Background and Significance

Sea water has 4 times the heat capacity and 24 times the thermal conductivity of air. As a result, even evolutionarily adapted sea mammals lose heat 4.5 times faster in water than in air. That heat loss leads to hypothermia even more rapidly with human divers. After 1 hr in 10°C water, or ¼ hr in 5°C water, a diver’s core temperature would fall below 95°F (35.5°C) and the diver would enter hypothermia, leading to loss of consciousness, organ damage, and eventually death. While physical conditioning can buy extra time underwater, it cannot fully compensate for the heat loss.

To mitigate the hypothermia hazard, thermal protection is required. Thermal protection is typically provided by a wetsuit. The wetsuit is stitched and/or glued together from tailored pieces of a 3-8 mm bubbled neoprene layer sandwiched between two 0.2 mm layers of cloth. The microscopic air bubbles in the neoprene make it flexible and thermally resistive, as air is a good thermal insulator. In 5°C water, a 3 mm neoprene suit would extend the time to hypothermia from 15 min to 1 hr, while a 5 mm suit would extend it to 1.5 hr.

Thicker suits offer more thermal protection but are less flexible. That makes movement more difficult and fatigues the diver faster. As a result, the thickest single suit on the market is 8 mm, while US Navy divers typically use 7/6 mm neoprene suits (7 mm chest, 6 mm limbs) as a compromise between protection and ergonomics.

Thicker neoprene is also more positively buoyant, which requires divers to add more ballast to compensate for it. This also means larger differences between the ballast needed at the surface and at depth. To illustrate, a 3 mm wetsuit needs 2 kg ballast at the surface and 1 kg at depth, while a 7 mm wetsuit needs 6 kg ballast at the surface and 2 kg at depth. This difference is typically dealt with using a BCD (buoyancy control device). However, the BCD taxes the attention of the diver to adjust manually and continually through the dive, thus distracting him from his primary tasks. The BCD also requires some expenditure in breathing gas, which shortens the available diving time. Overall, thicker neoprene suits incur significant loss of ergonomics compared to thinner suits.

A further problem of the neoprene suits is that the air bubbles providing the thermal protection shrink with depth as the ambient pressure increases, thereby degrading the thermal protection offered by the neoprene suit. Lab tests have shown that 8 mm neoprene from a top-of-the-line commercial suit loses ~50% thermal insulance at 30 msw (meters of seawater), compared to sea level.

Hence, there is much opportunity for improvement in terms of both ergonomics and thermal protection with depth.

The practical significance of such improvements is very large, since they would affect a very large number of divers across the world. Many of them are recreational divers, some are professional and commercial divers, and there is also a community of military divers as well. The diver suit market is a billion-dollar market worldwide, so the potential for making a great difference in the world is very large as well.

Specifically in naval operations, divers are used for routine ship maintenance, for reconnaissance, for EOD (explosive and ordnance disposal), and for special forces missions. Ship maintenance in particular often involves long stretches of continuous work in cold water (e.g. up to 9 hours), so thermal protection is a critical capability. Improving the thermal protection without sacrificing ergonomics can significantly extend the persistence time of naval divers in adverse conditions as well as allow more effective use of repair time. For example, better thermal protection would decrease the share of time needed for reheating the divers, e.g. by hot-water hosing from the surface, while improving the effectiveness of diver repairmen, and thus potentially shortening the overall repair time for the ship. In addition, improving diver suit ergonomics would decrease fatigue in the divers and extend the amount of time they can work on their mission without rest.  

Overall, both the military and civilian potential for benefits from thermal and ergonomic improvements of diver suits is very high and has motivated us to build and test our suits.