Trust Google satellite ?

[Dave_S]

I should say can you trust your own interpreting of Google satellite images ?

If I wanted to park nice and close to the beach (wadding distance) in the little bay here, it looks nice and safe going in but is it likely/possible the dark spot on entry is shallower than it appears ?

Would you trust it ?

P.S. have you images that show a deception.

[1000 islands]

Don't you have charts of the area or a depth finder so you know how much water there is.

[Dave_S]

Originally Posted by 1000 islands

Don't you have charts of the area or a depth finder so you know how much water there is.

These areas are uncharted and my depth sounder is straight down, I'm worried about rocks which won't show up until I'm on it.

[Snore]

Originally Posted by Dave_S

I should say can you trust your own interpreting of Google satellite images ?

If I wanted to park nice and close to the beach (wadding distance) in the little bay here, it looks nice and safe going in but is it likely/possible the dark spot on entry is shallower than it appears ?

Would you trust it ?

P.S. have you images that show a deception.

When I did the WaterTribe UFC race around Florida I used them extensively to scout stealth camping spots. I also used Google aerials to read some flats in Florida Bay looking for shortcuts. Property appraisers also have good aerial photos. But that was with a kayak. If I misread a shadow, there was no damage or tow bill.

I would never use anything but a to Gov chart to navigate.

[MartinR]

I would use it as an indication. Have someone in the bow looking down while entering. I have used aerials extensively, and in many cases they are better than the official charts for identifying dangers.

In Sweden there is a company, Hydrographica, that actually uses aerials in combination with spot soundings to produce very exact high resolution charts.

[Anders]

I use Google satellite to spot possible anchorages, when getting there I stand on the coach roof to see how deep it really is.

[boom23]

What they said...

Satellite images are just an indication/clue. You have to use your instruments, have eyes on the bow, and go slow (or use your dinghy with a depth gauge) to find out if a place is anchor-able.

Also, you should do it with the sun overhead or behind you, not in front of you.

This is particularly true in places like Fiji where the charts are almost mostly wrong or incomplete.

[krafthaus]

Those dark patches are often weedy spots. So agree with other posts that satellite images are a very good screening tool but as always, approach at an appropriate speed, watch depths and keep a good watch. Always best with the sun overhead or behind you.

[CaptTom]

Until last spring, I would have sided with those who say "always trust the current chart."

That was before I'd anchored off Dog Island, near Carrabelle, FL. Active Captain showed an anchorage out in open water, per the chart. But switch to aerial view and it becomes clear that the island had grown and the anchorage was in a newly-formed cove.

The reviews went back a few years, and my charts were current. So it's not like it happened so fast NOAA didn't have time to make this correction. Apparently it just wasn't a priority.

You can see some screen shots showing the anchorage location about three-quarters fo the way down this blog entry.

[wayne.b]

Originally Posted by Dave_S

I should say can you trust your own interpreting of Google satellite images ?

If I wanted to park nice and close to the beach (wadding distance) in the little bay here, it looks nice and safe going in but is it likely/possible the dark spot on entry is shallower than it appears ?

Would you trust it ?

P.S. have you images that show a deception.

===

There's an old saying that is still true: A good navigator never trusts any single piece of information, but seeks corroboration from as many sources as possible. When in doubt anchor in deeper water and use your dinghy to scout a safe path.

[hellosailor]

Dave-
In the field of remote sensing, which includes aerial/satellite reconnaissance, the gold standard calls for "ground conformation" of all images. That means someone has to go out, on the ground, and confirm that what appears to be there, is what actually is there.
The first thing regarding trust is to look for the DATE of the image. I couldn't read the watermark in that one, but many are two years old, not entirely up to date.
Then ask what is on the ground. If there is a military installation, or other area where the owners have valid concern for security, images are sometimes either blurred or blocked out. Not faked--but obviously concealed.
Looking carefully at that image, there appear to be coral(?) at varying depth, so that passage in would be threading a needle, depending on the scale, which I don't see. Coral of course grows in some areas, so it may be worse than an image shows. If there are cliffs, storm activity may bring debris down. All things to consider.
I might trust that image, but I still wouldn't proceed above "dead slow". You never know when someone has had a runabout flood and sink someplace inconvenient. I've seen small craft, large tires, supermarket shopping carts, 55g fuel drums, all dumped in less than 20' of water and that can turn 10' of water into a mere 6' very easily.
So trust, but verify. The photos never lie--but you need to be aware of their limits.

[redhead]

We have approached harbors, tired, sundburnt, hungry and wanted to believe there was enough water.

And then we ask the one question we ask before every question with no clear answer - "Are you willing to bet the boat?"

For us - I'd be in the dinghy going through while he waited outside for the VHF report.

[Cheechako]

I would trust it more or less. In the Bahamas etc people use visual all the time. The trouble is interpretation. In your image my interpretation would be that the dark extension on the right is reef. Ditto for the shorter one on the left. But the less prominent darker blotch stretching across the middle is just a deeper water image.
At any rate, just go in slow. You are not going to hurt your boat with a knock. Well I guess it depends on the boat, but I have hit solid, boat stopping objects in murky water a few times at good speed with a long keel stout boat with no damage. OTOH a fin keel/spade rudder production boat I managed in charter hit a rock at 5 knots causing 20k in damage.

[Dave_S]

This is what it looks like in Navionics.

Hellosailor, the satellite images in this case are 2018, but I take your point on age, I've just picked this image as an example so then next one might not be so current. Especially after looking at the changes on Captain Tom's blog, I wonder how much time that took to change, or is it an error on the chart. It could be the tip is misplaced to the east ?

The little bay in my image is about 250m across the mouth.

[kas_1611]

For shallow water I would only use a satellite photo as an indication but if you look at some bays in Google Earth, where the water is above about 5m deep, you can sometimes actually get a depth measure from the elevation. It does depend on the maritime contours but again it can give you an idea.

Even standing in the pulpit looking ahead with polarizing lenses you can not get a true judge of how deep or shallow water really is as seagrass can hide a shallow spot but look much deeper.

Basic rule of thumb is if you don't feel comfortable then don't do it. Anchor out deeper or motor round outside and survey the area from the dinghy. A 5m length of rope with a winch handle on the end makes a pretty good lead line. An overhand knot every meter gives you enough accuracy to tell if you can get in and anchor safely.

Google Earth is good for finding anchoring spots and you can use the ruler tool to check if there's plenty of clearance to swing but for depth I'd use it with a pinch of salt and a dollop of caution.