A surface marker (aka safety marker, aka safety sausage, etc) is an important piece of dive safety equipment on practically every dive whether it is from a boat or from shore. Some dive operators even require their divers to carry one and know how to use it.
Diving is an extremely safe activity when the rules are followed and common sense prevails. Having the right equipment for the dive falls into both categories.
As with most dive gear, surface markers come in many styles. Some are more practical than others and some have specific purposes.
The simplest surface markers usually collapse into a relatively small package sometimes secured by an attached bungee or an external bag with a clip. They are designed to be orally inflated at the surface. A diver would usually do this once a dive is complete. You may wish to inflate your marker just to make it easier for the dive boat and/or Divemaster to see you and your buddy in the water. Diver heads, particularly when wearing hoods or in bright sun (causing glare), or foggy conditions, can be difficult to see. Additionally, swells or waves may allow the boat to see you only when you’re at the peak of a wave or swell. Adding a marker that is brightly coloured (like orange or yellow) and stands several feet out of the water makes you far more visible in all conditions.
Some markers have an inflator that allows you to connect an LPI hose from your regulator (either for your BCD or drysuit, typically) and inflate them from the air in your tank. This is sometimes easier for people than orally inflating, especially if there is chop at the surface. On the other hand some divers feel that potentially removing an inflator hose and reconnecting it (especially with gloved hands) can be cumbersome. So it can be nice to have the option, but depending on where you’re diving you may or may not decide whether it makes sense for you.
Size is another thing to consider when it comes to surface markers. A smaller marker is typically approximately 3 feet in height. In relatively calm waters this will often be adequate. If you are diving somewhere in open water or that is known to have considerable wave and/or swell action than a larger marker, 4.5 – 6 feet may be a wiser choice. Area dive operators and shops will likely have a recommendation based on local conditions. Some larger markers provide a modest amount of positive buoyancy when inflated at the surface, so if you or your buddy tend to get tired or a little stressed at the surface this can be reassuring. Or, if you are diving somewhere remote, it is not a bad idea to have a little redundant surface flotation.
Digging a little deeper into the options available in surface markers is whether they are closed, open or semi-closed. Closed markers require a diver to manual release air when they want to; these markers should not be deployed at depth as they can over-inflate and burst. However, these will typically provide some lift at the surface. In the case of larger markers, that lift can be significant. Open markers are open at the bottom. This can make them even quicker and easier to inflate: just purge a regulator into them. However, they may need assistance standing up and holding air in them. They’re quick and easy to deflate and common for those just wanting to be spotted by a boat.
In my humble opinion, the most versatile of them all is the semi-closed. It can be inflated at the surface, like the others, but because it has an over-pressurization relief valve (OPV) just like one commonly found on BCDs, it can be inflated at depth. Usually, you’ll want to attach a spool or a reel to it, so that you have a way of keeping track of it while you’re still underwater. Why would you want to inflate a marker at depth? Well, there are many reasons. If you’re on a dive looking for something, or even if you aren’t and you find something – you may want to mark it so that you or another dive team can find it on a second dive. Over a short period, a light line and surface marker can be adequate for this. Perhaps you need to get a lift bag from your kit on the boat or you’re almost out of gas but you’d like to start in the same place on a second dive. This temporary method of marking a particular point underwater is easy and convenient and applicable to both boat and shore diving alike. Another important use for a marker that can be deployed underwater is letting a boat know that you’re ascending and where. Typically divers will come up the line they’ve sent up, so the boat operator can be waiting for you and your team a safe distance away. This provides excellent peace of mind to the divers as they come up.
There are a variety of other ways that surface markers can be useful to divers and several features (attachment points, etc) that can be considered, but ultimately, if you ever want or need to be seen at the surface, a marker will make the chances of that happening much, much greater.