Chocobar Suits

The experience of the K1 and K2 suits taught us that the fundamental idea of the segmented composite suit was valid, beneficial, and ultimately superior to the neoprene equivalents, especially in depth, and in both thermal and ergonomic aspects. However, the same experience also clearly indicated that additional factors, such as fit quality, sealing quality, and ease of manufacture could be just as influential on the overall performance of these suits. We therefore set out to resolve these issues as best as possible.

While custom building of the suit by 3D scanning of the specific diver was likely to produce the best fit and the best performance (all other things being equal), it was also true that such manufacture was complex and expensive. The point example was the high performance of the K1 suit fitted to the K1 diver, while the K2 diver using K1’s molds had to do a lot of compromising in the fitting, to avoid having to repeat the whole process.

To solve this issue, we focused on improving the manufacturing process. The set goal was to achieve a standardized procedure involving non-unique building blocks, which would simplify, streamline, and cheapen the fabrication process, allowing for quick rebuilding of suits while also offering sufficient good fitting.

Consequently, we came up with the idea that a universal build would require some variable radius of curvature for a plate. With such variable radius, the same composite piece could be fitted to different parts of the body having different radii of curvature. The trick was then to have some form of a tooth or cogwheel design, wherein the individual teeth could be positioned differently but as part of the same thin base that would be far easier to bend than a monolithic plate of the same total thickness. The result was a plate which in appearance resembled the striations of a chocolate bar. Hence, we called the resulting technique the “Chocobar”. The figure below shows a chocobar in sideview and in two different configurations (fully open and fully closed).

To determine the specifics of the Chocobar geometry, we had to set the geometric parameters in such a way that the base was relatively thin, e.g. around 3mm, while the height of the teeth, their spacing, and their top width would have to be such as to produce a desired radius of curvature.

To determine this radius, we took measurements of the radius of curvature of various body parts and at various locations on the human body. The resulting dataset was organized in a histogram shown on the figure above. Critically, the histogram indicated that the resulting distribution had two peaks. This meant that there were just two preferred radii, which meant that all possibilities on the human body could be covered reasonably well by preparing molds corresponding to just two radii of curvature. Basically, the smaller radius would correspond to Chocobar segments needed for the limbs, while the larger radius would correspond to the Chocobar segments needed for the flat parts such as the abdomen. Essentially, the segments could be bent as needed to fit the curvature of the body part and then trimmed along the edges to fit the area.

With the geometric parameters dialed to fit those two radii of curvature, sets of molds were designed and 3D printed in polycarbonate. The figure below shows the conceptual geometry of one such set of molds.

Briefly, the set contains a pan and a lid. The pan has ridges that would form the striations in the Chocobar cast, as well as a lip along the circumference to support and position the lid. The lid has a protruding plate, whose thickness would determine the overall thickness of the cast. Because the tooth height is fixed by the pan, this means the thickness of the base of the cast will be determined by the thickness of the plate of the lid. We printed multiple lids for the same pans, so that we would have a range of options for the base thickness. The figure below shows a set of such lids with a range of plate thicknesses.

We also printed multiple designs for the pan, to reflect the two difference radii as well as offer different overall area of the cast. It turned out that smaller casts were easier to extract without breaking. The figure below shows a closed mold in the oven.

The composite polymer mixture is shown to have overflown through the ventilation ports on top of the lid as the bolts were tightened to press the lid into the pan. This is expected and desirable as it ensure no air gaps would form under the lid and compromise the casts.

After baking, the molds would be opened and the casts extracted. The figure below on the left shows the cast on top of the lid with the pan removed. The figure on the right shows the same cast removed from the lid and flipped over to show the opposite surface. The flash would be clipped off to finish the cast.

The individual casts would then be trimmed and fitted to the corresponding locations in the body. In the K3 suit, we used a double layer of Chocobar in each pocket. The figure below shows the process.

The resulting suit would maximize the thermal protection through the double layer of hollow glass Chocobars. The figure below shows the suit.

The K3 suit was tested in dives by pairs, where the other diver wore a commercial suit for comparison. Automated dataloggers recorded the pressure and temperature inside and outside each suit. The experimental results are shown below.

The K3 was thermally superior to the 7/6mm commercial suit, by 4 to 5 degrees Celsius. Hence, it is the warmest suit to date. It also has ergonomic advantages due to having the flexibility of a 3mm suit. The significance of this comparison was also that the 7/6mm commercial suit is in very widely spread use in the civilian sector, while the US Navy also uses it as a standard wetsuit, e.g. for prolonged ship repair missions. Hence, the K3 would be a marked improvement in both the thermal protection and ergonomics of flexibility to the standard suit.

We also compared the K3 to a high-performance top-of-the-line commercial 8/7mm suit. The results are shown below.

The field tests showed that K3 is on par with the 8mm suit at depth in terms of thermal protection, while retaining strong ergonomics advantage over the 8mm. Bad ergonomics is why 8mm suits are in relatively rare use. Hence, the promise of the K3 is that it can provide the desired heavy thermal protection while essentially solving the ergonomics of flexibility problem of the thick neoprene suits.