Tonnage

[Ivan Cloherty]

#50 That about covers it John, the hydrometer such a simple piece of equipment (JofOz basically a brass type stick with a bulb) but so valuable and much guarded by the Mate with strict instructions not to drop it.

JS did you mention TPI if you did I apologise for the following

J of Oz Gross and nett tonnages on your UK/Suez/Panama certificates never changes, only if the ship is altered structurally and has to be remeasured.

Displacement changes all the time, you will have a different displacement upon arrival at a port than when you did sailing from the last port, because of the fuel. water and stores used on passage, on passenger ships it will be minimal because of normally short voyages and constant restoring, refueling etc.

TPI = Tons per inch immersion. The reason why we ring-bolt-kickers (another post) took the draughts every morning and evening (start and finish of cargo operations) was to calculate how much cargo we had discharged (or loaded) in that period. To be exact we'd take draughts for'd, midships, aft both on port and starboard sides, calculate the mean and compare it with the previous mean reading. Now for ease of calculations lets say the difference in the mean reading was 5 feet (60 inches) and we had a TPI of 100 then we calculated that we had discharged (or loaded) 6000 tons that day which was a good enough calculation to estimated our progress and time to sailing day, if everything remained constant.

To find total out turn or amount loaded then there would be more detailed observations and soundings, which involved bunkers, fresh water, stores, constants, ballast (if any) light displacement, density of water etc

Hope this helps.

Think I've mentioned before the names of the two tomes on the subject you can purchase that will help you sleep if you suffer from insomnia!

[Colin Wood]

A brass hydrometer was only used by government surveyors for checking loadline infractions. Cargo hydrometers where of glass and calibrated in air not a vacuum like brass ones. Glass cargo hydrometers came with a certificate which had to be renewed at regular intervals.

[John Arton]

Brass hydrometer on vessels were/are part of the load line certificate requirements to be carried.
Suez and Panama tonnages take the ships international load line certificate tonnage and deduct from it there own interpretation of enclosed water tight spaces above the freeboard deck. For example a raised focsle head which gives a larger bow height increases the vessels reserve bouyancy which can lead to a decrease in the vessels freeboard.
When the Suez canal authority came to do their calculations for their tonnage certificate, upon which their fees are charged, they take the view that as the enclosed watertight space of the focsle was included in the load line calculations, it had to be empty in order to contribute to the vessels reserve bouyancy, hence the need to empty it if mooring ropes etc were normally stowed there.
Another ananomally is if within the ships accommodation there was a games/ hobby room that being part of the enclosed water tight space above the freeboard deck and contributing to reserve bouyancy, if it was designated as a Suez canal crew rest room, so long as it was empty, then it could be used in calculating the Suez canal tonnage, which meant it was another space requiring emptying before each transit.
Rgds
J.A.

[Keith Tindell]

Thanks for that info John A, some time ago on this site i said i recalled on a ship going through the Suez, we had to empty the focsle, and not many members seem to remember it, this would have been the early sixties, and a real pain, had to sheet it up on deck. Always maintained it was done to put it in a more thievable position lol, kt

[Ivan Cloherty]

A brass hydrometer was only used by government surveyors for checking loadline infractions. Cargo hydrometers where of glass and calibrated in air not a vacuum like brass ones. Glass cargo hydrometers came with a certificate which had to be renewed at regular intervals.

Every ship I sailed on I used a brass hydrometer Colin, you were not allowed to polish them, only wipe them.

[happy daze john in oz]

Ivan, thank you for that, much appreciated.
I am with your assistance and that of John learning more each time.
A lot of info and history there that should be conserved somewhere before it is all lost.

[happy daze john in oz]

Ivan and John so far you have given me some very good info.
Now another one for you.
The Dead Sea is so called as to the high level of salt in it.

Am I correct in thinking that on the Plimpsol line there is something about North Atlantic waters?

I know oceans vary around the globe but does the salt content vary enough to effect the draught of a ship.
Or is it so insufficient that it is not taken into account?

[j.sabourn]

WNA is because of more expected inclement weather and is a mark on your plimsol which gives you more freeboard .The Dead Sea and more salty is immaterial , just means if loading in that density would make allowances the other way than if loading in fresh or brackish water . Forget all the magic stuff .The world is divided into zones and when in those zones you are not to have less freeboard than your plimsolls say , otherwise you are overloaded and if caught will pay the fine or in some cases finish up in gaol . If it was monopoly you would get maybe a free out of gaol card not so in this case. It is rare for generalcargo ships and I would imagine passenger ships to load to their marks , but bulk cargoes , ore ,grain, coal, coke, oil,do it all the time. Every ton possible is revenue a general cargo s ship will usually fill out before ever nearing its marks. In rare cases however it doesn’t so will also be restricted . JS

Salt water is 1025
Fresh water is 1000
And that is what your plimsols are based on.


you also have timber load lines , when carrying timber on deck you are also going to get s lot of water contamination to increase the weight , this will happen on passage , and apart from weight will also alter your stability which always happens on timber ships ,so they are allotted a different set of free boards to try and keep the ship within safety limits. It has in the past not been too successful in some cases . JS.

[happy daze john in oz]

John, thanks for that it settles a bet I had with a shore sider here who thought the salt level would make a difference.
But did know the Plimpsol line was the guide to the correct level of freeboard allowed.
Think that is my way of putting it, might not be quite right.

That is all my questions for now, and once again thanks to you and Ivan.
If you ever want a change of job educators you would do well at.

[John Arton]

Just to confuse other departments, us deck crowd talk about load lines but what in reality we are discussing is the freeboard of a vessel, freeboard being a measure of the ships reserve bouyancy when loaded to its load line or draft marks, freeboard being the distance from the load line marks to the uppermost continuous deck.
Rgds
J.A.