OSG Vision - Another Rule Beater

OSG Vision Photo from Towmasters

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?

  Crowley's AT/B - Rule Beater

K.C.

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

Vessel Displacement and how it is measured

A 200 meter long  PCTC upbound Westerschelde River (photo by K.C.)

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.

Vessel tonnage - Volume

A PCTC Alongsside

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.

The Tun - A pint's a pound the world around.

Illustration of sailors carrying a tun barrel in 1597 from The Pilgrims &; Plymouth Colony:1620 

The key to understanding the concept of tonnage with regards to ships  is understanding the dual use of the term ton.

 I remember in my grandmother's  kitchen, the answer to certain questions regarding conversions was:  "a pint's a pound the world around" . The first time I tried this phrase on an acquaintance I was sharply told that  obviously it couldn't be  true as it didn't take into account density.  But my grandmother managed her kitchen just fine. It true for water and  true enough for what she had to measure.

  I sometimes drive the high school cross-country ski club around in a 7 passenger minivan. Does "seven passenger capacity"" refer to weight or volume? The answer is neither, it is the number of people the vehicle can carry. But the designers of the car had to consider both the size of people and the weight. So the term "passenger capacity" could include either weight or size or both, or neither.

The original meaning of the word tun, (from this site) from which ton derives, was: "a big container". But later:

"the word also came to mean the capacity of such a container and was used as a unit of both volume and weight"

 To link ships with the tun:

This measurement was derived long ago to describe a ship's space for a common cargo — wine. Since wine was shipped in "tuns" that each held 8 barrels or about 242 gallons, a ship that could carry 8,000 wine barrels was considered a 1,000-tun ship. "Tun" evolved into "ton" and then into "gross registered ton." 

 A 1000 tun ship, I like that. I like the idea of a pint being a pound the world around, I like the idea of a tun being both a weight and a volume and a container the size of boxcar.  Throw out the calculator! A tun is a tun is a tun.

Things are more complex now of course -  that's another post.

BTW  -  I like to use Wikipedia for posts like this but the editors of the article  "tun" couldn't manage the dual meaning concept. From the article:

The tun is an old English unit of wine cask volume, holding about 954 litres, almost a cubic metre. Etymologically it is identical to the ton, a unit of mass or weight.

Ha! Etymologically  identical - so close. People can cope with the idea of  light being both a wave and a particle without breaking into a sweat but they can't cope with the idea of a tun being both weight and volume.

It's simple, a passenger is a passenger and a tun is a ton and a pint is a  pound, the world around.

K.C.

I see that Wikipedia does better with Tonne  here saying: "A full tun, standing about a metre high, could easily weigh a tonne."

Scope - Amount Recommended for Anchoring

Catenary Vector Forces 
A ship's anchor relies upon the weight of the anchor chain (also called cable)  to keep the forces acting on the anchor horizontal as much as possible. If the chain, at the anchor, is lifted 15 degrees it is estimated the anchor loses about half it's holding power.  Insufficient scope increases the risk of dragging anchor. Excess scope on the other hand increase the risk of damaging or breaking the chain.

When the amount of scope required is determined, the distance between the end of the hawsepipe and the water is usually  taken into account but  for convenience  the mate usually reports the amount of chain at the waters edge - for example the bow might report "6 shots in the water'.   It  also can be (usually when heaving in)  reported by how much is on deck.

Many references recommend a scope of between 5 and 7 (of chain) to 1 (water depth)

 Nicholls's Seamanship and Nautical Knowledge makes the following recommendations:

"The minimum scope of mild steel cable to use according to depths of water is given by the following rough guide:"

Below 20 m 6 to 8
20 m to 40 m 4 to 6
over 40 m less then 4

A ship  may be required  to anchor in as much as 100 meters of water (for example Fujairah Anchorage) with 10 shots of chain out the scope is less then 3 to 1.

Ultimately the  master must determine how much scope to use based upon his experience.

K.C.

Ground Tackle Details for PCTC

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About 10 shots of anchor chain from a PCTC 
A few details about the ground tackle of a 6500 unit PCTC (Pure Car Truck Carrier or informally a car carrier) - a 200 meter ship

On all ships the term ground tackle refers to a vessel's anchors, chain and windlass.

The anchor:  The anchor type is AC-14    The weight is about 8 tons

AC-14 Anchor

The chain: The chain consist of links, the type of link is called stud link, the size, which is the diameter of the wire used to form the links is 81mm.   The length of an anchor chain is measured in shots. One shot is 15 fathoms or 90 feet (27.4 meters).

Ship's anchor chain ranged out onto the drydock

The port anchor chain is 11 shots - 990 feet or about 300 meters  - total weight is 44 tons.
The starboard anchor is 10 shots - 900 feet or about 274 meters - total weight is 40 tons.

The weight of a 81mm diameter chain is 0.144 tons/meter - the weight of each shot therefore is 4 tons.

Each shot is connected by a connecting link.

Connecting Link

The connection between the chain and the anchor includes a swivel, an end link and a bending shackle

The Anchor shackle and bending shackle

.  Global Security has a web page with good details here.

The Swivel

The windlass: There are two separate,   hydraulically powered  windlass, one  for each side, the windlass is capable of recovering the chain at a rate of about 1 shot (90 feet)  in three minutes.

Scope refers to the amount of chain used at anchor - that will be the next post: Scope - Amount recommended for anchoring.

K.C.

Kennebec Captain - Now on Facebook

 I  am working on shifting posts of the "here is an interesting post/article"  to a Kennebec Captain Facebook page while using this blog for the more substantive posts. I haven't figured out the details yet but if you can find the Kennebec Captain Facebook page here.  If you have any tips / advice leave a comment.
K.C.

Failure of Anchor Gear on Cruise Ship

Professional Mariner Magazine reports that an 85 kt gust of wind pushed  a Carnival Cruise Ship off the pier where it was moored.  No surprise there. The standard mooring arrangement isn't going to hold a ship with that much sail area alongside in 85 kts .What caught my eye was this:

"The company said the anchor retrieval equipment malfunctioned after the incident."

I don't know what happened to the anchor gear, no details are provided. (It's standard practice to let go an anchor or two in this type of situation)  My guess is at some point during the excitement the anchor gear took a very heavy strain and damaged the anchor windlass. My experience has been that the windlass  will fail before the chain or anchor will. A heavy strain on an anchor windlass can bend the main shaft, or twist the winch so that the main gears are misaligned.

If you are using your anchor gear to hold the ship off the rocks it's a good thing if the chain or anchor doesn't fail. If the windlass fails you'll likely still be able  veer more chain or hold what you've got.

One thing is, after the yelling dies down and  you want to get out of Dodge you're going to have to recover your anchor and chain without the windlass.

K.C.