Some countries will put you in prison for carrying a ASP style baton. So we carry a flashlight. We keep a 6 C cell flashlight quickly at hand. I also walk on land with that flashlight. The following book is out of print but is a good start on how to use a 5-6 C cell flashlight like a police baton. It talks about how police have mis-used a flashlight and ended up killing someone. Defensive tactics with flashlights by John G Peters I have not read the following book, but it is still in print and is probably similar. Defense Tactics for Law Enforcement: Weaponless Defense and Control and Baton Techniques by Bruce Tegner Skip the portions about above controlling a subject, and carefully analyze the warning about which blows can be fatal. Also a rolling boat can be made just about un-board-able by turning off the stabilizers. That has worked for us. When someone wanted to board they were turned off, and boarding us was not practictal. Also we keep one of our EPIRBS in the pilothouse that can not been seen, but can be triggered if we are about to be boarded.