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Details for Benchmark: JV0579

N 39° 15.783 W 076° 34.750 (NAD 83)

Altitude: 30.05

Coordinates may not be exact. Altitude is ADJUSTED and location is SCALED. (more info)

Location:
In BALTIMORE county, MD View Original Datasheet
Designation:
857 4680 TIDAL 27
Marker Type:
tidal station disk
Setting:
massive structures
Stability:
Probably hold position/elevation well.

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Found as described while exploring the Fort. See photos.

CC76...

[Photos:]
photoJV0579 (1)
photoJV0579

Found while visiting the Fort today.

[Photos:]
photoclose up view of benchmark
photoit is here

Found in good shape. A bit of oxidation

[Photos:]
photo20140803_142008(1)
Found on Geocaching run at the fort

Recovered as described.

[Photos:]
photoJV0579-857_4680_TIDAL_27-1-2012322
photoJV0579-857_4680_TIDAL_27-3SE-2012322

#24 BM

[Photos:]
photo20120324112015

Saw this one by accident while checking out the cannons. Gotta be careful out there I almost got my head blown off. Cool benchmark thanks for another one of those things.

[Photos:]
photoP5180173

Found on a trip out to Ft McHenry

Doing a bit of geocaching in area

Nice spot

Saw it while looking around the area and doing the nearby cache.

I was at Fort McHenry today with my son's class on a field trip. The boys wanted to see the cannons so we made our way there. We got to the largest one and I looked down only to find this mark. Thankfully I had my GPSr with me and was able to grab a set of coordinates as well. My handheld read N 39*15.789 by W 076*34.732.

[Photos:]
photoFort McHenry #27

Recovered in good condition...

[Photos:]
photo857 4680 TIDAL 27 (JV0579) disk - Baltimore, MD
photo857 4680 TIDAL 27 (JV0579) area - view looking ESE

Found as described.

[Photos:]
photoClose Up
photoOverview
Poor cell phone photo.

This benchmark was an easy find as we toured the Fort.

[Photos:]
photoNGS Benchmark at Ft Henry
photoFt McHenry

Found as described.

Coordinates were off on this one. I had the same handheld coordinates as Seventhings.

[Photos:]
photo857 4680 Tidal 27 JV0579

Found as described. The mark is in the base of the largest gun in the northmost "Outer Battery". The battery is the first battery southeast of the Ravelin Battery, and the "Outer Batteries" extend south and west starting just south of the Ravelin structure. To reach from the old fort, leave the old fort by way of the Sally Port, make a half right turn and go straight ahead to the biggest gun. It's the only gun in the battery with an octagonal base. Handheld coordinates are N39-15.790 W076-34.731. The NGS datasheet for this includes a 2002 recovery by NGS that states that the Marker Type is incorrect - that the mark is a USCGS Benchmark disk. This is true, but it does have the classic tidal station line-through-a-circle at the center.

[This entry was edited by seventhings on Friday, July 16, 2004 at 11:42:00 AM.]

[Photos:]
photoJV0579 - the Mark
photoJV0579 at Fort McHenry, Baltimore, MD
Looking east-southeast, the mark is at the white notebook on the base of the large gun, upper right.

Unable to find marker. Then again, not exactly sure what a tidal station disk looks like. Unsure if coordinates are correct. According to my GPS, to be at the listed coordinates put me behind the middle of the three cannons noted in the 1971 description. As the area has seen weathering and ravages of time (it has been 27 years since it was last checked by the NGS), marker could have been removed, overgrown, or covered in renovations. Speculative thoughts. Unsure.

Documented History (by the NGS)

01/01/1922 by CGS (MONUMENTED)
01/01/1971 by NGS (GOOD)
DESCRIBED BY NATIONAL GEODETIC SURVEY 1971 AT BALTIMORE. AT BALTIMORE, AT THE SOUTHEAST POINT OF FORT MC HENRY, NEAR THE SOUTHEAST SIDE OF THE STAR FORT, BETWEEN THE INNER AND OUTER PROTECTIVE WALLS OF THE FORT, SET IN THE TOP OF THE NORTH SIDE OF THE OCTAGON-SHAPED GRANITE FOUNDATION FOR THE LARGEST AND MOST EASTERLY OF SEVERAL CANNONS AROUND THE FORT.
01/01/1976 by NGS (GOOD)
RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 1976 RECOVERED IN GOOD CONDITION.

Control Text

  • The horizontal coordinates were scaled from a topographic map and have an estimated accuracy of +/- 6 seconds.
  • The orthometric height was determined by differential leveling and adjusted by the National Geodetic Survey in June 1991. WARNING-Repeat measurements at this control monument indicate possible vertical movement.
  • This Tidal Bench Mark is designated as VM 429 by the Center for Operational Oceanographic Products and Services.
  • The geoid height was determined by GEOID99.
  • The dynamic height is computed by dividing the NAVD 88 geopotential number by the normal gravity value computed on the Geodetic Reference System of 1980 (GRS 80) ellipsoid at 45 degrees latitude (g = 980.6199 gals.).
  • The modeled gravity was interpolated from observed gravity values.

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