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1974 O'Day 20 electrical questions


Jul 19, 2019
Oday 20 East Tennessee
I just got this boat and have a couple of questions.
1) Where was the original battery location? This one is installed on the port berth under the cockpit. It is not square and is braced by a random 2 x 4. I am thinking of moving it to the locker on the starboard side of the cockpit. Is that a really bad location? Are there better locations?
2) My dad is an electrician and is planning to rewire the boat. Does anyone know where I can get a wiring diagram?

May 24, 2004
CC 30 South Florida
Battery location? It should be a dry and well ventilated Location. It should be convenient to service, add distilled water, clean the terminals and to replace. It is best to secure battery in a box to keep dry and contain spills. Batteries are heavy and when placed to a side it may cause the boat to list to that side. Try to divide weight loads evenly to both sides. Battery should not be located where flammable liquids may be stored. My preference to locate batteries is close to the center line and close to the distribution panel or block connectors. I cannot imagine that the electrical system in an Oday 20 would be much more than to power navigation lights, an anchor light, perhaps a cabin light and a 12V outlet. I'm sure your dad can trace and work out the schematics, purchase any wiring, connectors and components from a marine shop to insure your installation will have the safeguards required by a marine system. Home and automobile wiring and connectors may not be appropriate for marine use. Welcome to the forum and good luck.
Oct 19, 2017
O'Day 19 Littleton, NH
Welcome to SBO def,
You have joined a awesome group. There is so much experience and knowledge on here, you are sure to get everything you need and more.
Congratulations on your acquisition of your '74 O'Day. O'Day made nice boats.
Are you sure there was a battery originally? I don't know, but the O'Day Mariner was not originally produced with an electrical system. Night sailing was not part of the original plan for these little boats.
On the Mariner, which looks a lot like the 20, people often put the battery where the head was planned to be.
They seem to trim well with a little more weight forward.
Benny gave you some great pointers and please keep in mind that marine electric requires some unique considerations due to grounding and electrolysis.
I'm no expert, but there are those who are, on here.
Good luck.

-Will (Dragonfly)
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May 20, 2016
Catalina 36 MK1 94 Everett, WA
Tell your dad it’s not a house, boats require a different approach

1) use marine tinned stranded wire
2) no wire nuts - use crimp connections , ring or bent forks under screws.
3) support every 3’ watch for rub points
4) fuse for the wire
5) use bigger size - lots of calculators for wire size I use blue seas circuit wizard app. Watch voltage drop.
6) neutral and ground on 120VVAC only connect at source ie dock, inverter, generator.
Mar 2, 2019
Oday 25 Milwaukee
Welcome . Please keep in mind unlike houses boats vibrate .Wires chafe. Humidity from being near constant moisture causes corrosion rarely seen in a home enviroment . My basement is so humid we have tiger salamanders living down there !
Almost all Odays with any type of factory wiring had the wires run between layers of fiberglass . You are much ,much ,much better off starting from scratch . TRUST ME !
This way there are no surprises down the road. You will not find lamp cord ,bright orange extension cords or speaker wire being used where it shouldn't be .
Plan for expansion of circuits. We all thought we just need a few circuits . Along comes a stereo ,gps ,Bluetooth music,VHF radio,,etc...