"Hull Down"

[AndyHall]

If you read many reports from the CW era or before, or naval fiction (Patrick O'Brien et al.), you've probably come across the term "hull down," referring to a ship sighted at a long distance. If the weather is clear, you can see well beyond the horizon, and other vessels beyond that point will have their lower parts hidden behind the curve of the earth; sometimes only the sails would be visible. This is known as being "hull down" to the observer.

I took this photo today, that illustrates the phenomenon. These are ships anchored in the Gulf of Mexico off the beach at Galveston, probably waiting for a space to open in Houston, Texas City, or Baytown.

In this case, all three ships are beyond the horizon as viewed from my vantage point. At my elevation, about 17 feet, the horizon is about 4.43 nautical miles (5.1 statute miles) distant. But you can see plainly how only the upper part of the farthest ship, the Tanja Jacob, is visible. Tanja Jacob is "hull down."

 

[chellers]

Interesting; thanks for the lesson.

 

[DaveBrt]

If you read many reports from the CW era or before, or naval fiction (Patrick O'Brien et al.), you've probably come across the term "hull down," referring to a ship sighted at a long distance. If the weather is clear, you can see well beyond the horizon, and other vessels beyond that point will have their lower parts hidden behind the curve of the earth; sometimes only the sails would be visible. This is known as being "hull down" to the observer.

I took this photo today, that illustrates the phenomenon. These are ships anchored in the Gulf of Mexico off the beach at Galveston, probably waiting for a space to open in Houston, Texas City, or Baytown.

In this case, all three ships are beyond the horizon as viewed from my vantage point. At my elevation, about 17 feet, the horizon is about 4.43 nautical miles (5.1 statute miles) distant. But you can see plainly how only the upper part of the farthest ship, the Tanja Jacob, is visible. Tanja Jacob is "hull down."

View attachment 105915

When I was an officer on a Navy oiler, we made a game of trying to estimate the distance to contacts by visual observation alone, then checked with radar range. With lots of warships about off Viet Nam, we got lots of practice and became quite good. As I remember, a cruiser went hull down at 10 1/2 miles from our bridge (about 40' above the water line).

 

[Bee]

I love this sort of thing: math mixed with visuals/navigation + the sea thrown in for good measure

I went back and re-visited your other thread on this subject @AndyHall so that I can trick a sailor or two in my life into thinking that I am actually pretty savvy on this sort of thing

 

[Albert Sailhorst]

Interesting!.....Thanks!

 

[7th Mississippi Infantry]

I've witnessed this phenomenon many times while deep sea fishing in The Gulf of Mexico.

 

[AndyHall]

I went back and re-visited your other thread on this subject @AndyHall so that I can trick a sailor or two in my life into thinking that I am actually pretty savvy on this sort of thing

I completely forgot I posted that three years ago, sorry.

 

[Bee]

I completely forgot I posted that three years ago, sorry.

They had different content and they were both useful, and now my sailor friend says that I should give up the CW and study the sea, instead

 

[AndyHall]

Do both.

 

[Bee]

Do both.

He keeps chanting "it was the blockade" "it was the blockade -- you need to give credit due to the Naval Warfare of the CW!"

I should probably do this soon; it would boost my standing

 

[Dilandu]

Quite informative! Thank you!

 

[JPK Huson 1863]

Yes, adding my thanks! Never have been able to wrap my head around all-things-naval, makes it more interesting.

My husband says those mental holes his wife falls into, like repetition without a clue, have nothing to do with age. He lies better with age. It's a very fine marriage.

 

[Yankeedave]

For ground troops hull down is similar, where you use the military crest as a breastworks and such.

 

[Dave Wilma]

Patrolling vessels would space themselves so that the signal flags were visible. A string of ships could cover a wider swath of sea.

 

[AndyHall]

Patrolling vessels would space themselves so that the signal flags were visible. A string of ships could cover a wider swath of sea.

On a side note, there was an additional significance to staying within signaling distance, beyond its obvious tactical importance. The Navy's prize rules at the time required all vessels within signaling distance to share equally in the proceeds of the capture, whether they were actively engaged or not. So there was actually cash on the line, for commanders to show that their vessel was within that distance or, in some cases, to show that another Navy vessel was actually NOT within range.

As a result, in after-action reports, you'll see officers saying things like, "and at the time the last gun was fired and the vessel surrendered the Kanawha was less than 5 miles distant from the Admiral and her prize and within easy signal distance," and commanders of other ships closer to the capture insisting that the others were too far away.

 

[Mark F. Jenkins]

Quite apart from the valuable lesson, great photo!

 

[Mark F. Jenkins]

He keeps chanting "it was the blockade" "it was the blockade -- you need to give credit due to the Naval Warfare of the CW!"

I should probably do this soon; it would boost my standing

Always room for one more in the naval forum!

 

[Yankeedave]

It's a premise reflected in war gaming. The distance of commander and his troops effects that unit's performance.

 

[rebelatsea]

I completely forgot I posted that three years ago, sorry.

Oh dear, that's the sort of thing I've been seen to do !

 

[Yankeedave]

durn.