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Vessel tonnage – Volume
The term tons when applied to vessels may refer to either weight or volume as established in the previous post (here)
This post deals with the tons as a unit of volume, being equal to 100 cubic feet.
The volume measurements of a ship are legal and regulatory matters and are used only on paperwork, not on the day to day operation of the ship.
The random PCTC shown above has the following particulars:
Gross tons (GT) 57,623
Net tons (NT) 17,287
Suez Gross Tons 63,313
Suez Net Tons 62,897
Panama Canal Tons 57,510
Gross Tonnage is the total internal volume of ship in units of 100 cubic feet.
The difference between gross and net is more or less what you’d think. To use the analogy of a pickup truck, gross would be a measure of the volume of the entire truck and net would be the volume of the truck bed alone.
The net tonnage of a vessel is “the gross tonnage less certain deductions for for machinery and passenger spaces, crew’s quarters, store rooms and spaces used in navigating the vessel” (Merchant Marine Officer’s Handbook”)
There are different versions of both net and gross tonnage because fees and regulations are involved and there is more then one way to skin a cat.
Think of the problem of determining the number of board feet in a log.. Not as simple as you’d think. There are various rules to determine board feet of a log including: the Maine Rule, The Bangor Rule, The Holland Rule, The Scribner rule and of course the subversive International log scale.
Measuring the volume of a ship is the same deal, the spaces inside a ship are shaped weird and there is more then one way to scale a log or measure a cargo hold.
As a practical matter my document binder has three certificates which deal with tonnage, they are the International tonnage certificate and one each for the Suez and Panama Canals.
Finally, many vessels are designed with the rules very much in mind which explains why many tugs are 199.0 gross tons. I recall on the Snowbird, part of the galley bulkhead could be unbolted and removed. It was a tonnage door, installed for the sole purpose of converting a non-exempt space into a exempted one and in this case reduce the tonnage to 499 tons.
K.C.
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Would the stern swing to port?
What?? I have been researching the so called “Gross tonnage rule” and from a Coast Guard Auxiliary site I read:
“In other words, if a boat is moving a 5 mph east and you were in the vacuum of space, it would never stop traveling east at 5 mph. However, we all know when we stop our engine on our boat, we slow down”.
I wonder if I was in the vacuum of space and I backed the engine would the ship and the propeller begin to rotate in opposite directions? I mean assuming my engine is going to run?
Anyway speaking of ships in outer space the blog Strait of Magellan has safely circumnavigated the sun.
K.C.
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Vessel Displacement and how it is measured
Displacement
Displacement is the weight of the vessel and all weights on board. The units most commonly used are metric tons. The concept that weight and displacement of a floating vessel are equal is called Archimedes Principle.
Displacement = weight of the vessel + all the stuff on the vessel
Lightweight Displacement = weight of the vessel
Deadweight = all the stuff on the vessel.
Deadweight, abbreviated dwt is the carrying capacity of individual ships and is used to compare ships as well as a nations entire merchant marine and loses at war.
Deadweight includes cargo, fuel, water, lube oil, stores, the crew. It might seem odd to refer to paying cargo as dead weight but the term deadweight implies that the ship itself is alive. A sailing ship in danger might jettison deadweight, paying or not – the origin of the concept of general average.
Displacement is measured in two ways
- By summing up all weights on board and adding them to the lightship weight. This is done by a program, basically a spreadsheet. The lightship weight is supplied by the builder. The chief engineer supplies the fuel, lube oil. The chief mate manages the ballast. The program computes drafts, in meters, displacement in metric tons and GM in meters.
- The vessel’s drafts. The two factors that determine draft are displacement and the density of the water. Drafts can be converted to displacement using a table provided by the builder.
Using some real numbers the PCTC pictured above:
Lightship weight is 16,108 mt.
Here are some typical weights that comprise deadweights
Cargo: 8520 mt – 5500 standard cars at 1.5 mt each
Fuel: 2000 mt (Max 3095)
Ballast: 4000 mt (max 9523 mt)
Fresh water: 400 mt (max 420 mt)
Diesel oil: 100 mt (max 190 mt)
crew and associated gear and equipment is 135 mt
Total Deadweight is this case is 15,155 mt
Lightship weight + deadweight= Displacement
Displacement = 16108 mt +15,155 mt =31,263 mt
A PCTC is at one end of the deadweight/lightweight ratio spectrum. At the other end are large tankers. For example from this site:
A VLCC is a is a ship with a deadweight of from 200,000 to 315,000 tons. The standard VLCC is about 300,000 tons which will allow is to carry about 2 million barrels of oil. The lightweight of such a ship will be around 42,000 tons.
K.C.
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Tagged Displacement, measured, Vessel
Deadliest Sea – A review
-Captain Lloyd liked to keep the Coast Guard Cutter Munro upwind and at the ice edge during the fishing season in the Bering Sea.
-Peter Barry, who died when the fishing vessel Western Sea sank, was an Ivy League student.
- A pilot pushing a “Herc” to it’s limits is “flying the barber pole”.
- Running both the heater and the deicer on a Jayhawk helo requires two generators which reduces it’s range.
-The F/V Big Valley went down after leaving port early to avoid Charlie Madicott and the Coast Guard’s Alternate Compliance Program.
These were the kind of details that made Deadliest Sea: The Untold Story Behind the Greatest Rescue in Coast Guard History by Kalee Thompson a great read.
The book tells the story of the Coast Guard’s rescue of 42 crewmembers from the F/V Alaska Ranger. The book is mostly about the rescue itself, the role played by the Cutter Munro, the helo crews, it also tells the story of Ranger crew members.
I very much enjoyed Deadliest Sea – highly recommended.
K.C.
Alaska Ranger- shitty job shitty boat
Inside the Coast Guard’s Most Extreme Rescue Popular Mechanic article by author Kalee Thompson
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Scanner Review
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| Brother MFC-7360N Multipurpose printer/scanner |
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When I’m running coast-wise, it’s important to be able to get my various clerical chores done quickly so I can focus on more critical tasks. A key point is that it is more efficient and much quicker handling computer documents then paper ones. That means having a good scanner is important.
I’ve had several various scanners in my office over time but none as good as the Brother MFC printer/scanner. It prints fast, scans fast and the document feeder works much better then other models I’ve used. It also has software that is easy to use.
Imagine out the window I can see my green third mate is about to have a first encounter with the fishing fleet but I have a handful of paper to deal with. With this scanner I can shove the papers into the feeder, type in a file name, click the mouse button and then start a sprint out my office door. Before the ship closes a couple more ship lengths towards the nearest boat I’ll be on the bridge in time to show the new mate fishing vessel avoidance techniques and my documents will be safely on the hard drive.
K.C.
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Ship Generated Current – Ship’s Fast Water
I snagged the Dec/Jan 2011 issue of Professional Mariner out of the officer’s lounge the other day. There is an interesting article by St. Lawrence River pilot Capt. Hugues Cauvier; “Effects of the ship-generated sideways current”.
A ship moving sideways generates its own current. If the ship then moves ahead or astern, part of the ship remains in the current while part moves out of the current.
Jerry, a tug captain I sailed with sometime ago used to describe the currents and back eddies on the Inside Passage as “fast water” and “slow water”, the context being having the tug in slow water and the tow in fast water was a bad thing.
A ship moving sideways generates its own “fast water” Moving then either ahead or astern is going to poke the bow or the stern into “slow water” This would cause the ship’s heading to change. I have observed heading changes at slow speed which were not what I expected. This explanation seems reasonable. Next time I pull the ship out of its’ own fast water I’ll be watching.
K.C.
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Use of the GPS to regain the track-line to recover a MOB
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| Typical Maine GPS |
In the case of a crew (man) overboard many GPS units have a MOB (man overboard) button which will give the bearing and range back to the position of the ship when the button was pushed. The problem is the button may be overlooked entirely or it may not pushed in a timely manner. Even if it is pushed in a relatively timely manner it may be difficult to determine the distance between the MOB position on the GPS and the actual position of the crew in the water.
However, the crew member in the water has to be somewhere along the previous track. This track information is likely stored continuously and automatically on the GPS unit.
The GPS “PLOT”, which shows the previous track, can be an invaluable aid in locating the ship’s track while executing the man overboard turn.
It is important to know how to switch to the PLOT screen during the overboard emergency and it is also important to check to insure that it is set up properly to continuously record the ship’s track before the emergency.
The ship’s track may also be stored in other electronic equipment. For example “target trails” on the radar set at the appropriate time may also display the ship’s previous track.
K.C.
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OSG Vision – Another Rule Beater
Towmasters has a post up: Extreme ATB’s: Towing Vessels Or Something Else?
I can answer this. It is not a tow vessel, it is the house and engine room of a ship. Basically the designers and builder of this vessel have built a ship, broken it in half and then made arrangements to pin it back together. The reason they did this was to dodge regulations. The question is why does the Coast Guard approve it?
K.C.
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Playing Chicken at the Breakwater
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| Suez Canal Senior of Seniors Pilot gestures as he talks on his Phone |
I had a moment of schadenfreude reading Deepwater’s Marlboro Red. A big car ship on a windy day approaches the breakwater and the pilot boat refuses to board the pilot till they get some cigarettes, ha ha.
In ports in the United States, Japan and Europe safety first is the rule, competent, experienced pilots board well offshore when scheduled. On the other hand in ports where commerce is not king it’s a whole other ball game. Pilots rarely board at the designated pilot station and when they do board they may not be competent.
In a Persian Gulf port, after unmooring I’ve had the pilot let the tugs go and announce that it is too rough to disembark outside and get off, leaving me to navigate out of port. I’ve also had the pilot get on, make the tugs fast and then tell me to moor the ship on my own.
In ports like these the captain might arrive at the pilot station only to be told by port control the pilot will board at the breakwater and that there is no traffic in the channel. It’s wise to take all this with a grain of salt, keep an eye out for outbound traffic, have the bow thruster ready ….and have a supply of Marlboro Reds on hand.
K.C.
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Tagged Breakwater, Chicken, Playing
Program to aid Seafarers subject to pirate attack.
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| [Photo: ITF Seafarers' Trust: Rob Murray] |
A program ” to help seafarers who have been or may be subject to pirate attack.” The Maritime Piracy Humanitarian Response Programme (MPHRP) has been established:
“to assist seafarers and their families with the humanitarian aspects of a traumatic incident caused by a piracy attack, armed robbery or being taken hostage”
The announcement from the International Transportation Workers Federation (ITF) is here.
K.C.
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