Ive read through many posts on drysuits here, though admittedly not ALL of them, without finding the details I write below. If Ive duplicated something that has been discussed before, I duly apologize for missing it.
My purpose with this post is to present my point of view that baggy, over-sized drysuits are sub-optimal, and likely the cause of a persons issues with suit squeeze, leading to discomfort and lack of range of motion, and also trim and buoyancy issues. I am hoping to elicit comments and sharing of experiences on drysuit fit and the efficacy of gas addition to relieve one from suit squeeze, etc. So here it is, the engineers among can pipe in if I seem to botch the physics...
Unlike submarines, drysuits are non-rigid, the fabric flexes and collapses under hydrostatic (water) pressure. Pressure inside the suit is usually below ambient hydrostatic pressure (dictated to a degree by the setting of your dump valve). Also, given the suit is basically a somewhat deflated balloon, the more gas you put in it, the more buoyant it becomes (duh you say, I knew that !). These two things combine to make the relief of suit squeeze an interesting proposition.
Let me walk through a virtual experiment. We will use one full unopened can of Coca-Cola (I prefer it over Pepsi), or a can of beer if you prefer (also unopened), two zip-lock baggies of different size, and an aquarium (with or without fish). One zip lock bag is just big enough to hold the can of Coke inside when zipped shut, and the other zip-lock is much much bigger. Now, put the can inside the small bag, close the zip almost all the way and suck all the air out of it before sealing it completely. Put it in the aquarium and submerge it with your hand if you need to. The can is your body and the baggie is your drysuit, and this situation is analogous to you just submerging down a few feet with your suit dump valve fully opened. The small wrinkles on the baggie are just like those on your suit, and this represents a suit squeeze. If we actually used the smallest bag possible that would still hold the can inside, the addition of just a minute amount of air will puff the baggie like a balloon, with no wrinkles in the baggies surface, totally relieving the squeeze, and allowing your undergarments to fluff up and insulate you at their maximum capacity. Also, this minute amount of air would not cause you too much buoyancy changes given your other kit (tanks, weights, etc).
Now, lets change zip-lock baggies, and put the can in the x-large zip-lock, suck the air off it, and place in aquarium. Now we have the can sitting at the bottom of this much bigger baggie, which is also putting the squeeze on you like before. Now put the same amount of air into this bag, as you did put into the small bag above. What happens to that air you blew in ? It goes straight to the top of the bag, and does absolutely nothing to relieve the squeeze on the can down below. Your suit is still squeezing you, your insulation is pressed, your range of motion may be limited due to the fact that the suit fabric is plastered against your insulation and body. You will need to add much more gas to relieve the squeeze in this over-sized floppy suit; you may actually not be able to relieve the squeeze in a significant way before you have severe buoyancy and trim issues. You will have a large gas bubble moving about along the fabric wrinkles in your suit, but with marginal suit-squeeze relief.
Reading through some internet diving forums it is interesting to find people stating that they learn to live with suit squeeze, and sacrifice this in favor of warmth. I am here advocating that one can have less suit squeeze and therefore more warmth in a trimmer suit.
As far as Ive understood, the north Florida cave divers came up with the cave cut drysuit because they did not like the large wrinkles of fabric in an over-sized suit flapping away while on scooters, and creating drag. I would venture to say, that they found it easier managing suit squeeze and buoyancy/trim an added benefit of the cave-cut suit.
In some circles though, the cave-cut versus non cave-cut discussion rages on. Cave-cut may be at the extreme of a well fitting suit (or maybe not), but you do want a close-fitting suit as opposed to a baggy suit. Drysuit makers could follow form and function from outdoor clothing makers like Patagonia, North Face, REI, MEC, and others worldwide -- outdoor clothing is a very competitive and distilled industry. Looking at their patterns, the arms and armholes, butts, and crotches of these garments, designed usually with climbers and skiers in mind, one sees a trim fit with a high range of motion cut. The armholes are small allowing one to reach up far and back (as in reaching for tank valves) without maxing out the seam under the armpit, the crotches are gusseted allowing legs to spread easily apart (as in frog kicks). The butts are more sculpted allowing for more room without floppiness and excess girth at the waist, some even have "articulated knees" and curved elbows. The fit is as trim as can be without affecting maximum mobility.
It would seem to me the best suit is a suit that fits you closely, and is well designed to allow you to do the movements you may need to do, such as reaching your fins, your tank valves, etc. A baggy suit which may allow you to do this out of the water may likely be impossible to deal with underwater because it will be squeezed to your body and will not allow proper range of motion.
I'm sure all of the above is not news to many, but it was to me when I started diving with a drysuit (an oversized one).
...time to open that can of beer..
My purpose with this post is to present my point of view that baggy, over-sized drysuits are sub-optimal, and likely the cause of a persons issues with suit squeeze, leading to discomfort and lack of range of motion, and also trim and buoyancy issues. I am hoping to elicit comments and sharing of experiences on drysuit fit and the efficacy of gas addition to relieve one from suit squeeze, etc. So here it is, the engineers among can pipe in if I seem to botch the physics...
Unlike submarines, drysuits are non-rigid, the fabric flexes and collapses under hydrostatic (water) pressure. Pressure inside the suit is usually below ambient hydrostatic pressure (dictated to a degree by the setting of your dump valve). Also, given the suit is basically a somewhat deflated balloon, the more gas you put in it, the more buoyant it becomes (duh you say, I knew that !). These two things combine to make the relief of suit squeeze an interesting proposition.
Let me walk through a virtual experiment. We will use one full unopened can of Coca-Cola (I prefer it over Pepsi), or a can of beer if you prefer (also unopened), two zip-lock baggies of different size, and an aquarium (with or without fish). One zip lock bag is just big enough to hold the can of Coke inside when zipped shut, and the other zip-lock is much much bigger. Now, put the can inside the small bag, close the zip almost all the way and suck all the air out of it before sealing it completely. Put it in the aquarium and submerge it with your hand if you need to. The can is your body and the baggie is your drysuit, and this situation is analogous to you just submerging down a few feet with your suit dump valve fully opened. The small wrinkles on the baggie are just like those on your suit, and this represents a suit squeeze. If we actually used the smallest bag possible that would still hold the can inside, the addition of just a minute amount of air will puff the baggie like a balloon, with no wrinkles in the baggies surface, totally relieving the squeeze, and allowing your undergarments to fluff up and insulate you at their maximum capacity. Also, this minute amount of air would not cause you too much buoyancy changes given your other kit (tanks, weights, etc).
Now, lets change zip-lock baggies, and put the can in the x-large zip-lock, suck the air off it, and place in aquarium. Now we have the can sitting at the bottom of this much bigger baggie, which is also putting the squeeze on you like before. Now put the same amount of air into this bag, as you did put into the small bag above. What happens to that air you blew in ? It goes straight to the top of the bag, and does absolutely nothing to relieve the squeeze on the can down below. Your suit is still squeezing you, your insulation is pressed, your range of motion may be limited due to the fact that the suit fabric is plastered against your insulation and body. You will need to add much more gas to relieve the squeeze in this over-sized floppy suit; you may actually not be able to relieve the squeeze in a significant way before you have severe buoyancy and trim issues. You will have a large gas bubble moving about along the fabric wrinkles in your suit, but with marginal suit-squeeze relief.
Reading through some internet diving forums it is interesting to find people stating that they learn to live with suit squeeze, and sacrifice this in favor of warmth. I am here advocating that one can have less suit squeeze and therefore more warmth in a trimmer suit.
As far as Ive understood, the north Florida cave divers came up with the cave cut drysuit because they did not like the large wrinkles of fabric in an over-sized suit flapping away while on scooters, and creating drag. I would venture to say, that they found it easier managing suit squeeze and buoyancy/trim an added benefit of the cave-cut suit.
In some circles though, the cave-cut versus non cave-cut discussion rages on. Cave-cut may be at the extreme of a well fitting suit (or maybe not), but you do want a close-fitting suit as opposed to a baggy suit. Drysuit makers could follow form and function from outdoor clothing makers like Patagonia, North Face, REI, MEC, and others worldwide -- outdoor clothing is a very competitive and distilled industry. Looking at their patterns, the arms and armholes, butts, and crotches of these garments, designed usually with climbers and skiers in mind, one sees a trim fit with a high range of motion cut. The armholes are small allowing one to reach up far and back (as in reaching for tank valves) without maxing out the seam under the armpit, the crotches are gusseted allowing legs to spread easily apart (as in frog kicks). The butts are more sculpted allowing for more room without floppiness and excess girth at the waist, some even have "articulated knees" and curved elbows. The fit is as trim as can be without affecting maximum mobility.
It would seem to me the best suit is a suit that fits you closely, and is well designed to allow you to do the movements you may need to do, such as reaching your fins, your tank valves, etc. A baggy suit which may allow you to do this out of the water may likely be impossible to deal with underwater because it will be squeezed to your body and will not allow proper range of motion.
I'm sure all of the above is not news to many, but it was to me when I started diving with a drysuit (an oversized one).
...time to open that can of beer..
