Dear Boat Doctor,
I am trying to settle a debate with a friend. We are considering some wiring projects and discussing the type of wire to use. I feel it is important use marine-grade wire, but my buddy feels it is a waste of money, that marine-grade wire is the same as automotive-grade wire.

Bill Hampton
Bangor, Maine

Dear Bill,
In general, automotive wire can be used on boats, assuming that it is SAE (Society of Automotive Engineering) J378, J1127 or J1128 rated, but it is not recommended. Marine-specific wire is unique in a few ways. 

Most importantly, marine wire is larger for a given gauge size, up to 12% larger in some sizes. If you choose to use SAE wire, you must allow for this difference when using commonly available marine voltage drop tables.

Marine wire stranding is unique, the strands are much finer and each individual strand is tinned. The fine stranding makes the wire very flexible, allowing it to better survive in a moving, vibrating boat, while the tinned strands provide additional corrosion protection. Finally, the insulation is designed to stand up in the marine environment; it is oil, moisture and heat resistant.

Can you use automotive wire in your boat? Yes. Should you? Likely not. Marine wire is a bit more expensive, but in light of the other expenses and potential consequences, it is a wise investment for your boat.