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[Brian60]

Is it as simple as working out the (in our case not full size measurements) square centimetres of the hull to waterline depth ie, 300Lcm x 14Wcm x 6Dcm to waterline and then converting to kilo's to get ballast weight figure (Archimedes Principle) Or do you do the full hull to deck level?

[inertia]

Brian
Waterline.
Only the water below this level is displaced and so falls within Archimedes' definition and the consequent calculation.
(BTW Just in case any of the forum rivet counters are awake on a Sunday afternoon you'll find that volume is cubic centimetres. Square 'uns is area.  )
DM

[Netleyned]

Easy enough with a square box but working out the volume of a hull ain't so easy.
Best fill the hull with water to the waterline , pour into a measuring jug and you have the
volume. Can also be weighed.


Ned

[Colin Bishop]

 If you have an accurate scale model and know the displacement of the original ship you can simply scale down the displacement from the original - yes it does work! If not then you can get an approximate idea by applying a block coefficient to the hull and using that.
Block coefficients were discussed on this topic a while back.

http://www.modelboatmayhem.co.uk/forum/index.php/topic,8708.0/nowap.html

Colin

[Buccaneer]

I use a conversion factor of about 0.6 or 0.7, depending upon how much of the 'block hull' is missing around the bows and stern. I.e. Length x Beam x Depth to waterline x Conversion Factor. This works out pretty well for a guideline figure on something you are thinking of buying. For a new hull I do the same as Ned. Mark the waterline on the inside of the hull first and jack the hull up if required. 1 Litre of water equals 1 Kg displacement.

John

[Shipmate60]

If the hull is complete float in water and ballast till the water line is at water level.
Take out ballast and weigh it (including hull).


Bob

[ballastanksian]

The Royal navy used the block coefficient for a long time so it is pretty standard. Modern drawing programs can work out internal area once drawn if you are designing from scratch.

[Brian60]

Brian
Waterline.
Only the water below this level is displaced and so falls within Archimedes' definition and the consequent calculation.
(BTW Just in case any of the forum rivet counters are awake on a Sunday afternoon you'll find that volume is cubic centimetres. Square 'uns is area.  )
DM

Thanks Dave My Bad, it should of course have been cubes not squares

Easy enough with a square box but working out the volume of a hull ain't so easy.
Best fill the hull with water to the waterline , pour into a measuring jug and you have the
volume. Can also be weighed.


Ned

I'm going with the square box method to do my working out, measuring jug for volume is a no go as it is a double hull I am building and once the outside hull is added (inner hull built first) there will be no way to access the space for ballast, so its going in before the outer hull is glued into place.

[Colin Bishop]

Don't put it all in. You are bound to need some for final trimming purposes.

Colin

[Brian60]

Don't put it all in. You are bound to need some for final trimming purposes.

Colin

No Colin, I'll leave it a kilo or so short, using the above method I only need 8 kilo's. I think the way I am constructing this build might surprise some people once I start a build log.

[spooksgone]

I fill the hull up to the water line, on a level surface, with water, using a measuring jug. one litre of water weighs a kilo. This should tell me what the finished model will weigh.

[Popeye]

If the hull is complete float in water and ballast till the water line is at water level.
Take out ballast and weigh it (including hull).


Bob

I've tried various methods but have settled on this one coz it's easy and very accurate (first ensuring that the bare hull is waterproof).

[derekwarner]

 ,,..//.... there are many ways to complicate this


1/2 fill the bath wiht coldish water
add 20 gms of talcuim powder
add 100 mls of water based blackish paint
immerse the hool to the wafter line
remove the hool from the bath
accurately measure the newish wafter line created by the scum of the talcium powder on the black slime paint on the bath
record all of these measurements & e-imensions quickly before your good wife wants a bath 

its OK..........just blame me .... Derek

[Netleyned]

Do you have to waft the hool about?


Ned

[Popeye]

,,..//.... there are many ways to complicate this


1/2 fill the bath wiht coldish water
add 20 gms of talcuim powder
add 100 mls of water based blackish paint
immerse the hool to the wafter line
remove the hool from the bath
accurately measure the newish wafter line created by the scum of the talcium powder on the black slime paint on the bath
record all of these measurements & e-imensions quickly before your good wife wants a bath 

its OK..........just blame me .... Derek

Decisions decisions, life's full of decisions, though personally I'm a firm believer  in the KISS principle----Keep It Simple Stupid.

[derekwarner]

So Ned asks...."Do you have to waft the hool about? "

Wheel, the simpule answer is.....yes...the wafting allows the water based blackish  paint to 'adbsorb' a smallish % of the talcuim powder..so it dosnenen't leave powerdie marks on the new hool wafterline...............[or for the good wife to complain about as being on the inside of her bath tub....]

My response to Popeye is ssoooooooooooooo simple & need not be printed  :......... .....Derek