There’s been some discussions here about the accuracy of nautical charts. The seamount, 2400 meters below sea level, is 1600 meters high and covers an area of 14 square kilometers.
It is estimated that there are more than 100,000 seamounts taller than 1,000 meters (3,280 feet) in the world, but less than one-tenth of a percent have been explored, according to NOAA.
Had an oil run for Guatemala and Honduras working for Exxon out of Houston for about a year or so in the 90’s… The charts were sketchy at best. Watching that fathometer jump from plenty deep to effiing damn shallow would be an event that was not welcome… Tons of “Seamounts”. not charted. Do not envy anyone navigating that area, 400 thousand barrels at a pop (2 vassels} would have been a disaster.in waiting. Loved my job, but not that shit.
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In our waters the seamounts have been known to fishermen looking for fish such as Orange Roughy, Blue Nose and other deep water species. They keep the information to themselves but a couple of government agencies have charted many. A pinnacle of rock in a supposedly well charted region of New Zealand was discovered by the Royal Naval submarine Anchorite. It surfaced very rapidly after the event. The rock was well known to fishermen.
You can’t put a price on local knowledge
What would be considered “well charted”?
In this case the depths were in error by about 1600 meters but a ship staying outside the 100 meter contour would have had about 2400 meters of under keel clearance (UKC). That’s sufficiently well charted for commercial shipping.
When I was second mate I asked a English Channel pilot about all the charted wrecks of “unknown depths” in the English Channel. They are too numerous to avoid. He told me if anything was there someone would have hit it already,
Excellent question. The ICW is littered with pilings and wreck symbols:
It would be nice to know if the symbols were removed after the hazards have been removed as many indicate a hazard to navigation. That’s clearly not the case. Since the COE is constantly surveying these areas and passing the information to NOAA and the CG, how much effort would it take to remove the symbols from the charts when they are “updated”? I know,…given the disfunction of gumint agencies’ cubicle farms, it’s rhetorical question.
Back in the Jurassic period we used to confirm the depth over an isolated pinnacle that was a danger to shipping by conducting a wire sweep over the hazard and this was indicated by the symbol on the chart.
Surveying in soundings was usually done in lines 50 to 100 metres apart depending on the depth.
Modern tools such as LiDAR and sidescan sonar together with GPS have changed surveying techniques dramatically.
This is from the Canadian Sailing Directions.
Caution. — For today’s ships of normal draught in much-frequented waters, the reliability of most charts based on early surveys has been confirmed by the safe passage of ships over the years. Vessels with draughts approaching 30 m should exercise care inside the 200 m line in less adequately surveyed areas, even in recognized shipping lanes. In many instances, ships with draughts approaching 30 m may be testing the chart despite the fact that many shallower-draught ships may have passed previously. A ship venturing into unfrequented waters may also be testing the chart for the first time and should exercise due caution.
I recall some of the Canadian charts had a similar warning printed on them.
The 8° South parallel was used for years and years including yours truly, sailing through the Java Sea. Probably the only reason we missed the rock that was discovered at that latitude was it was before GPS and we were relying on the sextant and primitive radar.
If you compare the ENC to the paper chart looking version, a lot of them are cleaned up. Given most of the ICW charts like the one in that picture will be cancled by April, I think the Cartographers have shifted their focus to maintaining ENCs. Still a lot of questionable artifacts on the ENC, but comparing to the paper chart there are significantly less in my area.
What was the depth of this rock? With the mention of submarines and fisherman I assumed it was too deep to be a hazard to commercial shipping.
The rock now named Anchorite Rock after the submarine that hit it rises from a relatively flat plane of the Hauraki Gulf with depths of between 23 to 28 fathoms. The rock has 33 feet over it at MLWS.
With the advent of reliable outboards and GPS it can get quite crowded around it in good weather for fishing.
Post numbers converted for American readers. 
So the depths in the area are 42 to 51 meters (23 to 28 fathoms) and the rock is 10 meters (33 feet)
Not familiar with the area but it makes sense the resolution or sounding density is going to be lower there than near a port entrance. It also makes sense that if it is on or near a frequently used route it would be assumed to be safe. At least for the drafts of ships being used at the time. And just dumb luck, missing the rock or passing over in good weather.
Be a matter of time before it gets hit.
