Conference unifix::sailing

    Why bother, when a web of copper laid inside the hull will do?

    what is, and where does one obtain a "Web of Copper" ?

re .1:

Well, a Dynaplate is very easy to install. Installing an internal copper 
web/mesh/screen in a completed boat would be extremely difficult and
time-consuming. 

re .2:

The usual internal copper radio ground is bronze or copper screen (eg,
window insect screen) laid up inside the deck or bonded/glued to the
underside of the deck. Easily done when building the boat, much less
easily done if you have to remove the overhead or much cabin furniture.
I don't recall the number of square feet required, but it is substantial
enough that I wouldn't even think about doing it. I've seen boats with 
recessed Dynaplates -- kinda neat, actually. If you have access to the 
hull in an appropriate place and don't mind cutting a large hole, the 
recessing could even be done after the boat is built. I'd probably just
accept the drag of a surface mounted plate.

Alan

    O.K. let me simplify the original question.
  To anyone out there with an installed SSB and a Dynaplate for Ground.
    
   - What size is your Dynaplate?
    
   - How effective is your transmmitt and receive.  
    
   It may be that what I already have is adequate.
    I thought about using coper mesh but,like Alan said,it is kind of
    difficult,and more complicated space wise.
    

    How does an external lead keel work??   I think I have heard of using a
    wide copper web (2-3") to the keel bolts.   Any comments??
    
    Lee

    re Alan's comment about the screen.  Why would it be bonded to the
    underside of the deck ?  I suspected that we were talking building a
    capacitor out through the hull to the water here ... in the same way as
    we talked about earlier with tin foil in the bilges ... not so ?

Last year I installed a Furuno SSB on my Sabre 36.  Before beginning I consulted 
with several SSB "experts" and the summary of their recommendations and my
installation follows:

     1) Never measure your SSB's performance by receiving range. I have
        used a Radio Shack $100 portable with a SSB band and received signals 
        from all over the world.  The only true measurement is transmitting
        range.

     2) Dynaplates are essentially worthless.  The grounding system must be 
        wire mesh and as large of a surface area as possible (100 sq ft 
        minimum).  If you spend $2,500 on a SSB and $100 on a grounding 
        system you will have a $100 SSB.
  
        I was able to epoxy approximately 65 sq ft of bronze window screen
        to the underside of my v-berth, main cabin and quarterberth locker
        covers.  This was a very timeconsuming process as the covers had to
        be removed and stripped of varnish before the screen could be epoxied. 

     3) All thru hulls, standing rigging, pulpits, sail tracks, engine, keel,
        water tanks, etc. should be tied into the wire screen with 2"wide 
        copper strapping.  

        I used a combination of #6 wire, 1"wide and 2"wide copper braid.  All 
        connections were made with soldered terminals thru-bolted to the locker 
        cover, bulkhead, etc. 

I have not been able to completely evaluate the performance of the grounding
system.  There are so many frequencies and unlike VHF there are no calling
channels.  I have to scan to find an English language conversation, jump in at
the end, and ask someone come back.  During our last race/cruise to and from
Bermuda I did speak to boats in the Windward Islands, Virgin Islands, and 
Puerto Rico; the Yarmouth and Halifax, Nova Scotia Coast Guard; the Gander, 
Newfoundland Air Traffic Control Center; and daily conversations with "Herb" 
the private weather forecaster from Bermuda.  I have also placed telephone calls
through the ATT High Seas telephone operators in Ft Lauderdale and Manahawkin, 
NJ.  

Overall, I am very satisfied with the installation and feel that it was worth
the time and expense.

re .7

Can you explain to me in electrical terms why the wire mesh works and the
dynaplate doesn't? Is the mesh supposed to be an (AC) ground? If so, shouldn't
it be on the hull, not the locker covers? How does the overall SSB RF circuit
work?

--RS

It has been years since I pushed electrons for a living, and never at RF,
so if someone knws for real, speak up.

My initial guess would be that the wire mesh makes a better ground plane
for the transmitter.  I can't really explain why a mesh would be better
than the ocean for this, except by speculating that the dynaplate would
cause a local field in the water at RF frequencies.  This in turn would
mean that while the dynplate makes a perfectly good DC ground connection, it
does not make a good hig frequency ground.

The same arguement would apply to lightning protection.  While a given 
lightning bolt is DC, the series of succesive bolts in a lightning flash
and the resulting plasma decay of each bolt comprises essentially an RF
event, hence the static on your AM receiver.  Large plate area or wire mesh
will rpovide a better ground for lightning protection than a dynaplate of 
comperable surface contact area.

From an RF man from way back (but who has probably forgotten most of it by now
:-))...

If you stick an antenna up high above the surface of the earth, it will radiate
some given amount of energy in all directions. If you erect the same antenna
immediately above an ideal infinite ground plane (i.e. perfectly conducting
sheet) then you get the effect of a "mirror image" which effectively doubles the
size of the antenna, and also concentrates the RF energy into a more horizontal
band, rather than in all directions. Energy aimed at the sky is wasted, and can
increase your effective radiated power if aimed nearer the horizon instead.
Unless you are aiming to communicate with extra-terrestrials...

The sea provides a less than perfect ground plane, but it is not bad, as long as
you can get a good ground connection to it. At RF, this does not necessarily
need to be a direct connection. What the "foil/mesh-lined hull" is giving you is
something of a ground plane in itself, and also a degree of RF coupling to the
sea outside the hull so that the sea helps as well.

The alternative is a good low-resistance (at RF) connection to the sea. A large
area metal plate (probably a low-resistance copper alloy?), bonded through thick
straps, would probably suffice - but the larger the better. What's a Dynaplate,
though (I would like to know - I had never heard the term before reading these
notes)? A large low-resistance metal plate is a large low-resistance metal
plate. There may be a lot of technology in fairing it to the hull, lowering
hydro-dynamic drag, etc, but you cannot change the physics of electrical
conductivity by giving something a fancy name. However, a direct connection does
also give a DC path to ground (well, water) which could help as part of
lightning defences.

- Brian, G4FBN

    What I did to mount my Ham gear in my boat is to run my antenna up near
    the backstay and use a MFJ Antenna tuner to zero out my SWR to 1.1 on
    all bands. I then ran the ground to my zinc that I hung off the boat,
    or clip it to the anchor chain when at anchor. 
    
    It get's out great, although is directional. As my antenna is at the
    same angle as my backstay, and parallel to it when raised, it radiates
    best towards the rear of my boat and less towards the front. 
    
    Folks talking with me on the radio notice a 1 or 2 S-meter drop in my
    transmissions if I am swinging on my anchor rode. That's
    something akin to full volume down to about 60% volume for those of you
    who don't have S-meters on their rigs. The only time it matters is if
    the conditions are poor to begin with. 
    
    I run about 100W output using a ICOM rig and depending on band and time
    of day can work from Africa to Honolulu to Chile.
    
    Hope this adds to the creative Juices!
    Robert - WB7VVV

    A dynaplate is a porus metal (bronze maybe?) block somewhat smaller
    than a brick. Becuase it is porous, it has a very large surface area
    compared to its volume. It's purpose is to provide a radio ground.
    
    I was noticing in by just arrived "M & E" catalog, that they advertise
    the dynaplate as a "LORAN ground". Don't know if it is more effective
    with LORAN than SSB, or just that they sell a lot more LORAN sets.
    
    Bill
    
    

    
    	I'm not sure of the bonding deal- If I `glassed in a screen to the
    INSIDE of the hull, I would treat it like another metal appendage, not
    a ground plate- `cuz it's not. It's more like the plate of a capacitor,
    the other plate being the water, the insulator being your hull. Now, as
    frequency goes up, capacitors look like short circuits, so, yeah, it's
    a really good RF ground. But don't mix&match when lightning comes
    around! Bond everything straight to the keel, or some sort of EXTERNAL
    hunk of metal. If you make that mesh part of the circuit, I'd be afraid
    of funky things happening in a lightning storm. 
    
    	I'm not sure about the dynaplate for >10W power ranges.
    
    	Now, has anybody ever looked at bottom paint conductivity??? You
    might have a really fine, preinstalled, inherent plate! 
    
    	Scott (technerd third class)

    We used a SmartTuner with our SSB and just connected the ground to our
    diesel tanks and general 12V ground system. We had a crystal clear
    conversation with a ham in England from the Galapagos Islands, and the
    system generally got us to the High Seas Operator within about 2,000
    miles, so if you have nice big conductive tanks, that seems to work
    well. Also, there are perfectly acceptable groundless antenna systems
    you can use. Talk to your marine SSB person. Incidentally, out RF
    output was around 150W.

    re. : 7
    
    I have also consulted the" experts" and I understand that the wire mesh
    system of 65 sq.ft. of surface area is better than the Dynaplate I have
    right now ( 20 sq.ft.)or the one I am planning to install (40 sq.ft.)
    However I don't believe that the Dynaplate is worthless.
    You may be able to transmit 6-10 thousand miles,I'll be happy with 2-3 thou.
    It is like my sextant,it is plastic and not as accurate as the Tayana
    sextant but it will take me there even if it is a couple miles off the
    mark.
    
    
    re. : 10
    
    The Dynaplate is the market name of a sintered-bronze plate used as
    hull bonding installed on the the outside under the hull.
    The common dynaplates for marine usage come in 4 sizes
    
    2"W x 1/2"H x 6"L          equivalent to  12 sq.ft.of surfase area
    
    2 1/2"W x 1/2"H x 8"L          "       "  20    "           "
    
    3"W x 1/2"H x 12"L             "       "  40    "           "
    
    6"W x 1/2"H x 18"L             "       "  80    " 
    
    For an SSB intallation the larger surface area the better and 50 sq.ft. 
    is the minimum.
    Also the sq.footage indicated by the Dynaplate sizes by the mfg. is
    overstated.
    
    
    re. : 14
    
    It seems to me that if you have connect the SSB ground to your diesel 
    tanks you are grounded to the hull bonding system in which case if the 
    boat is fiberglass with encapsulated keel you must have an outside plate
    probably a Dynaplate.If you do what size is it?
    
    
    
    Mike K.   N1MBE

Does a dynaplate actually do anything useful? If so, how exactly does it
work?

The claim (as I understand it) is that the dynaplate has more surface area
than an equivalent size flat plate, and therefore forms a better Ohmic
connection to the ocean. This seems reasonable at an intuitive level.

But to fully understand this system, one needs to consider the (seawater)
current path from the dynaplate-to-seawater interface out to the ocean.

Examine the stylized cross section of a dynaplate shown below:


------------------------------------------------------------------------

Dynaplate
          .--+---.      .--+---.      .--+---.      .--+---.      
          |  |   |      |  |   |      |  |   |      |  |   |
          |   >  |      |   >  |      |   >  |      |   >  |
          |  <   |      |  <   |      |  <   |      |  <   |
          |   >  |      |   >  |      |   >  |      |   >  |
          |  <   |      |  <   |      |  <   |      |  <   |
          |   >  |      |   >  |      |   >  |      |   >  |
          |  <   |      |  <   |      |  <   |      |  <   |
          |  |   |      |  |   |      |  |   |      |  |   |
          |  |   |      |  |   |      |  |   |      |  |   |
__________'  |   `------'  |   `------'  |   `------'  |   `------------

Note that the current from the deep pockets must pass through the resistance
of the seawater channels to get to the open ocean. Now compare this
to a flat metal plate of the same total thickness:


------------------------------------------------------------------------

Solid metal plate

             |              |             |             |    
              >             >             >             >   
             <             <             <             <    
              >             >             >             >   
             <             <             <             <    
              >             >             >             >   
             <             <             <             <    
             |              |             |             |    
             |              |             |             |    
------------------------------------------------------------------------

The resistors are still there, but they're solid metal, so presumably much
lower resistance than the seawater.

It's possible that surface corrosion and contamination might play a role in the
overall resistance. If this is the case, having more surface area could help.
But you might be able to do better by using a material that is not as likely
to corrode and become contaminated, e.g. zinc. (Does a Dynaplate become
"gummed up" as it gets older?)

I had one on the last boat i owned. I honestly could not tell the 

difference between whith dynaplate and without.  I did not notice

any clogging.  However i'm no expert on electrical anything,

so i may not be adding anything here.

The manufacturer had some metal straps in the bilge, connected to the

strut bolts, and use these for grounding.

JIm