Duplex fuses in circuits?

[Wotname]

Originally Posted by deblen

The purpose of connecting rudderstock to hull with heavy cable is to ensure the rudder never rises above 0 V with respect to the hull,neg bat.,bronze/SS prop & shaft. No voltage difference-no current thru water-no corrosion. / Len

Hmm... you need to rethink this (IMHO).

This is analogous to saying if you put a heavy cable across the + & - posts of your battery, there will no voltage difference therefore no current flow and I know you know this is not true although it becomes true once the battery is discharged.

I can only assume you are confusing an electrical load with an electrical source.

The SS shaft and Al hull in seawater is a source on EMF, not a load. Placing a low resistance (even 0 ohm) load across this source aids current flow and this continues until the metals are not longer dissimilar ie one is corroded away.

It is possible to connect them together inside a more complex soloutions (like say impressed current galvanic protection) but this is not what you have described..

[Matt Johnson]

Thread steal since OP hasn't been back:

Our aluminum boat is a floating ground with isolated alt and starter (will be disconnected via solenoid after start). I want to be able to disconnect both pos and neg via switches.... and I happen to have two Bluesea 6010e switches. Battery bank two is an emergency bank and only brought onboard if there is a starting issue.

Here's wiring diagram v1.0 Please let me know any issues you see with my thought process.

Thanks,

Matt

[mitiempo]

Originally Posted by funjohnson

Thread steal since OP hasn't been back:

Our aluminum boat is a floating ground with isolated alt and starter (will be disconnected via solenoid after start). I want to be able to disconnect both pos and neg via switches.... and I happen to have two Bluesea 6010e switches. Battery bank two is an emergency bank and only brought onboard if there is a starting issue.

Here's wiring diagram v1.0 Please let me know any issues you see with my thought process.

Thanks,

Matt

As long as you have isolated starter and alt as you stated it looks good to me.

[mitiempo]

Getting back to dual fuses/breakers for a minute.

I see and agree with the logic of installing double pole breakers to switch positive and negative for each load as long as they are the type that breaks both poles simultaneously. On a metal boat this makes sense.

Dual fusing on the other hand doesn't make sense I don't believe. The problem is that there is little if any chance of both fuses going at the same time if a fault occurs. You could blow the negative fuse and still have a hot wire dangling loose somewhere.

ABYC requires all fusing to be in the positive conductor.

[deblen]

Originally Posted by Wotname

Hmm... you need to rethink this (IMHO).

This is analogous to saying if you put a heavy cable across the + & - posts of your battery, there will no voltage difference therefore no current flow and I know you know this is not true although it becomes true once the battery is discharged.

I can only assume you are confusing an electrical load with an electrical source.

The SS shaft and Al hull in seawater is a source on EMF, not a load. Placing a low resistance (even 0 ohm) load across this source aids current flow and this continues until the metals are not longer dissimilar ie one is corroded away.

It is possible to connect them together inside a more complex soloutions (like say impressed current galvanic protection) but this is not what you have described..

There-you have me!! I am embarrassingly wrong on that suggestion.
Connect only similar metals to a common bonding,if at all.
Use properly bonded zincs in salt water & check often.

https://marine.cat.com/cda/files/949222/7/corrosion.pdf

The use of marine aluminum for rudder & stock should be limited to aluminum hulled vessels only?

Am I doing any better?

Thank you Noelex & Wotname / Len

[svlamorocha]

Originally Posted by deblen

Wondered where you have been. Welcome

I have a diploma in Marine Electronic Engineering Technology from what Americans call a college,as opposed to a University,which are the only institutions in Canada that can grant a degree.
I am not an ABYC- certified Marine Electrician,but I have spent over 30yrs as a Marine Electronic & Electrical Tech.,among other electrical & electronic engineering jobs I've held.
(snip)
Please don't say something has to be done a certain way because ABYC says so.That is no help to "skeptics or other less knowledgable" folk.
We want the technical reasons,& with your training & experience,you should be able to explain the logic to us.
The OP asked about dual breakers/fuses in DC.
Though this thread has touched on lightening,isolated vs.un-isolated neg battery & earthing, I think we should(with apologies to OP) limit this thread to DC battery. There are several followers who are admitted non-electrical.

Thanks/ Len

I was working, I am not sure that matters much.

I responded to post #11, which provided incorrect advice to the fellow member who posted #8. That discussion was far from the original post but I did not want the author of #8 to go home with bad advice. I know that those posts had little to do with the title of the thread, but there was some incorrect info in there and I did not want other to get confused and start tying underwater metals because you said so.

I believe that by now other have explained (on the rudder example) why it is a bad idea to connect underwater metal parts without knowing what you are doing. And yes, corrosion is for the most part a direct current phenomenon, with the DC coming from a galvanic pair or a battery.

I do agree that codes and standards like those of ABYC are no the answer to all problems but I do believe that they are very useful to define an agreed standard of "good practice" and to allow people who do not actually understand the physics to get good results.

If it is still unclear why in most boats it is a bad idea to connect the battery negative to a bolt on keel, just say so and someone will chime in with just a little bit of relevant science.

Cheers

Charlie

[Cheechako]

Originally Posted by Great Knots

Hi all. My John Pugh design 26ft steel yacht has 2 fuses in each electric circuit. A typical circuit is as follows:
Battery positive, battery positive selector switch, positive buss, amp meter, fuse, switch, device circuit is for, fuse, negative buss, negative battery selector switch, negative battery terminal.
As you can see, there are 2 battery selector switches (positive and negative HV cables) as well as 2 fuses in each circuit. Is this related to the fact that she is a steel hull boat?

Many boats have a fuse at the appliance as well as a fuse closer to the voltage source. Usually the fuse at the appliance is lower value.
I have seen a few melted battery switches in my time. I guess one on the Negative also isn't a bad idea.

[noelex 77]

Originally Posted by svlamorocha

If it is still unclear why in most boats it is a bad idea to connect the battery negative to a bolt on keel, just say so and someone will chime in with just a little bit of relevant science.

There are basically two options to deal with the negative connection.

1. Isolate everything so that the battery negative terminal is not in contact with seawater. This is the best system, but requires extra expense so is only used on up market metal boats.

2. Consolidate all the negative battery connections to a single point. The chosen point is generally the engine. Easy and satisfactory for non metal boats.

If you connect the keel to the negative battery supply you will have two connections of the negative supply to seawater. The engine and the keel. These negative battery connections will not be at exactly the same voltage. So current will flow, hence corrosion will occur.

(I am simplifying this explanation. It ignores the complex issue of "bonding" which I assume your boat does not have. I am also ignoring the AC side. If you have a bonding system (a wire connecting all the underwater metal) then the answer is a little more complex, but a single negative battery connection point is still sensible.)

[deblen]

Originally Posted by svlamorocha

I was working, I am not sure that matters much.

I responded to post #11, which provided incorrect advice to the fellow member who posted #8. That discussion was far from the original post but I did not want the author of #8 to go home with bad advice. I know that those posts had little to do with the title of the thread, but there was some incorrect info in there and I did not want other to get confused and start tying underwater metals because you said so.

I believe that by now other have explained (on the rudder example) why it is a bad idea to connect underwater metal parts without knowing what you are doing. And yes, corrosion is for the most part a direct current phenomenon, with the DC coming from a galvanic pair or a battery.

I do agree that codes and standards like those of ABYC are no the answer to all problems but I do believe that they are very useful to define an agreed standard of "good practice" and to allow people who do not actually understand the physics to get good results.

If it is still unclear why in most boats it is a bad idea to connect the battery negative to a bolt on keel, just say so and someone will chime in with just a little bit of relevant science.

Cheers

Charlie

Thanks Charlie
ABYC- I support Standards fully. What I was trying to say was that there are many admitted electrically challenged folks posting questions about how to do things & they get answers such as "that's the way Nigel,Don or ABYC,etc say to do it".
I think it would be more helpful to add some brief tech reason/result of doing it wrong.

I was dead wrong on the rudderstock cable.

Not so sure why "earthing" the bat neg is wrong,or what problems it may cause.

Two observations I have made:

(1) If mast & other metal framework on a wood or fiberglass boat,are not connected to bat neg & a DC short to the mast or metal framework occurs-the breaker/fuse will not blow-because there is no path for current to flow back to bat neg. Now you have a DC live mast/framework.

(2) In the above situation (1),I have seen fried wires,antenna leads,damaged electronics-whatever path is available back to bat neg.
If the short is hi resistance,say,due to corrosion or other reason,the breaker/fuse probably doesn't blow & you can see all sorts of weird symptoms.

It has been my experience that it is very difficult to maintain isolated bat neg on small boats that are worked on by people of various abilities/beliefs/practices. This results in damaged wiring & eqpt,as current will travel as long as it can find anything that will conduct.
That is why I have come to the personal conclusion that it may be fruitless to even try. But it is good for business

In an ideal world,nobody would work on anything they aren't trained for,but...

I would appreciate your comments. / Len

[Matt Johnson]

Originally Posted by mitiempo

As long as you have isolated starter and alt as you stated it looks good to me.

Thanks Mitiempo.

Matt

[svlamorocha]

Originally Posted by deblen

(snip)
I think it would be more helpful to add some brief tech reason/result of doing it wrong.
(snip)
I was dead wrong on the rudderstock cable.
Not so sure why "earthing" the bat neg is wrong,or what problems it may cause.

AFAIK I have not said that it is "wrong" to connect battery negative to water. I say that:

a) (in most boats) battery negative is already connected to water through engine block and water intake (difficult to break) or transmission/shaft/propeller (possible to break with a shaft coupler)

b) it is a bad idea to have two connections of battery negative to water because that causes corrosion (someone has explained this alread in this thread and I could not explain it better)

c) connecting the exposed keel to battery negative (as you proposed) would create a second connection that will cause corrosion

The explanation of c) is similar to the explanation for the rudder (just replace "rudder" with "keel" but I will try again anyway. Given that the battery negatiove is already connecte dot water through the engine/transmssion/propeller, if you connect the keel to battery negative (directly or indirectly) you have two corrosion mechanisms:

- driven by the different galvanic potental of keel (made of iron or lead) and propeller (made of bronze or whatever). This applies all the time.

- driven by current that flows in the water for reasons external to the boat and "hops on" to the boat through the keel and "hops off" the boat (or the other way around), corroding away keel or propeller depending on which way the current flows. This applies for the most part when you are arouind other boats or marinas.

I am sure the explanation can be made more scientific but this should be a good starting point.

Originally Posted by deblen

(snip)
(1) If mast & other metal framework on a wood or fiberglass boat,are not connected to bat neg & a DC short to the mast or metal framework occurs-the breaker/fuse will not blow-because there is no path for current to flow back to bat neg. Now you have a DC live mast/framework.

(2) In the above situation (1),I have seen fried wires,antenna leads,damaged electronics-whatever path is available back to bat neg.
If the short is hi resistance,say,due to corrosion or other reason,the breaker/fuse probably doesn't blow & you can see all sorts of weird symptoms.

What you say does not make sense to me.

If the rig is isolated from DC negative (as many others and I believe is best practice when you want to connect rig to keel for lighting purposes) and the only fault to have is a frayed 12V positive wire that touches the mast, then there is no problem because:

- the mast will be hot with 12 volts of DC potential measured against the battery negative, no fuses will blow or breakers will trip, but no humans will be at risk (only 12V) there is no "short", there will be no weird symptons of any type or damage to electronics.

In fact technically there is no "short", which requires a full path back to the source.

Moreover, in most production boats at least it is very easy to keep the mast and rig isolated from DC negative inside the boat (ie excluding the water connection between keel and propeller). You just need to be careful when installing nav lights and VHF antenna. If the antenna is designed to have continuity between coax shield and mount (I have not seen those recently but they exist), then there is a little gadget you can install in the coax to break the DC path. With the nav lights in my experience there is no problem beyond following the instructions. That is the big difference with trying to isolate the engine from water, which is difficult to accomplish reliably.

In a nutshell, there is a good case to keep rudder and keel isolated from DC negative (inside the boat) . Practical proof of this can be seen in thousands of production boats (keel isolated from DC negative) and experience-based recommendations from Jefa and other manufacturers of steering systems (who tell you to disconnect rudder from the rest of the boat). You get the free benefit of being able to connect rig to keel for an effective lightning path

Originally Posted by deblen

(snip)
In an ideal world,nobody would work on anything they aren't trained for,but...

I will not argue with that.

[deblen]

Originally Posted by svlamorocha

AFAIK I have not said that it is "wrong" to connect battery negative to water. I say that:

a) (in most boats) battery negative is already connected to water through engine block and water intake (difficult to break) or transmission/shaft/propeller (possible to break with a shaft coupler)

b) it is a bad idea to have two connections of battery negative to water because that causes corrosion (someone has explained this alread in this thread and I could not explain it better)

c) connecting the exposed keel to battery negative (as you proposed) would create a second connection that will cause corrosion

The explanation of c) is similar to the explanation for the rudder (just replace "rudder" with "keel" but I will try again anyway. Given that the battery negatiove is already connecte dot water through the engine/transmssion/propeller, if you connect the keel to battery negative (directly or indirectly) you have two corrosion mechanisms:

- driven by the different galvanic potental of keel (made of iron or lead) and propeller (made of bronze or whatever). This applies all the time.

- driven by current that flows in the water for reasons external to the boat and "hops on" to the boat through the keel and "hops off" the boat (or the other way around), corroding away keel or propeller depending on which way the current flows. This applies for the most part when you are arouind other boats or marinas.

I am sure the explanation can be made more scientific but this should be a good starting point.



What you say does not make sense to me.

If the rig is isolated from DC negative (as many others and I believe is best practice when you want to connect rig to keel for lighting purposes) and the only fault to have is a frayed 12V positive wire that touches the mast, then there is no problem because:

- the mast will be hot with 12 volts of DC potential measured against the battery negative, no fuses will blow or breakers will trip, but no humans will be at risk (only 12V) there is no "short", there will be no weird symptons of any type or damage to electronics.

In fact technically there is no "short", which requires a full path back to the source.

Moreover, in most production boats at least it is very easy to keep the mast and rig isolated from DC negative inside the boat (ie excluding the water connection between keel and propeller). You just need to be careful when installing nav lights and VHF antenna. If the antenna is designed to have continuity between coax shield and mount (I have not seen those recently but they exist), then there is a little gadget you can install in the coax to break the DC path. With the nav lights in my experience there is no problem beyond following the instructions. That is the big difference with trying to isolate the engine from water, which is difficult to accomplish reliably.

In a nutshell, there is a good case to keep rudder and keel isolated from DC negative (inside the boat) . Practical proof of this can be seen in thousands of production boats (keel isolated from DC negative) and experience-based recommendations from Jefa and other manufacturers of steering systems (who tell you to disconnect rudder from the rest of the boat). You get the free benefit of being able to connect rig to keel for an effective lightning path


I will not argue with that.

You are most certainly correct in your tech explanation(s).

I don't agree that having a "hot" mast is OK.You are correct,to a point, in saying that it will cause no problems as long as it STAYS isolated from bat neg. & no leakage current flows to bat neg thru other eqpt on mast.

You are correct in stating the engine,shaft,prop are usually connected to bat neg & water.
My opinion & experience- Even in a 2 wire (isolated grd ) system,isolation of engine & prop are difficult to keep isolated,for reasons I've given in prev. posts.

A lightening ground to water would supply a leakage current path from a hot mast,thru lightening ground to water & thru water to prop(neg bat).
Spark gap or similar should be used in lightening ground to prevent this possibility?

Cheers/Len

[svlamorocha]

Originally Posted by deblen

You are most certainly correct in your tech explanation(s).

I don't agree that having a "hot" mast is OK.You are correct,to a point, in saying that it will cause no problems as long as it STAYS isolated from bat neg. & no leakage current flows to bat neg thru other eqpt on mast.

You are correct in stating the engine,shaft,prop are usually connected to bat neg & water.
My opinion & experience- Even in a 2 wire (isolated grd ) system,isolation of engine & prop are difficult to keep isolated,for reasons I've given in prev. posts.

A lightening ground to water would supply a leakage current path from a hot mast,thru lightening ground to water & thru water to prop(neg bat).
Spark gap or similar should be used in lightening ground to prevent this possibility?

Cheers/Len

I agree that there is at least respectable case for some sort of DC-block gap (such as a spark gap) in mast-to-water connections. In fact very recently I was involved in a project (catamaran though) in which we specified the new "Sidearc" lighting terminals partly for that very reason (avoid DC connection between rig and water that could create corrosion problems if rig gets ***accidentally*** connected to battery negative inside the boat because of salt, etc).

That would also deal with your worry about a DC-hot mast discharging the batteries, but my personal opinion is that the hot mast should be detected (dim tricolor or anchor light, voltage between rig and negative, etc) rather than "tolerated".

[deblen]

Originally Posted by svlamorocha

I agree that there is at least respectable case for some sort of DC-block gap (such as a spark gap) in mast-to-water connections. In fact very recently I was involved in a project (catamaran though) in which we specified the new "Sidearc" lighting terminals partly for that very reason (avoid DC connection between rig and water that could create corrosion problems if rig gets ***accidentally*** connected to battery negative inside the boat because of salt, etc).

That would also deal with your worry about a DC-hot mast discharging the batteries, but my personal opinion is that the hot mast should be detected (dim tricolor or anchor light, voltage between rig and negative, etc) rather than "tolerated".

Thanks for that information. Much to ponder
And we haven't added AC,other hot boats & hot marinas into the mix.
Cheers/ Len