What is the difference between a coastal crusier and a bay b
I agree that we can throw around anecdotal info all day long and not prove anything. BUT there actually has been a tremendous amount of work done on composites and the loadings imparted into various parts of a boats hull. This research has been performed for a wide range of reasons from military, to EU and Insurance standards, to various racing campaigns. With the ability to instrument full size boats and measure real loads there is an enormous amount of data becoming available. I disagree that" Only an extensive statistical analysis, or full-scale, carefully controlled tests will conclusively prove which underbody type is inherently safer, and then only for the exact configuration actually tested." As research is providing more precise information on strengths of materials and loadings felt by individual components of a vessel, it is not all that hard to actually calculate the loads imparted into a keel. Byond that there is a large sampling of boats out there of both types of construction. In talking to a fairly large number yacht designers and surveyors who see alot of both kinds of keels after the extreme impacts I''ve concluded this about encapslated vs external ballast:
What seems obvious is that properly engineered and constructed either encapsolated ballast or external ballast can work adequately in most grounding situations. Both can in fact be designed to withstand very extreme groundings. The problem is that few production boats are engineered as well as they should be if one of the prime design criteria is to withstand an extreme grounding and survive. Usually the prime design criteria includes a lot of issues such as budget, performance, ease of construction and so extreme grounding resistance becomes a bit more secondary.
To touch on some of the other points, for an equal keel shape and equal ballast, an external ballast keel should have a deeper more voluminous bilge than an encapsulated keel because the ballast occupies the volume of the encapsulation. The nice thing about externally ballasted boats is that they can usually be repaired to their original condition. The same cannot be said for encapsulated ballast boats.
In my experience I have not encountered an externally ballasted keel that can''t withstand substantially more than a 4 knot grounding. I have been aboard quite a few boats with externally ballasted keels that have run aground at pretty high speeds (in quite a few cases approaching 6 to 7 knots)and in each case the boats have come through with little more than superficial damage to the ballast (mushroomed lead in the case of rocks). That has not been the case in encapsolted keel boats.
In the most extreme case that I know of an externally ballasted Contessa 33 was dropped from a crane while being offloaded as deck cargo from a ship. While there was clearly damage to the internal framing, it was a pretty straight forward repair that is still intact and invisible after 15 years pretty hard years of useage. But of course that''s just another set of anecdotes.