Weight / Displacement / Ballast ... I'm confused!

[fastjedi]

Weight / Displacement / Ballast ... I\'m confused!

Silly question? .... well maybe

My Trailer Sailer is quoted as having a 'displacement' of 550kg and 'ballast' of 200kg (Cast iron lifting keel)

So how heavy is this thing I am towing around with my Fiat Panda (only joking)

Yacht, keel, spars, sails etc (not inc trailer)

a/ 550kg
b/ 750kg
c/ 750kg +mast, boom, sails
d/ non of the above!



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[VicS]

Re: Weight / Displacement / Ballast ... I\'m confused!

a/ 550kg

But strictly speaking kgs are units of mass, not wieght.

Weights should be expressed in newtons. On the surface of the Earth a mass of 1kg has a weight of approx 10 N

<hr width=100% size=1><font color=purple>Ne te confundant illegitimi.</font color=purple>

 

[Robin]

Re: Weight / Displacement / Ballast ... I\'m confused!

550kg plus the gear, outboard, fuel, water, mouldy sandwiches, beer cans etc

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[fastjedi]

Re: Weight / Displacement / Ballast ... I\'m confused!

Damn! the beer, I forgot about that .... isn't that an essential part of the yacht and therefore included in the 550kg?

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[peterb]

Re: Weight / Displacement / Ballast ... I\'m confused!

In the SI system of units mass is reckoned in kilograms. The Newton is a measure of force; that force required to give a mass of 1 kg an acceleration of 1 metre per second squared. As a result, under the Earth's gravitational pull a mass of 1 kg has a weight of about 9.81 Newtons.

Mind you, I've always thought that it was the wrong way round. Everyone knew about force pre-Newton; Newton worked out the relationship between acceleration, mass and force, so in effect he discovered mass. And it's a bit silly having a base unit (the kilogram) which is defined as a thousand times another unit (the gram)!

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[Althorne]

Re: Weight / Displacement / Ballast ... I\'m confused!

Just to add even more confusion I thought that displacement figures discribed the amount of water diplaced by the hull while in the water. Therefore the 550kgs talked about is totally irrellevent for trailing???????

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[BrendanS]

Re: Weight / Displacement / Ballast ... I\'m confused!

Either contact builder, or if they are no longer around, simply tow the whole lot to a public weigh station and have the whole rig, including trailer weighed, then no doubt at all about total including stuff on board

<hr width=100% size=1>There is no such thing as "fun for the whole family."

 

[MainlySteam]

Re: Weight / Displacement / Ballast ... I\'m confused!

By Archimedes the boat will displace its own weight of water (as long as it floats), so if you know its displacement then that is the weight you have to tow.

John

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[john_morris_uk]

Re: Weight / Displacement / Ballast ... I\'m confused!

Displacement and how much it weighs are same! Nuff said. However, boats always weigh (and displace) more than the builders claimed displacement figure! If you stripped absolutely everything out you might approach it. Last time my Sigma was weighed she was 500kg heavier than the builders plate says she is! (Hadn't emptied the fuel and water tanks, removed the dinghy, outboard..... etc etc)

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[charles_reed]

Re: Weight / Displacement / Ballast ... I\'m confused!

Weight of boat without gear = Displacement
Ballast = weight in keel and therefore the righting moment

No cruising boat is ever down its design displacement, I'd suggest adding a guesstimated 250kg for gear and another 500kg for the trailer, which gives your Panda about 1300 kg to drag around. You could always make sure by using a public weighbridge.

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[Guest]

Re: Weight / Displacement / Ballast ... I\'m confused!

Weight is anything you want to weigh .... has no real term in this context. Is also mass subject to gravity.

Displacement is the 'weight' of water displaced by the vessel when fully afloat and free of influences. This equates to the actual weight of all on the vessel and its own weight combined. There are various designations but these are for draft marked commercail vessels not yachts.

Ballast is any form of weighted material added to a vessel to increase stability and righting moments, can be in any form suitable such as water, concrete, lead, iron ingots etc.

In your case the diplacement is the builders weight on delivery as ex works and is usually well below that experienced on commisioned boat. The only way to ascertain correct overal weight is to use a Local Authority / Weights and Measures Weighbridge ... weigh trailer and then trailer + boat .... difference being boat !

Draft calculation of weight would involve considerable mathematics and boolean so is in practical terms out of the question.


<hr width=100% size=1>Nigel ...
So WHAT does the EU really stand for ????/forums/images/icons/cool.gif

 

[MainlySteam]

Re: Weight / Displacement / Ballast ... I\'m confused!

<<<Weight of boat without gear = Displacement>>>

I think Nigel has alluded to this being an incorrect statement. Displacement actually includes the vessel and everything in/on it including the crew. It is typically qualified by a condition describing the payload.

The builder of a production boat will know the displacement (weight) with no payload, typical for the boats he produces. Production boats with a non homogeneous structure, such as fibreglass ones, can, however, vary quite alot from boat to boat depending on, for example, the amount of resin, etc they managed or did not manage to roll into the cloth for the particular vessel.

As Nigel and Brendan at least have said, the best way is to weigh the boat on a weighbridge.

John


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[charles_reed]

Re: Weight / Displacement / Ballast ... I\'m confused!

or, more properly, as a litre of pure water at NTP.

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