NavList:

For those who have never heard of a "hydrostatic tube" it is a glass tube, closed at the top and open at the bottom,  mounted vertically on the deep sea lead. The inner surface is coated with a substance that changes color when wet. As the lead is lowered the water raises in the tube, compressing the air trapped in the tube, the higher the water goes, the deeper the measurement. The trouble with this method is the rapid change in scale with depth. The water rises half way in the first 33 feet. 2/3rds at 66 feet, 3/4 at 99 feet, 4/5 at 132 feet, 5/6 at 165 feet, etc. As you can see, it is only useful in fairly shallow water. gl --- On Mon, 3/5/12, Henry Halboth <hchalboth@gmail.com> wrote: From: Henry Halboth <hchalboth@gmail.com> Subject: [NavList] Re: About time - Antarctica To: NavList@fer3.com Date: Monday, March 5, 2012, 7:55 PM Hi all, As respects "how did they know when the weight landed on the bottom", I submit, when using a traditional sounding machine ..... 1. It is quite true that a hook type feeler was generally employed and held over the running wire in an effort to "feel" the instant of bottom contact or the attendant shock or change in vibration in the running wire, the an indicator of  contact, however ..... 2. The deep sea lead was normally "armed", i.e., a hollow in the bottom of the lead, intended for the purpose, was filled with tallow for the express purpose of bringing up a sample, or at very least an impression of the bottom, thus verifying bottom contact. No sample or impression = a suspect sounding. I am unable to comment on "axe blades" as sounding leads. As a practical sea story .... Some time in 1948, inbound for Boston from Monrovia, somewhere off Cape Cod, and in dense fog for 3 -days; speed about 4 kts.. At 0800 orders came down from the bridge, "rig for and commence deep sea sounding". Sounding commenced accordingly with an armed 100 lb lead and attached coated hydrostatic tube, and continuously carried out until at 1010 hours the report came to the bridge "18 fathoms, sand and shells". The course was changed and later that evening Cape Cod Light was sighted dead ahead. There is/was a single spot on the chart depicting an area about 1-mile in diameter and a sounding of "18 fathom, sand and shells" clearly delineated; the position had been established as closely as if by celestial navigation. Regards, Henry On Mon, Mar 5, 2012 at 6:15 PM, Lu Abel <luabel@ymail.com> wrote: The photo indeed shows Perry taking soundings, comments on their losing their weight and instead using axe heads as weights, etc.   But no where do they answer Bruce's question:  how did they know when the weight landed on the bottom?   For the sounder (person, not electronic device) to know that he had hit bottom, there would have to be a significant lessening of weight on the sounding wire.   That begs the question of how much 9000 feet of piano wire (what gauge?) weighs versus one or two axe-heads. Lu From: Gary LaPook <garylapook@pacbell.net> To: NavList@fer3.com Sent: Monday, March 5, 2012 2:57 PM Subject: [NavList] Re: About time - Antarctica See Peary's measurements of depth on page three: http://www.northpole1909.com/davies.html gl --- On Mon, 3/5/12, Lu Abel <luabel@ymail.com> wrote: From: Lu Abel <luabel@ymail.com> Subject: [NavList] Re: About time - Antarctica To: "NavList@fer3.com" <NavList@fer3.com> Date: Monday, March 5, 2012, 11:29 AM Good question.   Or, for that matter, when they say the Marianas Trench is 35,000 feet deep, how did they measure that?   Too far, I would presume, for sonar. Lu From: Bruce Pennino <bpennino.ce@charter.net> To: NavList@fer3.com Sent: Monday, March 5, 2012 10:49 AM Subject: [NavList] Re: About time - Antarctica They were measuring 1000s of feet of depth. How could they "feel" when the object touched or  bounced off the bottom? Bruce J. Pennino, P.E.                             ----- Original Message ----- From: Gary LaPook To: NavList@fer3.com Sent: Monday, March 05, 2012 12:27 PM Subject: [NavList] Re: About time - Antarctica Very much like using a hand lead line except it was a much heavier weight on a long wire which was on a motorized reel. This device was called a "deep sea lead." gl --- On Mon, 3/5/12, Bruce Pennino <bpennino.ce@charter.net> wrote: From: Bruce Pennino <bpennino.ce@charter.net> Subject: [NavList] About time - Antarctica To: NavList@fer3.com Date: Monday, March 5, 2012, 7:50 AM Just finished reading The Storied Ice by Joan Boothe. A very  good  overview book about all major explorations of Antarctica; many references.   Anyway, Antarctica explorers had a longitude problem. In 1926-27 the Discovery "was the first vessel in these waters capable of receiving Greenwich time signals directly, and her men used the signals to check longitudinal positions on the maps."   Only Deception Island was properly located.   Also,as the early explorers headed south ,they measured water depth for various reasons. How did they measure depths of several thousand feet with a drifting ship, angle of cable, flexibility(springiness)?    Boothe gives a brief overview of Cook's explorations....she says he was an extraordinary man.  Bruce Pennino