octo is longer to allow a second diver to breath and allow some freedom of movement near you. both should be able to continue diving with your arms locked. sharing your main would be a lot more uncomfortable. Also the octo is bright yellow to allow a second diver to easily see it and take it maybe without you knowing... no time to explain without air! I don't think padi or ssi teach it differently. In case your octo is broken or unavailable then yes you share your main but it is more like an emergency situation as you should take turns to breath
Scuba Diving
For all things related to recreational scuba diving - gear, safety, training, travel. Wanting to learn, new divers, experienced divers, professionals and technical divers. Underwater photography and videos are also welcome!
[Tend to avoid commercial diving and freediving topics]
My dive buddies keep it simple.
If they are out of air and they have time, they will get to me and take my octopus/secondary.
If they need my air and can't wait, they pull my main out of my mouth and Buddy breathe till we figure out who gets what regulator.
Seems simple that way. If they start grabbing my gear, I just wait and see what they want. They know how to buddy breathe, so I just trust them to give it back at some point. If not, I use my octopus.
The dive ends when you get in trouble, so either way you are starting for the surface. So move to upright facing means the length of hose does not matter.