There are two main causes of line entanglement when bottom fishing on the open seas: a strong undercurrent, and the changing of the current’s direction.
When there is a strong undercurrent, the sinkers will often be too light to keep the lines in place, causing them to drift and thus entangle with the lines of other anglers on the same boat. To prevent this from happening, distribute your range of sinker weights throughout the whole boat so that the anglers at the front of the boat will be using the heaviest weights while anglers at the back will be using the lightest (which should still be heavy enough for the weight to reach the bottom). This will ensure that only the lines at the stern drift: the rest will stay more or less in place.
To give an example, let us assume that it takes a size 4 sinker to reach the bottom. As the bow (front) of the boat will always face the current, anglers fishing at the stern (back) of the boat should use a size 4 sinker while anglers in the middle should use a size 6 sinker and anglers at the bow should use a size 9 sinker.
Why not simply have everyone use the same heavy sinkers to keep the lines in place? While this is a viable option, this will prevent anglers at the stern of the boat from covering as much of the water as they potentially could. Of course, if this is not desirable – such as when the fishing spot is directly beneath the boat – they can always opt to use a heavy sinker as well.
If you should ever find yourself in the situation where you end up fishing with strangers on the same boat, it is best to appoint a guide or leader for the boat to ensure that you are all appropriately spaced throughout the boat.
To prevent lines from getting entangled with each other during the change of current, anglers should identify when the current is about to change – using a tide table if you are not sufficiently familiar with the currents of the region you are fishing in – and retrieve their lines frequently during the change. This will prevent the lines from suddenly changing drift direction and end up getting twisted with another angler’s lines.