There are three problems with crimp connections:
UNDERCRIMPED connections do not have the metal surfaces of the inner crimp barrel and the wire closely coupled to produce a "gas-tight" seal that "welds" the two together. Undercrimped connections pull apart easily and may exhibit high electrical resistance while appearing to be intact.
OVERCRIMPED connections have been crimped hard enough to distort the wire at its exit from the crimp barrel, and may have cracks in the barrel itself. Again, overcrimped connections pull apart easily, but the point of failure is between the crimp barrel and the wire.
Even NOMINAL
crimp connections provide no seal
between the insulation and the wire, allowing salt to penetrate
between the strands and oxidize the wire. "Marine" crimps are
often protected with "soft center" shrink tubing, which retards this
deterioration.
INSULATED TERMINALS are extremely difficult, if not impossible, to crimp correctly. The plastic insulation keeps the crimper from applying the needed pressure to seal the terminal to the wire. These should be considered only for emergency repairs.
Still, there is
nothing wrong with crimp
connections. As used by aerospace and industrial contractors, and in
environments from desert to space, crimps are fine. But there is a
lot of engineering involved in making a proper crimp connection, the
correct tools are expensive, and most of the required inspections are
destructive, all a problem for the boatowner.
Even so, one of the
big concerns with delayed launches at Cape Canaveral is the effect the
salt will have on the crimp connections throughout the rocket.
A typical procedure to certify a crimp job is similar to this:
A matched set of crimping dies, terminals, wire, and a pull tester are obtained.
The dies are installed into the crimper, and the pressure is set
to the nominal value for the terminal and wire. Proper crimpers
will not release the terminal until the preset crimping force has been
achieved. (Proper crimpers are expensive, the cheap
automotive ones are worse than useless.)
Make 100 test crimps, onto short pieces of wire, to fit the pull
tester. Remember, statistics begins at 100.
Set the pull tester for minimum pull-out, and test the 100 crimp assemblies.
If any of the wires pull out of the terminals from the minimum specified pull, indicating that the crimp was not hard enough, then set the crimper to a higher pressure and return to step 3.
Set the pull tester for maximum pull-out, and test the 100 crimp assemblies.
If any of the wires pull out from the maximum specified pull, indicating that the wire was overcrimped causing a weak spot where it exits the terminal, then set the crimper to a lower crimping pressure and return to step 3.
When the test crimps pass inspection, then make up the wire assemblies using only the preset crimper and the batch of wire that was tested. New wire or new terminals require a new certification.