Dear Boat Doctor,
I am having a discussion with my brother-in-law about the best way to make electrical connections on my boat. I have traditionally used crimp-on terminals but he says I should solder the wires together. Can you help us settle our bet as to who is correct?   
Bob Flynn
Chicago, Illinois

Dear Bob,
There are many aspects to your question but I'll start with the direct one. I recommend crimping terminals to wires. It is much more convenient to crimp than solder and the terminal will be more flexible (to help avoid fatigue).

It is important to use a proper crimping tool. The cheap hardware-store tool (the one that crimps, strips, and typically cuts off screws) is not adequate, and I don't feel that it crimps the terminals fully. I vastly prefer the Thomas and Betts WT111M or a similar tool, as it doesn't crush the terminal and makes a very positive crimp.

Speaking of terminals, you get what you pay for. Cheap automotive terminals are pretty wimpy, the insulated part tends to fall off, the crimping part is pretty small and the metal overall seems brittle. I find Ancor or other high-quality terminals much better to work with.

Good terminals deserve good wire. Use marine specific cable; you'll pay a bit more but it's worth it. Marine cable is designed for the marine environment, the insulation will stand up better, the finer strands will hold up to vibration better and most importantly the copper strands are dipped in tin to minimize corrosion. Remember to reference an ABYC wire size chart to be sure you are using the right size cable. The lengths listed in those charts is round-trip, a device 5 feet from a battery or panel is a 10-foot round trip.   

Once you properly crimp on a quality terminal you should cover it, and a bit of the wire, with heat-shrink tubing. I like to use adhesive lined tubing, it has some goo inside it that melts when shrinking to totally encapsulate the terminal. I have had great luck with the heat shrink tubing from www.cableorganizer.com. I will typically use their 4-to-1 shrink ratio, dual-wall, adhesive-lined tubing. This tubing has a great shrink ratio and is loaded with internal adhesive to waterproof your connections. It is sold by the foot and is far less expensive than the little packs of tubing from the marine store.

One last note on tools: Invest in a heat gun to properly install heat-shrink tubing. A decent heat gun will work far better than a lighter. You don't need to spend a fortune on a heat gun, a gun from a big-box store is fine. As a side benefit, a heat gun is great for removing varnish.