posted 02-04-2009 10:42 PM ET (US)            

Electrical conductors in cables on a boat should never be smaller than 18-AWG, and power and lighting conductors not smaller than 14-AWG. This is required in federal regulations, although those regulations may not directly apply to small open boats with outboard motors. A conductor of 14-AWG can handle 25-amperes of current in open spaces and when not in a bundle with other conductors. You should consider voltage drop in any circuit when calculating the wire size needed.

See this discussion regarding marine wire:

http://continuouswave.com/ubb/Forum6/HTML/001447.html

Therein you will find much more detail about wire standards, and where to buy marine wire at reasonable prices.

A good source of technical information about marine electrical wiring, including the current capacity, a calculator for finding voltage drop, marine color codes, and temperature ratings can be found at

http://www.marinco.com/page/wire-tech-data

posted 02-04-2009 10:55 PM ET (US)            

http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr; sid=a31f9db592e93947ed3d72f58ba34aee;rgn=div5;view=text;node=46%3A4.0.1. 3.14;idno=46;cc=ecfr#46:4.0.1.3.14.19

for some federal regulations on wire material and size. An excerpt:

§ 111.60-4 Minimum cable conductor size.

Each cable conductor must be #18 AWG (0.82 mm2 ) or larger except—

(a) Each power and lighting cable conductor must be #14 AWG (2.10 mm2 ) or larger; and

(b) Each thermocouple, pyrometer, or instrumentation cable conductor must be #22 AWG (0.33 mm2 ) or larger.