by Chris Zeringue, Owner, MTS Marine Techincal Surveyors
The key to accuracy in a Vessel Draft Survey may very well be found in a hole in the ship.
I boarded my first vessel at the age of 17 in 1975. I was hired out of the local shape-up yard for the night shift aboard a bulker loaded with imported sugar. My job was to shovel sugar out of the vessel hold ribs (trimmer) so that the bulldozer/tractor could push the cargo to the crane bucket. My neighbor was the lead superintendent on the job and his son and I would ride to the shape-up yard with him and put our names on the list to try to get hired for a day or night. If there were not enough Union Hands for the job, they would then call out the names of the non-union hands (aka rabbits). On the days/nights that we did not make the cut, we would hitchhike or walk home, meaning we would have to cross the Mississippi River Bridge by foot at times. My other job during school was working nights and weekends for a mooring company.
The more I worked, the more I liked the Waterfront. While shoveling cargo in the bottom of ship holds, my neighbor (the superintendent) would throw an apple or orange down to me to eat. Looking up one day there was a man standing next to him just observing. When I went up out of the hold for a meal break, I asked my neighbor, Papa Deck, “who was the guy with you?” His answer was, “he is a surveyor, and his job is to verify cargo quantity and quality.” I knew from that moment that I would someday trade my shovel position to be a Surveyor.
In 1978, I was hired at my first Surveying (training) position. Now fast forward 42 years and I am one of the owners of a survey company specializing in Ag and Fertilizer products at www.mtsusa.net. I have traveled the world surveying and monitoring customer’s cargos and solving customer issues.
The one thing that has always bothered me when it came to the accuracy of cargo accountability on bulkers was how to account for water conditions. On bulk cargo carriers, cargo accountability is determined by way of a Vessel Draft Survey, based on water displacement. Many factors go into the calculations and equations, but the one factor stated to be the most important (reference- The Naval Arch, Draft Surveys) yet least controllable, because of water conditions and accessibility, is the reading of the draft marks. The draft marks are stenciled at 6 positions on the vessel’s hull (Forward/Bow port and starboard, Mid-ship port and starboard, Aft/Stern port, and starboard).
These number stencils (usually in meters) are normally 10-cm tall with 10-cm space between each number. The numbers are usually in equal numerical stencils (2, 4, 6, 8 then the next meter number). As the water touches the bottom of the number 4 (using 4 as an example) the reading is 40 cm, the middle of the 4 would be 45 cm and the top would 50 cm. Between 50 (top of the 4) and 60 (bottom of the 6), the surveyor has to make a visual judgment call. As in all surveys, the reading of the draft marks visually are judgmental calls. So, add in high swells, waves, chop, ice, obstruction, non-accessible points, and now you have guestimations.
On bulk vessels of Handy and Panamax size, the vessel’s average in TPC (tons per centimeter) is approximately 50-65. So, this means that the distance in Draft from the bottom of the Draft Mark stenciled number to the top (10-cm) represents up to 650 tons.
Even in a light chop, there is 600-700 tons of possible error, noted in this photo.
One could only imagine the judgment in .5 to 1-meter swells.
Or trying to read these in the dark of night, from a crew boat from a distance, or in heavy current. Because of anchors, buoys, and swift water, this is as close as the launch boat can safely get.
And while one is riding around the vessel obtaining drafts, the remainder of the survey (Ballast, Voids, Fuel, etc.) is out of his reach or control.
I once sent the below photo to a customer and said, “tell me where the water is and I’ll tell you what your tonnage is.”.
The Vessel Draft Survey consists of two parts, open and close, or light and heavy. The difference in water displaced between the two equals the quantity of cargo loaded (with adjustments made for ballast, bunkers, etc.). No matter the condition of the water which the vessel is sitting in, the show must go on. Time is always an issue with a vessel, and time is money. The drafts must be read, and from that, the calculations are made and the BOL (Bill of Lading) and Mates Receipt are set. Buyers and sellers trade on this number.
Many draft marks on the bow, stern, and offshore side are not accessible. I asked each of these guys in the below photo, what they had (without them saying out loud) and there was a large variance between each of their findings, and this was in calm water.
Try reading that draft from many meters away, looking down on it. This was the vantage point for the guys in the previous photo
Or try getting an accurate mid-ship draft, one of the most important readings of the survey, from this vantage point in swells.
Once the vessel is loaded, no matter what water conditions it’s loaded in, the vessel is to carry and deliver the BOL quantity (created by the Vessel Draft Survey). The seller sold the amount, the buyer bought the amount, and the vessel is paid freight on the amount. In many cases, the parties trading paper have no idea how the numbers were derived.
I guess this is why so many vessels now have a standard clause in their documents stating that they cannot guarantee the accuracy of the agreed-upon tonnage listed (verbiage differs, but generally states). It is stated that in optimal conditions, Vessel Draft Surveys are subject to .5% variances.
Now, as the vessel arrives for delivery, it is the position of the vessel to make sure that the arrival vessel draft survey matches the departure draft survey within close tolerances. If the cargo is delivered into a warehouse and the warehouse is not emptied and zeroed out immediately after the delivery, a loss/gain of cargo can’t be attributed to a certain vessel. In many cases, the tonnage on the “paper trail” is kept in close tolerances, regardless of the cargo aboard or delivered. In some cases, common cargo warehouses may take more than a year (and many vessel deliveries) to zero out all cargo. In a case where a vessel delivers to another vessel or onto barges, there is an instant check and balance, a shortage or overage is noticed immediately. On an overage, you will not hear a peep, but on a shortage you, as the receiver surveyor are looked at as if you are responsible for the shortage, just for being the messenger of bad news. In my opinion, shortages outweigh overages manyfold, due to the vessel wanting to error on the side of caution to not exceed destination arrival draft restriction requirements, or carry cargo which they will not get freight. In most cases, the source of the problem can be attributed to the conditions of the water surface at the load port, yet is hidden in a paper trail.
How could this issue be eliminated? And is there a more accurate way to read the drafts? Well, devices have been made (such as freeboard indicators) but are not practical in all water, wave, and current applications. Years ago I invented such a device, which worked very well, but it would have to be attached to the hull at the draft marks, which is not practical and can’t always be achieved. As I would say, when it is needed (in heavy sea swells and fast current) it couldn’t be used, and when it could be used (in perfectly calm water conditions) it is not needed. The one thing that keeps echoing in my mind is a hole in the ship (aka The Zounding Tube, named after the one who keeps thinking of it).
Having a sounding tube in the mid-ship point of the vessel (on a new build), or one Port and one Starboard, mid-ship, on a retrofit, through an existing ballast tank, which would go from keel to deck. With this, trim and list would not affect the readings because of their central location. In a perfect world, three tubes (one Fwd, Mid, & Aft) could be added, to adust for hog and sag. A chart could be applied so that an ullage/outage could be taken (from a fixed given point to the water within the tube/pipe) and converted to draft. This draft reading would not be affected by waves, swells, etc., due to hydraulic pressure and the fact that water is calm below the surface. Accuracy could be achieved. I have always asked myself if this is possible and would it work?
At this point I would have to leave the idea with Naval Architects and Class Societies, Vessel designers and builders, as I am not well versed in stress and build-out of vessels. One would think that as a proof of concept, a simple temporary test could be performed using a PVC pipe on the outer hull at mid-ship to compare reading accuracy. I guess as one works a lifetime at his/her craft, they hope to leave it better than they found it and also hope to leave their mark, as did Plimsoll in 1876.
I do know that billions of dollars are traded based on Vessel Draft Surveys, which are subject to accuracy by the water which the vessel lays afloat.
The views, information, or opinions expressed in this article are solely those of the author and do not necessarily represent those of TheNavalArch Pte Ltd and its employees
Owner, Marine Technical Surveyors (MTS)
Born in August of 1958, one of six children of a working class family, for Larry ”Chris” Zeringue, the old cliche of “born and raised on banks of the Mississippi River” could not be more true.
With his homes from birth to manhood being only yards from the river’s edge in the small town of Donaldsonville Louisiana – (all homesteads in settlement called Smoke Bend)
The Mighty Mississippi became Chris’s play ground as a child, passion as young man and gateway to the world as an adult.
By the age of 17 Chris was working on the river – his passion and pride for his work was only outpaced by his energy levels and tireless efforts as a hard worker and businessman.
After many years of working on the river, In 1993 Zeringue founded and co-owned Marine Technical Surveyors (with 2 other seasoned surveyors).
Zeringue worked day and night as a river rat and in suit and tie to see MTS to what it is today. MTS employs and has employed many great people, family and friends, over the past 28-years.
And like the waters of the river, and so many of its southbound vessels, Zeringue too would see his way across the world to many major ports.
Pursuing that same passion on the behalf of his customers – representing their cargo and their reputations in numerous ports in countless countries.
The Zounding tube is only one of many ideas that Zeringue has arrived at in his efforts to better represent the most accurate accounts of cargo.
For Zeringue, it is not the recognition of an invention that bring his ideas to life – but rather the pride, passion and energy he takes and puts forth in the responsibility of accounting for another’s goods
Lifting beams are universally applied gear used widely in various types of lifting operations, onshore and offshore. In this article, we will explore the design of a basic lifting beam and see what design checks are needed to establish the suitability of the beam for...
Spreader beams are universally applied gear which is widely used in various types of lifting operations, onshore and offshore. In this article, we will explore the design of a basic spreader beam and see what design checks are needed to establish the suitability of a...
Pad-eyes are one of the smallest and most universally used structural items in the maritime and Oil & Gas industry. They are used for a variety of purposes too: from a simple seafastening of a cargo to deck of a vessel, to complicated lifting operations involving...
by Michael Harwood, PE, PMP Overview Lifting by crane is a basic construction operation that dates back to at least Sixth Century BC (ancient Greece for example) and the lifting operation itself dates back much further. It is a very common operation in present-day...
Ever since the offshore industry has expanded to deeper waters, one topic of broad and current interest, that has dominated the industry, is the weight of topsides lifted offshore. Installation contractors advertise engineering feats accomplished by...