Ballast weight

[Geoff SleathParticipant @geoffsleath41411]

I've been musing on how much lead I'll need to ballast my 1100mm waterline length sailing barge. At a rough estimate, the volume needed to be submerged is about 7,360 ccs which converts to7.36kg. So the all up weight of the boat needs to be 7.36kg too.

Am I right in assuming that if I weigh the completed boat (including rig,battery and all other components), less ballast then the weight needed on the end of the keel will be the difference between that and 7.36kg?

My estimate is based on the beam at the centre (23cm), the depth below the waterline at the centre (4cm) and a guesstimated allowance for the reduced beam at bow and stern (80cm). Obviously the last figure isn't very accurate but I don't think it's hugely in error as the hull is quite boxy with a blunt bow.

btw we had our bath removed and replaced with a shower cubicle last year so I don't have a convenient test tank

Geoff

Edited By Geoff Sleath on 06/11/2014 14:37:57

[Geoff SleathParticipant @geoffsleath41411]

[Amy jane SeptemberParticipant @amyjaneseptember49770]

Hi Geoff.

With out being able to float test, then you'll not have much choice but to go with you calculations. Your reasoning seems sound to me, though as you say the hull is fairly box like, so a reasonable guess at end volumes will suffice. May I suggest that you make the keel removable, and the bulb a little over sized, and then saw /shave a bit off once you get to the pond?

Aj

[Geoff SleathParticipant @geoffsleath41411]

Thanks, Aj

It was back to 2nd form physics with Archemedes and I did that back in 1952 What did surprise me was just how heavy the barge needed to be to satisfy its waterline depth. The hull shell is pretty light so far (770gms) but there's lots of gubbins to be installed yet.

Geoff

[BanjomanParticipant @banjoman]

If you nevertheless want to check your calculations against reality by doing a flotation test once the basic hull is water tight, you might perhaps set the ol' Bambi eyes to work their magic on a family member, friend or neighbour who is still in possession of a bathtub?!

/Mattias

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