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Author Topic:   Battery Re-location to Console: Wire Gauge
pwitort posted 07-13-2005 11:48 PM ET (US)   Profile for pwitort   Send Email to pwitort  
What is the proper battery cable wire gauge to connect the motor to the batteries in the center console of my 1987 Outrage 18, approximately a 16-18 ft run? The engine is a 140- to 150-HP four-stroke. I want one continuous run (no intermediate connections). Hopefully the solution will fit through two 3/8 inch diameter holes in the engine shroud.


jimh posted 07-14-2005 01:08 PM ET (US)     Profile for jimh  Send Email to jimh     
When making a continuous run from the battery to the engine cowling it is probably best to use rather flexible cable, often called welding cable. This cable will have many, many very fine strands. This will allow proper flexibility and movement at the point where the cable enters the cowling. The cable has to be able to move with the engine as it turns and tilts. If you look at the cables that come with a new engine you will find they are of this type of construction.

You also want to use a cable whose insulation is rated for a marine environment, which typically means oil and water resistant. Finding reasonably priced cable of this type may be a challenge, particularly if you shop at ship chandleries.

Another option is to use the existing engine cables and splice them to a run of cable which is not quite as flexible. You still want a cable with multiple strands--the more the better generally--as the boat environment will have a lot of vibration. If the cable is too stiff it will not perform well when subjected to vibration.

The gauge of the wire has to increase as the length of the cable increases in order to maintain the same voltage drop.

Making good connections to large gauge wires often requires special tools for crimping and soldering, if solder is used. The choice to solder or not is another area of debate. Some feel that no soldering should be done as this causes the cable and connector to become too stiff, and this can lead to cracking from vibration.

jimh posted 07-14-2005 09:29 PM ET (US)     Profile for jimh  Send Email to jimh     
Regarding the affect of the battery relocation on boat performance, I know that many people have done this to take weight out of the transom in order to ameliorate the added weight of a heavy four-stroke engine. Even the factory has gone to this approach on many of their new models. However, I don't particularly see that this is a good design choice, and I explain why below:

First, from an electrical perspective, locating the battery in the console moves the battery farther away from its greatest electrical load, the starting motor. It also move the battery farther away from the source of its recharging current, the outboard motor charging circuit. As a result, the size of the electrical cables connecting the motor and the battery will have to be increased to reduce the voltage drop. From an electrical design, this is not an improvement.

Also, to look closer at the electrical situation, in really may be necessary to replace the cables with a new, single, continuous cable in order to reduce the voltage drop to a proper level. Consider this:

If the existing cable is of a length and wire gauge such that it just meets the minimum standard for voltage drop, it will be impossible to add on additional cable and not increase the voltage drop. That is, the new cable added would have to have no voltage drop in order not to cause the total voltage drop to exceed the maximum tolerable voltage drop. Or, perhaps more practically said, you will have to use a very large wire gauge for the added portion so as not to cause it to have any appreciable voltage drop. It may be cheaper and better to replace the entire run with a single piece of cable of the appropriate size.

Second, locating the batteries in the console will cause them to undergo greater motion. There will be greater pounding on the batteries in the console compared to a location at the stern. As everyone knows, in most cases the least motion on a boat occurs at the stern. This will cause more mechanical stress on the battery, as well as more stress on the hull to which the battery is strapped.

Third, when the boat in on plane, there will be more weight forward of the center of pitch resistance, so it will be harder for the propeller and hull to lift the bow of the boat. There will also be more weight located farther from the axes of movement, so the boat will have more momentum when pitching. As a hull goes on plane, the portion of the hull still in the water decreases and moves aft, until only a small part of the hull at the very stern is still in the water. If the batteries are in the stern they will be right over this area, and their weight will not contribute to pitching movements as much as if they are in the console.

pwitort posted 07-14-2005 10:53 PM ET (US)     Profile for pwitort  Send Email to pwitort     
Thanks Jim, good point about the possible consequence of using the existing cable.
I pushed with the dealer about using only one cable and he balked and only wanted to use the full length of the cable provided with the new motor ( in this case a 135/150 honda). He would join the stock cable with another marine rated battery cable (tinned wire too) and continue the run to the center console. That is how it was done for my current boat, although only black electrical tape was used and the resultant joint was actually down in the sump in the rear starboard corner of the 1987 Outrage 18. Needless to say this got wet on occasion and eventually corroded. I will not have an important battery connetion being anywhere near water if I can help it.
His reasoning was:
-the battery cable connection under the shroud is done with a connector not easily obtained (to make a new cable ) and/or the battery cable branches off to multiple places before it is terminated in a crimped end connection and replicating those 'branches' inside the shroud is something he doesnt want to do. This last reason, if true, would seem to be an issue... can anyone comment on what the battery cable connection(s) inside the Honda 135/150 look like?... does it go straight to a bolted termination with a standard crimped connector?


knothead posted 07-15-2005 09:13 AM ET (US)     Profile for knothead  Send Email to knothead     


When I moved my batteries to the console of my Montauk, I ran the positive cable from the motor to a Guest 1-BOTH-2 switch located on the starboard side near the back of the boat. The negative cable is run from the motor to a connecting stud (I forget the brand, bought at West Marine)located next to the Guest switch. Heavy gauge wire was then run from the switch and connecting stud to the console. I had connections swaged onto all connections. This eliminated the need to splice wires, kept the connections out of a wet area, and eliminated the problem of trying to run heavy gauge wire into the motor. After tightening all connections and testing, I covered them with marine silicone. The connecting stud has a rubber boot cover that fits tightly, and the Guest switch cover protects the positive leads.

This set-up has worked for the past 4 years with no problems, even with the boat being moored in salt water for 2 months at the time.

Good Luck


andygere posted 07-15-2005 12:13 PM ET (US)     Profile for andygere  Send Email to andygere     
I would not accept a splice in your main line starter and ground wires, and would insist on a continuous run of tinned cable of the appropriate size. My current Outrage and former Montauk both had wiring systems that were made up by splicing the stock engine starting and ground cables to the new cables (in both cases converted from a single to a dual battery system). In both boats, there was corrosion failure at the splices, which were done "correctly", if that's at all possible. Remember, these cables will lie in a rigging tunnel that is continuously wet, and subject to lots of vibration. The splices will fail, it's just a matter of when. On the Montauk, it left me dead at the dock, but luckily not stranded at sea. I got a little smarter with the Outrage, and replaced the wires before complete failure, although they were well on their way, and I was always suffering from weak batteries. If your dealer won't do it, you can do it yourself. I purchased a simple lug crimping tool for about $40, along with the tinned battery cable and the appropriate size lugs from Boater's World and West Marine, and made up the system myself. It took a bit of time, but I have complete confidence in the system, and the wiring, switches and connections are all neat and professional looking. Some chandleries will loan you the crimping tool, or have one in the store you can use to crimp the lugs onto your wires.

I would also put your battery switch in or on the console, and suggest that you consider a system with a voltage sensing relay that will automatically charge both batteries, but isolate your house and starting loads. This prevents house loads (lights, radios, electronics) from ever killing your starting battery, but still lets you combine the batteries to "jump start" the starting battery with the house battery. I purchased a switch cluster with a built-in voltage sensing relay from BEP marine, and have been very pleased with it.

Your dealer is being lazy, and that will leave you in the lurch eventually. The under shroud connectors for my Mercury 200 were virtually the same as the generic Anchor brand lugs available everywhere. Even if the Honda unit is not stock, the dealer should be able to order the part. If he won't do the job right, I recommend that you save yourself the money and do it yourself. It's not terribly difficult, you'll get a good result, and find the experience quite satisfying.

jimh posted 07-15-2005 01:24 PM ET (US)     Profile for jimh  Send Email to jimh     
I would never recommend running large gauge cables from the battery to the primary battery switch through the rigging tunnel without a fuse. If anything happened in the rigging tunnel, like a short circuit, you would have no way to shut off the current. You could have a dangerous fire situation in a very short time.

You should have the primary battery switch very close to the battery; never at the end of ten-foot cables. That is dangerous.

Most installations do not have a fuse between the battery and the primary switch. Typically these two are adjacent and only a very short and direct wire connects the two.

If you must have the primary battery switch ten feet from the battery, you ought to use a fuse between them, located close to the battery.

LHG posted 07-15-2005 03:11 PM ET (US)     Profile for LHG    
I thought the proper way to re-locate a battery forward is to use a terminal block designed for wires of this size. The original engine battery cables are attached to one side, and new MUCH larger new cables come off the other side, through the tunnel, and up to the new battery location.

I believe this is the recommended code procedure, and this allows easy removal of engine cables for service, repair, etc. All connections are above water, and easily inspected and serviced. Doesn't BW do it this way

pwitort posted 07-15-2005 03:26 PM ET (US)     Profile for pwitort  Send Email to pwitort     
Ok, Im settled on tinned marine battery cable; I have an economical source for 4-ought to #4... but still dont know what gauge to get for a 150hp motor and 15-20 ft of length. The amps info is hard to come by. As a gut feel guess Im expecting the final answer to be around #2 gauge which is about 3/8 inch thick OD (plastic included).Possibly a #1 which is about 1/2 inch OD.

Has anyone run the cable formulas for a honda 150 or equivalent ?

As to battery life in the console, my batteries sit directly on the floor ( the prior owner cut a hole in the bottom of the console and lowered the battery cases into that) which is the toughest environment shockwise as you point out. I do a lot of pounding in the ocean and the batteries have lasted 5 or more years before replacement. I replaced them only because they were not holding as strong a charge as was needed for the Voltage sensitive 150hp Yamaha (big difference with fully charged strong battery).

Sal DiMercurio posted 07-15-2005 04:39 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
I own a 20' Outrage that I moved two group 29 batteries for a year 2000..... 200 hp Evinrude into the ice chest in front of the councle.
I did this in 2000 with #2 welding cable & the Perko switch also inside the ice chest with lots of 1" holes drilled through out the whole ice chest [ sides ] for ventilation.
I've had absolutly no problems since.
The way to test to see if your cable is heavy enough or not heavy enough is, run a cable from where you are going to put your batteries to the starter.
Have some one at the engine with the cables hooked up to the starter also with a volt meter.
Turn the key to start the engine & if the voltage drops below 12 v. when you hit the starter, your cables are to light.
You mention #4,....forget it, thats far to light a guage, a #2 or even #0 if it's a real long run is needed, nothing less than #2.
knothead posted 07-15-2005 04:50 PM ET (US)     Profile for knothead  Send Email to knothead     


Guess I learned something new today. After reading your post and thinking about my set-up, I agree completely with you. DON'T rig yours like I did.

So-o-o-o, at the end of the season, I'll rewire by moving the switch foward, near the batteries, but outside the console, hmmm, have to think about that a while. I don't like thinking about having to stick my hand into a smoking console to turn off the battery switch.

I'll replace the switch in the back with an appropriate terminal block.

The reason for moving the batteries foward was to create clear deck space to be occupied by boys and their toys. Sadly, when they grow-up and I become a geezer cruiser, I'll move them back to the stern. Probably have a 4 stroke 50 hp on the boat by then. On second thought maybe not, probably won't be able to hear anyway at that age.


pwitort posted 07-16-2005 10:11 AM ET (US)     Profile for pwitort  Send Email to pwitort     
thanks all for the valuable info. I expect when this tread is finally done ( is a thread ever done?) it will be quite valuable as this is a foggy technical area with life impacting consequences. For reference, an older thread has some additional comments :

There is another thread that contains some postings on battery cable issues and is included here for completeness:

From the 03184 thread noted above, the Ancor site reference is invaluable:
at this site click on 'technical information' and then wire calculator... this calculator gives the required gauge for a given number of feet and amps.

From that calculator and for my 1987 18 Outrage, here are the recommendations: (11 feet is the (ample)distance from the Perko switch inside the console- a few inches from the floor conduit pipe- to a place above the starboard sump area, under the starboard gunnel where it could be connected to the stock cable that goes to the motor (busy area there with fuel line and feed through cleat). (17 feet is the full single cable distance from console to far side of 150hp Yamaha...18 feet would be the maximum needed for any other motor).
The entries in the table below give the required gauge for the amps and feet noted in the row and column (assuming no more than a 3 percent loss).

Amps 11' 17'

40 8awg 6awg
100 4awg 2awg
200 2awg 1/0
250 1awg 2/0
255 1/0 2/0
300 1/0 3/0
400 2/0 4/0
417 2/0 over 4/0
500 3/0
600 4/0
645 over 4/0

I expect that these ratings are for continuous current, and that is probablhy why myself and some others with currently 'below specification' wiring do not appear to have problems. A 10 second burst of current to the starter may not appear to cause any damage; however, when my butt connection near the sump got corroded, the plastic on the wire at that point melted! Cleaning up the connection resulted in a cool wire and a commitment to ensure this didnt happen again. Checking the voltage drop from battery to engine during cranking is an important test.

In a reply above, LHG asks if BW does the butt connection for their new boats...does anyone know? At least 2 dealers here in portland swear by it, but nobody I have found yet has done the true 'engineering' of the cables needed.

So, I still dont know what gauge to use and there may be issues with wiring inside the cowling and getting through the grommet (certainly dont want to leave space in the grommet for water to get through). I may just have them butt connect the standard cable under the gunnel and try to solve the problem myself once I get the boat back.

Apparently the Honda 150 has an additional positive battery cable that comes from the alternator to the battery. The alternator is rated at 40 amps, I think, and using the Ancor gauge calculator, 11 feet requires an 8awg wire and 17 feet a 6awg wire. Since this *is* continuous current and the stock Honda cable may need to be used, this is a good place to 'over spec' the additional cable. The 6awg cable will handle 80 amps at 11 feet and a 4awg will handle 127amps to 11 feet or 40 amps to 35 feet; since this is the smallest size the distributor has, Ill probably use 4awg.

Important note: if putting butt connnections up under the gunnel, plan carefully to avoid the feed through cleat area and possibly the metal fuel line.

pwitort posted 07-16-2005 10:18 AM ET (US)     Profile for pwitort  Send Email to pwitort     
I will be terminating the positive battery cable(s) on the perko distribution switch and the perko connects to the two batteries. What is the preferred connection for the negative/ground to get to the two batteries? Just some jumper between the batteries?

Also, when i got the boat there was a flat woven ground wire running from the console batteries to the gas tank through the see-thru portal in the is no longer there. I need to see if there is any other ground connection between the battery and gas tank... is that needed for safety or to give a better VHS transmission with the big ground plane of the tank?

jimh posted 07-16-2005 10:34 AM ET (US)     Profile for jimh  Send Email to jimh     
If I were rigging this boat, here is what I would do:

--I would install a marine grade lead acid wet cell starting battery in the stern, where Boston Whaler, the outboard engine manufacturer, and most every boat designer intended it.

--I would connect the engine to the starting battery using the stock cables.

--I would install a second house battery in the console. If warranted by the house loads, this battery could be an exotic gel-cell or AGM deep-cycle battery.

--I would use the secondary charging output of the motor to charge the house battery by extending the cable as necessary, but I would not increase the wire gauge. (The technical reason for this is that as the charging current drops the voltage drop in the wire also drops, so the battery will float to the full charge voltage even if there is a 0.1-volt extra drop in the wire at the full-charge current rating.)

I would bond the two negative terminals of the batteries together with a wire of 10-AWG.

In the event the engine starting battery failed, I would either:

--carry jumper cables to temporarily boost the starting battery from the house battery, or

--disconnect the house battery and move it to the engine battery for starting.

Putting 100 pounds of batteries in the console and investing in $200 of copper wire seems like far too much work, time, and money.

pwitort posted 07-21-2005 03:40 AM ET (US)     Profile for pwitort  Send Email to pwitort     
Thanks for your suggestions Jim.
For the kind of ocean motoring I do, I will always want two batteries hooked up all the time. The Oregon bar crossings, fishing close in to rocks, and the strong currents of the tidal rivers all call for a high level of reliability in being able to restart the engine quickly. you may not have the time to rig something up after the problem occurs.
I will have to settle for hooking into the stock Honda cables, and am using 1/0 cables for that and keeping the connection up under the starboard gunnels. A little pricey at $80, but an investment I feel ok about making.
Looking at the West Marine charts for battery cables, I think the 1/0 will provide all the capacity I need.
jimh posted 07-21-2005 08:44 AM ET (US)     Profile for jimh  Send Email to jimh     
[This article thread has been moved from the PERFORMANCE area.]

Extra caution in warranted when operating in dangerous waters.

According to the wire size calculator at

if you have 1/0 cable it should carry 250-Amperes of current with less than a 3-percent voltage drop over 12-feet (about the distance from transom to console on an 18-foot boat). It sounds like it should be fine.

pwitort posted 07-23-2005 12:15 PM ET (US)     Profile for pwitort  Send Email to pwitort     
Thanks Jim.

One interesting/confusing difference with Ancor and West Marine is that West marine uses double the cable length...coming and going to the load. I wonder if Ancor implicitly includes that?

jimh posted 07-23-2005 11:37 PM ET (US)     Profile for jimh  Send Email to jimh     
Say--that is a very good point! I don't know the answer. You should consider both the positive and the negative in the overall length of the cable. More research is needed.
bwc8418 posted 07-26-2005 03:01 PM ET (US)     Profile for bwc8418  Send Email to bwc8418     
When I purchased my whaler, there were 2 batterys in the CC, I did not know about them being originally located in the stern. Anyway, I did notice that I was not getting enough cranking power to my motor with the incorrect gage wire that was there, so I ran two runs of tinned #2 from West Marine from the CC to engine, I have absolutly no problems charging both batteries with the Honda 150, or the former Johnson that i had before. I checked the voltage drop chart, and for the number of feet, not sure how many now, but settled on #2. Like I have indicated it works fine, I get 14.6 reading from the engine to the battteries for charging and running.
pwitort posted 07-30-2005 10:23 AM ET (US)     Profile for pwitort  Send Email to pwitort     
Since i had to have something workable for the dealer, i ended up going with 1/0 wire from the console to a point under the starboard gunnel above the sump where it is bolted together to the stock cable from the honda 150. This will work for now and I look forward to a continuous run of wire some day from cc to engine.
One thing that you do get with these bolts back there is the ability to hook up other things... like the kicker motor electric start and possibly a crabpot puller motor. These are better done in the console, but having the attachements back in the rear is almost like having the advantage of the batteries back there.

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