So it may be just a matter of time before lead keels end up by the way side as copper based bottom paint has?
Iron keel....
- Thread starter NYSail
- Start date
That's not the kind of lubrication this discussion needs.
I'm mostly interested in how each material influences design. For instance, the less dense iron would require a larger keel, or at least a more ballasted one.. That affects the design process since you either need to increase the depth or the amount of iron in it. Or you can reduce the size of the rig to require less ballast. Maybe the boat would need to be more wide for stability. I've noted the greater drafts of the Beneteau's. I always ascribed that to the goal of better upwind performance. Now I wonder if it's also because of the less dense iron.
There are some designs with extremely long, thin keel sections holding a bulb. I'm guessing you wouldn't build those from lead. They have to be iron or even steel. As the keel gets longer the bulb is further from center of buoyancy (Engineers don't kill me here) and the the bulb can actually be smaller reducing the weight of the boat. That's an example of a material's physical properties affecting the design.
The stub is another example. I would expect a designer to use one to lower the center of gravity for the lighter iron keel. But lowering the ballast would work with any material - as long as it stays attached to the boat.
I'm mostly interested in how each material influences design. For instance, the less dense iron would require a larger keel, or at least a more ballasted one.. That affects the design process since you either need to increase the depth or the amount of iron in it. Or you can reduce the size of the rig to require less ballast. Maybe the boat would need to be more wide for stability. I've noted the greater drafts of the Beneteau's. I always ascribed that to the goal of better upwind performance. Now I wonder if it's also because of the less dense iron.
There are some designs with extremely long, thin keel sections holding a bulb. I'm guessing you wouldn't build those from lead. They have to be iron or even steel. As the keel gets longer the bulb is further from center of buoyancy (Engineers don't kill me here) and the the bulb can actually be smaller reducing the weight of the boat. That's an example of a material's physical properties affecting the design.
The stub is another example. I would expect a designer to use one to lower the center of gravity for the lighter iron keel. But lowering the ballast would work with any material - as long as it stays attached to the boat.
Unfortunately, the pictures of boats which suffered from the grid structure being ripped out after a grounding all require an under-water camera. 
Shemandr, That is somewhat true. When a keel is designed, the weight is not the only consideration. The area of the keel (planform) has equal importance as it provides lateral resistance. The combined planform of the keel and rudder and the optimum weight of the ballast go hand in hand. You don't want a keel with such a small planform that it can't sufficiently resist leeway or point well. That's where the advantage of lead come in. For instance, if a designer wanted to design a keel with 15 square feet of keel planform, he/she can use cast iron or lead. If using cast iron, the design weight of the ballast would be adjusted by the shape of the keel foil. (the thickness) A fatter keel foil section would have to be used if the design had to be limited to 15 square feet and meet the design weight and draft requirement. Another option would be to add a bulb which adds wetted surface area and increases drag.
On the other hand, a lead keel with the same planform would allow the designer to lower the center of gravity by designing a stub into the hull structure because less volume is needed to achieve the same weight as a cast iron keel. If a lead bulb of the same proportions as the iron keel was used, the benefits are again helping to lower the center of gravity.
Gunni, Many thousands of boats are sailing today with keel stubs. There have been a small number of problems with boats designed with and without stubs and to my knowledge there is no evidence indicating that one design is structurally better than the other. Lack of maintenance, groundings and poor construction techniques are probably the most likely causes of failure. I respect your choice when selecting a boat but I would not consider the keel material to play a major role in the selection of a boat, (although I do have an obvious preference)
I feel that the build quality, the reputation of the manufacturer and the long term care the boat has received in the past deserve greater consideration. Stuff happens, even to an Oyster. To each their own!
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She The actual concept is "righting moment" and more or less like foot-lbs or a cheater bar, you can use a lot of weight not very deep, or a lot less weight quite deep either will provide the same righting moment. A lot less weight is of course faster. The keel works in conjunction with the beam so a beamy boat provides more form stability and requires less keel weight. The catamaran being the ultimate example of form stability.
The other function the keel provides is lift and like a wing long and thin is more efficient than short and fat. So except for bumping the bottom a long thin keel with the mass concentrated at a bulb is a good deal.
Usually those are stainless steel fins with lead bolted to the bottom. Mars keels website is interesting.
The other function the keel provides is lift and like a wing long and thin is more efficient than short and fat. So except for bumping the bottom a long thin keel with the mass concentrated at a bulb is a good deal.
Usually those are stainless steel fins with lead bolted to the bottom. Mars keels website is interesting.
Man some of you guys are smart! Thanks so much for all the input. I would definitely chose a lead keel if given the option, however above the waterline is also very important. This results in a limited amount of boats when one has to consider a budget. Sounds like keeping an extra eye and a little tlc should suffice when owning an iron keeled boat....... always a give and take.
Greg
Greg
I think we are missing the boat on this discussion. Until the boat heals significantly, the position of the keel weight has little bearing on stability. Most of your stability comes the over all weight of the boat and it lifting out of the water as the boat heels. Depending on how you sail your boat, you may not notice much difference where the weight is.
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Thanks to all inputers!
Well actually the original discussion was about maintenance of a iron keel.... but I do appreciate the education you guys shed on the subject of keels. Amazes me always about the wealth of knowledge in these forums.
Thanks to all inputers!