Log in
Article search:

Q & A

ballast

when we fitted out our narrowboat we was told although not an exact method 1 ton should lower 1 inch.we are now considering a dutch style barge at 60'x 12'is there a rough guide for this size as a feel being wider than a narrowboat it can't be the same method

Asked by: mick turner  | 12.19pm, Wednesday 7 April


WW says:

1 ton will approximately lower a 70ft narrowboat by 1 inch, but it is definately not an exact science, unless you know exactly the shape of your hull!
It is far easier to work in metric for the calculations...
1 Ton is 1016kg about, so it is easier to think about metric ton of 1000kg. If you add 1 tonne to anything to a boat, it will lower the boat by a volume which displaces an equal mass of water.
Water is 1000kg per cubic metre.
Therefore, on a 70ft boat, 1000kg will, assuming swims of around 15ft each end, lower the boat by around 3cm (just over an inch).
If you treat each swim as an approximate triangle, you can then calculate the approximate surface area of your boat, in metres squared. If you then divide 1/area, it will give you the approximate amount the boat will be lowered (which is volume [of water for 1 tonne] divided by the surface area to give you the depth...)
So, this means that, for a 60ft by 12ft boat, each tonne (1000kg) of ballast should lower the boat by around 2cm (0.02m).
Hope that makes sense!

Mark Langley  | 6.30PM, Monday 19 April


Readers say:

thanks mark for me it makes sense as maths was an easy subject so i should be able to get a rough idea

mick turner  | 6.51PM, Wednesday 21 April

You must log in to post an answer.