How to measure a ship - Part 2 - Ships Nostalgia
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How to measure a ship - Part 2

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  #1  
Old 7th April 2006, 18:47
fred henderson's Avatar
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Question How to measure a ship - Part 2

Tmac has listed and defined the basic tonnages used to measure ships. Some of the replies brought in dimensions. I thought the definitions of the main ship’s dimensions may be of interest: -

PERPENDICULARS These imaginary lines come into various measurements. The Forward Perpendicular is a vertical line at the intersection of the stem and the waterline. The Aft Perpendicular is a vertical line drawn through the centre of the rudder stock.

MOULDED DIMENSIONS This concept comes into a number of dimensions. It is the distance between two points measured from the inside of the shell plating. It was originally from the outside of the frames, to which the plates were riveted. The frames were shaped using patterns that were made from the full size hull lines drawn on the Mould Loft floor.

LENGTH BETWEEN PERPENDICULARS As the name indicates, this is the distance between the two imaginary Perpendiculars.

LENGTH OVERALL The horizontal distance over the extremities of the ship from stem to stern.

LOAD LINE LENGTH The length of the water line of a ship lying in the water. There are different load lines for different situations, from Light Water Line (The water line of a ship carrying only her regular inventory, but no cargo) to Deep Water Line (The water line at maximum loaded draught in seawater).

LENGTH ON THE WATERLINE The horizontal length between the points where the bow and the stern pass through the waterplane at the summer load line, excluding the shell plating. (i.e. moulded)

BEAM (MOULDED). The greatest moulded breadth measured from side to side at the outside of the frames but inside the shell plating.

BREADTH OVERALL The maximum width of the ship measured from the outer hull on the starboard side to the outer hull on the port side, including rubbing bars, permanent fenders or structures, including overhanging bridge wings, or an aircraft carrier flight deck and the like.

DRAUGHT FORWARD The vertical distance between the summer load line and the underside of the keel measured at the forward perpendicular.

DRAUGHT AT THE STERN The vertical distance between the summer load line and the underside of the keel measured at the after perpendicular.

MEAN DRAUGHT The arithmetic mean vertical distance between the summer load line and the underside of the keel of each of the two perpendiculars.

MAXIMUM DRAUGHT The vertical distance between the summer load line and the underside of any permanently protruding structure or equipment, for example a Sonar dome.

BASE LINE The upper side of a flat plate keel.

DECK LINE A line extended from the highest point of the upper freeboard deck to the ship’s side. This point is recorded on the outside of the hull by a short line welded on the shell plating above the Plimsoll mark.

DEPTH The vertical distance between the Base Line and the Deck Line measured at the point half way between the perpendiculars.

FREEBOARD The vertical distance between the Waterline and the Deck Line.

AIR DRAUGHT The vertical distance between the Summer Waterline and the highest point of the ship.

Fred
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  #2  
Old 7th April 2006, 19:07
Jeff Egan Jeff Egan is offline
 
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Fred, when piloting ships under the bridges on the Tyne we had a bridge card which we were supposed to get signed if there was any doubt over a ships "Air Draft" the Master would sign after entering his air draft which was variable depending on the vessels load or light condition. Is it as you say in fact the distance between the Summer load line and the highest point on the ship or the variable distance between the water line and the highest point on the ship.
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Old 7th April 2006, 20:11
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Regarding air draft I had an old friend now gone who was on those P,O liners which ran to Sydney in the sixties, and we were talking about striking the top masts on various ships, One of those ships had to strike her topmast to pass under Sydney Harbor bridge,I did not think it was true and he was getting mixed up so i sent an Email to Sydney Harbor authorities to confirm,they replied it was true and after the incident with the mast there was a plate on the bridge of the vessel concerned stating that she did not fit under the bridge,but I cannot remember the name of her
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Old 7th April 2006, 20:11
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Air Draught

Jeff
Air Draught is an interesting concept, as it is a mirror image of Draught in any loaded condition. If a ship is presented to you as a pilot with a specified Summer Draught that is near the river limits, you will be concerned to ensure that passage is made at a sufficiently high tide to ensure safe navigation. If the ship is in fact not fully loaded then you will be more relaxed.
With an Air Draft that is near bridge limits, you will be concerned if the ship is not fully laden. You then have the possibility of ballasting down to Summer Draught, or making passage under the bridges at low tide. In any event as the official Air Draught is measured from Summer Draught you, or the Captain, can calculate the actual Air Draught from her current loaded condition.

Fred
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  #5  
Old 8th April 2006, 11:19
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Excellent work Fred, I think between us we have just about covered it.
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  #6  
Old 8th April 2006, 11:23
Jeff Egan Jeff Egan is offline
 
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Fred years ago we used to get a lot of German coasters going up river to Dunston Staiths to load coal, some of them had whip aerials on the top of their masts that the masters forgot to include in the air draft. The noise on a still night as the aerial clanged off the underside of the high level bridge could be heard half way across town I think.
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Old 15th February 2008, 10:59
John Williams 56-65 John Williams 56-65 is offline  
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Speaking from a practical point of view, as a marine plumber, the most useless tool a shipbuilder repairer could have is a spirit level.
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  #8  
Old 15th February 2008, 11:40
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Quote:
Originally Posted by John Williams 56-65 View Post
Speaking from a practical point of view, as a marine plumber, the most useless tool a shipbuilder repairer could have is a spirit level.
Sulzers supplied one with the RTA engines to ensure the SIPWA sensors were fitted parallel to the liner top. Graduated in degrees from my recollection.
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Old 15th February 2008, 15:53
surfaceblow surfaceblow is offline  
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I sailed on several ships that required the antennas and after mast to be lowered to get into some of the loading ports. Since the after mast had the 10cm radar on it the USCG had to be informed and get their permission.
On one transit up river the Chief Mate waited for the last minute to take on ballast for the required air draft. After starting the ballasting the Chief Mate took off to climb up to the top of the crane to determine if we will clear the bridge. While I was watching the ballasting from my office computer I got up to get a cup of coffee looking out my port hole I could see that the crane would not clear the bridge at the rate of ballast going in. So I started the second ballast pump. The Chief Mate called back on the radio 15 mintues later after passing under the bridge that we cleared the bridge by 6 inches.
After docking I asked the Chief Mate into my office and showed him the graph with the ballasting rate and draft on the computer and told him that he should think about waiting to the last minute on ballasting. In the afternoon the Captain came in my office and thanked me for turning on the second ballast pump and letting the Chief Mate tell him about problem.
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  #10  
Old 15th February 2008, 21:27
vectiscol vectiscol is offline  
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Not quite technically correct with some of those definitions, Fred. Suggest you check the Load Line Regulations for the definitions of length for Load Line, and be aware that design draft of a ship might well be different from the full load draft to her assigned Load Line.
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Old 16th February 2008, 02:21
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Explanation of Load Line Length
LOAD LINE LENGTH is an IMO (International Maritime Organisation) term and was an attempt to ignore funny shaped ships being built to cheat length. What they are defining is a length at 85% of the height of the hull above the top of the keel measured parallel to the waterline and thus ignoring the upper sections of flared bows, counter stems etc.

REGISTERED LENGTH is the old way of measuring length and is often still quoted in the U.K. again it may be helpful to consult the drawings of the vessel if determining load line and registered lengths.
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Old 17th February 2008, 12:28
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Load Line Length

Sorry gentlemen, I was trying to provide a set of simple definitions that would be understandable to the general membership. Perhaps it should be: -

LOAD LINE LENGTH: The length given in the International Load Line Certificate and as defined in Article 2 (8) of the International Convention on Load Lines 1966 as modified by subsequent Protocols.

I hope that you will agree that it is also the length used in freeboard calculations.

Fred
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  #13  
Old 17th February 2008, 14:30
JimC JimC is offline  
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Air draft!

What happened with 'maximum height above water level'? I am fully aware as to why the term 'air draft' is used but it did make me think. Actually I always think of the word 'draft' as a downward or 'below' term. Come to think of it: what was the term used when nearly all UK ships were fitted with telescopic masts to pass along the Manchester Ship Canal?
I used to take rigs down the Clyde under the Erskine Bridge. We had 4' below the cans on the bottom and 4' below the underside of the roadway from tops of the legs. All this had to be achieved by passing under the bridge at the exact centre of the river width as the river bed sloped upward to either bank. Scary! Actually, a package did eventually hit the bridge and it was closed for some time (I wasn't the towmaster by the way!).

Jim C.
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  #14  
Old 16th March 2009, 10:51
Captain Scarface Captain Scarface is offline  
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CLANG!! That'll be the Erskine Bridge then

Quote:
Originally Posted by JimC View Post
What happened with 'maximum height above water level'? I am fully aware as to why the term 'air draft' is used but it did make me think. Actually I always think of the word 'draft' as a downward or 'below' term. Come to think of it: what was the term used when nearly all UK ships were fitted with telescopic masts to pass along the Manchester Ship Canal?
I used to take rigs down the Clyde under the Erskine Bridge. We had 4' below the cans on the bottom and 4' below the underside of the roadway from tops of the legs. All this had to be achieved by passing under the bridge at the exact centre of the river width as the river bed sloped upward to either bank. Scary! Actually, a package did eventually hit the bridge and it was closed for some time (I wasn't the towmaster by the way!).

Jim C.
Aye Jim that is still spoken about by older hands. Hard to believe but a similar CLANG happened in Norway not long afterwards and it was not the last either.
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  #15  
Old 16th March 2009, 14:24
Allan Wareing Allan Wareing is offline  
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Clang

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Aye Jim that is still spoken about by older hands. Hard to believe but a similar CLANG happened in Norway not long afterwards and it was not the last either.
Hi Jim, I was on the Federal Lines ship Middlesex as an O.S when we scraped our way under the Railway Bridge just below Latchford Locks on the Manchester Ship Canal. The pilot was going very slow as we had touched the gauge wire when approaching. Only the foremast touched and the table just scraped it's way under but the four shackles holding the topping lift blocks were sheared off and the blocks came clattering down to the deck (the topmast had of course been 'struck -unfortunate phrase ! -and was lying safely in side the lower mast. It was certainly a tight squeeze and we left quite a scar under the bridge with a lot of rivet heads shorn off.
The scar was visible for a long time after that, I lived near the Locks and used to look at it whenever I was on leave. In fact I worked on Latchford Locks as telephone boy before going deep sea in 1937
Regards,Allan.
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