I'm not aware of a difference in shaping of iron vs. lead keels. Please elaborate. How does shape relate to physical properties of the metal or method of fabrication? I assume both are cast.
Iron is cheaper than lead. Keels are all cast regardless of which material so it's a price choice manufacturers make without regard to us. Also, because it's more dense, lead is a more effective ballast
This is the kind of thing you say when you don't understand how boats are made to go faster.
My understanding is that Beneteau is pretty open about the fact that they use iron so that they can deliver the boats at a certain price point. I agree with your points about iron providing more strength than lead, and that can help for some of the lifting surfaces, but for ballast lead is the higher performance option.
Actually Tungsten is much heavier than gold or lead. Its also super expensive. I've always been curious why they don't make a shell out of stainless sheet metal and back fill it with lead. That would give zero maintenance.
Gunni, I'm have to differ with you here. Keels, whether cast in lead or iron, don't come out of their mold perfectly fair. As they cool they can distort and shrink. If templating a keel for perfect shape is important to an owner/racer, it is much easier to tweak a lead keel that is too plump by removing material in some parts than it is to tweak an iron keel. I agree with you that lead is not as strong as iron in thin areas like the trailing edge of a keel, however, great strength isn't needed there. For performance purposes, the trailing edge of a keel should not be sharp. The preferred shape should be a blunt, squared off edge. This goes for rudders also. For a 42' boat, the trailing edge should probably be about of 1/4" or less in width.
Ted, I will refer you back up to the photo in post #4 - does it look like the designer had any problem creating a slim foil section or achieving the required ballast with iron? Modern boat design and manufacturing techniques have made it possible to build properly ballasted iron keel boats that point very well and at a price which results in more boat for the owner. That is likely why NYSail is shopping for a boat that has an iron keel rather than a lead keel - he sees which choice gives him more boat.
In AAs like this, it seems obvious that such comments reflect the flaw and cheaper production practice of using iron which has no effect on speed but can negatively affect performance because of the lighter keel weight.
Gunni, I think that you may have misunderstood what I was trying to illustrate. Pouring a keel using cast iron or lead is not the issue. Both materials can be used to make any desired keel foil shape. The point I was making was that if you compared two identical shaped keels that weighed the same, the lead keel will have a noticeably lower center of gravity. As we know, lead is denser than iron and therefore less is needed to achieve the required weight that the designer intended. To maintain the identical planform of the two keels, the designer of a lead keel boat would provide a fiberglass stub moulded into the hull which is the shape of the upper portion of the keel ballast where they mate. Because the stub is lighter than the ballast, the ballast is lower in the keel and therefore the center of gravity is lower. There is no way to achieve this with cast iron when comparing two identical keel shapes. It's not about designing a keel with the proper amount of ballast, it's about doing it with less surface area and a lower center of gravity, both of which are performance boosters. The lower density of cast iron makes it impossible to achieve the same righting moment as an identically shaped lead keel.
All boats are a compromise. Hope you find a well maintained boat without issues.
Oh, not keel stubs, sorry, I wouldn't own a boat with a keel stub. I 'm real glad that my keel bolts directly to the structural grid of the hull, not a molded fiberglass appendage of unknown strength. The construction is complex, and prone to design and construction error. Why, to get the ballast a little lower?
