Packet & APRS Aboard a Kayak
© 2004 by Steven K. Roberts
This article first appeared as the
cover story in
the Spring, 2004 issue of CQ VHF Magazine.
update: I sold this boat a few years ago, but keep this article on the
site as an example of a small integrated system. Current work is
focused on a 44-foot pilothouse sailboat named Nomadness.
Adventure Tracking: A Bit of Context
is a strange phenomenon. Think about it: if the
government required us all to have real-time location-trackers affixed
to our vehicles, it probably would (and should) trigger a full-scale
revolt . But Big-brotherish implications aside, the
of this technology is unmistakably seductive, and has spawned a
microculture of folks whose every movement is trackable... not only by
fellow hams, but by anyone with a Web browser.
Back in the 80s, I used to fantasize about exactly this. I
most of that decade pedaling 17,000 miles around the US on a
computer-laden recumbent bicycle,
back then it was challenging enough just to maintain an ongoing textual
narrative on the primitive online services of the day (a process that
has now been re-invented as blogging). I remember pedaling
imagining the logical evolution of this: readers watching a
display of my location on a slowly scrolling zoomable map, multiple
telemetry channels presented as a virtual console, a succession of
helmet-cam images playing in another window...
All of this is now pretty easy, and is part of the Microship
project: the technomadic adventure substrate that has
tattered, overloaded recumbent bicycle (now on display in The Computer
History Museum in Silicon Valley). These two amphibian,
pedal/solar/sail micro-trimarans are packed with enough technology to
more than fulfill that long-ago road-fantasy, but what I want to tell
you about here is much simpler: a pile of off-the-shelf stuff
packaged in Pelican boxes and lashed to a tiny boat. In
the process, we can look at a few packaging techniques that will let
you put APRS into all sorts of nasty places where electronic devices
usually don’t stand a chance.
Strawberry Island during a
recent solo 6-day tour. Three Pelican boxes contain
navigation, and power management gear.
There is an old adage that the average completion time of a homebuilt
boat is 137 years. With that in mind, and needing a dinghy for shore
excursions (landing gear notwithstanding), I added a 19-foot Aire Sea
Tiger to the Microship fleet. Given this
quickly deployable playboat, I have been unable to resist the allure of
local exploration of the endlessly interesting waters here in the
Appropriately dubbed Bubba,
this wonderfully stable and buoyant craft
spends a lot of its time in salt water, with occasional river
excursions. I carry a full suite of camping gear, as well as
laptop backpack in a sealed case, so computing horsepower under the
stars is not a problem. What is more challenging is the set
resources needed underway: battery management, navigation
communications, and APRS.
As you can see in Photo 1, Bubba
carries a few things not normally
found lashed to a kayak. In addition to the two big
mounds (filled with gear in about a dozen sealed “dry bags”), there are
three interconnected waterproof Pelican cases:
- The black box
on the bow
contains a KPC-3+ packet TNC, a wonderful old
Yaesu 290, a USB-serial interface for the Mac laptop, a headless Garmin
GPS-35, 24 amp-hours of 12V sealed lead-acids, a Micro-M+ solar charger
(using the 30-watt Solarex PV panel lashed to the forward gear mound),
an AC unit for those times when I have shore power available, a
Statpower inverter for laptop and digital camera chargers, a MAHA Ni-MH
charger for all the pocket gadgets that use AA batteries, a bicolor
navlight retrofitted with Luxeon 1-watt LED emitters, a 350mA constant
current source for same, and a Mobri radar reflector.
- The yellow box,
my legs when I’m paddling, carries a
cartographic Garmin GPSMAP-76S, separate steering compass, switch for
the navlights, button for the horn, and internal foam-lined space for
the Canon digital camera (in its own waterproof case), Aquarian Audio
hydrophone, binoculars, and basic emergency tools.
- The gray box
at the stern
(barely visible in the photo) carries a
homebrew 1-watt white LED sternlight, 350 mA constant current source,
small yacht horn, and a fiberglass bike flag on a Hustler bayonet-mount
supporting a 2-meter twin-lead J-pole. The interior of that
carries tools, patch kit, and electric air pump.
These three boxes are constantly exposed to salt water, which is about
the nastiest stuff around when it comes to electronics. In
some wag once quipped...
corrodes. Salt water corrodes absolutely.”
Pelican boxes themselves do an excellent job of keeping out the
elements, but as soon as we add connectors and external devices, we’re
asking for trouble. The wiring harness on Bubba was designed
the assumption that it would be soaking wet most of the time, and thus
uses undersea-pluggable connectors made for oceanographic applications,
integrated into a spiral-wrapped assembly that can dry out whenever
given the chance. This cable bundle consists of four DC wires
one piece of coax.
Let’s look at the wiring diagram for the system...
diagram for the complete system. A waterproof harness
the three Pelican cases containing
As much as possible, I took advantage of off-the-shelf
subassemblies: one of the major lessons that has emerged from
decades of building complex machines is that life is too short to
re-invent the wheel. This whole system came together in a
of weeks, largely because I didn’t insist on over-complicating anything
with custom electronics, computer control, integrated user interfaces
on ad-hoc networks of wireless-linked PDAs, or anything else
Microship-like and tres geeky. As such, it’s not quite as
or tight as it could be, but it works well and can easily be replicated
by others who want to add these capabilities to tiny boats.
The schematic is arranged to show the three separate boxes, linked by
the simple wiring harness. Most of the action is in the black
on the left half of the drawing...
Two hefty Powersonic
12V, 12AH Sealed Lead Acid Batteries comprise the
ensuring that I have a comfortable margin of operation in this
often-overcast part of the planet. Fully charged, they can
the high-brightness LED navlights for at least a week of all-night
paddles (very rare!), and also provide continuous APRS tracking for a
few days. This is one area in which overkill doesn’t bother me; it’s
nice to have ample power (and on a kayak, weight is not as much of an
issue as on a bicycle or backpack... though I do confess to grumbling a
bit when I have to drag all this stuff up a cliff for the
Internal wiring is very simple, and most of the action is in the
vicinity of a big double terminal strip made by Blue Sea Systems
(located under a chunk of foam inside the box shown in Photo
2: The inside of the black Pelican case at the bow.
The primary charge source for an autonomous mobile system like this,
is, of course, photovoltaic, and a Solarex MSX-30 module provides a
steady couple of amps on sunny days. Because of the proximity
radios, I elected to use the Micro
charge controller, which
generates no RFI. This comes as
an easy-to assemble kit... and can handle up to 4 amps of charge
When in the lab, visiting waterfront friends, or ducking into a marina,
I am free to take advantage of shore power with a little Guest
waterproof charger from West Marine. When AC is
throw a toggle switch
to select this
as a charge source instead of solar (they otherwise interact, and I
didn’t want to deal with blocking diode losses and their unpredictable
effects on the respective charge managers).
Raw battery voltage to everything (except the Yaesu, which has its own
10-amp fuse) is switched with a 5-amp circuit breaker and connected to
the positive bus bar. There are two additional items in the
department: a Maha charger for the seemingly unlimited number
AA batteries in my life, and a small Statpower inverter that generates
115 VAC to feed my laptop charger, digital camera charger, cell phone
charger, PDA charger... well, you get the idea. I know, it’s
very efficient to go from DC to AC and back to DC, but until the
industry standardizes its power protocols and provides universal
conversion widgets, we are stuck with 115VAC as a sort of lingua franca
in such situations.
3: Luxeon high-brightness white emitter retrofitted into
marine sternlight. Silicon grease was used for thermal
and a scrap of dowel was machined to fit original bulb socket.
One of the key requirements for this system is
although I don’t usually choose to kayak at night (especially in busy
shipping lanes), it does happen occasionally, often as a result of bad
planning. When it does, I insist on being as visible as any
small craft, though from the perspective of an oceangoing freighter
that’s not saying much. Being power-limited without an
the thought of off-the-shelf incandescent navigation lights was
disturbing... even the smallest would consume a total of 15 watts for
the bow bicolor and white sternlight. Instead, I bought a
of small Aqua
Signal Navlights from West Marine, tossed the original
incandescent bulbs, retrofitted Luxeon 1-watt high-brightness LED
emitters (complete with heat sinks), then drove them with 350 mA
constant current sources made by TaskLED. These do
generate a bit
of RFI, but it hasn’t been a problem on the kayak (though it is on the
Microship)... and the net effect is a beautiful suite of navlights for
about 1/5 the power of the traditional solution.
Photo 3 shows the sternlight assembly with the fresnel lens
removed. This mounts on the gray Pelican box at the stern,
the constant-current source just inside the enclosure. Seeing
this at night, it is difficult to believe it is but a single white LED;
around camp, I use it as a utility area light both inside and outside
Pelican box at the stern carries the white LED
navlight seen in Photo 3, as well as a bayonet-mount J-pole antenna,
and yacht horn. Note waterproof connector.
Of course, one of the primary justifications for all this was the
tracker. Shown unpackaged in Photo 5, this is based on the
excellent and very popular Kantronics KPC-3+, particularly attractive
in this application because of its low current drain, general utility
as a TNC, and dual-port capability that make it easy to switch between
packet and APRS without fiddling with cables.
The TNC is grafted to one of my all-time favorite 2-meter
the venerable Yaesu 290. As a long-time aficionado of
bicycle-mobile and other power-limited operating environments, one of
my pet peeves is the fact that almost all “mobile” rigs have a standby
current drain on the order of an amp. This is simply
in anything other than a car, but this Yaesu radio (like its 70 cm
mate, the 790) draws about 50 mA when just sitting there... yet can
still put out 25 watts. As such, I don’t mind leaving it on
the time, a necessity in an application like this.
The third essential component in the tracker assembly is a GPS, and I
suppose I could have run NMEA data from the cartographic unit on the
yellow “console” box between my legs. I wanted the
and reliability of a stand-alone unit, however, so opted to add a
dedicated Garmin GPS-35 for APRS use. The little toggle
the photo lets me kill this to save power when using the rig for
general packet operation, as when doing email by the campfire.
One other detail is visible in the photo: a
converter. This allows use of my USB-only Macintosh iBook
When starting the Bubba project, my initial intent was to use one of
the simple, low-power, and practically bulletproof PIC-E
TAPR as the APRS tracker. But I couldn’t resist the allure of
added packet capability, especially since all the other components
would be on board regardless.
5: Packet/APRS assembly before installation in the
black box at the bow.
Now that we’ve taken a quick look at all the core gizmology, let’s talk
for a moment about the special considerations involved in taking this
delicate and expensive gear into a corrosive environment.
Unprotected boards would only last a few minutes, and even traditional
weatherproofing techniques are not enough to defend against the aqua
regia that splashes regularly across a enclosure lashed to
An excellent start, of course, is the use of Pelican cases... these
folks have refined their technology over the years, and unmodified
boxes are quite capable of protecting their contents even when
submerged. Their new models, like the yellow one in Photo 6,
cam-actuated latches that are easier to use, as well as automatic
pressure-relief valves that can’t accidentally be left open.
But all bets are off when you start drilling holes and adding
connectors. Even some of the seemingly robust products in the
marine marketplace turn out to be unreliable in a genuinely harsh
environment (not the cabin of a pleasure yacht), and a good connector,
badly installed, can allow the introduction of water when the
temperature drops and the box pulls a vacuum. I was fortunate
enough to be able to find some undersea-pluggable connectors from
are widely used in oceanographic and
other underwater applications, so I trust them. I was a
less confident in the gasketed BNC bulkhead connector for the 2-meter
antenna, but it has so far held up to real-world abuse (including a
pressure test)... I treat it occasionally with Boe-Shield to prevent
surface degradation. And I fight crevice corrosion by making
that all threaded fasteners are assembled with stainless steel
Wherever objects are mounted to the boxes, they are either gasketed or
sealed with an aggressive black silicone (don’t use this around coax,
as it outgasses acetic acid... and never apply it to fiberglass if you
ever intend to use other adhesives, including epoxy). This was the
technique used to handle the wire feedthroughs for the LED navlights,
the horn, and the J-pole bayonet (another candidate for occasional
treatment with Boe-Shield). The two switches on the yellow
are sealed with gasketed rubber boots.
The wiring harness is an interesting problem: it runs about
feet and is subjected to cyclic abrasion, seawater immersion, and
occasional yanking stresses. The inline splices are all
and wrapped with self-vulcanizing rubber tape, and the whole assembly
is spiral-wrapped (allowing drainage while still providing excellent
mechanical support and abrasion resistance). The RG-58 coax
hard-wired to the bayonet-mount J-pole antenna, eliminating the need
for another connector... although this does make the harness much less
convenient to stuff in a bag and carry around.
All this is basically playing by the rules for harsh-environment
packaging, but I went just a little further (given the dollar value of
the contents!). Since grit can compromise gaskets, I
treat the Pelican seals with silicone grease... and inside the black
box there is a VCI, or vapor-phase corrosion inhibitor. This
adhesive-backed sponge-like unit slowly outgasses a substance that
bonds with exposed metal surfaces, preventing oxidation; you can see
the edge of it just in front of the Yaesu rig in Photo 2.
6: The paddler’s-eye view of unladen Bubba, cruising the
waters near Camano Island, Washington.
The System in Use
Having a stable power system, decent lighting, and a live tracker on a
kayak has added considerably to the quality of the paddling
experience. During a 6-day adventure last fall, I kept my
(courtesy of Steve Dimse, K4HG)
linked from the daily update page on my website. Local
kept an eye on my progress and popped by to meet me as I approached
towns; farther away, some folks kept a window open on their desktop at
work and periodically loaded the Terraserver page showing a
satellite’s-eye view of my current location. There was a
that in an emergency, help would not be far away… and in camp, alone on
a tiny island in the fog, I amused myself with a couple of hours of
fireside packeteering while sipping an adequate merlot and listening to
the nightbirds. Not a bad life.
The confluence of raw nature, muscle power, and sophisticated
technology has always been alluring. With a little extra
attention to packaging, this can be extended into places that would
normally fry the delicate electronics that have become such a seductive
part of our geek lifestyles.
7: A plot of the posits captured during an island
Bubba. Cypress is
unpopulated, with high
cliffs… coverage was very sparse after rounding the north end.
Steve Dimse, K4HG, for the findu.com site and map graphic; Bill Vodall,
WA7NWP, for APRS configuration help and capturing posits; Ken Glaeser,
KA9YGN, for power management help and J-pole fabrication.
the author: Steven Roberts, N4RVE, spends his
building geek adventure substrates on Camano Island,
Daily project updates and photos appear on the Microship Live Page.