Re: Butt connector or solder ?
It is difficult to make an inference about how two wires ought to be spliced together from the OEM practices of automotive, aeronautical, or spacecraft assemblers because in general the use of a wire-to-wire splicing is likely prohibited in their OEM practices.
A wire-to-wire splice is by its nature a sub-standard practice, generally used only for repairs or rework. So let's not argue about how NASA does it--NASA likely does not use wire-to-wire splices.
I agree that nowadays in modern electrical devices you see a preponderance of wires terminated in crimped connections, but this is not necessarily because a solder connection would have been inferior. On my boat I typically choose to solder all wire terminations into their terminal connectors. I have never had one break from vibration. By soldering the connection you create a good seal between the wire and the termination. The worry with crimp connections is that water can penetrate into them and cause corrosion. It is difficult for water to penetrate into a soldered connection.
The risk of water intrusion is ever-present in a boat. I think it is a much greater risk than wire fatigue from vibration. I therefore choose to solder most all connections. (If your boat vibrates so badly that solder wire connections rapidly fracture from the movement, your boat has other problems you should attend to first before the conversion to all-crimp connections. Most small boats to not experience the vibrations that occur during a rocket launch.)
An exception are those extremely large diameter conductors; they are typically too large to solder effectively. Terminals for large cables are often dead-ended. If you crimp them and properly seal the wire end, intrusion of water will be minimized.
