What follows are some tips
for navigating with a laptop. A laptop can perform the same
function as a GPS chartplotter, with some added benefits. I use
mine on the boat for email, internet weather predictions, and
music.
If you already have a laptop, then you obviously save money by not
buying a chartplotter. Even buying a laptop solely for the
purpose of keeping it on the boat is going to be cheaper than buying a
chartplotter, since you don't need the latest and greatest model of
laptop. The downside of using a laptop instead of a dedicated
chartplotter is that laptops do not have outside daylight-readable
displays, so they must remain inside the cabin, and they're not water
resistant anyway. You can buy an external daylight-readable
display and mount it in the cockpit while the laptop stays in the
cabin, but they're expensive.
The main consideration if you're buying a laptop for the boat is going
to be screen size, followed by battery life. Larger screens are
obviously easier to read, but harder to lug around and draw more
power. The longer the
laptop's battery lives, the less drain on your boat's batteries.
You will want a 12V DC power adapter such as those sold by Targus,
Kensington, and
iGo, and you may want
to wire it directly into the boat's power instead of using a cigarette
lighter adapter (CLA). A 12-volt adapter is much more efficient
than using an inverter. It used to be conventional wisdom that a
computer required the "pure" sine wave power of an inverter, and this
may still be true for a desktop, but a laptop's power supply can
tolerate a lot of fluctuation, and there's no sine wave for DC
anyway.
My laptop is easily powered by a single
15-watt solar panel in full sunlight, as long as the battery is
charged. The laptop
I used in the Bahamas draws a whole lot more power (6+ amps) while
charging than while it was
running fully charged (about 2 amps).
1 The moral is:
try not to run the laptop when there's no external power going to it
(solar, alternator, etc.) meaning you can use it all day for navigation
and music but at night you should switch to your ipod.
Here are some tips for minimizing the power consumption of your laptop:
First, if you have the luxury of buying a dedicated computer for the
boat, buy a new laptop with a low-power processor. These change
almost too fast to list any here but there are some recent
ultra-low-voltage Celerons. While not exactly speed-demons at
933MHz, they use around 20% of the power of faster models.
Whatever you do, do
not run
Vista. It requires far more memory and CPU power than Windows XP,
which translates directly to more amp-hours out of your battery
bank. Maybe this will change in the future but it's
unlikely. Windows 2000 is also still a robust choice.
If you run Windows, install gobs of memory (1-2GB) and go into "My
Computer->Properties->Advanced->Performance
Settings->Visual Effects and select "Adjust for best
performance". Also go to Advanced->Virtual Memory->Change
and disable the virtual memory file. This will save a lot of hard
disk activity and battery life.
You also probably want to have it sleep aggressively (say, after 10
minutes of inactivity) but only hibernate after 10 hours or so.
Anything less and you consume more power writing the hibernation state
than you save by being in hibernation. Also, have the display
blank after a few minutes of inactivity, because the display consumes
almost as much power as the CPU. You will probably need to keep
the screen bright for daytime navigation, so it helps to turn it off
whenever you can. This also means you shut the lid of the laptop
every time you are not using it. Even it it's running, the screen
will be off.
If you want to get really medieval, download
SpeedSwitchXP to reduce
the operating frequency of the laptop's CPU and save even more power.
GPS
To navigate with your laptop, you need a way to connect it to your
GPS. Currently almost all GPS data cables use DB9 serial
connectors, and almost no laptops have serial ports
anymore. A DB9 connector looks like this:
So
you need a way to convert the serial to the laptop's Universal Serial
Bus (USB) format. You can get an adapter from Radio Shack or
Keyspan, or search for "serial USB converter" on the Web. The
converter will look like this:
I prefer to use cables that provide both data and power so I'm not
replacing GPS batteries all the time. They're not much more
expensive than data-only cables. You can buy the cable with the
CLA adapter and cut the adapter off if you decide to hard-wire the
power
into my boat's 12-volt system.
Plug the GPS into the data cable, the data cable into the USB
converter, and the USB converter into the laptop's USB port. You
may have to insert a CD for the USB converter's device driver, or
Windows may recognize it on its own. Make sure you install the
device drivers on the adapter's CDROM before plugging it into the
laptop.
Now you need to figure out which COM port Windows has assigned to your
GPS. On your computer's desktop, right click on "My Computer" and
select Manage. Then click on Device Manager, and finally click
the + next to Ports (COM & LPT). You should see a listing
that reflects your model of USB converter, and a COM port number next
to it. If you don't, reboot, and check that your USB converter
driver installs correctly. If it still doesn't work, you might
have to adjust the speed on the COM port. 9600 baud or lower
should work.
Your GPS speaks in a language (or protocol, in computer lingo) called
NMEA (named for the National Marine Electronics Association).
Whenever it's turned on and plugged in, it transmits NMEA
"sentences" through the data wire into your computer. These
sentences give useful information like your latitude and longitude, and
the satellites the GPS is tracking. Now you
have to find some way to listen.
Software
You can communicate with your GPS using a number of software
tools. There are plenty of commercial navigation programs (
Landfall
Navigation
has a fairly comprehensive list) but most are in the $500+ range.
Their main appeal in the past was that they included "chart kits" for
certain regions of the country. Now that the government is giving
away electronic charts for free, it's a bit hard to justify their
prices. However, most of the shareware navigation programs either
can't read the free charts without calibration (see below) or don't
show your current position from the GPS. One of the best
free/shareware navigation programs is
SeaClear.
I download all of the charts in a section of the country and copy them
to several different CD-ROMs, so I have backups. (My boat is
trailerable so I need a lot of charts). It would take
between 5 and 10 CD-ROMs to hold all of the charts available for the
US, but if your laptop has a DVD writer, you would only need 1 or
2. I also copy most of the local charts that I'll be using for
the short term to my computer's disk drive.
Maptech has a free downloadable version of its navigation software
called Chart Navigator. It's very useful for examining all those
NOAA charts you just downloaded, and can do things like scale in and
out, or automatically load an adjoining chart if you click on the edge
of your current chart. It can interface with the GPS to
upload and download waypoints. It does not, however, provide your
current position from the GPS. For this you have to purchase
Maptech's full-featured navigation program.
My favorite tool for waypoint management is
GPS Utility. GPSU
allows you to specify the
COM port that your GPS is talking to. You can also change the
baud rate (speed) settings if you are unable to connect to your
GPS. Once you connect, start the Interface Monitor if you want to
take a gander at the raw GPS data. You will recognize latitude
and longitude
information in the text.
There are several differences between a chart that you've downloaded
and an image of the same area, or an image that's copied from a
nautical chart, even though they may look the same on your computer
screen. Just as HTML documents contain information that you see
and information that's hidden (such as hyperlinks), so electronic
charts contain both visible images and additional information.
The chart's file on your computer contains what you see
on your screen, but it also contains references to, among other
things, specific lat/lon locations. This is how you create
waypoints: you click on the chart and your computer "knows" where
you're clicking because it "knows" the exact area that every point on
the chart represents. If you're only working with U.S. charts
then you can skip the next section, since the entire U.S. is covered by
the free NOAA charts.
For areas outside the U.S., it's possible to obtain simple images of
charts (usually Admiralty charts), which you can then calibrate using
SeaClear or GPSU.
For example, you can click on the point on your chart represented by
the intersection of latitude 38 and longitude 122, and tell your
computer that's where you've just clicked. By using between two
and four such "calibration points," your computer can extrapolate the
location of any other point on the chart with very good accuracy
(depending, of course, on the quality of the original scan). Any
image recorded from a chart is usable in GPSU, as long as the image is
not stretched or skewed.
GPSU will show your current position, but it doesn't yet understand the
NOAA chart format, so you can load the charts, but they load as images,
so you need to calibrate them.
Memory-Map also
looks promising but I haven't had a chance to try it
yet. It would be most useful if you already own one of the
hand-held devices that it supports.
Once you've got your GPS connected to your chart software, you will be
able to track your position and log your track. You will also be
able to click on a spot on your screen to establish a waypoint, which
you can then upload to your GPS, which saves a lot of typing and
character-searching. You can also download and upload routes and
tracks. Clicking on a point on your small computer screen isn't
as accurate as clicking the Mark button on the GPS, but most GPS models
allow a simple correction. Press the Goto button and select the
waypoint you want to correct. When you're as close to the mark as
you are comfortable getting, highlight the Distance To Mark field on
your GPS's navigation screen. You can now set the distance to
zero, which automatically adjusts the location of the waypoint to
reflect your position. Remember to upload the waypoint from the
GPS into your navigation program next time you're using the computer,
or you'll have two different versions.
Where Am I?
It's possible to get a position fix from Maptech's Chart
Navigator. The simplest way is to just look at the lat/lon on
your GPS and scroll your screen pointer around the chart. Chart
Navigator displays the lat/lon of the pointer at the bottom of the
window. However, this method is prone to error when you're
bouncing around in the ocean.
The second method uses an "A-B line". For this method, you have
to have at least one known waypoint programmed into your
GPS and into Chart Navigator. Press the Goto button on your GPS,
and select the waypoint. The GPS will give you a distance and
bearing to the waypoint. Now click on the "A->B" toolbar
button at the top of Chart Navigator. Click on the chart
somewhere in the neighborhood of where you think you are. This is
your A point. Click on the chart again on or near your
waypoint. This should be the same waypoint you selected for the
Goto on your GPS (although Chart Navigator will show the full name and
your GPS will most likely show the 6-character abbreviated name).
Now you can go back and drag the A point around on the chart until the
range and bearing at the bottom of the Chart Navigator screen match the
range and bearing shown on your GPS. I find that it's also easier
to remember a range and bearing when I jump below to look at the
computer than it is to remember a lat/lon to several minutes and
seconds of precision.
You can download your track from a day sailing to GPSU, where it will
be displayed on the chart, or to a program like Google Earth, where it
will be displayed over a satellite image. For racers, the track
can give valuable information about VMG and optimal tacking
angles. It can also tell you if you were being set by currents
during the race (just in case banging into the mark didn't give you
that information already).
Backup GPS
A USB-only GPS unit, without a display, can be had for as little as
$40. These make a great backup in case your primary GPS
fails. Depending on how many USB ports your
laptop has, you may need to purchase a USB hub to connect more than one
GPS, although it's not particularly useful to have more than one
running simultaneously, since navigation programs will only use one COM
port as input at a time.
Laptop Backups
Most laptops were not designed for the "harsh marine
environment." On the other hand, they're not much more
susceptible
than the typical chartplotter. If you're going to bring
your precious laptop on a boat, you should have a backup. My
preferred method is the simplest: a second disk drive. You can
either buy either a desktop-sized 3.5" drive with an enclosure or the
smaller 2.5" laptop drive. You also have the choice of purchasing
a drive and enclosure separately or as a complete kit. The
advantage of purchasing the drive separately is that the whole thing is
much cheaper than the preassembled alternative. Plus you can
upgrade the drive yourself in the future if you need more space.
The disadvantage is that it involves a minor amount of fiddling with
computer cables and tiny screws, although the instructions on most of
these enclosures
are very clear and simple.
The 2.5" laptop drives are more expensive than the 3.5" drives for the
same amount of space. However, they are physically much smaller
and can be powered entirely from your laptop's USB port. My
external drive is so small that it sticks to the lid of my laptop with
two strips of Velcro. The other disadvantage of the 3.5"
enclosures is that they need to be powered via 110VAC, most likely
requiring an inverter. (One note of caution: if you have so much
stuff plugged into your laptop's USB ports that you need the hub
mentioned above, do NOT plug the 2.5" drive enclosure's power cable
into the hub. It will work, but only sorta, because the hub can't
provide enough power for the drive all the time. Plug the drive's
power connection directly into the laptop and plug everything else into
the hub.)
You can use imaging software like Ghost, backup software like Acronis
TrueImage, plain old Linux (GNUParted), or even Windows XP SyncToy
Powertoy to keep the two disks synchronized.
If you run Linux you can get a much smaller memory footprint than
Windows, and you could manage the two drives with RAID mirroring, but
you
would have to run WINE to get any popular navigation software to work,
and this is going to clobber your efficiency and require a
faster/hotter/more power-hungry CPU.
1. For the geeks: this laptop was a 1.7MHz Intel Pentium M,
21-watts
TDP.