War stories aside;
Mechanical (crimping) connections are formed by plastic deformation of the metals. The resultant connection starts out tight and then loosens over time.
IMHO this is pure speculation and your own personal theory. If it is not please direct us to a white paper supporting this claim. A properly crimped connection will be cold formed and will not "loosen" over time unless done incorrectly. If crimps are ok for NASA, Boeing and many other high tech high critical use applications they will be more than fine on your boat and have been on millions of boats and cars, and trucks and on and on and on. Most of the crimps on my own boat were 30 years old when I bought her and still passing current just fine. There were two solder joints that had failed both due to capillary action of solder creep up the wire which caused fractures.
Once the connection loosens slightly, its conductivity plummets; this is why high power DC connections often overheat - they become poor conductors, and the current increases over time - until the connection is hot to the touch, or your boat burns to the waterline.
This is EXACTLY why the ABYC says solder only should never be used. In an over temp situation the solder can melt and you'll have a live wire. If you are soldering you must crimp first or have anotehr means of mechanical connection.
Exposure to humid air and salt increases oxidative degradation.
This is why heat shrink crimp connections and tinned wire should be used. As one who lives in the North East, where nearly every home has a deep well, with LONG wire runs and fairly high amp draws, we just don't see these failures. You said "humid", how "humid" are wires sealed 200+ feet below the surface, that live underwater for their entire working life span and that last for 15, 20 years or more or until the pump fails? When almost every industry uses crimps reliably, without solder, including aerospace, and have been for years and years and years I think perporting that you must solder and crimp is over the top. Perhaps 2% of boaters know how to actually make a real solder joint. The rest will only make things worse.
The well at our old house was 245 feet deep and a true artesian. It over flows out the well cap almost all year. The crimps are about 240 feet below ground and totally submerged! The three wires connecting the pumps are CRIMPED and HEAT SHRINKED with what are called Stakons (basically adhesive lined crimps). These bare copper, non-tinned, wires have been under water now for over 13 years only crimped and heat shrinked..
Next time I replace my well pump I will be sure to let the well guy know that his hundreds of wells he's installed are going to fail because they are not both soldered and crimped..
I'm sure he'll get a real chuckle out of that.
Crimped connections are a perfect candidate for crevice corrosion - the interstitial spaces between wires and between the wires and the connector pull in water by capillary action. Oxidative and galvanic corrosion increase the looseness of the connection.
First, in a PROPERLY executed crimp there will be NO interstitial spaces for water to wick. A proper crimp is cold formed and becomes a solid mass of copper. Water does not penetrate the solid copper pipes in your house and it does not penetrate a properly executed cold formed crimp as it becomes a solid mass at the crimp/lug/wire interface. Cheap crimp tools do not always make a true cold formed or cold welded connection.
The battery lugs & wire harnesses on my wife's car are crimped and not even hermetically sealed nor is tinned wire used. Her car is blasted with wet road salt all winter long, the engine bay looks like a salt lick right about now, and has been for six years. The car also resides only 40 some-odd yards form the moist salt air of the Atlantic ocean 365 days per year. It also lives outdoors as I have more important things to put in the garage like boat stuff.
I've yet to replace a battery cable on any of our vehicles nor a "crimped" wire harness. Perhaps I should call Honda and warn them of the impending battery cable disaster that is awaiting them for not using solder??
A hermetically sealed connection, using the heavy duty adhesive lined heat shrink I use, the same type of heat shrink used by WELL DRILLERS to seal SUBMERGED wires, is not and will NOT be exposed to moist salt air when done correctly. These connections are water tight. Remember we have millions & millions of wells and well pumps in this country that are not soldered, and reside submerged below hundreds of feet of water pressure. What keeps these connections dry? Adhesive lined heat shrink only!! If you have no "salt air" or no moisture you have NO corrosion.
Vibrations, and harmonic frequencies of all of the primary vibrations on a sail boat concentrate naturally at stress risers - the crimped connection is a huge stress riser, and will often fail through vibrational induced brittle fracture at the connection point.
Funny this is the exact reasoning the ABYC uses for NOT using solder and for using marine grade, tinned, MULTI-STRANDED wire that meets UL-1426. The multi stranding and strain relief built into either heat shrink crimps or insulated crimps prevent work hardening by design solder creep does not.
Sure if a person with high soldering skills solders and crimps a terminal and uses a heat sink to prevent creep beyond the strain relief a solder joint will work fine. The harsh reality is that perhaps less than 2% of all boaters know how to solder properly or will ever do enough of it to develop the skill set. As I said above they can do more harm by soldering, without experience, than they can do with proper crimping tools and connectors.
Vibrational analysis has proved over the last century or so that a properly soldered connection will last many orders of magnitude longer than a mechanical connection.
Can you please point us to a reference white papper that supports this "factual" claim in the marine environment??
Perhaps you should spend some time educating the engineers at NASA, Lockheed, Boeing, Lear Jet, SAE, ABYC, Blue Seas, Paneltronics, Prestolite Electric, Hinckley, Hatteras, Carrier Corp, 3M, Ford, GM, Honda, Toyota, Otis Elevator or any other company that uses millions of crimps reliably.
Many of the horror stories of soldered connections are no doubt from uninformed boaters using acid core solder that he had left over from the plumbing project to solder wires. The acid flux will eat the copper and tin in about a week. And of course, it is perfectly easy to make a solder joint look great and be useless; cold solder joints are difficult to detect - you have to know how to solder.
Thank you for making my point..
Very few boaters know how to solder correctly and SHOULD NOT.
Mechanical joints are easier to test (pull on the wire) but you will never make acceptable crimped connections with the Wal-Mart crimper that came free with the 12 feet of 12 gauge wire.
We're in full agreement!! You need the proper tools and quality conenctors like those made by Ancor, FTZ or AMP.
The best of both methods can be had, and the drawbacks of each reduced, by soldering a connection first and then adding a mechanical connector.
Again, this is bass ackwards. You should never solder first then crimp as it defeats the entire mechanical cold formed crimp. It can also damage the dies on the crimp tool. Here's what NASA has to say:
"4.3.4 Crimping. Stranded wire shall be used for crimping (Requirement). Crimping of solid
wire is prohibited. Crimping of solder tinned wire is prohibited."
Somebody want to tell NASA they are wrong..