Others in this thread have already posted, but I'll add my own experience, which just happened a couple of weeks ago. My wife accidentally shot me with some wasp spray. Smelled bad, irritated my skin, but did ABSOLUTELY NOTHING to incapacitate me in the short term! Were I intent on attacking anyone it would have served as no deterrent at all.
I washed it all off and then called the doctor to ask about long-term effects. Her comment was that, as long as you didn't get any directly into your eyes, and as long as you washed it off thoroughly and soon, there should be no long-term consequences. If you DO happen to get it directly in your eyes, she said, you want to immediately wash them out very thoroughly with fresh water, and then should go to see an ophthalmologist.
1 - something that will stop a wasp
2 - something that will stop a bear
Doesn't seem like there is much to consider. Put a new label on the bear spray and just remember what it really is.
It would be hard to disguise bear spray, as it has a huge spray tip with a safety on it. Probably not advisable either, then you are not declaring an illegal substance...
Mind you I would never advocate wasp spray. Thats just asking for trouble.
Cutlass is too big for boat use. So is machete. How you gonna swing it if someone gets inside? And a cutlass may cause problems with customs. I prefer a kukri. It's just a really big bush knife. But the real ones from Nepal are cheap, high carbon steel, razor sharp, battle proven to be incredibly lethal. Only thing better is a Smatchet, and those are impossible to find....
"Cutlass is too big for boat use. So is machete. How you gonna swing it if someone gets inside? And a cutlass may cause problems with customs. I prefer a kukri." ==> A kukri is nice, two are even better. Many years ago I modified a kali stick kata for a pair of kukri. The problem with all the edged weapons mentioned is that they are optimized for slashing and in the confined space on or in a boat (except possibly for a catamaran) a thrusting weapon is better - or at least one with a serviceable point for stabbing. Edged weapons take a lot of training and if you are dealing with an armed intruder that has chosen to bring a knife to a potential fight, it is possible that they may know something about using it. I have found that a pair of wakasashi (like small samurai swords) are a good compromise. They are relatively short for good maneuverability in a confined space, they are relatively light weight so they are fast, and you can stab or cut as needed. If one wants less than lethal force the flat of the blade can be used, or the back which is not edged but will deliver a more concentrated blow without cutting (and one can strike with the pommel as well). With two weapons one can parry with one while attacking with the other. As mentioned, lightning fast stabbing attacks are much more effective than sweeping slashing motions that most people tend to instinctively use when the adrenalin kicks in - and have the advantage of keeping your weapon between you and your opponent. In a knife fight you are going to be cut - accept it and be ready to fight through the pain and blood. Get some training - and get a couple of practice knives similar to the one(s) you want to use, and practice. The kind that leave marks are best and you will see how many times you are cut (you can get cut a lot and still keep fighting - so can your opponent). You can also get goggles with dark glass (eye protection is recommended when practicing) which will simulate the darkness which is the preferred time for miscreants to put their nefarious plans into action. After training in a classroom situation, do some practice on your boat with its confined spaces and movement. Of course the suggestion by the original poster was likely for people with minimal martial arts experience.
A lot has been said about bear spray, but using high potency spray in large volumes inside a confined space is likely to cause you and your family as much problem as it will the intruding miscreants. This can be tested at little cost using a keychain size spray inside an old shed or other confined space. Note how long the effects linger - especially if there is carpet to absorb it. I suspect that bear spray could make your boat unlivable for some time (perhaps the word 'overkill' comes to mind). And, as has been noted, the substance may be illegal in some jurisdictions. Further, it is not available everywhere - I have never seen it here in the Philippines as there are no bears here.
Perhaps there are cans of wasp spray with relatively benign ingredients that do not cause any problems - but the target is the face of the assailant and the 'other ingredients' I previously posted about certainly seemed able to cause distraction if not incapacity. Perhaps a quick check of the 'other ingredients' is needed. Simply jumping overboard is likely to eliminate most of the symptoms and an alert individual with a boat hook is then likely to be able to keep them from re-boarding.
Another item that is seldom mentioned is the use of the boat's million candlepower handheld spotlight in the off hand to blind the miscreant while one wields the duty fish club to render them senseless. No illegal items here - one can shine the light into someone's face and note that their hands are instinctively raised to cover the eyes - including the hand wielding the knife.
Wasp spray was likely mentioned because it provides a way for one to disable a lightly armed intruder from a distance. The closer the intruder gets the more likely one is likely to be harmed. Boats are littered with everyday items that provide much greater range than a knife, especially if all one has to do is defend a small opening. What long narrow implements are stored below in the boat? A spare boat hook, oar, paddle, whisker pole, or any other long narrow sturdy item that might be used to vigorously thrust into the base of the throat of an intruder silhouetted in the hatch while you are still concealed in the darkness below. A bit of imagination, preparation, and warning will go a long way to provide security (of course, thirty years of individual armored combat experience with various medieval weapons doesn't hurt either).
This exact thread was in a gun forum years ago. I KNOW this will sound like lawyer gibberish, etc, and I'm not arguing that you'd be "safer" using a gun. However, at least in the good ole Litigous USA, if you spray someone with wasp spray, it can be a problem. Why? Believe it or not, because of the WARNING on the side of the can and the DIRECTIONS! Yup, as absurd as it sounds, some "experts" chimed in and pointed out that, legally and technically, you can be in big doo - doo. Now, if someone were going to hurt me, I'll take my chances. People who believe in protecting themselves will often say, "Rather be judged by 12 than carried by 6". But, if you do use wasp spray, be aware that you better have a good reason, and even then... Legally, it's better to use pepper spray on a perpetrator, because THAT is what it's supposed to be used for. Hey, I'm NOT a lawyer - don't blame me! lol...
Check out Castle Doctrine, its really interesting stuff. I don't know exactly how other countries see it, but it varies from state to state here in the US.
One of the principle arguments around it is regarding using things that are even strictly illegal to defend one's self. For the most part it protects from criminal prosecution. So for instance, if a young single female living in say Chicago uses a weapon to "dispatch" a would be assailant that has broken through her window in the middle of the night, all the criminal statutes are thrown out if self-defense is established. Even though firearm possession within city boundaries is a class II felony. It also dictacts exactly what is nessasry for "use of force" in ones home or residence. Notice the wording of "Does or does not have duty of retreat." That is even more mindbogling, that means that for instance if you fought off a would be robber, but didn't try to run away, you would be screwed. In texas you can do just about anything to anyone even in the dead of a moonless night, because a lot of Castle Doctrine there is grandfathered from the cattle hustling days, basically it doesnt exist in Texas. That includes "Fleeing felon" situations, meaning you can shoot an unarmed man in the back at night if hes on your property, OR your neighbors.
As you said, its a whole 'nother monster when it comes to Civil suits, where just as you said, something as simple as a "Warning label" could be used to establish that there was intent to cause bodily harm. However, Castle Doctrine covers that as well in some states, you get a "Cant sue me" card if you have avoided the criminal case using castle doctrine. I also think it would be very very hard to convince a jury of peers that someone who sprayed an assailant in the eyes with a can of wasp spray, kicked them off the boat and called the authorities should see financial damages.