Semi-dry ... purpose?

[Ready4Launch]

If a dry suit is to keep you dry for really cold temps and a wetsuit keeps you wet but warm in cold to warm temps, then what is the purpose of a semi-dry suit that gets you somewhat wet?

 

[Ready4Launch]

Why would I want one?

 

[Strategist.]

If a dry suit is to keep you dry for really cold temps and a wetsuit keeps you wet but warm in cold to warm temps, then what is the purpose of a semi-dry suit that gets you somewhat wet?

Keeps you semi-dry and warm for temps between really cold temps and cold to warm temps

 

[CuzzA]

Why would I want one?

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.

 

[MaxBottomtime]

It's like being semi-pregnant.

 

[Ready4Launch]

It's like being semi-pregnant.

I wouldn't know.

 

[johnohuk]

They are generally cheaper than a drysuit, early in my dive career I picked up a Scubapro 6.5mm semi dry and used it for a few yrs, from ice diving to the keys.. lovely suit, virtually no flushing and it was only hands/head that got cold. I sold it as soon as I could afford a new dry suit. Yes, there a secondhand drysuits around but you end up diving wet with a lot of them anyway!

I ended up buying a Waterproof W1 recently, which is almost a semi-dry with the wrist/ankle/zip seals and this is perfect when you don't want a drysuit (20-28C like winter Red Sea). Below 20C I always dive my o-three ri 2-100 and above 28C, a Scubapro everflex 3mm.

 

[tbone1004]

I dive a 6mm/5mm O'Three "semi dry" but I bought it as a wetsuit. Wanted something warmer than my 5mm but not as stiff and thick as a 7mm for teaching where I can't be in a drysuit. I also really like it for cave diving. I don't like the 7mm or thicker semi-dry suits for the reasons listed above

 

[MAKO Spearguns]

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.

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

 

[CuzzA]

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

And that, my friend, is why I called in your expertise. Great write up. I would argue a freediving suit would be the preferred way to go for temps that require significant thermal protection.