tech notes


  • Corrosion
  • Corrosion Notes
  • Marine Guard Systems
  • Boat Building Tips

Ocean Currents Marine Electric, Inc. is highly experienced and is recommended by many knowledgeable Captains, Marine Surveyors, and shipyard managers throughout the world for marine corrosion control. With our over 25 years of experience of precision testing, circuit analysis, and along with being in the field service electricians (actually making corrections to the electrical system that started the problems) we have a unique, deep and thorough understanding of many types of corrosion.

We can efficiently resolve galvanic corrosion, bonding problems, and stray current corrosion on all types and sizes of vessels. We offer electrical surveying and corrosion surveying for insurance companies, expert witness testimony, and pre and post purchase surveys for boat brokers and owners. 

We resolve boat electrical leakage problems detected by MARINA GUARD marina electrical systems monitors. We are top experts for steel, aluminum, wood, and fiberglass boats. We supply and install all Electro Guard corrosion control systems, and service Capac systems.


General hull type recommendations
Note: These recommendations are here to help you get started, as a service to Captains and technicians. But there are very specific bonding connections, zinc placement, and procedures for these types of hull materials that one must use to avoid hull corrosion problems and AC system safety.
Ocean Currents Marine Electric, Inc. is available to design systems and resolve any problems which may be present.

Fiberglass Hulls

  • Bond thru-hulls, engine, rudder shaft, and main DC negative buss, with #6 wire to one or more zincs plates. "You can’t have too many!"
  • Shaft collar zincs on prop shafts.
  • Connect shorepower AC ground wire to bond system through a “galvanic isolator”, or use an isolation transformer, preferably with voltage boosting capability.
  • Monitor bond system free potential.

Steel/Aluminum/Ferro Cement Hulls

  • Coat hull carefully with epoxy to reduce exposed reactive metal if possible.
  • Install lots of zincs. Can’t have too many!
  • Connect shorepower AC ground wire to bond system through a “galvanic isolator”, or use an isolation transformer, preferably with voltage boosting capability.
  • Monitor hull free potential constantly.

Wood Boats

  • Disconnect only the through hull bond system or use an Electroguard control system to keep bonding system protection level low enough to prevent de-lignification. (white powder buildup from over zincing wood boats.) Test wood boats very carefully to determine the minimum zincs required, but provide sufficient zinc life.
  • Keep a bonding system for large metal objects for AC safety grounding. (engines, main DC negative system)
  • Connect shorepower AC ground wire to bond system through a “galvanic isolator”, or use an isolation transformer, preferably with voltage boosting capability.
  • Isolate any zinc plate mounting bolts from hull.

All Boats

  • Additional provisions may be required for AC safety grounding, lightning protection, ham/loran radio grounding, electrical noise, and trolling wire fishing.
  • AC safety grounding is a life safety issue, do not disconnect green shorepower grounding wire from your boat! You or swimmers may be electrocuted!
  • Bond sinks and cabin metals to AC ground preferably, for safety.

New marinas commonly install the NFPA (National Fire Protection Agency) recommended MARINA GUARD brand shore power monitors. Many deaths from electrocution occur in marinas from leaking AC power problems on otherwise well maintained boats. It is very difficult for the untrained owner or even electrician to detect leaking AC power. Technically, if your shorepower AC neutral wire is connected to your AC shore ground wire on board your boat, some of the normal AC power flowing back to the shore power source ( an electrical service on the beach) flows dangerously back to this service through the water, instead of all of it through the AC shore power neutral wire as it should. In common low conductivity fresh water this can kill swimmers and divers!

If the Marina manager detects this problem coming from your boat, the AC system must be sorted out, and problems resolved. There may be multiple pathways where the neutral to ground is connected, but experience and precision testing equipment can locate these problems. Contact Ocean Currents Marine Electric, Inc. for this critical field service.

Customers have questions, and boat builders need to build boats safely.

Recommended books:
* "Boat Owner’s Illustrated Handbook of Wiring” by Charles Wing
* IEEE standard 45
* ABYC Standards
* Ancor products catalog
* Blue Seas products catalog


Wire: What kind of wire should I use?

Generally, if you are wiring a power or sail vessel under 65’, you use flat 2-conductor tinned wire like Anchor/Cobra/HSC style #14-2 “flat boat” type. Use typically #14-2,  #10-2, and #10-3 for DC systems, and round untinned #12-3 for AC outlets.  Battery cables are usually red or black PVC insulated, or black rubber DLO jacketed tinned cables.  Tinned wire is excellent for all DC systems, as the low voltages of DC systems cause small corrosion resistances to cut the amperage and voltages even in lightly corroded wires quite a bit.

Generally if you are 65’-100’, use the same Anchor/Cobra/HSC style #14-2, #12-2, #10-2 tinned “flat boat” for DC systems, round 12-3 untinned “commercial marine” (an actual type) cable from a marine electrical supply house for AC systems.  This marine commercial cable has a thicker jacket for AC than the thin flat cheap DC type cables.  For batteries, it is best to use “diesel locomotive cable” or DLO type double rubber insulated and tinned cable for batteries and feeders. Welding cable is not very good for a number of reasons. 

Vessels over 100’ generally have all “commercial marine” cable for everything, both AC and DC, with battery cables in DLO once again. 

You can buy all the cables you need from Hardware Specialty Company, 206-624-5785, Seattle, and they ship worldwide.

If this in an inspected vessel (commercial use, lots of passengers), all the cable will have to meet USCG regulations which call for UL listed devices and cables throughout.  The cable will be commercial marine type at the least, sometimes aluminum jacket armored cable (TSGU-A type) as the next upgrade, and finally an IEEE-46 approved TSGU-LS (LS is for low smoke when burning) type cable.  Depends on the tonnage and passenger capacity, see the CFR’s.

Sizes of wire:  This all depends on what the classification agency (or design specification agency) recommends.  Standard wire sizes for the amperage expected to carry are in the ABYC or in front of the Anchor products catalog. This is only a guide, consult the appropriate USCG and ABYC literature for exact rules to follow. 


What are the regulations for wiring boats? 

The primary agency in the USA is the USCG.  For pleasure boats, there is only one small part, CFR 183.01 (code of federal regulations part 183.1) about 3 pages worth of electrical regulations, and they only apply to GASOLINE powered boats.  But they are absolutely important, they are LAW. There are no regulations for diesel powered pleasure vessels at all, any size.  Yes, it’s a free for all. However, the insurance companies require surveys, and Surveyors expect safe boats that meet industry standards.  There is a private group, the American Boat and Yacht Council (ABYC) that has developed recommended standards which are always followed by Ocean Currents Marine Electric, Inc.  These recommendations are not law, but are recommendations only, but well serve to set the standards of wiring, system design, and mechanical design.  Unfortunately, copies of the entire regulations must be ordered for $300.00, but check your library’s reference section,  they may have a copy. They are not on the Web...yet.

If you are a commercial fishing boat, you must meet sections of the USCG CFR’s , gas or diesel, and if over 100 tons, depending on your usage, location of service, and passenger loading, different sections of the CFR’s. 

If you are a commercial charter boat subject to inspection, (typically, with paying passengers) you must meet USCG of course, with special sections in the CFR’s like old section “T” and thus NFPA, UL, and Institute of Electrical and Electronic Engineers “IEEE Std. 45”, a book orderable from the IEEE. 


What kinds of circuit breakers should I use?

To start with, for small DC circuits, the Carling (brand) type “AA”, or Blue Seas “World breakers” are perfect.  These are very commonly seen in yachts and commercial boats under about 100’.  They are about 2½” X  ¾” wide, and have an operating lever that is made to fit through a round hole.  They are available up to 80Amps size.  This AA type breaker is usually rated “AC/DC” and can be used for all AC or DC loads. For loads over 80Amps, a slightly different “AN” type breaker is used.  It has 10-32 or ¼-20 studs for attaching wires, and is about 1” wide, available in sizes up to 150Amps.  This “AN” type breaker is a more heavy-duty version of an “AA” type breaker, so it is seen on all sizes of vessels.  It too is usually rated “AC/DC”, be sure to check, because there are some surplus breakers that are only DC rated.  The “AN” type breakers are often only rated for a maximum voltage of 65VDC.  Should you have a 120 volt direct current wiring system, you must only use certain AC rated breakers. 

All these breakers have a “curve” or a graphical rating of how may amps for how long will trip the breaker.  A 100Amp breaker will hold 100Amps continuously, but a 125Amp load will take, typically, 10 seconds to trip this 100Amp breaker.  A 200Amp load will instantaneously trip this 100Amp rated breaker.  So, the larger the over current situation, the quicker the opening of the contacts.  Standard breakers have suitable medium curves, but beware of odd surplus breakers. An anchor winch always uses special, very slow curve breakers, that can take the winch motor stalled out at maximum amps for a long time before tripping. Breakers are also rated on “AIC”, (Amps Interrupting Capacity) which must be used near high power sources like battery banks, carefully follow these ratings to avoid fires. See manufacturer’s charts on this.

If you need a 200Amp breaker, there are special 2-pole or 3-pole parallel breakers available.  They pass the current through each coil in each side to trip at higher ratings. You cannot use just two regular 1-pole circuit breakers in parallel (side by side), because the load will go through whichever one has the least internal resistance first, causing your load to trip at the setting of a single pole. They must be carefully matched by the manufacturers only. Often the breaker of choice is the Bussman “187” series high power DC breakers, because they are compact, surface mount, and have 5,000AIC ratings. These are UL listed for gas engine rooms, being totally sealed, and have nice big studs to mount cable lugs to. They are for DC only.

Always use a circuit breaker when going to a smaller size wire, to protect the downstream wire from burning up if there is a short.  The USCG and ABYC both want battery switches within 6’ of the batteries when going to anything but starter motors, fuses or breakers for panels, winches, and smaller loads within 7” of the battery switch.  This protects smaller downstream wires from higher amperages available upstream from the batteries. Like the speed limit gets slower when you get off the freeway for good reason. Never connect small wires to batteries without a fuse!

For AC panels, on commercial boats and yachts over 100’, regular shore type circuit breakers are generally used.  These are mounted in custom-made enclosures. 

For loads over 150Amps, for inverters, fuses work fine.  Special fast-acting type “T” fuses are best for most brands of inverters, not only for their fast response time, but because the wide mounting lugs and internal construction keeps the voltage drop down as the normal daily high power goes through the fuse. 

The above information is only suggestions of what is generally used in the marine trade.  Consult the appropriate USCG, IEEE, NFPA regulations and ABYC Standards and Recommendations for exact requirements.