Why do Kraken Yachts use lead for ballast?
In the pursuit of safety at sea, Kraken is including many important and expensive features as standard in its new range of blue water cruisers; and all within its competitive standard prices.
One of our major (and costly) decisions has been to use lead – not cast iron - for the Kraken 50 ft yacht's ballast.
As many boat buyers will have noticed, ever more large production yachts are now sold with an iron rather than a lead keel. This is done for one very simple reason.
It saves the builder loads of money. Cast iron is far cheaper than lead.
But against lead’s higher cost, one must balance the fact that it is much more effective. In every respect.
Consider weight and volume. Put simply, 1000kg of cast iron takes up 0.137 cu.m; while 1,000kg of lead takes up 0.090 cu.m. IE 35% less.
If you find imperial volumes easier, 1,000 kg of cast iron takes up 4.83 cu.ft. This compares to only 3.178 cu.ft. for the same weight of lead. In other words a tonne of lead is 1.652 cu.ft. ‘smaller’ than a tonne of cast iron. You may be surprised that 1.652 cu.ft. holds almost exactly 12 (Imp) gallons of fresh water!
Now multiply these figures by 6.3 (the Kraken 50’s Zero Keel ™ weighs approx 6,300 kg) and you can see that an iron keel is far ‘bigger’ than a lead one of the same weight... before the iron starts to rust!
More important still, the much higher volume of iron adds displacement to the yacht. As a famous Dutch designer once said “I don’t like iron keels. Compared to lead, iron floats.”
This may seem a strange thing to say. But he’s right.
Although a boat with an iron keel weighs the same as it would with a lead keel of the same weight, it displaces much more...because of iron’s greater volume. So the boat rises out of the water as a result. Kraken designer Kevin Dibley agrees with another prominent designer who says that “the reduction in waterline beam (BWL) and the extra buoyancy low down in the more voluminous iron keel combine to make the boat more 'wobbly' (i.e. less stable).”
The less voluminous lead keel also has less wetted surface area than an iron one of the same weight - whether it’s bolted to the yacht’s bottom or contained within a sleek bulb that is an integral part of the hull. Reduced volume reduces wetted surface area (and thus skin friction) - which increases speed through the water. As Kevin Dibley summarises “drag is reduced, thus increasing performance.”
Fitting a cast iron keel to a performance blue water cruiser is a major false economy.
If you combine lead’s advantages of reduced wetted surface area (i.e. extra speed) and lower displacement (i.e. extra stability), it’s easy to see why the best yachts - be they hot racers or high quality, safe and stable blue water cruisers - always have lead keels. Lead costs a lot more than iron, but it’s worth every extra buck.