I won't go into our specifics in too much detail but some of the things that can be used include the following. The first key is identifying in time. Then
-Lights. The USCG tends to use 1000 Watt Xenon's. Strobe is also a powerful disorienting feature. The military classifies this under the heading of Ocular Interruption. If they can't see you, they can't board you. Navy even trains in laser. But then they also do in non lethal munitions designed to provide ocular and auditory disruption. Green light is called a dazzle gun. Also, laser.
-Smoke. Can include tear gas in this classification as well, but regular smoke can give you time. Let's keep in mind that most of these are not sophisticated pirates but three to a boat types looking for easy scores and often will move on at the first resistance. There are also liquids that accomplish similar due to the burning and the smell.
-Sound-Can be very painful.
-Tasers-Law enforcement's favorites along with guns shooting rubber balls but tasers really need something more to back them up as many men can keep going. To me, tasers are too late, meaning you failed to prevent boarding.
-Projectiles. These can take many forms and be used even to set their boats on fire. This includes grenades which when detonated can do all sorts of things including light and sound. You can even use compressed air to launch some.
-Water. Perhaps the easiest projectile and you have ready access especially if you have a fire pump connected to an engine. Hoses or water cannons.
Now there are others, most of which are shown on the attached link and a few used in commercial ships that sail certain areas. These others are used when anticipating larger numbers of invaders with more sophisticated weapons. Commercial ships also must deal with underwater efforts.
https://www.marineinsight.com/marin...ti-piracy-weapons-for-ships-to-fight-pirates/
Avoiding is still the best defense, but there are areas we're still on high alert. The intent of our systems is to let them know we're aware and have some form of defense. Even if you had guns, you'd hope these could avoid using them. Last thing you want to do is get in a gun battle with a large group of pirates.
As to anchoring, we don't leave a dinghy or tender in the water and we generally have someone up and on watch. We do set up a field using cameras and electronics and alarm if anyone crosses the field. Only once has it gone off and nearly scared the elderly couple in the dinghy witless. However, they soon had plenty of light to see they were headed straight toward the side of our boat. We flipped the light to LED the moment we saw them. I'm in the minority as I don't like to anchor at night. Mostly day to swim or relax. Anchoring just isn't our thing. Cruising security is in areas off shore of Nicaragua, Venezuela and Honduras today. Marina security is largely an issue when you're not aboard and we accomplish that with cameras and alarms.
There are also elaborate systems that cost more than ransom. There's a pain ray that cost the only ship I know to have it over $3 million each. It also can be lethal or worse than lethal.
Electric fences have been used on commercial ships but the warning is to use only if you have non-flammable cargo.
Here's a somewhat dated DOD booklet on non-lethal. Current administration has changed direction and dismissed the concept in favor of lethal.
https://defenseinnovationmarketplac...loads/2018/02/2015_DoD_NLWP_ANNUAL_REVIEW.pdf
On the other hand the Marine Corps is looking for laser systems to mount on vehicles.
I think the key elements for boats are lights, sound, smoke, smell and water. Any one or two of those can be an incredible deterrent.
