GPS Lock Time

[halimark]

Looking for info, I replaced my softop with welded aluminum hardtop and now my Lowrance HDS 7 takes quite some time to lock on and or refined itself. Annoying when one wants to find drift speed and reef position quickly. Sometimes takes 3 mins now, this never happened with sunbrella softop. Unit is on dash as far inside (away from windshield) as possible, side windows are not in so walls are still solid aluminum for now. I will install slider and side window when I decide what to put in. So question for experienced aluminum guys? Would you wait for window install and see, live with it this summer? Do I move unit far foreword on dash and drill new holes or buy and mount external antenna? Opinions, ideas?

Thanks


HM

 

[Stosh]

Get the antenna
Stosh

 

[quicksilver11]

GPS needs "line of sight" to the satelites, so you will most likely need to move it near the window or
like Stosh says get the Antenna which is probaly the best option

 

[fshnfnatic]

Had a friend do the same thing and found the only solution was an external antenna.Not too hard to install and not
too expensive either.That would probably be your best bet.

 

[halimark]

I looked at external antennas Sat, seem expensive at $300 then I must get a NIMI cable at $35-$135 depending what one?? Think I will cut the windows out and get some glass installed, move the unit forward on the dash, do some more research, then see if it go's back to as fast as it was before hardtop.

Thanks

HM

 

[jack fish]

I have a metal hard top and both my standard horizon plotter and hand held gps get a signal and I have never had a issues with it dropping out. I don't have a external antenna.


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[halimark]

Seams to be the norm. Some hardtop messes with others don't. Not sure why. I am proceeding with plan above before spending for external anntena.

HM

 

[Rockfish]

How is your position accuracy currently Halimark? If it is having trouble finding satellites it can be out by a hundred feet or more even if it is working. It will typically vary somewhat which I suspect is dependent on a number of factors including how many satellites it can lock on to at a given time. I like mine down around 14 feet (less than the length of the boat) and it is there most of the time even though my plotter is rather dated. That is every bit as important as time to lock on. I do have a separate GPS antenna on the glass hardtop feeding the primary chart plotter.

My impression is that newer units seem to be faster and better at resolving location than those of years back especially with some obstruction and with built in antennas. Still asking any unit to work well trying to find satellites through a metal roof and what signals it can grab through windows may not give the best results; although some units, boat design and mount locations seem to be much better at it than others.

I think in your situation with a new metal roof that your unit is telling you it now needs an external antenna to be fast and I suspect to be highly accurate as well. More windows may help but I think you are going to find the best answer as others have said is to eat the cost of an external roof mounted antenna. There are some situations where continuous high location accuracy is a safety issue.

 

[Tugcapitan]

Exactly what Rockfish says.
You'll get "HDOP" error if your unit is only locking on to those satellites it can see through the window. Most units will display the amount of error they are experiencing through menu options.
Almost every antenna's mounting instructions say 'in an unobstructed position as high as possible on the vessel'
External antenna for the win.

 

[jack fish]

I'am not a GPS expert and was not aware of hdop. So when fishing yesterday I selected it on my chart plotter display and it reads 1.9
I think it's 1.9 feet but not sure. Went too the gps page and it had a lock on a fair number of satellites. Should have counted and recorded. Took the hand held on the back deck and it displayed the same position as the plotter in the cabin. And the same number of locked satellites. Hope I'am not fooling myself on my location Relative to rock piles due too lack of external antenna ?


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[Tugcapitan]

DOP Value is calculated on a scale of 1-20. jack fish's rating of 1.9 is "excellent". It takes a rocket scientist's list of calculations to convert error rating into an actual measurement of how many metres off position you might be. The scale below gives you an indication of whether or not one should be concerned about the accuracy of their unit. I've heard that some units may also use a scale of 1-30, but I haven't come across that yet.



< 1 Ideal Highest possible confidence level to be used for applications demanding the highest possible precision at all times.
1-2 Excellent At this confidence level, positional measurements are considered accurate enough to meet all but the most sensitive applications.
2-5 Good Represents a level that marks the minimum appropriate for making business decisions. Positional measurements could be used to make reliable in-route navigation suggestions to the user.
5-10 Moderate Positional measurements could be used for calculations, but the fix quality could still be improved. A more open view of the sky is recommended.
10-20 Fair Represents a low confidence level. Positional measurements should be discarded or used only to indicate a very rough estimate of the current location.
>20 Poor At this level, measurements are inaccurate by as much as 300 meters with a 6 meter accurate device (50 DOP × 6 meters) and should be discarded

 

[jack fish]

Thanks tugcaptain. It's nice too learn something new.


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[halimark]

X2 Tugcapitan

Tonight I will investigate more to find out more details, how many sats, where and try and find that DOP value. Never really worried about all this before, kind of turn unit on and there is the boat on the chart. Tonight I will learn more.

Thanks

HM

 

[Tugcapitan]

No prob.
After doing some digging through the manuals, I was able to find some HDOP to metres info.
HDOP Accuracy in metres (rough)
<1 -- 3-4m
1 -- 3.7-4.8m
1.5 -- 5.5-6m
2 -- 6.5-8m
2.5 -- 8-12m
>3 -- Houston we have a problem(at least for dropping lines on our fave Hali spot!)

The units I'm using are mounted at the top of the mast about 60 feet up. The only time we really experience error is when landing a barge next to an empty ship which blocks the antennas signal in one direction.
Other times one may want to pay attention are when navigating in very close proximity to a high rock wall, in fjords (like parts of Grenville Channel), if the antenna is accumulating ice, or if in a dust storm or something.

Under perfect conditions right now, my two units are reading HDOP 1 and 1.5.

 

[finaddict]

Looking for info, I replaced my softop with welded aluminum hardtop and now my Lowrance HDS 7 takes quite some time to lock on and or refined itself. Annoying when one wants to find drift speed and reef position quickly. Sometimes takes 3 mins now, this never happened with sunbrella softop. Unit is on dash as far inside (away from windshield) as possible, side windows are not in so walls are still solid aluminum for now. I will install slider and side window when I decide what to put in. So question for experienced aluminum guys? Would you wait for window install and see, live with it this summer? Do I move unit far foreword on dash and drill new holes or buy and mount external antenna? Opinions, ideas?
Thanks
HM

HM, I was having the exact same issues with my gen 1 HDS-8. The fiberglass hardtop was interfering with signal reception, particularly in heavy fog. I got the Point1 external antennae and mounted on hardtop and the difference was night and day. It attaches to your NMEA2K network backbone. I went from 3-4 satellites with weak signals and sometimes it took a while to achieve that, to the full 12 satellites and signal reception booming in. I would highly recommend it.

 

[Mike_R]

Have you considered selling your current GPS and buying a new one with an external attennae?

 

[halimark]

I have not entertained selling at this point. Yes gen 1 HDS 7 but only 3 yrs old. Never worried with ragtop, im not saying this is a show stopper but inconvenient when drifting and waiting for speed and position to "catch up". Tonight I will learn more, find the DOP number and sats.

Must say Tugcapitan

You tradesman wow me every time I see a tug with tow transitting our waters. Profecional, friendly, safe and alsways worth a look with the bino's. Even spent an hour of fishing time last month watching the tugs pull a log boom from the harbor before we launched, logging area North Island. My family from Ont thaught it more fun to watch than the fishing (yes they clapped). Thanks

HM

 

[Aces]

Thanks for the education on the DOP values, Tugcaptain. I'm going to check that out tomorrow

 

[halimark]

Education I have received. I just spent an intimate hour with lap top, manual and HDS 7 in boat. DOP numbers were 1.5-5.5 depending on how I held unit. Mounted in old position number was 1.5. Tilted or further back in boat number jumped to 5.5, max number mounted was 2.4 over the hour, when moved forward completely number was still 1.5. Not completely sure what all means but numbers seam good with Tugcapitan's info above, and a move forward probably not going to help. Now I will spend the $350 on windows before any more moves. If issue remains then another $350 for antenna. I will provide an update when done so others may gain some knowledge. That's for the help.

HM

 

[Tugcapitan]

Hey Halimark, nice troubleshooting.
Now you know the new top is definitely a problem.
If it were my boat I'd probably want more windows anyways, so you're not losing anything by putting them in.
Also if it were my boat, I'd be unsatisfied with an HDOP reading over 2. Sounds like when you have it mounted as far forward as possible on the dash, you get 1.5 which is good, but an alteration of course where the roof gets in the way of a couple satellite feeds is going to give you problems. Try the windows and see what happens, but my guess is you'll end up with an external antenna. Good luck!