Tear gas and pepper spray use different irritants, but they both are intended to incapacitate. THEY CAN INCAPACITATE THE USER JUST AS EASILY AS THE TARGET.
I have been tear-gassed. It was a required element of my military training. We walked into the tear-gas filled training chamber with our gas masks on. A competent and insistent sergeant them made sure we took them off for the required three minutes. Those of us with better breath-holding skills than others were given a not so friendly punch to make sure we received the full benefit of the training exercise. Those three minutes were incredibly long ones, and I can attest the after effects persisted until the next day.
Some things to think about:
There are various legal limits* on both the possession (fact of and amount) and the concentration of oleoresin capsicum, the active ingredient in pepper spray. Ten percent seems to be a common legal limit in the US — 17% can be acquired online (sometimes referred to as “Hot,” “Bear,” “Dog,” etc.) This is another of those “know before you go” issues.
As an oily liquid, sprayed upwind, pepper spray may leave the user incapable of further self-defense from blow-back. Waiting for an attacker to be suitably downwind may be impossible. Pepper sprays are available in gel and foam formulations which reduce the likelihood of blow-back in a breeze and pose a worse removal problem for an attacker — but they require good aim under stress.
There are pistol configuration pepper spray devices that may help with the aiming issues, but they look like pistols (mini-flare guns) and may invite a firearm response before they are even employed.
In addition to aiming issues, there is the blessing to the Tsar issue — [God Bless and Keep the Tsar far away from me.] Delivering a deterrent shot of caspicum at 8-25 feet is preferable to within arm’s reach. Again, pistol configurations help, but…
Most pepper spray equipment is designed for purses and hiking trials — not marine environments. In addition to keeping the equipment secured to prevent inadvertent discharge, it needs to be protected from corrosion. A plastic bag with a desiccant pack should be fine.
If you have pepper spray aboard, everyone with access should know how to use it. […and the First Aid for exposure.]
Wasp Spray as an alternative.
Some personal security gurus advocate wasp spray. These extended-range, stream sprays are oily carriers for plant-based toxins designed to destroy insect nervous system function — they are potentially dangerous in several ways. Rather than being an immediate surface irritant they are designed to be absorbed. Designed for insects they may do nothing but piss off a human malefactor. Some edge-market products may, in fact be lethal, especially to children.
*Wikipedia is not a definitive source of legal information, it has been provided as a reference for illustrative purposes only.