Navigation In the 0-3 Fathoms Zone

[chala]

Originally Posted by catty

However I will qualify this with the proviso that having worked from that particular fathom chart over many years it is surprisingly accurate. However at night I would be running down the lines of soundings to close the coast and certainly not go inshore of the last sounding, until a daylight recky could be made.
One is certainly taking a chance in these remote areas , closing the coast at night.
If the tide is high the chances of clobbering something are certainly reduced while you work out if the anchorage is tenable at low water.
Regards.

Because it was still daylight the coast did not look that close and did not reveal much as for a bit of a cliff, maybe suitable as a windbreaker.

The approach was made pretty much the way you describe it?

The question is would 5 soundings (chart .s post 16) be considered a line of soundings?

Point B 4.5 Meter C.D. Point A 0.2 meter C.D. Point ! 1.8 meter C.D.

The night been moonless the lowest tide at 23.16 (post 15) did not reveal anything.

In my view an official chart ought to be accurate but so much of this chart is inadequately Surveyed. In 1960 Hiscock wrote about the Bowen strait “ in all its length the chart shows only eight soundings”. 51 years later it still shows eight soundings. Fortunately this may change as I have noticed lately some survey ships in the region.

[S/V Alchemy]

Originally Posted by MarkJ

I work on a "Shopping Cart Principle"

If sailing in an area so shallow that a shopping cart thrown overboard by some louts (Eric, for example) is going to ruin the keels paint then only sail there with eyes apeeled....

If you don't like the Shopping Cart senario, try coral head, or rock etc.

If there is only 1 meter under the keel I am going dead slow. Dunno what those in the Bahamas do....


Mark

I agree, and if you don't have ye olde crewe to swing ye lead line, offset your depth sounder to add two feet (0.6 m) to your keel's depth. That will cover many contingencies...except in those places where the coral has grown a lot since Captain Cook last thumped the deadwood on Endeavour.

[boasun]

Just have to remember that your boat is always doing survey work in thin waters. Plus the needing to keep in mind is the state of the tides also. Anchoring in plenty of water, only to find out that you did this at high tide and now at low tide you are sitting on the bottom. Hmmmmm!

[David_Old_Jersey]

The bottom also changes, in some places slowly over years - in other's far more quickly (especially after Storms), the coastline (and shore - including the underwater bit) is in constant movement. But there is probably an APP that gives live! updates of what is happening several fathoms down 24/7........or at least someone will sell you pretty pictures that appear to do that.

[rgscpat]

Local knowledge can be helpful ... what is the history of the hydrographic survey/survey methods, when was the area last surveyed, what is the bottom type, are there areas subject to shoaling...

[boasun]

Originally Posted by rgscpat

Local knowledge can be helpful ... what is the history of the hydrographic survey/survey methods, when was the area last surveyed, what is the bottom type, are there areas subject to shoaling...

Is this the old saw about the one who runs aground the most, knows the harbor the best.




Not necessarily true...

[chala]

Originally Posted by catty

If the tide is high the chances of clobbering something are certainly reduced while you work out if the anchorage is tenable at low water.
Regards.

Interestingly I prefer low tide if you get stuck then you will refloat and back track. When checking on Valentia East passage mentioned in a Cruising Guide I did it at low tide. I found more water on the West of the indicated leads.

[chala]

Originally Posted by S/V Alchemy

I agree, and if you don't have ye olde crewe to swing ye lead line, offset your depth sounder to add two feet (0.6 m) to your keel's depth. That will cover many contingencies...except in those places where the coral has grown a lot since Captain Cook last thumped the deadwood on Endeavour.

This can be done mentally. Good to keep the sounder to a meaningfull value.

[chala]

Originally Posted by boasun

Just have to remember that your boat is always doing survey work in thin waters. Plus the needing to keep in mind is the state of the tides also. Anchoring in plenty of water, only to find out that you did this at high tide and now at low tide you are sitting on the bottom. Hmmmmm!

This remember the thousand islands out of Tanjong Priok, this was before GPS.

[chala]

Originally Posted by boasun

Is this the old saw about the one who runs aground the most, knows the harbor the best.




Not necessarily true...

At least he get extra skill. This thread is getting momentum.

[gravosa]

Originally Posted by chala

Should a mariner be able to trust that enough navigable water exist between the “Open Sea” and a spot sounding of 2 fathoms (3.7 meter) in a charted 0 to 3 fathoms zone? (0 to 5.5 meter zone)

i think for you is the best thing to do is to sell your boat and move to alice springs or somewhere in wioming or idaho and grow corn

[chala]

Originally Posted by gravosa

i think for you is the best thing to do is to sell your boat and move to alice springs or somewhere in wioming or idaho and grow corn

Is it what you did?

[catty]

Originally Posted by chala

Interestingly I prefer low tide if you get stuck then you will refloat and back track. When checking on Valentia East passage mentioned in a Cruising Guide I did it at low tide. I found more water on the West of the indicated leads.

Feel free to roar around in poorly surveyed, low vis water at any time you like. The only reason I like to pick a time approaching high tide,in this area, is that over the years since these old fathom charts were made most of the lumps visible at low water have been reported. With the tidal movement being over 2 meters at most times (at least ones draft?) in the area in discussion, the chances of clobbering things are possibly less than at low water. Nice to anchor in safe water and investigate a more comfortable anchorage at low water with the dingy, if one is staying a few days.

By the way when you mention anchoring at Valencia island do you mean tucking in behind the western side of Annesley point near the houses, or Valencias island?

[gravosa]

Originally Posted by chala

Is it what you did?

no i am not, i am former master mariner. but you are worrying to much about shalow waters. have peace of mind go to wioming, nebraska, idaho, montana, siberia, no problems with fathoms

[Don1500]

Originally Posted by gravosa

no i am not, i am former master mariner. but you are worrying to much about shalow waters. have peace of mind go to wioming, nebraska, idaho, montana, siberia, no problems with fathoms

That answer was too deep for me.