Patents grant exclusive use of an idea to one person.
Most of the patented stuff seasteaders would want to use is things like paints, motors, solar panels, watermakers, electronics, etc that we will just buy.
Protecting your own ideas
Most countries would not let someone patent an idea after it has been published. (The US is an exception - you have up to 1 year after publication to patent the idea). So one way to make sure that you can use an idea in the future is to publish it, this way nobody else can patent it.
The other way is to file a patent on your idea. You can publish your idea immediately after you file. You should mention that there is a "patent pending".
Patents and ships
"Article 5ter Paris Convention demonstrates a concern to leave the channels of international commerce free from the burdens that would result if vessels had to conform to the patent laws of all nations that the vessel or vehicle visits during its lifetime. Different inventions are likely to be patented in different countries, and the same invention may be patented by different parties in different countries. Article 5ter Paris Convention places foreign-owned means of transport beyond the reach of domestic patentees’ exclusive rights. This prevents the international traffic of goods and persons from being obstructed by seizures at the borders and other measures." From paper in links below.
So if we flag our seasteads with some country that is part of this agreement then we don't have to worry about patents outside of that country, which we may never visit.
There are a number of countries with shipyards where the fees for violating patents is very small, and the chances of getting accused of violations are also small.