Displacement & weight

[chappy]

This sounds like a pretty dumb thing to say, but i am going to say it anyway!!!! /forums/images/graemlins/blush.gif.
Is a displacement of a boat mean the weight of the boat or is it something else.
If it is something else then what does displacement mean, & does anyone know how heavy a jaguar 27 is & also the displacement they have.
Cheers.
Dave.

 

[boatmike]

Basically yes. The displacement is the weight of water the boat "displaces" which is equal to its weight.

 

[Swagman]

The displacement of a Jaguar 27 is 2540 kgs or 5600 lbs.
Cheers
JOHN

 

[chappy]

Thanks boatmike, & swagman.
So if my boat displaces 5600ibs will this also be the weight of the boat ?

 

[Appleyard]

On the same subject,what is Thames Tonnage? and why is it different from displacement?

 

[boatmike]

Re: Displacement & weight

Yes!

 

[boatmike]

Re: Displacement & weight

Thames Tonnage is complicated but is was originally as I understand it the measure of how much cargo a vessel could contain based on measurement of the hull (I think!) Nowt to do with displacement or weight of the vessel itself.....

 

[Swagman]

Yes, BoatMike has already confirmed your displacement is your wieght.

If you recall Archimedes in his bath it may help.

Imagine a swimming pool full to the brim with water at sea level.
Slide your boat in and then were you to capture all the water it DISPLACES from the pool and weigh it - then that's the same as the weight of the yacht.
If the yacht were heavier it would diplace more water - if it were lighter it would displace less.

Fill the pool with murcury - and do the same - and you'd get the same result. The volume of the murcury displaced would be a lot less - but its weight would be the same as the boat - or the water it displaced above.

On my part have absolutely no idea of the basis for Thames Tonnage so will leave that to others to clarify to all............

 

[ashanta]

Re: Displacement & weight

This is laden weight as if you were a load carrying vessel. My boat weighs/displaces 3.5 tonnes but the Thames weight was 6 tonnes on my registration.

Regards.

peter.

 

[boatmike]

Re: Displacement & weight

Sounds about right. Assumes your "hold" is full of coal I think!
Actually thats why its complicated. Its based as I understand it on volume. You could fill your hold with feathers or lead.... I think originally it was a measure of the laden weight of a Thames barge based on a given cargo. Ought to know I suppose as Grandad was a Thames Lighterman, but I don't.... Anyone else know how its calculated?

 

[BrendanS]

Re: Displacement & weight

I've been told it was originally derived from estimating the number of 'tun' barrels of wine a ship could carry. No proof that is correct though

The formula for calculating Thames Tonnage is on this thread
http://www.ybw.com/forums/showflat.php/Cat/0/Board/ym/Number/460373/an/0/page/27/view/collapsed/

 

[snowleopard]

Re: Displacement & weight

displacement figures may be quoted by the manufacturer as 'dry' - empty tanks, no stores or crew. others may quote it on the basis of an assumed load.

the only true measure of displacement is the actual weight when you're sailing but that can be a difficult thing to determine. if you get the boat craned out, the driver may be able to tell you the weight, then you need to add the weight of crew and anything else that's not on board when it's being lifted.

 

[Guest]

The reason for the name ...

Displacement is so named because weight of ships is calculated by the volume x density of water displaced when they lie afloat.

Archimedes bathtime brought the revelation that for an article to float - it must reach equilibrium by the act of displacing its own weight in water.

 

[Shantyman]

Re: The reason for the name ...

Thames tonnage was a fomula which included length and beam but bore no accurate relationship to the actual weight (Displacement!) of the vessel.

I have book somewhere with the exact formula. will post it later if I can find it!

I dooooon't think it had any connection with barges.

Regards

Shantyman.

 

[tsmyth]

Re: The reason for the name ...

Why has no one advised Chappy now to run down the street naked crying "Eureka"?

Ray

 

[boatmike]

Re: The reason for the name ...

Possibly not a pretty sight......

 

[alan]

Re: Displacement & weight

So, in Spring when all the boats that have been hauled out for the winter are put back in the water, can we expect the level of the sea to rise by a few millimetres ???????????????? I am concerned as I live only a few hundred metres from the beach ...............

 

[oldharry]

Re: Displacement & weight

As others have said, the displacement is effectively the weight of the boat. BUT, the manufacturers quoted displacement figure is very rarely the true dispalcement. The quoted figure is the weight of the hull as it comes out of the builders workshop, and will not include all the extra fixtures and fittings - toilet, cooker, gas bottle, electronics, quite often not even the engine, water and fuel, not to mention all your personal gear, life jackets clothes, bedding, inflatable, cabin mattresses, etc etc.... I have even seen figures quoted which did not include the sails and rigging! It does not allow either for water absorption in the hull after a season or more afloat.

So if the all up weight matters - i.e. if you are planning to tow it home behind the Land Rover (if so dont forget the weight of the trailer as well!) you will find the actual weight of the boat is considerably more on the tow hook than the quoted 'dispalcement' figure. If the outfit is near the towing limits, it is well worth taking it to a local public weighbridge and checking it - which is what the Police will do if they think you are overloaded. By that time its too late to avoid extra costs (fines etc), and in a severe case they can put a 'stop order' and refuse to allow you to continue your journey. It then gets very expensive as you hire in alternative heavy transport to get the boat home!

 

[chappy]

Re: The reason for the name ...

[ QUOTE ]
Possibly not a pretty sight......

[/ QUOTE ]
quite true /forums/images/graemlins/grin.gif

 

[jfm]

Swagman that's true, except the swimming pool need not be at sea level, it can be on the top of Everest or on the moon. The weight of the displaced water will still equal the weight of the yacht