Enter line cutters. Line cutters are very sharp blades which attach to the propeller shaft of the vessel. If a line of any kind gets wrapped around the propeller, the blade will cut the line before it gets severely wrapped and fouls the prop or shaft. There are many different styles of line cutters for various different propeller arrangements. Sounds like a great idea, right? No more diving under your boat with a mask and a knife to cut away those pesky lines. Anyone who has had to do it will attest to the PITA factor, as well as the possibility of being injured while swimming under your boat while it is rocking in the waves.
Many years ago, I had a co-worker with a powerboat and he was proud of the fact that he had line cutters installed on his boat. When he encountered a field of crab pots, rather than carefully dodging them, he would just plow straight through them, cutting any lines he happened to encounter. By doing this, he was intentionally causing derelict crab pots. What's the big deal?, you say... That stupid waterman shouldn't have put these things in my way! I'll just cut the lines and teach him a lesson!
Now I don't necessarily have an issue with line cutters. It's a safety issue. If I pick up a stray line accidentally and it wraps around my prop shaft, it could render my boat inoperable at at an inconvenient or possibly dangerous moment depending on the current, wind, and surrounding shallow areas.
The "big deal" is the environmental and fisheries impact of all those derelict crab pots littering the seabed. In 2010, a study was done on the impact of derelict crab pots on the Chesapeake Bay. It is estimated that as many as 150,000 additional derelict crab pots are added each year by a combination of abandonment, buoy loss, and lines being cut. When a crab pot is lost, it continues to catch crabs because it still has bait in it, even though the waterman will never be able to retrieve it. Eventually, the crabs and fish that enter the pot will die, in effect re-baiting the trap and attracting more crabs and scavenger species. A lost crab pot will last about four years before it eventually rusts away and is no longer a hazard. Doing the math, that means that as many as 600,000 derelict crab pots are littering the Chesapeake Bay at any given time. The study estimates that every abandoned crab pot on the seabed will kill about 50 marketable crabs per season. That's up to 30 MILLION crabs a year lost to derelict pots! And that's just the marketable crabs. What about the smaller ones that are not marketable which are also killed? These crabs will never grow into larger, marketable crabs, and will not get a chance to reproduce for next year's crop. Here's a couple of pictures of derelict crab pots that were recovered during the study:
So I've said all that to make a point about line cutters. I don't fault anyone for installing them. I get the safety aspect of having them installed. But please be responsible in their use. Consider them emergency equipment that is only used when you accidentally pick up a crab pot line. Don't go blindly plowing through every crab pot field in your path without regard for all the marine life you will kill, as well as the livelihood of the watermen who spend their lives doing hard work so that you can eat delicious steamed crabs. Just one more way you can do your little part to help the bay and the environment.
Here's a link to the 2010 study: http://ccrm.vims.edu/publications/pubs/rivers&coast/vol5_no3_marine_debris_1.pdf