Davecole
New member
Can any one help me with the diferrence between displacement and actual boat weight, Is there anyone that can explain how to calc ,I need it to be able to, too obtain insurance any help please
Dave
Dave
Displacement v actual weight
- Thread starter Davecole
- Start date
G
Guest
Guest
OK ... taking your words as written ....
Displacement is the volume of water displaced when the vessel is freely floating and such volume will equal the total weight of the boat and all items thereon at that time. It is a direct relation to overal weight. (Imagine as if the boat was lifted as is and placed on a weighbridge ....)
Actual Boat weight .... now here we have a choice ... are you saying as above in total with all gear and items on or as designed with only limited as supplied from builder ? There is also another one ... that is Light Ship when it is empty of fuel, stores, people etc.
To calculate .... if you like Boolean Maths or Simpsons Curves Maths - then yes you can calculate from design plans (line plans .... ) but is a lengthy difficult calc. Draft survey does not work on yachts - no data available to carry out the maths !
You have to either consult Builders / Dealers or search out such as Bristows or other Book of Yachts for info.
Try me ... what boat and year ? I may have a Bristows etc. to help .....
Insurance ?? Never had to declare a weight to insurance before on a yacht ... SSR yes ... but then normally you would use TM or just quote builders data ....
Displacement is the volume of water displaced when the vessel is freely floating and such volume will equal the total weight of the boat and all items thereon at that time. It is a direct relation to overal weight. (Imagine as if the boat was lifted as is and placed on a weighbridge ....)
Actual Boat weight .... now here we have a choice ... are you saying as above in total with all gear and items on or as designed with only limited as supplied from builder ? There is also another one ... that is Light Ship when it is empty of fuel, stores, people etc.
To calculate .... if you like Boolean Maths or Simpsons Curves Maths - then yes you can calculate from design plans (line plans .... ) but is a lengthy difficult calc. Draft survey does not work on yachts - no data available to carry out the maths !
You have to either consult Builders / Dealers or search out such as Bristows or other Book of Yachts for info.
Try me ... what boat and year ? I may have a Bristows etc. to help .....
Insurance ?? Never had to declare a weight to insurance before on a yacht ... SSR yes ... but then normally you would use TM or just quote builders data ....
G
Guest
Guest
They're the same thing.
Try Googling "Archimedes" and "Eureka!"
Try Googling "Archimedes" and "Eureka!"
Richard10002
Well-known member
Assuming that your question relates to a question on the proposal form, what is the actual question you are being asked?
Displacement and weight are the same... you might also be being asked about tonnage, which is a function of volume, (I think).
What kind of boat?
Displacement and weight are the same... you might also be being asked about tonnage, which is a function of volume, (I think).
What kind of boat?
roly_voya
New member
Re: Displacement v actual weight - Just had to do it!
I assume you either have a custome boat or one from a defunct builder - if not ask the builders on production boats they will know, on one off's they might. Mine didn't and I needed an acurate displacement to calculate power for new engine.
If you need displacement there are only 2 ways to do it by far the easiest is to arrange as part of your next haul out to include weighing. Some cranes/hoists have built in gauges but often not very accurate. To be accurate you either need an electronic load cell on the crane hook or to be able to weigh boat and travel hoist on wighbridge (most comercial docks have one). You can hire load gauges but you will have to consult with lift company and there are ins problems so better if they do it. Its also expensive (£150+ per cell)
The complicated way to do it means you have to have either a full lines plan or the ability to draw one from the boat. Measure the area at each station, calculate the average area for each section between stations and multiply by the section length. add it all up and you have a perfectly good enough estimate. If you can put the lines onto a basic CAD package its suprisingly simple as you can auto-calculate the areas (this is the way I did it).
If its registered tonnage you need its done on a measurment formula (based I believe on how many barrels of herring the ship will hold!!) - PM me and I can send it you
I assume you either have a custome boat or one from a defunct builder - if not ask the builders on production boats they will know, on one off's they might. Mine didn't and I needed an acurate displacement to calculate power for new engine.
If you need displacement there are only 2 ways to do it by far the easiest is to arrange as part of your next haul out to include weighing. Some cranes/hoists have built in gauges but often not very accurate. To be accurate you either need an electronic load cell on the crane hook or to be able to weigh boat and travel hoist on wighbridge (most comercial docks have one). You can hire load gauges but you will have to consult with lift company and there are ins problems so better if they do it. Its also expensive (£150+ per cell)
The complicated way to do it means you have to have either a full lines plan or the ability to draw one from the boat. Measure the area at each station, calculate the average area for each section between stations and multiply by the section length. add it all up and you have a perfectly good enough estimate. If you can put the lines onto a basic CAD package its suprisingly simple as you can auto-calculate the areas (this is the way I did it).
If its registered tonnage you need its done on a measurment formula (based I believe on how many barrels of herring the ship will hold!!) - PM me and I can send it you
cliffordpope
New member
Re: Displacement v actual weight - Just had to do it!
Or you could fill it with water up to the waterline, and measure the volume as you pump it out into barrels! Add a factor for the hull thickness.
I'd just get an approximation from consulting data on similar boats. Then do some simple hull measurements and imagine it is divided into separate tanks. Use appropriate approximations for the shape of each one - ie some may be simply V-section, others more rectangular with rounded corners. Add them up and see how it compares with the comparative figures from other boats.
You can get a check on the waterline area by placing a known weight in the boat (eg a group of people) and measuring how much it sinks by.
If you have it on a trailer you can get a very rough estimate just by looking at the tyres and comparing with known weights of boats on similar trailers - ie 2, 5, 10 tonnes?
How accurately do they need to know?
There's always the old Thames Measurement of course. That's done purely by formula, and gives a lovely old-fashioned figure in 94ths of a ton.
Or you could fill it with water up to the waterline, and measure the volume as you pump it out into barrels! Add a factor for the hull thickness.
I'd just get an approximation from consulting data on similar boats. Then do some simple hull measurements and imagine it is divided into separate tanks. Use appropriate approximations for the shape of each one - ie some may be simply V-section, others more rectangular with rounded corners. Add them up and see how it compares with the comparative figures from other boats.
You can get a check on the waterline area by placing a known weight in the boat (eg a group of people) and measuring how much it sinks by.
If you have it on a trailer you can get a very rough estimate just by looking at the tyres and comparing with known weights of boats on similar trailers - ie 2, 5, 10 tonnes?
How accurately do they need to know?
There's always the old Thames Measurement of course. That's done purely by formula, and gives a lovely old-fashioned figure in 94ths of a ton.
oldharry
Well-known member
Re: Displacement v actual weight - Just had to do it!
[ QUOTE ]
If you have it on a trailer you can get a very rough estimate just by looking at the tyres and comparing with known weights of boats on similar trailers - ie 2, 5, 10 tonnes?
.
[/ QUOTE ]
Thames masurment has nothing to do with the weight or displacement My 6 tons TM boat weighs in at around 3.5tons dispalcement.
If you have a trailer, the tyres markings will only tell you the maximum axle weight the tyres are rated for, which should be well in excess of the trail load. The trailer should have a plate giving it's maxim,um permissible load, but this is not a reliable guide to the actual weight of the boat, which may be seriously mismatched anyway! But get it weighed at the local public weighbridge, put the boat on, and get it weighed again. Useful too if you ever get road checked by the law.
Otherwise get the makers quoted figure which will be adequate for insurance purposes, or next time it is craned out, as the driver to tell you what load his strain gauge is showing.
I feel sure if you tell us what boat you have, someone here will know anyway!
[ QUOTE ]
If you have it on a trailer you can get a very rough estimate just by looking at the tyres and comparing with known weights of boats on similar trailers - ie 2, 5, 10 tonnes?
.
[/ QUOTE ]
Thames masurment has nothing to do with the weight or displacement My 6 tons TM boat weighs in at around 3.5tons dispalcement.
If you have a trailer, the tyres markings will only tell you the maximum axle weight the tyres are rated for, which should be well in excess of the trail load. The trailer should have a plate giving it's maxim,um permissible load, but this is not a reliable guide to the actual weight of the boat, which may be seriously mismatched anyway! But get it weighed at the local public weighbridge, put the boat on, and get it weighed again. Useful too if you ever get road checked by the law.
Otherwise get the makers quoted figure which will be adequate for insurance purposes, or next time it is craned out, as the driver to tell you what load his strain gauge is showing.
I feel sure if you tell us what boat you have, someone here will know anyway!
andy_wilson
New member
As already put, displacement is the weight of water displaced by the underwater sections whilst floating. This is equal to the weight of the boat and everything theron.
Of course there is also 'dry' weight, and 'Tonnage' for registration, which bears no relation to any 'weight' but is a measure of hull volume related to some archaic load capability.
I'm pretty sure that if she floats around her designed waterline, then whatever the designer intended will be fine for the insurance company. I'm equally sure that if you quoted them the Registered Tonnage they would be happy with that.
There could be a factor of 2 between those two figures.
Of course there is also 'dry' weight, and 'Tonnage' for registration, which bears no relation to any 'weight' but is a measure of hull volume related to some archaic load capability.
I'm pretty sure that if she floats around her designed waterline, then whatever the designer intended will be fine for the insurance company. I'm equally sure that if you quoted them the Registered Tonnage they would be happy with that.
There could be a factor of 2 between those two figures.
