Best Anchor App

[blu-ray]

Re: Best Anchor App / not my only concern

First of all my experience on anchoring is from much larger boats; ex BM3 437 ft DDG Destroyer) my situation is Large fresh water lake (1800 + mi shoreline). Our usual anchorage is overnight in secluded shallow coves, usually Backed toward beach. Even with my little boat at 31ft LOA makes me anxious... to pivot about. Of which my Lowrance fancy touch screen ele's won't set proper anchor watch too! Hence I almost always set "3 point" ie the plow anc. on bow (windess) a separate #13 Fluke galvanized also with 8 ft of 3/8 plasticoated welded link w/shackles and safety wired, off bow cleat at close to 35-40 degrees "V". then I will Walk in a line and tie off to a tree or a sand screw. I have a third anchor if I need for rear, (if I don't want to swim or walk in) I like to back in with BIII's tilted up and about neck high off swim step, draft to bottom about 4 ft
My concern is NOT drifting or dragging, I know how to set anchors, I know I won't move much laterally What my Sounder Does well is the depth alarm. I have had it warn me with as little as 4 inchs of drop. If they are releasing from Dam I can just let out a little to rear and take up on bow anchor lines.
I don't think an app could do that!

 

[Tonka Boater]

A quick follow up on smart phone GPS accuracy....

I have an extra iPhone 5 that doesn't have carrier or data service so I plan to use for music and as a track recorder/GPS on my boat to record the distances that I travel. Since it has no service I decided to test the accuracy of the GPS on short 15 mile trip on land with the wifi turned off. I mounted it to the windshield of my truck and started recording a track. Along the way I marked waypoints at stop lights a few known areas and made note of my relative location.... I emailed the track to myself after my trip and viewed the track on Navionics' website with the satellite overlay. The results? Westie is correct, the tracks are within about 10' of my actual location but the overall track and the distance were surprisingly accurate. Some spots that I marked were dead-on others were close and many were within 10' or so. Not too bad and about as good as using a sextant and navigating by the stars with a paper chart but not nearly as good as a dedicated chart plotter.

My takeaway.... a standalone smartphone is a great tool on the boat for tracking the distance you travel and recording tracks. Without wifi or a supplemental GPS signal, it's not accurate enough for reliable navigation in tight waters, let alone as an anchor alarm. I would use it for my sole navigation device on the lakes in my area because its accurate enough to get me to the channel markers, restaurants and landmarks, and most lakes have shallow waters marked pretty well.

 

[FootballFan]

A quick follow up on smart phone GPS accuracy....

I have an extra iPhone 5 that doesn't have carrier or data service so I plan to use for music and as a track recorder/GPS on my boat to record the distances that I travel. Since it has no service I decided to test the accuracy of the GPS on short 15 mile trip on land with the wifi turned off. I mounted it to the windshield of my truck and started recording a track. Along the way I marked waypoints at stop lights a few known areas and made note of my relative location.... I emailed the track to myself after my trip and viewed the track on Navionics' website with the satellite overlay. The results? Westie is correct, the tracks are within about 10' of my actual location but the overall track and the distance were surprisingly accurate. Some spots that I marked were dead-on others were close and many were within 10' or so. Not too bad and about as good as using a sextant and navigating by the stars with a paper chart but not nearly as good as a dedicated chart plotter.

My takeaway.... a standalone smartphone is a great tool on the boat for tracking the distance you travel and recording tracks. Without wifi or a supplemental GPS signal, it's not accurate enough for reliable navigation in tight waters, let alone as an anchor alarm. I would use it for my sole navigation device on the lakes in my area because its accurate enough to get me to the channel markers, restaurants and landmarks, and most lakes have shallow waters marked pretty well.

I tend to agree with comments about accuracy. Over the past few months whenever I am in a canal, ditch, river - with visible constraints have paid a lot of attention to the what the chartplotter is showing versus the charting app on my iPad. They are right next to each other on the helm.

Experience has shown numerous occasions where I can determine visually that the boat is in the dead center of the canal/ditch, the Chart plotter showed dead center, and the iPad showed not in the center.

Although I am a huge proponent of the iPad mounted at the helm for use with active captain, it does not replace a chart plotter.

Regarding anchoring, I don't typically require the same level of accuracy as I do in navigational situation. When we anchor, we look for places without the concentration of boats like you would see in a mooring field. I select location and setup assuming there may be some movement with settling.

First I find visual objects which I can test holding. Second after an initial period of time, I setup up the chart plotter (N up, Track on, zoom all the way in) which forms a circle pattern as the boat swings.

All that said, I set the phone based anchor alarm app and keep it near wherever I am. I am periodically checking the chart plotter. If the alarm goes off on the phone, I am headed straight to the chart plotter to see what is "actually" occurring.

The part I don't understand and fully appreciate: is a location error of a few feet that important when anchored?

My post is not intended to be argumentative. Just trying to determine the impact of accuracy within a few feet for an anchor alarm.

thanks,

Mark

 

[Airboss]

It would be hard to argue that GPS precision or accuracy is more important to aviation than any other user group. "a Jumbo jet with 400 passengers shooting an approach in fog in to JFK" for example.

The original GPS system was not accurate enough to do this safely. So WAAS was developed to enhance accuracy. WAAS is a series of ground based transmitters that "augment" GPS accuracy. As noted below (excerpted from Wikipedia) it was designed to provide an accuracy of up 7.6 meters 95% 0f the time. Although it often provides 1 meter accuracy it can be WRONG by 25 feet all of the time and Wrong by greater than 25 feet 5% of the time.

WAAS objectives[edit]

Typical WAAS service area. Dark red indicates best WAAS coverage. The service contours change over time with satellite geometry and ionospheric conditions.
Accuracy[edit]

The WAAS specification requires it to provide a position accuracy of 7.6 metres (25 ft) or better (for both lateral and vertical measurements), at least 95% of the time.[2] Actual performance measurements of the system at specific locations have shown it typically provides better than 1.0 metre (3 ft 3 in) laterally and 1.5 metres (4 ft 11 in) vertically throughout most of the contiguous United States and large parts of Canada and Alaska.[3] With these results, WAAS is capable of achieving the required Category I precision approach accuracy of 16 metres (52 ft) laterally and 4.0 metres (13.1 ft) vertically.[4]

Integrity[edit]

Integrity of a navigation system includes the ability to provide timely warnings when its signal is providing misleading data that could potentially create hazards. The WAAS specification requires the system detect errors in the GPS or WAAS network and notify users within 6.2 seconds.[2] Certifying that WAAS is safe for instrument flight rules (IFR) (i.e. flying in the clouds) requires proving there is only an extremely small probability that an error exceeding the requirements for accuracy will go undetected. Specifically, the probability is stated as 1×10−7, and is equivalent to no more than 3 seconds of bad data per year. This provides integrity information equivalent to or better than Receiver Autonomous Integrity Monitoring (RAIM).[5]

Availability[edit]

Availability is the probability that a navigation system meets the accuracy and integrity requirements. Before the advent of WAAS, GPS specifications allowed for system unavailability for as much as a total time of four days per year (99% availability).[citation needed] The WAAS specification mandates availability as 99.999% (five nines) throughout the service area, equivalent to a downtime of just over 5 minutes per year.[2][5]

The accuracy depends upon receiving the WAAS stations on your device (which won't often happen on a ground based vehicle).
A device also receiving GNSS (Russian Satellites as noted in a post above) can approach the accuracy of a WAAS GPS.

Cell phones using cell towers and other types of augmentation can APPROACH , but not equal, WAAS accuracy.

At best a CELL PHONE is not going to be more accurate than the system it is using for reference which in the case of GPS/GNSS/WAAS is:
1 meter some of the time
Better than 7.6 meters most of the time
Worse than 7.6 meters (25 feet) 5% of the time.

Another major concern should be: How accurate or reliable is the APP? What do you know about the developer of the APP? Does the APP come with any guarantees of accuracy or reliability?

Yes there are some augmented systems out there for surveying that are accurate to a few centimeters but they cost hundreds of thousands of dollars. That ain't your cellphone.

Look here>> http://fulcrumapp.com/blog/gps-accuracy-experimentation/

For the results of a test of different devices done under fairly well controlled circumstances. Zoom in on the map to see the distance of variation among devices. It certainly is worse than "inches" of accuracy.

I don't believe in the Easter Bunny, the Tooth Fairy, nor cell phones with "inches" of GPS accuracy.

I am certainly not going to risk my boat nor safety on a cell phone GPS using an app designed by God knows who, when anchored near shore or shoals, or shipping lanes.

If 25 foot accuracy most of the time fits your needs then go ahead and try it. Just don't go to sleep thinking your iPhone is more accurate than a certified navigation system on a jumbo jet.