On Sat, 8 Nov 2003 09:09:57 -0500, "Jim Woodward" jameslwoodward at
attbi dot com wrote:

As a metal boat owner, I don't have a choice. The boat looks like a series
of Faraday cages, with metal watertight doors pulled down against very thin
gaskets and all the thru bulkhead fittings of minimum size. There will be no
3" gaps; one of the advantages of metal is that you have a good chance of
keeping fire and flood in one compartment if you're careful.

Sure wish I could get by your boat to test it out. Every wire going
from compartment to compartment is a great antenna for 2400
Mhz....right through those watertight bulkheads. It would be
interesting to see how far the usable signal got with the transmitter
that close.

Even if I had a choice, however, I'd probably stick with wire. A boat is
not a house or office. Aside from alternators, we have a variety of sources
of potential interference -- radios (150 watt sideband and 25 watt VHFs),
radar, and so forth. 802.11 "should" ignore all of that. But "should" is a
big word at sea. Although the 10baseT pairs could also act as antennas and
could pick up RFI, my instinct is that it's a safer choice.

The only 2400 Mhz RFI source on your boat is probably your microwave
oven at 2450 Mhz. There is no interference from 150W of HF through
the wireless.....LIKE THERE IS ON EVERY WIRE OF THE NMEA SYSTEM aboard
the boat. NMEA wiring cannot be effectively shielded as long as
manufacturers keep using hookup wire that's not shielded (Garmin) and
even stupid Icom, itself, who made the M802 HF-SSB forces you to
connect NMEA B (-) to the SHIELD OF A BNC CONNECTOR to hook NMEA input
to the HF SSB with DSC. How stupid! Of course, NONE of the plastic
boxes the damned cheap marine crap comes in is shielded in the first
place against the HF transmitter or your 5W walkie talkie on deck.
There's no FORCED standards, just NMEA suggestions from the NMEA the
manufacturers control....sorta like the fox guarding the henhouse.

As for using either the AC or DC lines, I have the same objection. And even
in relatively small boats, the AC system is usually split bus (so you can
plug in two 120V 30A lines to a dock), so you have to do some capacitive
coupling.

There's 2 primary transformers sitting on top of the floating dock at
Ashley Marina. The powerline router signal coupled through them, to
my amazement, good enough to get the WiFi through them.

Of course in saying all of this, I do have the advantage that we're doing a
major refit, and it's very easy to lay in an extra conduit for the network
(actually it isn't even extra as we'll have a conduit for phone and
signaling anyway). Certainly if I were adding a network to an existing boat
that wasn't well set for easy access everywhere (that's another topic), I'd
certainly take a shot at using wireless and test the hell out of it at the
dock.

On the larger boat, that's very nice. But, most boat manufacturers,
in their attempts to maximize profits, don't put in even the most
rudimentary conduit. The wires are just haphazardly laid in behind
some panel squished between the panel and the fiberglass shards
sticking out. The Endeavour was like that. The Amel Sharki is a
different class. The overhead has conduit leading from the outside of
the void between the cabin overhead and the deck into the void where
there are wires to go in. There's plenty of space, but, alas, no way
to fishtape from this little conduit nipple to the next. I finally
made up a ring slider I could tie the fishtape to and slide it along
the existing French wiring in the void to the other conduit nipple on
the other end. It serves quite well. The void acts about 1 to 1.5"
high over the main salon. Many wires go through there forward and
aft.

Do you have a strong high-channel-number UHF TV station in your area?
Might be fun to play with a portable TV to see how far inside the boat
its signal gets, but that's only 1/3 the network's frequency at 800
Mhz. Do cellular phones work inside?



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"