I'm in the middle of a repair of problems caused by electrolysis. One
destroyed bronze prop, several destroyed SS bolts which hold the stuffing
box plate in place. I found the connection from the electrode to the steel
parts adrift due to a grounding, but that's recent and not the cause of the
damage. I feel the underlying cause is that the shaft, prop and stuffing box
/ plate / bolts were insulated from the main zinc by the skeg bush. It
won't happen again, and an additional zinc on the prop shaft is clearly
required.
But this all got me to thinking - how can one check the effectiveness of the
zincs? It's easy enough to swim under the boat in summer and look at the
extent of marine growth, make sure the zinc is still there, etc. But is it
possible to check that the zincs are actually doing their job of maintaining
a voltage difference? I could easily connect a voltmeter to the rudder
shaft or the prop shaft - but what could I use as a reference point, and
what are the appropriate voltages? I'm specifically NOT looking for a
commercial piece of electronics, just a simple test I and other owners can
do now and then. We've got pretty basic wooden boats, mostly 18 to 25 ft
long, mostly over 20 years old - some going back a lot longer than this.
All moored permanently in Mordialloc Creek Victoria Australia - we try to
slip them every year and re-do the antifoul etc, but sometimes the
maintenance gets a little delayed. It would be nice if we could at least
check that the zincs are working ....

Any reference sites or suggestions?

Regards
David Flew

Do a google search on Proline fishing black boxes. An article in there
about how to check your boat may help you.
Gordon

"David Flew" wrote in message
...
I'm in the middle of a repair of problems caused by electrolysis. One
destroyed bronze prop, several destroyed SS bolts which hold the stuffing
box plate in place. I found the connection from the electrode to the
steel
parts adrift due to a grounding, but that's recent and not the cause of
the
damage. I feel the underlying cause is that the shaft, prop and stuffing
box
/ plate / bolts were insulated from the main zinc by the skeg bush. It
won't happen again, and an additional zinc on the prop shaft is clearly
required.
But this all got me to thinking - how can one check the effectiveness of
the
zincs? It's easy enough to swim under the boat in summer and look at the
extent of marine growth, make sure the zinc is still there, etc. But is it
possible to check that the zincs are actually doing their job of
maintaining
a voltage difference? I could easily connect a voltmeter to the rudder
shaft or the prop shaft - but what could I use as a reference point, and
what are the appropriate voltages? I'm specifically NOT looking for a
commercial piece of electronics, just a simple test I and other owners can
do now and then. We've got pretty basic wooden boats, mostly 18 to 25 ft
long, mostly over 20 years old - some going back a lot longer than this.
All moored permanently in Mordialloc Creek Victoria Australia - we try to
slip them every year and re-do the antifoul etc, but sometimes the
maintenance gets a little delayed. It would be nice if we could at least
check that the zincs are working ....

Any reference sites or suggestions?

Regards
David Flew

"Gordon" wrote in message
...
Do a google search on Proline fishing black boxes. An article in there
about how to check your boat may help you.
Gordon

Are you thinking about the Pro-Troll Blackbox maybe?
http://www.protroll.com/blkboxbook.html

Hi,

I've been considering the use of Polyfuses (made by Raychem among others)
instead of circuit breakers in an electric panel on my boat. They are a lot
cheaper (like $0.50 each) and smaller than a breaker. The specs say "100A
maximum current" for a typical 5-10A fuse. This is the maximum fault
current that can be used to trip such a device.

The typical C series Carling hyd./magnetic circuit breaker has a
interrupting capacity of 7500A @ 80VDC. This is the toggle type circuit
breaker that you see on most new boats.

My question: is 100A interrupting enough? If there is a short in a typical
wire, will fault currents exceed that? I don't know enough electrical
engineering to determine if this would be a safe application for these
fuses. I do know of one kit plane builder (who is an EE) who thinks they
are o.k. And one maker of boat parts who is offering them:
http://www.lalizas.com/products.asp?S0=5&S1=13&S2=37

This is a kit plane builder who uses them:

http://www.expbus.com/pages/avionics_expbus.htm


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)

Evan,

The capacity of the wire has little to do with the maximum current it
can carry. A #18 wire can carry several thousand amps for a second or
two. You have to consider the maximum possible amps that could be
dumped through the device and a 4 battery house bank can dump a bunch of
amps.

Lalizas makes sub-panels so I would assume the panel would be fed
through a heavier capacity breaker at the main. Kit planes have a
single battery and maybe a 35 amp alternator.

Evan Gatehouse wrote:
Hi,

I've been considering the use of Polyfuses (made by Raychem among others)
instead of circuit breakers in an electric panel on my boat. They are a lot
cheaper (like $0.50 each) and smaller than a breaker. The specs say "100A
maximum current" for a typical 5-10A fuse. This is the maximum fault
current that can be used to trip such a device.

The typical C series Carling hyd./magnetic circuit breaker has a
interrupting capacity of 7500A @ 80VDC. This is the toggle type circuit
breaker that you see on most new boats.

My question: is 100A interrupting enough? If there is a short in a typical
wire, will fault currents exceed that? I don't know enough electrical
engineering to determine if this would be a safe application for these
fuses. I do know of one kit plane builder (who is an EE) who thinks they
are o.k. And one maker of boat parts who is offering them:
http://www.lalizas.com/products.asp?S0=5&S1=13&S2=37

This is a kit plane builder who uses them:

http://www.expbus.com/pages/avionics_expbus.htm



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Yes, you'll see an article at that site about checking your boat for
correct potentials and how to fix problems discovered. You don't need a
downrigger. Use an old zinc hooked to a piece of wire and dangle over the
side. Check voltage between that wire and ground.
G
"nospam please" wrote in message
...
"Gordon" wrote in message
...
Do a google search on Proline fishing black boxes. An article in there
about how to check your boat may help you.
Gordon

Are you thinking about the Pro-Troll Blackbox maybe?
http://www.protroll.com/blkboxbook.html

Polymeric circuit protection devices are a kind of Positive
Temperature Coefficient (PTC) thermistor. They have a really steep
non-linear tempco, so that their resistance climbs rapidly after they
reach a certain temperature. This process is reversible, so they
conduct normally after cooling down. However, it's important to
understand a couple of things about them:

1) Their 'trip current' depends on anything that affects their
temperature.

2) They don't remain 'tripped' if you don't allow some current to flow
to keep them hot. With some types of loads, they will oscillate off
and on at a rate that depends on how fast they can cool down. With
other loads, they may deliver enough current to the load while hot
('tripped') to cause damage.

The manufacturers web sites have lots more info on this. My
experience has been that polyswitches are good for protecting
batteries, wiring, motors, speakers and other relatively rugged
components. They are less useful for protecting electronics.

Surplus DC circuit breakers are frequently offered on ebay. They have
the advantage of incorporating a switch into the breaker, simplifying
wiring.

Paul Mathews

"Evan Gatehouse" wrote in message ...
Hi,

I've been considering the use of Polyfuses (made by Raychem among others)
instead of circuit breakers in an electric panel on my boat. They are a lot
cheaper (like $0.50 each) and smaller than a breaker. The specs say "100A
maximum current" for a typical 5-10A fuse. This is the maximum fault
current that can be used to trip such a device.

The typical C series Carling hyd./magnetic circuit breaker has a
interrupting capacity of 7500A @ 80VDC. This is the toggle type circuit
breaker that you see on most new boats.

My question: is 100A interrupting enough? If there is a short in a typical
wire, will fault currents exceed that? I don't know enough electrical
engineering to determine if this would be a safe application for these
fuses. I do know of one kit plane builder (who is an EE) who thinks they
are o.k. And one maker of boat parts who is offering them:
http://www.lalizas.com/products.asp?S0=5&S1=13&S2=37

This is a kit plane builder who uses them:

http://www.expbus.com/pages/avionics_expbus.htm

"David Flew" wrote in message ...
I'm in the middle of a repair of problems caused by electrolysis. One
destroyed bronze prop, several destroyed SS bolts which hold the stuffing
box plate in place. I found the connection from the electrode to the steel
parts adrift due to a grounding, but that's recent and not the cause of the
damage. I feel the underlying cause is that the shaft, prop and stuffing box
/ plate / bolts were insulated from the main zinc by the skeg bush. It
won't happen again, and an additional zinc on the prop shaft is clearly
required.
But this all got me to thinking - how can one check the effectiveness of the
zincs? It's easy enough to swim under the boat in summer and look at the
extent of marine growth, make sure the zinc is still there, etc. But is it
possible to check that the zincs are actually doing their job of maintaining
a voltage difference? I could easily connect a voltmeter to the rudder
shaft or the prop shaft - but what could I use as a reference point, and
what are the appropriate voltages? I'm specifically NOT looking for a
commercial piece of electronics, just a simple test I and other owners can
do now and then. We've got pretty basic wooden boats, mostly 18 to 25 ft
long, mostly over 20 years old - some going back a lot longer than this.
All moored permanently in Mordialloc Creek Victoria Australia - we try to
slip them every year and re-do the antifoul etc, but sometimes the
maintenance gets a little delayed. It would be nice if we could at least
check that the zincs are working ....

Any reference sites or suggestions?

Regards
David Flew

You can use this 'simple' procedure to monitor electrolytic corrosion
before and after the installation of zincs: Connect an ammeter
between the 2 metal structures that are suspected of having galvanic
potential differences (this is done in the water, of course). If
there is a potential, a current will flow in the ammeter. Note the
current, which can range from microamps to amps, depending on the size
of the structures. Then, install the zinc(s) and re-measure. The
current should diminish. You can also sometimes measure the current
in the bonding attachment for the zinc itself. If there is no
current, the zinc is doing no good. With some thought, you can make
sense of the current polarities as well.

Paul Mathews

"Evan Gatehouse" writes:

I've been considering the use of Polyfuses (made by Raychem among others)
instead of circuit breakers in an electric panel on my boat. They are a
lot
cheaper (like $0.50 each) and smaller than a breaker. The specs say "100A
maximum current" for a typical 5-10A fuse. This is the maximum fault
current that can be used to trip such a device.

The typical C series Carling hyd./magnetic circuit breaker has a
interrupting capacity of 7500A @ 80VDC. This is the toggle type circuit
breaker that you see on most new boats.

My question: is 100A interrupting enough? If there is a short in a
typical
wire, will fault currents exceed that?
snip

What you are asking is really, "What is the short circuit available on this
boat?"

The answer is dependant on the size of the house bank.

5,000 amps DC would not be considered unusually large.

BTW, what you are asking is the answer to a coordination study, something
consulting electrical engineers do for a living for large industrial
facilities.

For the device in question, you need to determine the maximum let thru
current under a bolted fault condition.

The manufacturer can provide this info.

HTH


--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
Visit: http://home.earthlink.net/~lewhodgett for Pictures

Paul, Maybe I missed something. Perhaps you can help me to figure how
to connect an ampmeter under water.




(Paul Mathews) wrote in message . com...
"David Flew" wrote in message ...
I'm in the middle of a repair of problems caused by electrolysis. One
destroyed bronze prop, several destroyed SS bolts which hold the stuffing
box plate in place. I found the connection from the electrode to the steel
parts adrift due to a grounding, but that's recent and not the cause of the
damage. I feel the underlying cause is that the shaft, prop and stuffing box
/ plate / bolts were insulated from the main zinc by the skeg bush. It
won't happen again, and an additional zinc on the prop shaft is clearly
required.
But this all got me to thinking - how can one check the effectiveness of the
zincs? It's easy enough to swim under the boat in summer and look at the
extent of marine growth, make sure the zinc is still there, etc. But is it
possible to check that the zincs are actually doing their job of maintaining
a voltage difference? I could easily connect a voltmeter to the rudder
shaft or the prop shaft - but what could I use as a reference point, and
what are the appropriate voltages? I'm specifically NOT looking for a
commercial piece of electronics, just a simple test I and other owners can
do now and then. We've got pretty basic wooden boats, mostly 18 to 25 ft
long, mostly over 20 years old - some going back a lot longer than this.
All moored permanently in Mordialloc Creek Victoria Australia - we try to
slip them every year and re-do the antifoul etc, but sometimes the
maintenance gets a little delayed. It would be nice if we could at least
check that the zincs are working ....

Any reference sites or suggestions?

Regards
David Flew

You can use this 'simple' procedure to monitor electrolytic corrosion
before and after the installation of zincs: Connect an ammeter
between the 2 metal structures that are suspected of having galvanic
potential differences (this is done in the water, of course). If
there is a potential, a current will flow in the ammeter. Note the
current, which can range from microamps to amps, depending on the size
of the structures. Then, install the zinc(s) and re-measure. The
current should diminish. You can also sometimes measure the current
in the bonding attachment for the zinc itself. If there is no
current, the zinc is doing no good. With some thought, you can make
sense of the current polarities as well.

Paul Mathews