Semi-dry ... purpose?

[boulderjohn]

Okay, trying to put all of that into a concise post....

There is a myth that the water that gets inside a wetsuit keeps you warm. It does not. The less water that gets inside a wetsuit, the better. One way to help is through a super good fit that allows little space for water. Another way to do it is through really good seals at every point that water can enter. A semi-dry suit will (hopefully) fit really well and also do the best possible job of keeping water out through good seals at the point of entry. Some will get in, but it should be the least amount possible.

 

[tridacna]

Thanks for mentioning me. I'm not sure my understanding of the issues is more useful, but I will give it a shot.

Exchange of water into and (particularly) out of a wetsuit results in undesirable heat loss. Many people will refer to this as water pumping into and out of a wetsuit. This is caused by water leaking into the suit at various openings and also by movement of the diver. Leakage down the neck and directly onto the spine is also particularly uncomfortable.

I think when people refer to semi-dry wetsuits, they are thinking about a suit that has seals at the ankles and sleeves and often has an attached hood. They typically also have zippers on the torso and some have zippers in the hood as well. One of the big objectives is to preclude water transfer at the neck. Obviously you can not make an excessively tight joint at the margins of a hood and a jacket or you will choke someone. So the semi-dry suits generally try to avoid leakage at the neck by having an integrated hood.

Semi-dry suits do NOT (my understanding anyway) have completely waterproof zippers - which are used in dry suits.. Dry suit zippers are too expensive, not stretchy and also vulnerable to sand and wear and damage. If you are going to use a dry suit zipper, then you pretty much need to make a dry suit.

The semi-dry zippers do leak, but the manufacturers try to minimize seepage by using smooth rubber seals and also generally layering the neoprene.

The semi-dry suits also generally will use leg cuffs and wrist cuffs which have smooth rubber on the inside, which is quite effective in reducing seepage .

Most semi-dry suits are going to have the interior of the neoprene glued with nylon or some fabric material. This internal fabric material generally increases the strength of the suit, but tends to reduce flexibility.

So attached hood, seals on the zippers and seals on the wrists and ankles and neoprene that has fabric on the inside and outside are the attributes which come to mind when I think of a typical semi-dry scuba suit.

A freedive suit is generally considered to be a two piece wetsuit having a hooded jacket and separate pants that may be cut as a farmer john or as high pants. Generally a freedive suit has an exterior with a lycra or nylon fabric, however the inside is left "bare" with no nylon material. As mentioned, having fabric on only one side of the neoprene is going to enhance the flexibility of the suit, but the trade off is that the interior is somewhat vulnerable to finger nail cuts etc. (if improper handing of the suit occurs - generally when removing the suit).

Note that there is no mention of a zipper in a freedive suit - without a zipper, there is no need to provide extra backing layers or seals in an attempt to reduce seepage - this is a major source of leakage which is completely avoided.

The smooth interior of the freedive suit, allows sealing of the suit at the face seal, at the wrists and the ankles. The smooth interior also tends to inhibit water migration inside the suit itself. The suit can leak at the bottom of the jacket where it contact the pants, but this is pretty minimal and if the diver uses an elastic rubber weightbelt this also serves to isolate any water in the bottom of the body from the torso. If the a farmer john pants are used, there is essentially zero water getting to the diver's body from the bottom of the jacket opening.

With a smooth interior, integrated hood and no zipper, donning a freedive suit requires the use of an internal suit lubricant and a somewhat different technique to put the suit on and take it off. Once the suit is properly prepared with lubricant, it is very quick and easy to get into the suit. It is NOTHING like wrestling your way into a wet 7 mm scuba suit. The difference between the ease of putting on a freedive suit versus a scuba suit increases when you are talking about thicker suits.

Keep in mind that freedivers in cold water are VERY concerned about wearing too much neoprene, Neoprene compresses at depth causing a significant loss in buoyancy (and thermal insulation). This swing in buoyancy associated with suit compression is easily addressed by a scuba diver, since a BC is worn.

Without the benefit of a BC, a freediver needs to be underweighted at the surface, must fight buoyancy on the descent, will reach neutral buoyancy at some depth and then have to fight negative buoyancy during the ascent from depths which are below the "neutral zone". It should be easy to understand that minimizing this detrimental buoyancy swing is of overwhelming importance. Keep in mind that the significant (and unavoidable) chest compression during the breath hold further exacerbates the buoyancy swing issue. A freediver wants to maximize their time underwater and this means minimizing their exertion, so minimizing the amount of buoyancy swing from a wetsuit is a major consideration.

A freedive suit is designed to provide the maximum possible thermal protection, with the least amount of neoprene. The less excess neoprene a diver wears, the less the buoyancy swing will be.

These suits MUST be as thermally efficient as possible. In addition, the freedive suit must be flexible and comfortable to allow relaxation during the breathe up and unrestricted movement for active swimming and it must not leak or pump water in or out. Thus zippers (which leak and prevent stretching) and extra layers of neoprene which are intended to reduce seepage from the zippers are something to be avoided. In generally, we say that a 5 mm freedive suit is probably as warm as a typical 7 mm scuba suit (and it is going to be a lot more flexible).

Dive Safe

Dano

Someone please turn this into a sticky.

 

[lexvil]

I know these suits use “compression resistant” neoprene but what is the effect of compression at depth, scuba diving will have the user at depth for a fairly long time, even without water flushing through what are the thermal properties of a 5mm at 50ft for an average dive at depth?

Thanks for mentioning me. I'm not sure my understanding of the issues is more useful, but I will give it a shot.

Exchange of water into and (particularly) out of a wetsuit results in undesirable heat loss. Many people will refer to this as water pumping into and out of a wetsuit. This is caused by water leaking into the suit at various openings and also by movement of the diver. Leakage down the neck and directly onto the spine is also particularly uncomfortable.

I think when people refer to semi-dry wetsuits, they are thinking about a suit that has seals at the ankles and sleeves and often has an attached hood. They typically also have zippers on the torso and some have zippers in the hood as well. One of the big objectives is to preclude water transfer at the neck. Obviously you can not make an excessively tight joint at the margins of a hood and a jacket or you will choke someone. So the semi-dry suits generally try to avoid leakage at the neck by having an integrated hood.

Semi-dry suits do NOT (my understanding anyway) have completely waterproof zippers - which are used in dry suits.. Dry suit zippers are too expensive, not stretchy and also vulnerable to sand and wear and damage. If you are going to use a dry suit zipper, then you pretty much need to make a dry suit.

The semi-dry zippers do leak, but the manufacturers try to minimize seepage by using smooth rubber seals and also generally layering the neoprene.

The semi-dry suits also generally will use leg cuffs and wrist cuffs which have smooth rubber on the inside, which is quite effective in reducing seepage .

Most semi-dry suits are going to have the interior of the neoprene glued with nylon or some fabric material. This internal fabric material generally increases the strength of the suit, but tends to reduce flexibility.

So attached hood, seals on the zippers and seals on the wrists and ankles and neoprene that has fabric on the inside and outside are the attributes which come to mind when I think of a typical semi-dry scuba suit.

A freedive suit is generally considered to be a two piece wetsuit having a hooded jacket and separate pants that may be cut as a farmer john or as high pants. Generally a freedive suit has an exterior with a lycra or nylon fabric, however the inside is left "bare" with no nylon material. As mentioned, having fabric on only one side of the neoprene is going to enhance the flexibility of the suit, but the trade off is that the interior is somewhat vulnerable to finger nail cuts etc. (if improper handing of the suit occurs - generally when removing the suit).

Note that there is no mention of a zipper in a freedive suit - without a zipper, there is no need to provide extra backing layers or seals in an attempt to reduce seepage - this is a major source of leakage which is completely avoided.

The smooth interior of the freedive suit, allows sealing of the suit at the face seal, at the wrists and the ankles. The smooth interior also tends to inhibit water migration inside the suit itself. The suit can leak at the bottom of the jacket where it contact the pants, but this is pretty minimal and if the diver uses an elastic rubber weightbelt this also serves to isolate any water in the bottom of the body from the torso. If the a farmer john pants are used, there is essentially zero water getting to the diver's body from the bottom of the jacket opening.

With a smooth interior, integrated hood and no zipper, donning a freedive suit requires the use of an internal suit lubricant and a somewhat different technique to put the suit on and take it off. Once the suit is properly prepared with lubricant, it is very quick and easy to get into the suit. It is NOTHING like wrestling your way into a wet 7 mm scuba suit. The difference between the ease of putting on a freedive suit versus a scuba suit increases when you are talking about thicker suits.

Keep in mind that freedivers in cold water are VERY concerned about wearing too much neoprene, Neoprene compresses at depth causing a significant loss in buoyancy (and thermal insulation). This swing in buoyancy associated with suit compression is easily addressed by a scuba diver, since a BC is worn.

Without the benefit of a BC, a freediver needs to be underweighted at the surface, must fight buoyancy on the descent, will reach neutral buoyancy at some depth and then have to fight negative buoyancy during the ascent from depths which are below the "neutral zone". It should be easy to understand that minimizing this detrimental buoyancy swing is of overwhelming importance. Keep in mind that the significant (and unavoidable) chest compression during the breath hold further exacerbates the buoyancy swing issue. A freediver wants to maximize their time underwater and this means minimizing their exertion, so minimizing the amount of buoyancy swing from a wetsuit is a major consideration.

A freedive suit is designed to provide the maximum possible thermal protection, with the least amount of neoprene. The less excess neoprene a diver wears, the less the buoyancy swing will be.

These suits MUST be as thermally efficient as possible. In addition, the freedive suit must be flexible and comfortable to allow relaxation during the breathe up and unrestricted movement for active swimming and it must not leak or pump water in or out. Thus zippers (which leak and prevent stretching) and extra layers of neoprene which are intended to reduce seepage from the zippers are something to be avoided. In generally, we say that a 5 mm freedive suit is probably as warm as a typical 7 mm scuba suit (and it is going to be a lot more flexible).

Dive Safe

Dano

 

[MAKO Spearguns]

I don't have data on compressibility. Presumably a suit that compresses less at depth should be warmer and it would have less loss of buoyancy.

 

[CuzzA]

For those that dive privately off an outboard powered boat, I'll share probably the best thing we do during the colder months diving wet, and that is to tap into the engine's raw water cooling system. The water exiting the engine from the tell tale is around 125 degrees F. Run a hose to the deck overflowing a bucket. You'll have to mix some colder sea water from another bucket to prevent scolding yourself, but we then fill our suits with that hot water before splashing and our suits will retain that heat for about twenty minutes. Back on the surface another bucket in the suit feels like you're sitting in a hot tub. It is glorious.

 

[caruso]

Semi-dry is a marketing term and it's rather misleading. You're going to get just as wet as you would with a wetsuit but you won't be experiencing quite as much of a drop in your body temperature because there won't be as much flow of cold water in and out of the semi-dry suit due to tighter seals at the feet and wrists. Mine uses velcro to keep the seals tight and it has an integrated hood- one less place for water to get in and out.

 

[Trailboss123]

Why would I want one?

I will try to be as objective as possible and answer your question to the best of my ability, while making some assumptions about where I think you are coming from and will focus on the word in your subject title "PURPOSE".

I think most of us, if water temperature and surface temps were not a consideration, would prefer to dive in a wetsuit or no exposure protection at all vs. a Drysuit- if we could comfortably do so.

Why?
1. Better overall movement, comfort, freedom, streamlining and flexibility underwater
2. Less overall expense
3. Less complicated on many levels (easier to travel with, no additional undergarment required, no additional hose or air source required to manage suit squeeze)
4. No additional skill set required to learn how to manage 2 different buoyancy characteristics simultaneously (BCD and Drysuit). I have an issue with anyone who says that drysuit diving is not an advanced skill that requires some additional training. I am not saying that it is overly complicated or massively difficult, but there is definitely additional knowledge and training required.
5. All things being equal and in almost all circumstances: less lead/weight required in order to descend and compensate for the positive buoyancy characteristics of the drysuit and undergarments).
6. Probably not going to sweat your A$$ off donning and doffing and walking in and out of the water on 75+ degree sunny dive days

That being said, there are times in which the luxuries and benefits of those things mentioned above just simply do not outweigh the conditions you will find yourself diving in- such as:
1. Water temps
2. Number of dives being done in a day relative to water and surface temp/conditions
3. Surface interval temps, surface interval conditions, surface interval length
4. Length of dives in given conditions
I could go on and on...

Me? Most of my dives are in a drysuit given all of the variables in my dive life.
My wife?- Given the variables in her dive life and the latest options for really good semi-dry suit options out there these days, she is definitely considering some Semi-Dry options-

Why? She doesn't want to deal with undergarments, she doesn't want to learn how to add and then vent air from a dry suit. Doesn't want to spend any more money than possible, given her commitment to diving. She will never do more than 1-2 dives a day in cold water and cold surface temp conditions. The cold water conditions she is going to dive in are not so extreme to outweigh the benefits of the new school semi-dry suits.

It is all relative-- but hopefully, something I have said will be helpful to you in making a decision for your circumstances and your purpose for diving?

SD Combat Semi Dry Wetsuit
https://ww2.scubapro.com/en-GB/SWE/divewear/wetsuits/products/novascotia-75.aspx

 

[REVAN]

Semi-dry is misleading. You'll be diving wet, but with little exchange of water due to the seals, consequently resulting in far more exposure protection compared to a traditional wetsuit, but less than a drysuit with undergarment. I own a semi dry wetsuit, but I'm convinced a much better approach to those in between temps is to instead use a freediving wetsuit, which is different from a scuba suit. Perhaps Dano @MAKO Spearguns can provide the technical explanation. My thoughts are it's a much tighter fit and higher quality neoprene.

Dido on the freediving suit. That has become my solution and I like it way better than the semi-dry. The freediving suits are way more comfortable and every bit as warm (if not better), while being easier to work with when doing multiple dives (i.e. - no issues putting on for second, or third dive, when wet).

 

[guyharrisonphoto]

There are a few misconceptions about semi-drys circulating here. First, the quality semi-drys have a true dry zipper that does not allow water intrusion. They also have skin seals at the wrists and ankles (often double seals that can be rolled under) and a skin neck roll seal. A quality semi-dry allows very little water intrusion (I have done dives where water penetrated into the arms and legs but my core stayed dry). To the extent water gets in (they are designed to allow for this, of course) they allow pretty much zero water flushing or exchange. So, once the water gets in, it is warmed (to keep you warm) and does not get flushed away with colder water. The entire purpose of a semi-dry is to keep water flow to the absolute minimum without trapping air like a drysuit.

Semi-drys are very, very warm. The really good ones (I just replaced my 10 year old Mares with a Waterproof Combat--the best seim-dry in the business) also have low compression neoprene and stay warm at depth.

For recreational diving, I think they are as good as a dry suit. But, for ice diving, extreme cold water (under 40 degF) or long tech dives with multi-hour run times, a drysuit would have the edge. Similarly, if I lived where the water was cold as opposed to only doing one or two colder water trips a year, I would consider going dry.

For me, I really like the streamlined fit and ease of use with a semi-dry. I hate drysuits, with the undergarments (including Depends, the dirty little secret most drysuit divers don't tell), bulk, and "swimming in a trash bag" feel. If I put a thermolution heated shirt underneath my semi-dry, I am good to go for even really cold water because the heat stays trapped in.

There is a reason you see hardly any freediving suits on scuba divers. They are different tools for different things. Freedive suits are very hard to don and need lubrication. They are soft neoprene and so have real compression issues at depth. They are delicate and not as sturdy as scuba wetsuits. They are warm, true, but these other disadvantages are huge and there is a good reason you see them even less than you see drysuits.

 

[MichaelMc]

I hate drysuits, with the undergarments (including Depends, the dirty little secret most drysuit divers don't tell)

Ahh, so if you just pee freely in your semi-dry, how does that work..., with the semi-dry no flushing aspect?
(I do not go in my suit either as it is rather non flushing, but I think having it both ways is hard without a valve to help.)

Freedive suits are very hard to don and need lubrication. They are soft neoprene and so have real compression issues at depth. They are delicate and not as sturdy as scuba wetsuits.

I dive a skin in farmer john hooded beavertail industrial rubber suit, same style as free-diver but heavier with a lower chest zipper. It is not fragile. Donning takes lube and prep, but is easier than wet neoprene. I have not dove a semi-dry, and the differences have always been interesting, as my fitted skin in seems a lot like a seal that goes all the way up my arms and legs.