Having dived for over 20 years I've used all sorts of equipment (even horse collar BCD's).
Despite doing a huge number of PADI courses, I've found those courses teach very little about equipment.
Learning which equipment works best has been trial and error, and unfortunately sometimes wasting money when I've made a bad decision.
When diving in warm water you can get away with basic equipment. When diving in cold water and on deeper dives you need more reliable equipment.
First of all I'd like to not call it scuba equipment but life support equipment. We are not meant to be underwater so we need equipment to keep us alive, equipment failure can lead to death or serious injury.
From my own experience this is how you can get the best, most comfortable and safe dive gear at the lowest cost.
Last time when you were in the tropics, did the dive store give you a thin ill fitting suit?
The water was warm so it sort of did the job.
Varoius companies sell suits that are only 0.5mm. My personal advice is don't buy them, you'll freeze. Even in the warmest water you'll need a 3mm suit.
Its always good to have a bit extra in case you come across a thermocline (A.section of water that can be up to 10C colder). Often when diving in warm water, back on the boat I'm the only person not shivering, the other people are wearing very thin suits.
The thicker your wetsuit is, the more it plays around with your buoyancy. The trick is to be warm with as thin a wet suit as possible. A good fitting 5mm can keep you warmer than a badly fitting 7mm.
I remember my first dive in Korea the water was 8 degrees Celsius, my wetsuit did not do the job, and I was extremely cold. After that dive I did lots of experimentation and research to find the best solution. This is what I found to be the best answer.
Insulation will be determined by 3 major factors. Fit, thickness and leakage.
Areas of leakage are ankles, wrists, neck, zip, and seams.
A technique I use to completely stop leakage at ankles is to use neoprene socks and boots.
Roll the end of the sock so there is a small hump, then place the socks under the wetsuit. The hump helps create a water tight seal. Then do the same with the wetsuit. Place the boots over the rolled wetsuit. The seal is so good that when I get out of the water my calves look huge as all the water goes down the legs but no water escapes.
Do the same with your gloves. Have the glove go over the wetsuit, and then put an elastic over the glove. Gloves leak! They all leak badly. The leaking is through the stitching.
Try this, fill up your gloves with some tap water and then watch the water leak out through the stitches. There's your heat loss! The best gloves you can get are seamless.
You'll pay a premium, however you'll be able to dive with thinner gloves and keep your hands toasty warm.
Usually wetsuits seal fairly well around the neck. Problems occur when you wear a hood. As soon as you have the neck seal go around the bib of a hood the seal leaks badly. I've found better results with a shorter dry suit hood that goes OVER not under the wetsuit neck seal. Your neck will be a little colder BUT your body will be a lot warmer. Placing the hood over the wet suit helps to provide a better neck seal.
Finally there is the zipper, despite the flaps under the zipper, its like water going through a colander. A solution I've found (actually a copy of a Mares product) is to wear a shorty over the top of your long wetsuit (preferably front zipped). Front zipped suits are easy to get on but you need help to get them off.
The final area where suits leak is through the seams. Even though the sewing needle does not penetrate the neoprene, there will be places (lots of them) where the holes from the inside of the suit meet the holes from the outside. I use Camaro suits as they are seamless but unfortunately they are not making seamless suits anymore, plus they've become super expensive. The shorty over the long suit stops a lot of this leakage.The thicker the neoprene the less leaks you'll get.
Finally if it's really cold you can wear a 2-3mm vest under the long wetsuit.
This will give you a total of 10-13mm (depending on shorty and vest thickness) around the torso and only 5 mm on the legs and arms where you need flexibility.
Do not go thicker than 5mm for the long suit! If you place a shorty over a 7mm suit you'll have 10-12mm around the shoulders and won't be able to move your arms!
I've used this combination and been very comfortable down to only 8 Celsius. It's as close as you can get to having a semi dry suit, but at a much lower price, with the added bonus of having a wetsuit set that will take you from 8/10 to 28 degrees Celsius. With a 5mm long + short + vest you can chop and change the combination.
A semidry suit costs more and is much more limited in use.
In case you are wondering why wetsuit prices vary so much. There are lots of different grades of neoprene out there. From stiff and hard to stretchy and soft. Whatever you choose, keep in mind that in no time it will have all sorts of cuts nicks and scratches on it. Better grades of neoprene are much more comfortable.
Usually you get cold not in the water but out. Those trips back to shore on a rubber zodiac boat in cold weather are horrendous. The solution is a dry suit.
Dry suit diving however is more complex in terms of buoyancy control, and you'll wear more weight. It takes some time to learn how to use them.
Basically there are 3 types.
1. Neoprene (Standard, compressed and crushed)
2. Butyl or trilaminate
3. Combination of the two
Neoprene offers some insulating properties and also some stretch for movement, so you can have a tighter fitting suit.
Butyl has no stretch, so the torso is elongated so that you can get in and out of the suit. Because it's oversized it has straps to then tuck everything in. It has no insulating properties so you need to wear some insulating undergarments.
The combination suit will have neoprene legs and a butyl torso. When diving in a dry suit the diver is not exactly horizontal but slightly elevated.
This means the air in the suit is around the torso. It is the air that provides insulation.
The legs get no air, hence no insulation in a butyl suit so legs can get very cold. To keep legs warm a solution is to make the legs of the suit from neoprene.
As for types, I make no suggestion but GET ONE if you are going to be diving in cold water. Even in a base model dry suit you'll be much more comfortable.
Now that you're warm and toasty, you'll some regs.
Most regs are rated at a water temperature of above 10C. There are standards such as EN250 for classifying regulators. Why the cut off point is exactly a nice even number such as 10 I don't know. Most warm water regs can go a bit under 10C. However it's better to be safe than sorry and get a reg that is rated for cold water.
Why? Regulators are classified on the basis of delivering air to only ONE diver, i.e. you don't have another diver sharing your air from an octo.
This is critical. A warm water regulator may not freeze on you and free flow at 10C on your own, but if you need to share air, all hell could break loose. Imagine having to deal with one panicked diver with no air and yourself with a free flowing reg all at 30 meters in cold water.
Another issue is balanced vs. unbalanced. Unbalanced regs are the regs you used when you did your open water course. Dive shops like them because they are cheaper to buy, have less moving parts and hence are cheaper to service.
An unbalanced reg will be harder to breathe from, the deeper you go. The best reg for deep dives is an overbalanced reg. Such a reg however is super sensitive on the surface and very easily free flows.
I personally use an overbalanced reg, as it breathes effortlessly, and to solve the surface free flow problem I have installed a shut off valve which I use on the surface. The shut off valve is located between the reg and the hose and takes 5 minutes to install.
These are your options:
1. Warm and shallow, and if on a budget, an unbalanced reg (piston or diaphragm-usually piston) will do the job.
2. Cold and deep, you'll want a balanced diaphragm reg.
3. Cold and very deep you'll want an over balanced diaphragm reg.
4. Warm and very deep dives you'll want a balanced piston regulator. At deep depths a piston regulator will deliver more air than a diaphragm regulator.
What about the mega expensive titanium regs?
For those that dive Nitrox, or use high Oxygen blends the worst reg you can use is titanium. In a high oxygen environment a contaminated reg or tank (usually a build up of compressor oil particles) can ignite. Metals do burn, and guess which metal ignites and burns the easiest? That's right, titanium.
With all that neoprene around your feet and legs, you'll have problems with "floaty" feet.I solved the problem by changing to IST fins (anyone want to buy some very used Mares fins). Any plain heavy fin will do the job. Look for fins that have lots of rubber.
These are no gimmick fins. Just plain ol' heavy, tough as nails fins. As they are heavy they solve the "floaty" feet problem, plus they really propel you through the water. Best of all, the price is low. As much as I hate wasting money on gear if you will be diving in cold water and the tropics you'll really need two pairs of fins. Heavy and large size (dry suit boots are big) for cold water. Light and smaller sized for overseas travel. You can get away with just one pair of large sized light weight fins, but then you'll want ankle weights with the dry suit, and boots (not slippers) with the warm water gear. With luggage allowances sometimes as low as 15kg, you need to save weight.
There are all sorts of very expensive gimmick fins out there. I can't comment on those fins as I have not used them. I am however very happy with my inexpensive, heavy and tough fins.