Semi-Dry vs a good 7 mm with Hooded Vest, How Much Difference?

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I have wet, semi-dry, and dry suits. I switch between each depending on weather and water temperature.

Wetsuit:
When I purchased my wetsuit, I also purchased a matching shorty designed to be worn over it for extra thermal protection. The shorty came in 2 versions, with and without hood. I purchased the model without hood so that I could also use the shorty for very warm water diving, and I generally prefer a separate hood as I find an attached hood to be a bit restricting.

What I found when diving my wetsuit + shorty is that when diving temperatures where the combination is needed, I am never truly warm, and I fatigue much quicker, especially out of the water and doing anything on the surface as the layers of neoprene are bulky and restrictive. I found it was not worth the hassle to were this 2 layer combo due to the bulk and impact on range of motion while still not being totally comfortable (warm) during the length of a dive (30 to 60 minutes).

I have even added a formfitting 2mm neoprene pullover vest type top to wear on my upper half as a base layer under my wetsuit. but that only adds to the bulk of the layers when combining the other 2 pieces, and only improves things marginally.

Semi-dry:
A small handful of years ago, I was offered a great deal on a nearly new semi-dry duit. As I have posted in other discussion threads a few times, my suit fits and seals so well that I could probably add a chest inflator and upper arm dump and dive it as a drysuit. I like diving my semi-dry when the water is cold but the air temp is warm, and my suit does a great job of keeping my comfortable throughout the length of my dives....plus, since my suit keeps me relatively dry, I am also comfortable when I get out of the water heading back to the car, instead of shivering uncomfortably as I would when peeling my wetsuit off.

A semi-dry should fit snugger than a wetsuit per-se...it should hug your body comfortably snug without causing any major restriction. The body hugging nature will be more restrictive when donning the suit but that sensation should ease away quite a bit when in the water as the suit material tends to relax a bit when wet.

The biggest concern once should have when shopping for a semi-dry is fit. It really does need to be comfortably snug all around. Any pockets of air or gaps arounds the body will reduce its ability to keep one comfortable. The second concern is how well the seals at the neck, wrist, and ankles fit, as they play a major role in limiting the ingress of water into the suit. I had the neck seal of my suit altered as it was initially too big which allowed cold water to flow down my neck and back. If you find a suit that fits well but the seals are too large, then inquire if they can be altered, or find someone to do it after you purchase it...this can also be a fairly straight forward DIY project if you have that penchant.

Drysuit:
I spent the majority of the last 10 years living in Belgium. Unless one has quite the constitution, the wetsuit season is quite short, at least for me. The diving in Belgium is mostly quarries and a few lakes, and the water temp only gets to about 68F for the better part of 3 weeks in late July/early August. After a few years of diving in my wetsuit/shorty combo, I got tired of feeling like the Michelin man while still being cold, and my season was cut short as it was just too cold for me to dive comfortably prior to the beginning of June or past mid-October. This was a dilemma because my preference was to dive often, and there were less folks crowding the dive sites when the water was colder, so visibility was better as there were less people stirring up the bottom.

The solution to my dilemmas of a truncated season, and quest to be comfortable in the ever present cold water was found in purchasing a drysuit. While a drysuit is not the end-all be-all solution for every dive scenario, it provides relatively unparalleled comfort (warmth) when diving in cold water. It provides the ability to comfortably do multiple dives in a single day....there are few things worse, in my opinion, than pulling on a damp wetsuit for a second dive on a cold day, regardless of water temp.

The major drawbacks of a drysuit are 2 fold:
1. The cost of the suit - drysuits tend to be more expensive than the other options available, and there may be ancillary expenses such as the possibility of needing new fins with a larger foot pocket to accommodate boots.

2. Because it is the air in the suit that keeps one comfortably warm, one has to re-learn their special awareness/how to control their body position in the water. It kind of feels like learning how to dive again as initially there tends to be a lot of flailing around like a novice diver....but this is surmounted rather quickly if one is able to get in the water (pool/confined water preferably) often to work on this, my guestimation is it takes somewhere between 6 and 10 dives on average get comfortable diving ones first drysuit (as with most things, for some it might take more or less).

Just like the semi-dry, the primary major consideration is how the suit fits. A good, proper, comfortable fit is so paramount that no other feature is worth considering if the fit is not correct. A drysuit that does not fit properly is not only a bane to dive, but can add to the danger that is already prevalent in diving.

All-in-all, there are a lot of choices available on the market. Do what works best for your budget, and the type of diving you plan to do most frequently, but if you are going to spend a lot of time diving in waters around 45F like your original post hinted, then I urge you to consider investing in a drysuit for the sheer comfort it provides....diving is just simply more enjoyable when you are comfortable.

Hope that helps.

-Z
Fantastic reply! Thanks so much for all the information.

I absolutely love exploring this stuff and quickly become an equipment snob every time I take on a new hobby. I will certainly explore drysuits this winter but right now I am experiencing the spectrum of wet diving and want to find my limits. I like the flexibility of layering in a 7mm but it seems like I can gain a little bit more thermal efficiency with a semi-dry. I'll likely end up with both . . . and a drysuit!
 
I dive a hooded Hollis 8/7/6 semi-dry here in the Puget Sound. Coupled with XS Thug 8mm boots and 5mm gloves. This summer the water has been in the 50° range at depth and I'm comfy in this setup for 45 min - 1 hour dives. It is easier on me to don/doff than all the excess of multi piece suits. The chest zipper is nearly waterproof and easy enough by myself. The other plus to this setup is I don't have to concern myself with s-folds in my hood.
Based on my experience, I predict that my personal limits are going to be about the same as you just mentioned regardless of which setup I next attempt. My next setup will either be a custom semi-dry or the best off-the-rack option Bare has. Drysuits will be my next adventure but not until winter.

Thanks to everyone who has posted so far. I appreciate everyone's time and effort.
 
With the lead time on drysuits, if you order now you may get to use it this winter. Probably not the start of winter though.
 
I did one dive in a 7mm Henderson with 2mm hooded vest and made it about 15 minutes at 35‘ in 45 degrees before it became unbearable. I have been using an Accel 8mm semidry for last 8-10 dives and it’s bearable for 20 minutes in low 40’s and 70-80’ deep.. If it had a watertight zipper would go quite a bit longer. I don’t have much cold tolerance or "bioprene".


Did you even read the original post? :sad2: Or just trying to get your post count up?
Yes I did….there’s no sense in adding hooded vests and comparing semi drys to 7mm’s when diving that cold…just go dry…it’s that simple. I can dive for hours while you’ll only last 10-20 min….diving is supposed to be enjoyable, seeing how long you can bear 40 degree F water is ridiculous and frankly unsafe.
 
I think one of the most important factors in the OP's original question is depth. If he is diving relatively shallow, say 40 feet or less, a 7 mm suit may work quite well. If he is planning 80 or 100 ft or more, then that is a much more of a "thermal challenge".

Also, important are the ambient air temperature and number of dives. If he wants to do one dive a day (and potentially has access to a warm water source) then a 7 mm suit could work quite well, assuming that he has really good boots and gloves. If it is multiple dives per day and there is not a really good place to get dry and/or warmed completely, then the suit (any wetsuit) becomes more of a challenge.

I would suggest looking at a good "freedive" type of wetsuit. These suits have no zippers, an integrated hood, Farmer john pants and a smooth rubber interior that allows almost zero influx or migration of water. Besides the added warmth of this type of suit, the elimination of the interior nylon liner, significantly improves the flexibility and stretch of the neoprene material itself and also the comfort of the suit in the water and between dives. The benefit of no liner really comes into play when you are talking about thicker suits.

3 finger mittens and wearing a neoprene sock under a neoprene wetsuit boot (two layers) also markedly improves warmth in really cold water. You can not neglect feet and hands.

Hopefully those topics/ideas are more beneficial then telling the guy "no" and that he has to spend several thousand dollars - when in fact he may NOT really have to.
 
I think one of the most important factors in the OP's original question is depth. If he is diving relatively shallow, say 40 feet or less, a 7 mm suit may work quite well. If he is planning 80 or 100 ft or more, then that is a much more of a "thermal challenge".

Also, important are the ambient air temperature and number of dives. If he wants to do one dive a day (and potentially has access to a warm water source) then a 7 mm suit could work quite well, assuming that he has really good boots and gloves. If it is multiple dives per day and there is not a really good place to get dry and/or warmed completely, then the suit (any wetsuit) becomes more of a challenge.

I would suggest looking at a good "freedive" type of wetsuit. These suits have no zippers, an integrated hood, Farmer john pants and a smooth rubber interior that allows almost zero influx or migration of water. Besides the added warmth of this type of suit, the elimination of the interior nylon liner, significantly improves the flexibility and stretch of the neoprene material itself and also the comfort of the suit in the water and between dives. The benefit of no liner really comes into play when you are talking about thicker suits.

3 finger mittens and wearing a neoprene sock under a neoprene wetsuit boot (two layers) also markedly improves warmth in really cold water. You can not neglect feet and hands.

Hopefully those topics/ideas are more beneficial then telling the guy "no" and that he has to spend several thousand dollars - when in fact he may NOT really have to.

So here is a counter thought, and is the logic I applied when my wife was looking at purchasing a drysuit and the shop suggested she load up on neoprene:

The more neoprene one wears, the more lead they will need to submerge. The amount of lead ballast needed to submerge a 7mm suit with a 5mm or 7mm shorty on top or underneath will have the diver overweighted at depth as the suit compresses and loses buoyancy...this can be considered a safety issue if the divers BCD/wing suffers a casualty.

For my wife, the shop was suggesting a 7.5 to 8mm wetsuit with a matching 5 or 7mm shorty on top....of course my wife was leaning towards the advise of the shop because what does her husband know, right?........surprisingly, I was able to get her to understand/accept that a drysuit may require a similar amount of lead to submerge but it offers a redundant source of buoyancy to her wing should she have an issue with either.

With that much neoprene, dropping weights to begin an ascent with a compromised BCD/wing is a non-sequitur, as the neoprene will regain buoyancy as one rises in the water column, the diver will quickly experience an uncontrollable ascent with high risk of injury.

While using the drysuit as a source of buoyancy is not ideal (and yes I know there are different thought camps on this topic), it serves as a suitable backup should an equipment SNAFU arise.

-Z
 
I would suggest looking at a good "freedive" type of wetsuit.
The downside to a freedive suit,especially the better ones made out of the softer Yamamoto 39 neoprene, is that they don't stand up to extended periods of compression on scuba. The bubbles collapse after a relative few number of scuba dives and a 7mm suit becomes equivalent to a 5mm and then a 3mm etc.
 
I've used freedive suits while scuba diving quite a bit and did not notice any difference in compression of the rubber versus a scuba suit. I'm not sure that this is a real concern.
 
I think this really depends on fit. I rented a half-dozen different 7mm in Monterey before I bought an Aqualung SolaFX semi-dry. I can tell you for sure that not having a hood at all makes a big difference; I was freezing on Dive #3 even though it only lasted 20 minutes. But I don't find a big difference between the semi-dry and the wetsuit. Part of that is I am portly and wear an XL/2X depending on the manufacturer. The larger you are, the more variability there is in body dimensions, especially when the suit is designed for someone much taller (or shorter) than you. The integrated hood is too big in the skull and too small in the neck, the legs are too long, arms are too baggy, for me.

So overall, I think there's more variation due to fit and the reduced warmth of neoprene over time. I would prefer to try on suits in person and get the best fitting one, regardless of whether it was semi-dry or not. I ended up deciding to try a custom jacket wetsuit from Otter Bay, I'll let you know in six months how that turned out! Otter Bay Wetsuits You otter be in an otter suit
 
After many years with multiple suits, today is 2,5 mm or Dry, and an open cell for freediving.
no more thick wetsuits for me
 
https://www.shearwater.com/products/perdix-ai/

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