clyst
Well-Known Member
The registered tonnage indicated on part 1 register is the DISPLACEMENT tonnage and not actual weight of boat yes ???---- I hope /forums/images/graemlins/tongue.gif
cheers
Terry
cheers
Terry
registered tonnage quick reply needed please
- Thread starter clyst
- Start date
Robin
Well-Known Member
Registered tonnage is a measurement of capacity/volume not of weight or displacement. It is calculated from length, beam and other dimemsions and is I think supposed to represent available cargo carrying capacity, the rules being the same for leisure or commercial vessels.
Aja
Well-Known Member
Guess. that's what I did! They wont come round and check.
Donald
Donald
G
Guest
Guest
[ QUOTE ]
..is the DISPLACEMENT tonnage and not actual weight of boat yes ???----
[/ QUOTE ]
As an aside, displacement tonnage IS the actual weight of the boat
..is the DISPLACEMENT tonnage and not actual weight of boat yes ???----
[/ QUOTE ]
As an aside, displacement tonnage IS the actual weight of the boat
clyst
Well-Known Member
cheers Robin . yes I think you are right . Many thanks for your quick response
jwilson
Well-Known Member
Registered tonnage is nothing to do with the actual weight or displacement. It is calculated by measuring the hull, and derives from an ancient way of taxing ships according to how many 'tun' barrels of wine or herrings they could carry (honest - I'm not joking).
There are variations - Thames Tonnage was one, currently the Registrar of Ships issues rules for how a surveyor is to measure the hull. Often it roughly corresponds with weight, but there may be very wide variations. No weight is measured when calculating registered tonnage, so don't rely on it for booking a crane or a road transporter.
There are variations - Thames Tonnage was one, currently the Registrar of Ships issues rules for how a surveyor is to measure the hull. Often it roughly corresponds with weight, but there may be very wide variations. No weight is measured when calculating registered tonnage, so don't rely on it for booking a crane or a road transporter.
Plomong
Well-Known Member
Here's my tuppence worth:
Gross Tonnage is the volume of all that is below the Tonnage Deck plus spaces between the tonnage deck and the upper deck, plus enclosed spaces on the upper deck (deckhouses, etc). Usually expressed in Moorson Tons (Volume in cu. ft divided by 100).
Register Tonnage or Net Tonnage (not registered - register) is gross tonnage less the volume of spaces that do not earn, such as engine rooms, bunkers, accomodation, etc., again expressed in Moorson Tons.
For small ships in the UK, it used to be accepted to calculate Register Tonnage as:
RT = (0.45 x L x B x D) / 100
where all measurements are in ft, L and B are overall and D is the distance between the underside of the deckhead in the saloon on the centreline and the lowermost point within the hull, excluding such items as pump wells in the bilges.
I don't know if this formula is still accepted. It does give a good approximation to the required value.
Hope this helps.
Gross Tonnage is the volume of all that is below the Tonnage Deck plus spaces between the tonnage deck and the upper deck, plus enclosed spaces on the upper deck (deckhouses, etc). Usually expressed in Moorson Tons (Volume in cu. ft divided by 100).
Register Tonnage or Net Tonnage (not registered - register) is gross tonnage less the volume of spaces that do not earn, such as engine rooms, bunkers, accomodation, etc., again expressed in Moorson Tons.
For small ships in the UK, it used to be accepted to calculate Register Tonnage as:
RT = (0.45 x L x B x D) / 100
where all measurements are in ft, L and B are overall and D is the distance between the underside of the deckhead in the saloon on the centreline and the lowermost point within the hull, excluding such items as pump wells in the bilges.
I don't know if this formula is still accepted. It does give a good approximation to the required value.
Hope this helps.
clyst
Well-Known Member
How can it be ?? If you immersed ONE Cu Ft of lead into water it would displace ONE CuFT of water . Are you suggesting One cuft of water weighs the same as One cuft of lead ??
Krusty
Well-Known Member
[ QUOTE ]
If you immersed ONE Cu Ft of lead into water it would displace ONE CuFT of water
[/ QUOTE ]
OF COURSE IT WOULD, BUT IT WOULD SINK!
Displacement tonnage is the weight of water diplaced by the boat AFLOAT, and is therefore EXACTLY equal to its weight ashore and dry.
If you immersed ONE Cu Ft of lead into water it would displace ONE CuFT of water
[/ QUOTE ]
OF COURSE IT WOULD, BUT IT WOULD SINK!
Displacement tonnage is the weight of water diplaced by the boat AFLOAT, and is therefore EXACTLY equal to its weight ashore and dry.
duncanmack
Well-Known Member
[ QUOTE ]
How can it be ?? If you immersed ONE Cu Ft of lead into water it would displace ONE CuFT of water . Are you suggesting One cuft of water weighs the same as One cuft of lead ??
[/ QUOTE ]
You're a nutter! /forums/images/graemlins/grin.gif
If you hammered the cubic foot of lead into a boat shape (or any shape that would float) and put it in the water then it would displace its own weight of water. If you hadn't made the sides of the "boat" high enough then it would sink.
If you had made the sides high enough then it would float.
One ton of lead weighs the same as one ton of water.
How can it be ?? If you immersed ONE Cu Ft of lead into water it would displace ONE CuFT of water . Are you suggesting One cuft of water weighs the same as One cuft of lead ??
[/ QUOTE ]
You're a nutter! /forums/images/graemlins/grin.gif
If you hammered the cubic foot of lead into a boat shape (or any shape that would float) and put it in the water then it would displace its own weight of water. If you hadn't made the sides of the "boat" high enough then it would sink.
If you had made the sides high enough then it would float.
One ton of lead weighs the same as one ton of water.
VicS
Well-Known Member
[ QUOTE ]
Are you suggesting One cuft of water weighs the same as One cuft of lead ??
[/ QUOTE ] No but the apparent weight of the lead will be less than it was in air by the weight of a cubic foot of water.
In the case of a boat it floats at the point where the weight of the volume of water displaced is equal to the weight of the boat.
A little revision of some very basic science and Archimedes principle in particular is called for. Remember those Eureka, or displacement, cans!
Are you suggesting One cuft of water weighs the same as One cuft of lead ??
[/ QUOTE ] No but the apparent weight of the lead will be less than it was in air by the weight of a cubic foot of water.
In the case of a boat it floats at the point where the weight of the volume of water displaced is equal to the weight of the boat.
A little revision of some very basic science and Archimedes principle in particular is called for. Remember those Eureka, or displacement, cans!
billcowan
Well-Known Member
I think this endlessly repeated thread is more entertaining than the anchoring one. In that there are less died in the wool opinions, and more people struggling to grasp concepts.
By the way, does anyone know how they measure displacement tonnage of ships? is it calculated from the known (from the plans) volume of ship below the waterline, or is there a fancy way of 'weighing' ships?
By the way, does anyone know how they measure displacement tonnage of ships? is it calculated from the known (from the plans) volume of ship below the waterline, or is there a fancy way of 'weighing' ships?
Bajansailor
Well-Known Member
Re: measuring displacement tonnages of ships
Re measuring displacement tonnage of ships - in a nutshell, this is carried out by measuring the drafts using the draft marks on the hull forward, aft and midships, and then using the vessel's hydrostatic tables to calculate the displacement of the ship.
After measuring the drafts, and making corrections (if necessary) for the position of the draft marks (in relation to the length between perpendiculars, or LBP), the quarter mean draft is calculated. This draft takes into account possible hogging or sagging of the ship along its length. The QMD is then used in conjunction with the hydrostatic tables to obtain the displacement. These displacements in the tables are usually calculated for 'standard' salt water (SG 1.025). If the vessel is in brackish or fresh water, then this has to be allowed for by measuring the density of the water.
If the ship is trimming significantly, eg down by the stern in the lightship condition, then two trim corrections will have to be applied - there are two basic formulas for calculating these. These trim corrections will be added or subtracted (depending on if they are -ve or +ve) from the previously calculated displacement.
We will then have the actual displacement of the ship, at those draft marks, in water of that particular density.
If the ship is in fresh water, she will be a bit deeper in the water compared to if she is salt water.
This calculation procedure is usually referred to as carrying out a 'Draught Survey'. The Chief Officers of cargo vessels will usually do draft surveys in every port prior to discharging cargo, and upon completion. The difference in calculated displacement between the initial and final draft surveys will be the quantity of cargo discharged or loaded.
Note that allowance will also have to be made during each draft survey for the quantities of Fuel Oil, Diesel Oil, Lube Oil, Fresh Water and Saltwater Ballast on board at the time - this will involve sounding all the tanks on the ship, and using the tank tables in the Hydrostatics data to calculate the weight of fluid contained within each tank.
Re measuring displacement tonnage of ships - in a nutshell, this is carried out by measuring the drafts using the draft marks on the hull forward, aft and midships, and then using the vessel's hydrostatic tables to calculate the displacement of the ship.
After measuring the drafts, and making corrections (if necessary) for the position of the draft marks (in relation to the length between perpendiculars, or LBP), the quarter mean draft is calculated. This draft takes into account possible hogging or sagging of the ship along its length. The QMD is then used in conjunction with the hydrostatic tables to obtain the displacement. These displacements in the tables are usually calculated for 'standard' salt water (SG 1.025). If the vessel is in brackish or fresh water, then this has to be allowed for by measuring the density of the water.
If the ship is trimming significantly, eg down by the stern in the lightship condition, then two trim corrections will have to be applied - there are two basic formulas for calculating these. These trim corrections will be added or subtracted (depending on if they are -ve or +ve) from the previously calculated displacement.
We will then have the actual displacement of the ship, at those draft marks, in water of that particular density.
If the ship is in fresh water, she will be a bit deeper in the water compared to if she is salt water.
This calculation procedure is usually referred to as carrying out a 'Draught Survey'. The Chief Officers of cargo vessels will usually do draft surveys in every port prior to discharging cargo, and upon completion. The difference in calculated displacement between the initial and final draft surveys will be the quantity of cargo discharged or loaded.
Note that allowance will also have to be made during each draft survey for the quantities of Fuel Oil, Diesel Oil, Lube Oil, Fresh Water and Saltwater Ballast on board at the time - this will involve sounding all the tanks on the ship, and using the tank tables in the Hydrostatics data to calculate the weight of fluid contained within each tank.
Bilgediver
Well-Known Member
And it would sink. We are talking about objects floating. So if we used the lead to make a boat from lead sheet then we would have to make the boat big enough to displace at least the same weight of water as the lead. then the displacemnet would equal the weight of the lead.
John
John
boatmike
Well-Known Member
Quite correct. However after sailing for over 50 years, and working in the industry for over 30 building things wot float I still dont know how to calculate the gross tonnage (tunnage) of my catamaran. I can only think about taking each hull as a mono and doubling it, but there is loads of volume over the bridgedeck too... does this count? I have only once been asked for it, (guess who by?) and just can't find an accepted way of calculating it. (No I refuse to fill it up with herrings!) Does anyone actually know?
It appears to me that any reasonable number you put down is accepted for registration but sod it how on earth are you supposed to do it? /forums/images/graemlins/confused.gif
It appears to me that any reasonable number you put down is accepted for registration but sod it how on earth are you supposed to do it? /forums/images/graemlins/confused.gif
cliffordpope
Well-Known Member
Thames Tonnage is:
(Length-Beam) X Beam X Beam/2, all divided by 94.
(Waterline length, I think)
The result used traditionally to be expressed in whole tons and remaining 94ths.
Thus my boat is 2 54/94 tons, which is not a bad approximation to her displacement, calculted at about 2 1/2 tons.
Of course for many boats the formula is wildly inaccurate, but it has a nice old fashioned ring to it, a bit like part ownership being expressed in 64ths.
(Length-Beam) X Beam X Beam/2, all divided by 94.
(Waterline length, I think)
The result used traditionally to be expressed in whole tons and remaining 94ths.
Thus my boat is 2 54/94 tons, which is not a bad approximation to her displacement, calculted at about 2 1/2 tons.
Of course for many boats the formula is wildly inaccurate, but it has a nice old fashioned ring to it, a bit like part ownership being expressed in 64ths.
G
Guest
Guest
As another reply said ...
Reg Tonnage is a factor of Vol. based on 100 cu.ft per Long Ton. It is in two parts ... Net Reg Tonnage (NRT) and Gross Reg. Tonnage (GRT) .... neither of which are applicable in any way to a pleasure boat / yacht. They are Cargo based terms from the old days of barrells and bales carried on ships many many years ago.
For a Yacht ... best is to substitute Overall Weight (Displacement) ... as that is the only actual weight you have to go on.
Reg Tonnage is a factor of Vol. based on 100 cu.ft per Long Ton. It is in two parts ... Net Reg Tonnage (NRT) and Gross Reg. Tonnage (GRT) .... neither of which are applicable in any way to a pleasure boat / yacht. They are Cargo based terms from the old days of barrells and bales carried on ships many many years ago.
For a Yacht ... best is to substitute Overall Weight (Displacement) ... as that is the only actual weight you have to go on.
vyv_cox
Well-Known Member
Re: As another reply said ...
When my boat was measured for Part 1 I was told that the registered tonnage was a value originally derived from the weight of wool that it could carry! Wool is the last thing I want on board, except perhaps cardboard, so in my case the Voluntary Registered Tonnage is zero.
When my boat was measured for Part 1 I was told that the registered tonnage was a value originally derived from the weight of wool that it could carry! Wool is the last thing I want on board, except perhaps cardboard, so in my case the Voluntary Registered Tonnage is zero.
G
Guest
Guest
Lead and water .... silly billy ....
Of course the lead will weigh more than its equivalent volume of water ... it will sink.
1 cu.m object floating at zero freeboard will displace 1 MT of freshwater at density 1.000. QED.
put it another way ... for an object to float with a freeboard ie your yacht - the total weight of water displaced must be in terms of volume at density less than the volume of the yacht hull .... the greater the difference - the greater the freeboard.
Where's Archimedes when you need him ??
It's funny actually because there was a German Sales guy going round Ports selling weigh-scales ... using the lead and water argument to discount Draft Survey calculation of cargo weight. He had to be kicked off from sales - because his argument had a block of heavy material placed in a maesuring cylinder, water level observed before brick, and after placing brick in. Of course the brick sat on bottom of glass ... so amount of water rise was totally out of step etc. Believe it when some terminal guys actually believed it !!
Of course the lead will weigh more than its equivalent volume of water ... it will sink.
1 cu.m object floating at zero freeboard will displace 1 MT of freshwater at density 1.000. QED.
put it another way ... for an object to float with a freeboard ie your yacht - the total weight of water displaced must be in terms of volume at density less than the volume of the yacht hull .... the greater the difference - the greater the freeboard.
Where's Archimedes when you need him ??
It's funny actually because there was a German Sales guy going round Ports selling weigh-scales ... using the lead and water argument to discount Draft Survey calculation of cargo weight. He had to be kicked off from sales - because his argument had a block of heavy material placed in a maesuring cylinder, water level observed before brick, and after placing brick in. Of course the brick sat on bottom of glass ... so amount of water rise was totally out of step etc. Believe it when some terminal guys actually believed it !!
G
Guest
Guest
Draft Survey yes ... but I think he\'s asking builders ship weight
as per builders ...
That is done by Simpsons rules and calcualtion based on known steel used in construction and volume calculation of finished vessel.
Design drafts are observed once vessel afloat and compared.
Light displacement as barnacle is possibly asking about is actually checked over the vessels life ... and amended by what is wrongly termed "Ships Constant" ... which accounts for various extras on board as well as changes to steel / structure / fittings to the vessel ie a change of lifeboat and davits can easily alter 50 MT in a vessels displacement.
Because of the sheer difficulty of placing a ship on scales ! it is basically calculated.
The post about Draft Survey - is a cargo based calcualtion that we do as Inspectors as part of our work. It is an approximation that is accurate enough. Based on a Japanese Engineers theory and derivation. The proper way to do it is long and tedious ... by multiple measurement around vessel while afloat ... then Boolean curves etc. - To be honest, it's so long since I even looked at Boolean system - that I couldn't do it now ....
as per builders ...
That is done by Simpsons rules and calcualtion based on known steel used in construction and volume calculation of finished vessel.
Design drafts are observed once vessel afloat and compared.
Light displacement as barnacle is possibly asking about is actually checked over the vessels life ... and amended by what is wrongly termed "Ships Constant" ... which accounts for various extras on board as well as changes to steel / structure / fittings to the vessel ie a change of lifeboat and davits can easily alter 50 MT in a vessels displacement.
Because of the sheer difficulty of placing a ship on scales ! it is basically calculated.
The post about Draft Survey - is a cargo based calcualtion that we do as Inspectors as part of our work. It is an approximation that is accurate enough. Based on a Japanese Engineers theory and derivation. The proper way to do it is long and tedious ... by multiple measurement around vessel while afloat ... then Boolean curves etc. - To be honest, it's so long since I even looked at Boolean system - that I couldn't do it now ....