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Go Back   SailNet Community > On Board > Gear & Maintenance > GPS / ChartPlotters; Totally Baffled
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Thread: GPS / ChartPlotters; Totally Baffled Reply to Thread
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Topic Review (Newest First)
12-29-2010 10:25 PM
TakeFive I've been meaning to reply to this thread for several days, but did not have time. I see some reference to possibly navigating using base maps instead of marine charts. Based on my experience that would be a big mistake. I have a few pictures that you may find interesting.

First, last season my only real-time electronic navigation device was a little Oregon 400c handheld (although I just bought a GPSmap 640 today). I do not attempt to plot routes with the handheld, but I have plotted routes into numerous marinas and coves on my computer using SeaClear software and downloaded NOAA digital raster charts. I then use software (G7toWin and MapSource) to transfer these routes from my computer to the Oregon.

I get some comfort from plotting these routes on NOAA charts, then transferring the routes to other software and handheld devices, because I get a useful cross-check by overlaying the route plotted using the NOAA charts with the commercial maps provided by Garmin and others. So far, for the limited area where I sail, I've seen good agreement between the NOAA charts, Garmin charts, and my personal observations of shorelines, navaids, and depth soundings. Unfortunately that is not the case with MapSource base maps.

Here, as an example, is the route for a westward exit from my harbor as plotted on the NOAA raster chart with SeaClear. GPS is especially useful here because there are no markers for the channel, and there pretty serious mud flats over near the island:


When I transfer this route into the Oregon, you can see good agreement - the route follows the same relationship to the depth contours (note that North points right in this case):


When I look at this on Google Earth, I also see the route following the same path through the channel:


Finally, here is the exact same route overlayed over the base map that Garmin provided with my MapSource software. Note that your version of MapSource may have a better base map, or even be able to pull the marine charts out of your GPS. Unfortunately, the marine charts in the Oregon 400c cannot be viewed in MapSource, and I did not want to spend the $$$ to buy them, since I am perfectly happy plotting my routes in SeaClear:


As you can see, the MapSource base map shows my route going over land. I have checked the projection and datum for my charts, and have made every adjustment possible to get this fixed.

My basic point is that I would never use base maps to plot a course over water. However, if you have a GPS without marine charts and do not want to buy them, you could use software like SeaClear to plot routes and mark waypoints, obstacles and other POIs, then transfer those over into your handheld GPS to observe your real-time position vs. those POIs. In this case, the POIs would be probably more reliable than anything your base maps show.

Others here have pointed out the risk of dropping a handheld overboard. I alleviated this by buying a $10 bicycle handlebar mount for my GPS and attaching it to the top of my guard rail. That put the screen in a very convenient location that allowed me to glance at it occasionally without taking my eyes too far away from where they should be. I will mount the GPSmap 640 in the same place for next season.
12-21-2010 12:12 PM
landmineop Got a waterproof pc on ebay. Has charts, navigation software and GPS. Fills all my needs along with paper charts. Between the two along with watching where I go, all is right with the world. The waterproof Pc was the best electronic buy I have made. I think the guy still has a couple on ebay.
12-21-2010 11:37 AM
rjg23
Garmin 60csx

Been using a Garmin 60csx (discontinued handheld chartplotter) and paper in and around Casco Bay for the past 5 years. This combo has served me very well in all conditions. I'm not a "bells and whistles" type (probably because I don't have the coin) so this GPS has provided all the info and routing utilities needed.

Still available via retail, for around $200. Then you'll need the charts.
12-21-2010 09:06 AM
NCountry Garmin handheld, lap top, Opencpn.org, NOAA nautical charts. Plug handheld into usb on lap top. Works GREAT! Very accurate. Through the barrier reefs coming into the Keys and the Hawk Channel I was able to call out depths to the helm to within 1 foot of accuracy. Even the old sailors were impressed. Great stuff and the price is right. (Opencpn and the NOAA charts are free!)
12-21-2010 08:14 AM
PalmettoSailor
Quote:
Originally Posted by harbin2 View Post
Until a year ago, I had never used a gps or chartplotter and didn't see much use for them on a boat. I sail over most of the Chesapeake where most sailing is line of sight. snip...The bluecharts are much more detailed (depths, land and water features, etc.). The 441 came with the charts preloaded and I can't imagine having a unit that didn't have them.
harbin2
I'm also a Chesapeake sailor and my experience is similar. I got a deal on a Lowrance unit with 5" color screen that came with a free enhanced chart of US waters. I think its similar to the 5" Garmin that comes with loaded Bluechart mapping. I use a paper chartbook for planning, seeing "the big picture" and often refer to it when entering a new river/cove/anchorage. I use the chartplotter as primary during the "enroute" phase of my travels and find its often handy to help determine when to tack. Here on the Chesapeake, its good to have a screen large enough to show some detail when zoomed out to 10-15 miles so you can zoom out far enough to see when you can tack to round the next point and still see the depths so you know its ok for your draft.

It's also a great help in making decsions about the days destination. A chartplotter does a great job of reminding you if your speed made good isn't going to get you to your intended destination in an acceptable time frame so you can start thinking of a "Plan B" lest you have to enter an unfamilar anchorage at night although a mistake here on the Chessy is only likely to result in sticking your keel in the mud, vs smacking a rock or reef.
12-21-2010 07:56 AM
PalmettoSailor
Quote:
Originally Posted by bljones View Post
If i have had Lasik, do I not now have the Mark II Eyeball?
No, what you have is the MKI Mod.1. The MKII is digital and is still in beta testing with the DARPA.
12-18-2010 09:18 AM
harbin2 Until a year ago, I had never used a gps or chartplotter and didn't see much use for them on a boat. I sail over most of the Chesapeake where most sailing is line of sight. I used a little B&W handheld Garmin once in the fog and it allowed me to back out of my anchorage. Last spring I purchased a Garmin 441 and I love it. I now see numerous uses I never saw before. No, it doesn't replace charts or other basic tools of navigation (especially common sense including looking where you are going). But it is a fantastic tool.
I also purchased the new Garmin software "Homeport" that I loaded on my laptop. Homeport includes the Basemaps. I had to transfer the bluemap charts onto a thumb drive that I plug into my laptop to get the charts. The whole thing is a little cumbersome but it does give you a clear picture of the difference between the basemaps and the bluecharts. The bluecharts are much more detailed (depths, land and water features, etc.). The 441 came with the charts preloaded and I can't imagine having a unit that didn't have them.
harbin2
12-16-2010 07:46 PM
LinekinBayCD
Quote:
Originally Posted by sck5 View Post
I used to think radar wasnt necessary until the day I got stuck in a pea soup fog in the middle of chesapeake bay with boats and ships all around that I could hear but not see. I wouldnt sail in a fog prone place like Maine without it, though you could get away without it in other places. I wouldnt want to rely on DR in a place with major tidal currents and fog. People do it but they are braver than I am (or maybe they have more insurance)
The combination of a chartplotter with a radar overlay is probably the best navigation tool you can have on board whether in fog or clear weather. The radar is the best confirmation of the accuracy of the chartplotter. Very nice in the fog. If I had to chose between losing the radar or chartplotter I'd rather have the radar working in Maine fog.
12-16-2010 02:48 PM
sailingdog
Quote:
Originally Posted by bljones View Post
If i have had Lasik, do I not now have the Mark II Eyeball?
Depends on how good the surgeon was. A bad one, you might end up with Mark 0.1 eyeballs. In bad cases people with poorly done Lasik procedures can have issues with glare and such at night.
12-16-2010 12:35 PM
bljones
Quote:
Originally Posted by sailingdog View Post

Also, the Mark I Eyeball is usually your best and most important navigation tool.

If i have had Lasik, do I not now have the Mark II Eyeball?
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