluorocarbon impregnated surfaces — at the University of Canton in the People’s Republic of China. Tests were made on a flat plate, towed submerged. The plate was bare metal in the initial test runs and then it was coated with the fluorocarbon paint.
The data taken showed the polymer-coated 2-meter plate to have its drag reduced by about lO.BJ at a towing speed of about 4 knots. A 2-meter merchant hull shape was also towed in the Canton tank. Initial test runs were with this small hull covered with a commercial polyurethane type or anti-fouling paint. Then, with the fluorocarbon paint sprayed on top of the standard paint, the runs were repeated. Of interest is the fact that this polymer paint is about half the cost per gallon or the commercial paints in use — at about $80. The results were even more startling. At a towing speed of about 4 knots (about the maximum for the Canton tank) the reduction in drag for the combined paint job approached 25J. This reduction is achieved relative to a normal “rough” antifouling covering — and justifies the 25J reductions in fuel comsumption observed in other tests.
At the completion or the tests, the Chinese Navy was so impressed by the results that they initiated a program for the hull painting of their new-construction “Sub Chasers,” the equivalent of our small DEs. The Chinese have also programmed for the painting or one of their Whiskey submarines — the polymer paint to be applied over a standard zinc chromate type of preservative coating.
A few more characteristics of this polymer paint — in order to understand the paint’s practicSlity — are: it can be applied at as lgw as -60 F ~d has a thermal envelope or -100 F through 750 F; it is a very slick type of lubricant; it is non-flammable; it doesn’t tend to wash orr; it makes a very hard coating, resistant to abrasion; it is non-toxic; there is no noticeable leaching over a long period of time and hence the danger or this coating polluting harbor waters is minimal; the polymer liquid mechanically bonds to and penetrates treated surfaces; and fluorocarbons are chemically benign.
But what does not show up in tests so far, is the probability that, in reducing drag, it would also significantly reduce the self-noise of a submarine — so important to passive detection.