I think that there are a lot of very practical reasons why Bilge Keels (twin Keels) make sense, but none of them have much to do with sailing ability. Which is not to say, that it is not possible to design a very workable bilge keel design, which will offer reasonable performance, shallower draft and so on, but twin keels generally require taking a hit on performance as compared to the same hull and rig with a deeper draft fin keel. The reality is that by necessity, bilge keels with a shallower draft will have end up with some trade off of greater displacement (since more ballast is required to achieve the same vertical center of gravity), less stability, and/or more drag (more wetted surface and frontal area).
In theory you can try to optimize the configuration of the bilge keels to produce the best performance possible, but you can also do the same thing with a deeper fin keel, so it becomes something an arms race with the deeper fin wining in term of performance at any level of optimization.
Similarly, a deeper fin keel of equal stability and weight to a particular bilge keel design would also tend to have a better motion comfort since its deeper draft would generate a higher roll moment of inertia and better dampening.
But in a broad general sense, cruising boats are rarely optimized for out and out performance. Instead they are optimized for the practical requirements of their purpose, which means greater carrying capacity, simplicity, and robustness than would appropriate for a goal of simply going as fast as a boat possibly can. In that vein, bilge keels might be seen as simply another worthwhile compromise in performance for cruising practicality.
I don't know where you read that bilge keels are becoming more popular in the U.S. but I personally don't believe that bilge keel boats are becoming more popular around here. If anything I would suggest that they are a very hard sell here on the U.S. Atlantic Coast and so would probably take a bigger depreciation hit at resale time. That said, they may be a cult boat that holds their value since so few models are available on the market.
My own personal concern with bilge keels and the reason that I personally would not buy one for myself, is is similar to my concern with wing keels. In my experience when you accidentally run either aground, it is far harder to get free. An argument might be be made that a shallower draft boat is less likely to run aground as frequently, and that arguement may have merit for some people, but it does not work acceptably well for my own personal preferences.
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Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay and part-time purveyor of marine supplies
Last edited by Jeff_H; 02-09-2012 at 03:57 PM.