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Ballast

can you tell me how to work out how much ballast I will need for a 50 by 10 wide beam narrow boat

Asked by: Chris  | 2.09pm, Saturday 10 May


WW says:

This depends on a number of things - not least, the intended draught of the boat. As a rule of thumb, a 70ft x 7ft boat is reckoned to be 1in lower in the water for every tonne of ballast that is added. You boat has approximately the same area so the same rule should apply.
Another variable is the weight of the fit-out. If you are planning an open layout with some fairly light freestanding furniture, you will need more ballast than if you have lots of heavier built-in furniture and large tanks.
Assuming you are fitting the boat out yourself, the best approach is to ballast the boat so that it is sitting 2 to 4in high in the water. Arrange the floor boarding so that any board that does not have a permanent fitting like a galley unit or a fixed bed over it can be lifted. When you have finished the fit out, you can then add or remove ballast to achieve the desired draught and get it sitting level.
Having removable floor boarding has the further advantage that you can gain access to the bilge to mop up major spills that always seem to occur at some time in the boat's life.
The most common form of ballast is concrete paving slabs. These are cheap but the are difficult to move about and fit into tight corners. They also absorb a certain amount of moisture. Engineering bricks are more expensive but they are denser, much easier to lay and more resistant to moisture.
Personally, I would avoid the common practice of laying the ballast on building felt. This is done to protect the base plate from being scratched by mobile ballast. The problem is that, if you do get a spillage, the moisture under the felt takes much longer to dry out. If you are concerned about scratches, a layer of Waxoyl on the base plate and some careful placing of the bricks so that they can't move around too much should do the trick.

Graham Booth  | 3.05PM, Saturday 10 May

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