REEFS, & THE LIKE CRASH AVOIDANCE, DETECTION!!

[Snore]

Originally Posted by Simi 60

Pretty lines on a screen don't necessarily mean reality in real life

While nothing is fool proof- Navionics sonar chart is damn close.

Do yourself a favor and research it! Inlets and bays that have marginal detail on the NOAA charts are easy to navigate with a sonar chart.

Yes a prudent mariner should never rely on any one data source—-

[JPA Cate]

Originally Posted by Posh

Dear sailors & the like
I am in search of the latest tech. to avoid my cat of hitting reefs, containers etc, & the like that are out there as hazards & is a must have.
I am talking about if there is anything better by all means let me know, forward sonar.......what is the best available out there?
from a screen perspective, in color, detailed info, alarms, & from what is below all the way to the front, I will appreciate your feedback, questions & so on regarding this investment, but is also a safe way to cruise & be safe, more & more cat & others are hitting reefs & this is not cool.
Please advise.
thanks

Hello, Posh,

The catamaran that destroyed itself at Huahine a couple of years ago now, more or less, was driven too close to the reef with a normal tradewind wind and sea condition. No one was actively on watch, and the course was far too close to the reef for safety, so that was a failure of seamanship, and a too great trust in electronics.

I think what everyone is trying to emphasize for you that reliance on fancy electronics is the wrong place to put your focus, and the more effective will be to hone your and your crew's watch keeping skills. The electronics are seductive, I'm sure, but the human eyeball evolved to keep us safe, if we will but use them.

Ann, cruising full time since March of '89

[Simi 60]

Originally Posted by Snore

While nothing is fool proof- Navionics sonar chart is damn close.

Do yourself a favor and research it! Inlets and bays that have marginal detail on the NOAA charts are easy to navigate with a sonar chart.

Yes a prudent mariner should never rely on any one data source—-

I have.

Its only as good as user input accuracy so if you are in areas rarely travelled, they get little to no user input.

Where I am anchored right now, according to navionics is land and all around us is land and drying banks.
Reality has us in 20ft of water

Conversely I can show areas where there is depth according to navionics yet we would be well aground if trusting their charts.

[Snore]

Originally Posted by Simi 60

I have.

Its only as good as user input accuracy so if you are in areas rarely travelled, they get little to no user input.

Where I am anchored right now, according to navionics is land and all around us is land and drying banks.
Reality has us in 20ft of water

Conversely I can show areas where there is depth according to navionics yet we would be well aground if trusting their charts.

Yikes —- haven’t seen errors that bad— yet. Check St Augustine in NOAA vs SonarChart. Sonar is way more accurate. Your analysis is likely correct, for far flung spots. Sonar is likely not the best tool.

Like I said Navionics is one more tool in the tool chest.

[Simi 60]

Originally Posted by Snore

Yikes —- haven’t seen errors that bad— yet. Check St Augustine in NOAA vs SonarChart. Sonar is way more accurate. Your analysis is likely correct, for far flung spots. Sonar is likely not the best tool.

Like I said Navionics is one more tool in the tool chest.

I wouldn't call Brisbane Australia far flung.
It is a capital city and we are only 25 miles from the centre of town.

[Paul L]

Originally Posted by Snore

Yikes —- haven’t seen errors that bad— yet. Check St Augustine in NOAA vs SonarChart. Sonar is way more accurate. Your analysis is likely correct, for far flung spots. Sonar is likely not the best tool.

Like I said Navionics is one more tool in the tool chest.

Isn't the entrance at St Augustine fairly regularly re-buoyed as the bars drift? Last time I went through you had to get the latest buoy positions from the port office website. ( small buoys that are hard to see from the sea side). So how are these continual changes handled in the sonarcharts? Do they take the latest info, do some kind of an.average, use the most common? Just wondering what their algorithm takes into account?

[Jim Cate]

We have experienced friends who struck a ledge somewhere in the NE cruising grounds of the USA (don't remember the details). They were following a crowdsourced Navionics chart which showed deep water when they struck.

As I understand things, these charts take lots of data points input by the crowd and then interpolate between them. In this case, the interpolation between two deep soundings didn't take into account the ledge in between them... BANG!

Our friends, strangers to the area, didn't know about the ledge, but the locals did, and so they didn't sail over it, and thus there were no crowd sourced soundings for it. I may have the methodology wrong, but that sort of error creeping in makes me very leery of such charts.

Jim

[AedanC]

I would never trust a Navionics Sonar chart, the area marked 0.5m ringed in red in this photo is actually 19m. It’s in a reasonably well travelled channel with small ferries going through many times per day and hundreds of pleasure craft passages on a summer day.

[Dave_S]

I assume you guys are talking about the maps from Navionics not the sonar charts you create yourself from running around in your dingy. I intend to trust the ones made myself 100%.

Originally Posted by Dave_S

I have spent a fair amount of time researching this. This is what I plan.

This is my solution.... https://www.navionics.com.au/sonarchart-live Hop in the tender and go and map the anchorage or follow the tender up the river or through the bar or into an atol. It is a pita but it is a 100% solution where all others are less than.

I will also permanently mount a camera to the mast top spreader and keep satellite images of the areas. Maybe a drone. This should reduce the amount of times I have to put the tender in.

I looked at forward facing sonar and decided against it, even the manufacturers best attempts at trying to make it look good, didn't.

I'm sure it is a valuable tool in skilled hands, it was too valuable for me and I didn't think I'd spend enough time getting to understand it fully to get the full benefit.

Originally Posted by AedanC

I would never trust a Navionics Sonar chart, the area marked 0.5m ringed in red in this photo is actually 19m. It’s in a reasonably well travelled channel with small ferries going through many times per day and hundreds of pleasure craft passages on a summer day.

Attachment 184677

Originally Posted by Svan

+1 for using Navionics Sonar Chart paired with a good bow watch and good sun up high.

I was amazed at the detail available everywhere in the Bahamas or Great Lakes on Navionics.

Originally Posted by Simi 60

Pretty lines on a screen don't necessarily mean reality in real life

Originally Posted by JPA Cate

Hello, Posh,

The catamaran that destroyed itself at Huahine a couple of years ago now, more or less, was driven too close to the reef with a normal tradewind wind and sea condition. No one was actively on watch, and the course was far too close to the reef for safety, so that was a failure of seamanship, and a too great trust in electronics.

I think what everyone is trying to emphasize for you that reliance on fancy electronics is the wrong place to put your focus, and the more effective will be to hone your and your crew's watch keeping skills. The electronics are seductive, I'm sure, but the human eyeball evolved to keep us safe, if we will but use them.

Ann, cruising full time since March of '89

[AedanC]

Good point, I definitely meant the Navionics ones.

[belizesailor]

Originally Posted by Simi 60

I have.

Its only as good as user input accuracy so if you are in areas rarely travelled, they get little to no user input.

Where I am anchored right now, according to navionics is land and all around us is land and drying banks.
Reality has us in 20ft of water

Conversely I can show areas where there is depth according to navionics yet we would be well aground if trusting their charts.

I too have anchored ashore using Navionics. [emoji16]

Im not sure how Navionics reconciles their chart incaccuracies with user collected data. If depth sounds are presented for where they show a land mass do they just toss it out?

[pbmaise]

Pop a crew member into the dinghy with a hand held sounder and two-way radio when in serious doubt.

[blubaju]

Originally Posted by Svan

+1 for using Navionics Sonar Chart paired with a good bow watch and good sun up high.

I was amazed at the detail available everywhere in the Bahamas or Great Lakes on Navionics.

You really think they are measured? I do not think so. Sailing with your sounder on you can watch them readjusting. Why readjusting if they were correct? They are funny to see, thats all. Navionics was better, for Philippines, newest data, I sail and anchor on land, surprisingly hit nothing following my old tracks. The new (???) Charts are all offset. Both, for the app and plotter, it cannot be my electronics as c-map & openCPN show correct positioning. 2004 a container port opened in subic bay, 15 years later still no trace despite several reports. This is not the only mistake, hundreds for the Philippines only. Again, best reef avoidance AND anchor place finding, make a satellite picture overlay, do not trust any chart .

The track below is from March 31, 2017, the chart a few days ago. Track on plan2nav goes correctly around the island. Comment of Navionics: we believe to have the best charts available! Didn't a US warship run into Tubataha reef 2 years ago? They probably had the newest Navionics charts, was really about same time, only, her captain trusted his chart, not the Philippine coastguard warning him!

The wonderful eye-catching depthlines are computer-generated, not measured, maybe in 20 years they have enough data, depends where of course

[Sojourner]

I disagree with the negatives on forward facing sonar.... I havent taken Wake into reef country yet, but have poked through some very thin passes here in the Med. The entire key is to use it under engine and at walking speed. It'll show you everything just fine, but only a few dozen meters ahead at best, so you gotta be ready to jam it in reverse.

For when we venture into the pacific/carib, my options/plan is 1) timed arrivals and departures, only when the sun is high 2) masthead camera 3) drone 4) google satellite 5) one of the girls on a spreader or using the handheld depth sounder in the dinghy running ahead.

[blubaju]

Originally Posted by Sojourner

I disagree with the negatives on forward facing sonar....



For when we venture into the pacific/carib, my options/plan is 1) timed arrivals and departures, only when the sun is high 2) masthead camera 3) drone 4) google satellite 5) one of the girls on a spreader or using the handheld depth sounder in the dinghy running ahead.

Forward looking sounder is great in a muddy bay or river or when dark.

Plans are here to be changed, we are not a ferry boat, timed arrivals as departures occasionally happen, mostly not. Sun sleeps early in the tropics and fast, sun is high a few hours only.

Strongly recommend ge2kap + openCPN with real chart overlay, not only Google Earth on a secondary display. It is a tremendous help and it is free! opencpn.org ge2kap: www.gdayii.ca