All good advice and postings. I don’t mean to repeat as much as to emphasize or ditto the previous posting’s recommendation to purchase
and read the following books
Nigel Calder's Boatowner's Mechanical and Electrical Manual (Ditto on the bible comment)
Charlie Wings Marine Electronics Books has good explanation and examples
Ed Sherman also has several good marine electrical books.
After reading these books, I’d recommend:
1) Creating an electrical inventory worksheet (item, watts/amps, usage during night sailing and more). This will help you design and size your circuit breaker panel, figure out your battery sizing and your charging
needs (e.g. alternators, solar
2) Create a wiring diagram that includes which wires run through the engine room (higher heat, thicker wire), which wires will be bundled/conduit, where the circuit protection and switches will be located and so on. At some point you’ll need to make decisions on lightening protect (or not), grounding/bonding and whether your running an SSB
3) As many have mentioned, there are several DC marine wiring calculators available on mobile devices that follow ABYC E-11 wiring standards (or ISO). Some of them will save/email the wire runs so you can sit in the boat, even the engine room, with a tape measure and start documenting all the wire runs you will need in the calculator (the calculators at a minimum should give you the wire size, voltage drop and ampacity and some will even some the wire amounts by size, type and wire color so you know whether your buying
a few feet or as some already mentioned by the roll; 25’ 50’, 100', etc.).
4) For rewiring an entire boat, I’d recommend investing in good electrical tools (ratcheting crimpers, good wire strippers, etc.) that will improve the quality and efficiency of job. This includes borrowing or buying a lug crimper. The marine environment
can wreck havoc on wiring, so also invest in good marine wiring, marine connectors, heat shrink tubing for the connectors and so on, so that you’re not having to repair the work you did or risk damage to equipment
. This money
saved on less expensive wiring and connectors is little compared to your labor and the potential damage to expensive motors (e.g. windlass
, pumps) and electronics
when the corrosion
eventually increases voltage drop.
5) In addition to using the correct wire size, ABYC also has specification on the installation
(e.g. connector types, supporting the wire at specific lengths, circuit protection, and more).
6) And remember, that unlike a car that is ground to the chassis, wire lengths for wire size calculations on a boat are almost always round trip (positive and negative length) unless you’re grounding to the engine (e.g. alternator
There are a number of good web sites that list tips, tools and recommendations in addition to the wealth of knowledge on this forum. And in the past I’ve found good wire design examples that the other boaters have generously posted. I've even found designs for the model boat that I was re-wiring.
Good luck on your project and please don’t hesitate to post questions during the project.