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I'm soon to embark on a chilly scuba dive around 5-7C at 18m, of which we'll be wearing 7mm semi-drys with shorties. The next thickest I think is actually a drysuit for really cold waters, but not sure if there is a thicker wetsuit. However this got me thinking then about diving in warmer temperatures as well as colder.
For what temperatures would you wear different thicknesses of wetsuit, including none, and shorties?
Edit: We did drysuit in the end for these temps.
Wet suit thickness is a very personal thing. I for instance dive in a 3mm shorty in 15C and higher and 3mm one piece for temperatures under 15C and above 6C
Remember that you can also layer. So I would say a Dry Suit with thick under garment or a 7mm wet suit with a 3mm chicken vest underneath. Some nice thick gloves and hood and if you really cold then wear a 2nd layer of 5mm over the top.
Here are some good guidelines.
"Shorty wetsuits and dive skins are generally used in warm tropical waters with temperatures of 75°F- 85°F (24°C- 30°C) and above, depending on personal preference. Dive skins do not provide thermal protection, but do provide protection from accidental stinging by sea lice, fire coral and other small marine hazards. Shorty wetsuits provide a modest amount of thermal protection for core body areas.
2mm - 3mm (1/8 in.) wetsuits are generally used in warmer waters with temperatures of 70°F- 80°F (21°C- 27°C) and above, depending on personal preference. During cooler weather, additional warmth can be achieved through the use of a 3mm hood, addition of a 3mm hooded vest under the wetsuit and/or use of a 2-piece 3mm wetsuit.
4mm - 5mm (3/16 in.) wetsuits are generally used in cool waters with temperatures of 60°F- 70°F (16°C- 21°C) and above, depending on personal preference. During cooler weather, additional warmth can be achieved through the use of a 3mm-5mm hood and gloves, addition of a 3mm-5mm hooded vest under the wetsuit and/or use of a 2-piece 5mm wetsuit.
6mm - 7mm (1/4 in.) wetsuits are generally used in cooler waters with temperatures of 50°F- 60°F (10°C- 16°C) and above, depending on personal preference. During cooler weather, additional warmth can be achieved through the use of a 5mm-7mm hood and gloves, addition of a 5mm-7mm hooded vest under the wetsuit and/or use of a 2-piece 7mm wetsuit or semi-dry 7mm wetsuit. Semi-dry wetsuits have Neck seals, wrist seals and ankle seals that adhere to your skin to minimize water entry."
It's a question of the right tool for the job. For diving in temperatures below 14 degrees Celcius, a drysuit is best. When diving below 7 degrees a wetsuit really isn't the right tool for the job and is dangerous as you'll be extremely cold and will suffer on the surface. Even diving a 7mm wetsuit with a shortie over the top still isn't sufficient when compared with a drysuit.
A drysuit also gives you additional or backup buoyancy should your BCD fail.
Even when the surface temperature is 25 degrees, a drysuit is useful as it's a lot colder at depth or when submerged for a long time. You will vary your drysuit undergarments depending on the temperature.
For dives in very cold water the less you're exposed to the water the better. For the same thickness, dry gloves keep your hands much warmer than wet gloves as there's no liquid to conduct heat.
If you absolutely must dive in 5 degree water in a wetsuit, it's vital that it's a semi-dry where your wrists, ankles and all zips are sealed to avoid flushing of cold water which could cause the 'gasp' reflex. You must also make sure that you can get into a warm location to change and get out of the wetsuit as soon as possible after the dive. You do not want to be exposed to wind chill in a wet wetsuit.
Getting cold is at best uncomfortable, it shortens your dive, it is really unpleasant, and can put you at great risk, not least of giving up diving.
For UK winter diving (typically 5 to 7 degrees), virtually everybody dives with a drysuit for those reasons. I dive with drygloves and a heated vest which I can thoroughly recommend especially if you're doing long duration dives.
