It's a Question of Design
The nature of our canal network is such that canals average from 3 to 5 feet in depth. That’s one of the restricting factors on how low our canal boats can sit in the water. The other factor is the design of the hull itself.
In order to maximise load capacity, a canal boat is like a long rectangular box. The restricted depth of water means no keel is fitted for stability & somehow there needs to be a clean flow of water along the hull to the propeller.
Therefore at the back of the boat, underwater, the hull is shaped to a point and this section of the boat is known as the swim.
The top plate of the swim, parallel to where we stand and steer, is known as the uxter plate. It is necessary for this uxter plate to be 1 to 2 inches underwater to prevent propeller ventilation. Ventilation
is where the prop can draw air in around itself causing noise and poor steering.
And therefore we need canal boat ballast
to keep the boat stable in the water.
Stability and Safety
It is vital that any canal boat ballast
is fitted with a focus on final stability and safety.
There are regulations enforced on Commercial BSS examination
s concerning the height of deck drains, weed hatch and skin fittings above the waterline, while it is not a requirement on Private Craft BSS Examinations it is very much worth while considering and following these regulations.
There are stability and safety parameters determined by the Recreational Craft Directive so if you are at all unsure of any of these areas discuss them at length with your canal boat shell builder
or BSS examiner
. This section is intended to be a guide only, giving an overview of the canal boat ballast
Where is the Ballast
Ballast is fitted into the shell directly onto the bottom plate. It is standard practice to lay the canal boat ballast
on top of a non absorbent layer to separate it from the steel of the hull. If an air space can be incorporated between the canal boat ballast
& the bottom plate, even better & this can be achieved by laying the canal boat ballast
onto a non reactive spacer material such as large plastic tile spacers.
Treat the bottom plate with a thick layer of bilge paint or similar which further protects the steel from any condensation water or future leaks. It is worth it at this stage. Once the canal boat ballast
is in, it will be a very long time, if at all, until the inside of the plate is exposed so treat it now & forget about it!
Types of Ballast
Different types of canal boat ballast
are available, the most common of which are concrete pavers or engineering bricks.
Any material such as this should be as dense as possible to prevent soaking up any moisture that may get into the bilges. For example, a standard house brick is designed to absorb water in order to ensure a good bond with a wet mortar. Some of these varieties can have a 20%-30% water absorption rating.
A class A engineering brick is designed to be dense and strong and must have a rating of less than 4.5% water absorption by mass. This would be the obvious choice.
Other types of canal boat ballast
include iron ingots & lead weights.
Any metal canal boat ballast
should be protected from contact with the steel of the base plate to avoid galvanic corrosion.
Also ensure that canal boat ballast
is well secured from moving around, especially when laid in areas that will be inaccessible in the future. A clout into a bank or lock side could permanently affect the way the boat sits & handles if the canal boat ballast
Leave allowance for the positioning of heavy items such as waste tanks and iron stoves. A common rule of thumb is to ballast the boat two thirds to the bow, one third to the stern. A pivot point will be created relative to the ratio of ballast front and rear around which the boat will turn. Remember there is a heavy lump of iron in the boat at the stern in the form of the engine & its components. Batteries, calorifier
, heating system and stern gear all add weight to this area.
Consider a heavier bottom plate. 12mm or 15mm plate will be heavier than 10mm and call for less canal boat ballast
. If considering this, talk to your builder and use his experience.
Finally, accept there will be some fine tuning at a later date. Plan for access into the bilges so you can see whats going on in terms of moisture and consider fitting an automatic pump into the cabin bilge area, at the lowest point, just in case. A good place for this would be on the cabin side of the steel engine bay bulkhead as most boats will be trimmed with a slightly bow up attitude.