How deep is the water?
We all know that “echo sounders” in their various guises have been around for longer than most of us have been on this watery planet. But the standard echo-sounder fitted in your average ship has its limitations. Fishing vessels use a specialised version which is beyond my knowledge. Does a normal commercial vessel need a depth sounder that will give an accurate reading when the water is 3 miles deep? I wouldn’t have thought so. Nor do they work particularly well when there’s next to nothing under the keel. I’m not suggesting for one moment that ships regularly steam along whilst almost aground, but it’s not uncommon for a ship to take the ground when loading. Ports and harbours are fickle places, liable to silting up a bit, most are tidal and the water density can range from a Specific Gravity of 1025 (“Salt” water), to an SG of 1000 (“Fresh” water) and all points between. All the above affect the ships draught. But this is about ascertaining the depth, not stuff like “Fresh Water Allowance” and so on. Sometimes it’s necessary to use the time honoured “Hand Lead Line”. A length of rope with a weight on the end. That’s the principle, made a bit more complicated in practice. If a sounding is to be taken in port to see if the ship has actually taken the ground then even a first trip apprentice could do it. Difficulties arise when the ship is moving through waters of unpredictable depth. However, that’s pretty “old hat” these days, but what a Lead Line can show that an echo sounder can’t is the composition of the sea bed. The “lead” weight has a hollow in its base that is filled with “tallow” (or whatever the modern equivalent is). If the sea bed is just “rock” then nothing will show, but mud, sand, gravel and so on will. As good charts always show the sea bed composition, a vague idea of the ships location can be guessed at. Before the days of Radar, RDF etc ships coming through the Western Approaches to the English Channel would take constant soundings using this method.
In my C&W time (early 1960s) some of the more experienced Captains used to insist that the crew kept the skill alive as shallow water cable-work occasionally demanded it. Just as an aside, some of the real “old salts” could get a pretty good idea where they were by simply observing the colour of the sea. A lesson I’ve put into practice myself on a few occasions (mainly for fun or as a bet).
All that lot was just an introduction as to why that little grating was stuck on the ships side under the bridge wings! Just for the leadsman to stand on and sing out his merry calls of “By the mark…..” (Hence the American author naming himself Mark Twain after the calls made during his American river steamboat time).
Then there’s the “Patent Deep Sea Sounding Machine”. I don’t know if it’s still a legal requirement for ships to be fitted with this thing, but for most of me sea-going life it was. Early ships such as “Norseman” had it fitted below one of the bridge wings (this one is behind the leadsmans platform), the other common place was right aft. Placing it aft was the easier option as the wire could be fed over a simple sheave, whereas deploying the wire over the ships side required a “sounding boom” which required rigging and generally fitted with a little special gizmo at the outer end of the boom. Another little aside. The “ deep sea” machine could be used for more than one purpose. If the line was simply attached to the 28lb lead weight then depth and bottom composition was all it did. However. Even well into the 1970s many ships (most, in fact) sent meteorological reports every few hours. Mostly the reports only included what could be seen or measured from the bridge. Some ships were asked to do more. Particularly those that worked off the beaten track. For some reason or other RFA “Pearleaf” was one of these. Although the weight was still attached, there was a tube sealed at its upper end also clipped to the wire. This tube was coated internally with some reddish brown stuff which changed colour as depth pressure forced water into the tube. On recovery, by placing the tube against a scale a pretty accurate depth was calculated. A Thermometer could also be attached. “Pearleaf” was equipped to go a big step further. She carried many “Bathythermographs” which measured everything you can think of. Probably only of use to the compilers of charts and data needed by submarines. So, an old bit of kit still in use during the age of nuclear submarines.
“Norseman” also had a bit of equipment I’d never seen before…or since, for that matter. A steam sounding machine. I described this machine and its use when writing the “Norseman” episode of my life in the “Nautical, strange but true” tales, so I won’t go into that any more, except to remind you that this thing used 56lb cannon balls as weights, and could “sound” depths as much as those found in the Mariana Trench.
My version of the “manual” sounder is entirely from plasticard. It could have done with being a bit more detailed, but as it isn’t all that easy to see I’ve just left it the way it was.
The steam machine is (to me) horrendously difficult to photograph in a completed state, so this is one I took 20 odd years ago during the first construction, but I hope that you can at least see its place in the scheme of things. This is an all aluminium model, and after all these years, it’s looking as careworn as the real one.
