Drysuit vs 7mm Wetsuit in Southern Australia

Ask ten divers in Melbourne, Hobart or Adelaide whether you need a drysuit and you will get ten different answers, most of them shaped by what the person answering happens to own. The honest answer depends on three things: how cold the water actually gets where you dive, how many dives you want to do in a day, and how many months of the year you want to be in the water.

This guide works through that decision for southern Australian conditions, and it is a genuinely different calculation from the one divers make in Queensland.

What southern Australian water actually does

The single most useful fact is that southern Australian water is cold for most of the year, not just in winter.

Port Phillip Bay and the Mornington Peninsula sites sit in the low to mid teens through winter and only reach the high teens or low twenties at the peak of summer. Tasmanian sites are colder again and stay cold longer. The South Australian gulfs swing more widely, warm enough for a 5mm in late summer, properly cold when the giant cuttlefish aggregate at Whyalla through winter.

Compare that to Sydney, where a 7mm and a hood will get you through the coldest month, or Queensland, where 3mm is often generous. The southern states are a different diving climate, and gear chosen for Sydney conditions underperforms badly at Lonsdale Wall or Waterfall Bay.

Where a 7mm wetsuit still wins

A good 7mm semi-dry with a hood, gloves and boots is not a compromise choice, and for a lot of divers it remains the right one.

It wins on cost. A quality 7mm plus thermal accessories lands well under a drysuit system once you count undergarments. It wins on simplicity: nothing to flood, no valves to service, no course to take, no buddy needed to zip you in. It wins on shore diving convenience, because you can be suited up alone in a car park in five minutes. And it wins on single-dive days, where the cold rarely becomes the limiting factor before your gas does.

If you dive Blairgowrie Pier or Rye Pier a handful of times over summer, do one dive and go home, a 7mm is entirely adequate and a drysuit is money you did not need to spend.

Where a drysuit changes everything

The drysuit argument is not really about being warm on one dive. It is about the second and third dive.

In a wetsuit, you get out cold and wet, you stand in the wind at a pier car park, and you get back into a suit that is now colder than the water. Surface intervals stop being rest and start being endurance. By dive three you are shivering, your gas consumption has climbed and your decision-making is worse. In a drysuit you get out dry, put a jacket on, drink something hot and get back in comfortable.

That difference decides how much diving you actually do between May and October. Divers who buy drysuits in the southern states almost universally report the same thing: they did not just get warmer, they started diving through winter instead of stopping.

A drysuit also matters for:

- Long or deep dives, where a wetsuit's insulation compresses away exactly when you need it - Winter aggregations like the Whyalla cuttlefish at Point Lowly, which happen precisely when the water is least inviting - Cold, long shallow dives, such as extended macro or photography work at Edithburgh Jetty - Tasmania generally, where the season for a wetsuit is short and the season for a drysuit is all year

The honest cost comparison

A 7mm system, bought well, runs roughly:

- 7mm semi-dry wetsuit: $400 to $900 - Hood, gloves and boots: $150 to $300 - Total: roughly $550 to $1,200

A drysuit system:

- Neoprene drysuit such as the Fourth Element Hydra: around $1,100 - Membrane drysuit such as the Bare Aqua Trek 1: around $3,499 RRP, often discounted - Undergarments: $165 for a basic top and leggings, up to around $849 for a premium undersuit - Rock boots, if the suit ships with socks: $89 to $150 - Drysuit specialty course: budget for two dives of instruction - Total: roughly $1,300 at the entry point, $4,000 plus for a membrane system

The interesting number is the entry point. A neoprene drysuit plus a basic thermal base layer lands close to a premium 7mm system. That is the comparison most southern Australian divers should actually be making, and it is much closer than the headline drysuit prices suggest.

The rule of thumb

Stay in a 7mm if: you dive mostly in summer, you do one or two dives a day, you often dive alone from shore, and diving is an occasional rather than a weekly thing.

Move to a drysuit if: you want to dive through winter, you do three-dive days, you are in Tasmania at all, you are getting cold enough that it affects your gas or your judgement, or you have started skipping dives because of the cold.

The tipping point for most people is not temperature, it is frequency. Around the point where you are diving twice a month year round, the drysuit stops being a luxury and starts being the thing that makes the diving enjoyable.

If you are on the fence

Two practical suggestions. First, hire a drysuit for a weekend before buying one, which most southern dive shops will arrange alongside the specialty course. Doing a real two-dive day in one tells you more than any amount of reading.

Second, if you are going to buy, do not underestimate the accessories. A drysuit with a thin hood and cheap gloves still gives you a cold head and cold hands, and a diver with cold hands ends the dive early regardless of what the rest of them is wearing. The extremities are where southern Australian divers most often get the balance wrong.

Header photo: A Reef Life Survey diver on the wall at The Sisters, Tasman Peninsula, by Peter Southwood, CC BY-SA 3.0, via Wikimedia Commons.