The following thread and post in a sub-forum of Technical Diving Specialties reminded me of a design I have been playing with that might be worth peer review. The context is long duration dives, in water below 50° F, and deeper than 130. I considered posting there but didnt want to hijack the thread and though a broader audience might be constructive.
I have heard of studies at the Navys Experimental Diving Unit which indicates that low density blended Neoprenes used in recreational wetsuits are warmer than Rubatex G-231 until about 130. My impression is it is more like 50, but is completely absent of quantitative data. I am told that G-231 is about 14 Lbs/Yard² and popular blends are about a quarter of that.
1. Most of the hood covers a relatively inflexible part of the anatomy so high flexibility, stretch, and tensile strength over the skull are of minor importance; but good insulation is because the head conducts heat faster per unit of area than other parts of the body. In most of this area a thick low-compressive/high density material could be used. Nylon lined Rubatex G-231 is very expensive and has had complaints of poor bonding. Why not use skin-2 Rubatex for this portion? It is available up to ½, is much less expensive, and is more available than lined. I was thinking of using 3/8 around the skull.
2. The area around the neck requires a lot of stretch and tensile strength, especially if the hood is zipper-less. Fortunately, the neck has a relatively small surface area with relatively low near-surface blood circulation; which causes high heat loss from the skull. I was thinking of a skin-in/Nylon-out 7mm high-stretch Neoprene blend. Run it from the entry edge of the hood up to about jaw-line and up to the face hole around the chin, a little wider than the mouth. Elimination of zippers is desirable for a better fit to reduce water circulation, simplify using unlined material in the back, not compromise flexibility, and improve reliability in the field.
3. The face-seal portion also requires higher tensile and stretch, but less bulk. This area could use a 5mm skin-in/Nylon-out high-stretch Neoprene blend. I was thinking of something like a 1 to 1½ wide strip around the face hole ending at the portion of the 7mm neck material from around the neck.
Attached is an image of what I have been thinking of. Let me be the first to say that I totally suck at tailoring, but it strikes me as an appropriate blending of material properties and requirements.
The problem of joining seams of different thicknesses is compounded when the thickest material is completely unlined. My thought is to glue surfaces flush to the inside. The Nylon-lined exterior seams can be sewn. Seams that meet the thickest un-lined Rubatex could be re-coated with wetsuit cement and the excess thickness rolled over and glued down. Granted, it is a laborious process, but something I would be willing to do.
Not many people are old enough to have used unlined Rubatex suits. They are much more flexible than Nylon lined and required careful technique to don and doff without tearing usually in the area where you grabbed it to pull. My theory is using unlined material in this limited area that sees negligible stress would minimize the disadvantage in exchange for less heat loss at depth.
Comments welcome.
ScubaBoard > Scuba Diving Central > Technical Diving Specialties > DIR > Otter bay hood with/without neck skirt? http://www.scubaboard.com/forums/dir/366959-otter-bay-hood-without-neck-skirt.html
I have heard of studies at the Navys Experimental Diving Unit which indicates that low density blended Neoprenes used in recreational wetsuits are warmer than Rubatex G-231 until about 130. My impression is it is more like 50, but is completely absent of quantitative data. I am told that G-231 is about 14 Lbs/Yard² and popular blends are about a quarter of that.
Background information: Lower density blended foam Neoprenes produced in Asia dominate the wetsuit market today and have virtually replaced Rubatex G-231. Asian blends are more flexible, lighter, stretch easier, more available, warmer in shallow water, and less expensive. The problem is they compress much more under pressure that their insulation value drops quickly with depth.
Two factors come into play that makes it difficult to quantify insulation value of the material at a given depth and the ability to maintain a very thin film of water without circulation. Less flexible materials tend to pump water as the body moves unless the fit is excellent. In my mind, hoods offer a unique design opportunity.1. Most of the hood covers a relatively inflexible part of the anatomy so high flexibility, stretch, and tensile strength over the skull are of minor importance; but good insulation is because the head conducts heat faster per unit of area than other parts of the body. In most of this area a thick low-compressive/high density material could be used. Nylon lined Rubatex G-231 is very expensive and has had complaints of poor bonding. Why not use skin-2 Rubatex for this portion? It is available up to ½, is much less expensive, and is more available than lined. I was thinking of using 3/8 around the skull.
2. The area around the neck requires a lot of stretch and tensile strength, especially if the hood is zipper-less. Fortunately, the neck has a relatively small surface area with relatively low near-surface blood circulation; which causes high heat loss from the skull. I was thinking of a skin-in/Nylon-out 7mm high-stretch Neoprene blend. Run it from the entry edge of the hood up to about jaw-line and up to the face hole around the chin, a little wider than the mouth. Elimination of zippers is desirable for a better fit to reduce water circulation, simplify using unlined material in the back, not compromise flexibility, and improve reliability in the field.
3. The face-seal portion also requires higher tensile and stretch, but less bulk. This area could use a 5mm skin-in/Nylon-out high-stretch Neoprene blend. I was thinking of something like a 1 to 1½ wide strip around the face hole ending at the portion of the 7mm neck material from around the neck.
Attached is an image of what I have been thinking of. Let me be the first to say that I totally suck at tailoring, but it strikes me as an appropriate blending of material properties and requirements.
The problem of joining seams of different thicknesses is compounded when the thickest material is completely unlined. My thought is to glue surfaces flush to the inside. The Nylon-lined exterior seams can be sewn. Seams that meet the thickest un-lined Rubatex could be re-coated with wetsuit cement and the excess thickness rolled over and glued down. Granted, it is a laborious process, but something I would be willing to do.
Not many people are old enough to have used unlined Rubatex suits. They are much more flexible than Nylon lined and required careful technique to don and doff without tearing usually in the area where you grabbed it to pull. My theory is using unlined material in this limited area that sees negligible stress would minimize the disadvantage in exchange for less heat loss at depth.
Comments welcome.
