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post #6 of Old 09-06-2002
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What is the difference between a coastal crusier and a bay b

Good question. You have to look at how an encapsulated keel is constructed. In most cases that I have encountered, the laminate for the hull of the boat is continued downward into the keel area so that there is a sharp turn in the laminate at the point that the hull turns down into the keel. In properly engineered bolt on keel there are heavy tranverse frames at the top of the keel that distribute the loads outward into the hull. In the case of the daggerboard scabboard the scabboard is glassed in at the hull and deck creating a large lever arm. But in the case of most encapsulated keels there is very little framing involved. The loads are being applied perpendicular to the comparatively thin skin of the hull. This results in more flexure and that flexure can result in fatigue over time. It can also pry the sides of the encapsulation and waterproof membrane at the top of the keel loose from the ballast keel.

In an encapsulated keel, the watertight membrane is below the ballast keel where it can be exposed to the full impact and abrassion of rock or coral. Generally above the ballast keel there is a thin membrane that simply keeps bilge water out of the ballast cavity. In a bolt-on keel the hull passes across the top of the keel so that the watertight membrane is not exposed to the actual impact with coral or rock.

The laminated keel itself is difficult to layup well as the yard crew is forced to work in the narrow confines of the keel cavity. In my experience trying to repair encapsulated keels the glass work at the bottom of the keel is often quite thick but very poorly laminated. Big voids, unwetted out cloth and unreinforced lenses or resin are quite common. Placing the ballast so that it is properly adhered to the sides of the ecapsulation is quite trickly. Last year when this was discussed I believe that we found by walking through boat yards and tapping on keels that somewhere between 25% and something less than 50% of encapsulated keels had voids between the encapsulation and the ballast keels.

What this means in a hard grounding is that the skin is more easily pierced in an encapsulated keel, there is less to resist the ballast keel from being forced upward and once forced upward the boat has damage that is next to imposible to to repair. I have cited as an example my family''s Pearson Vanguard that clipped a rock at 4 knots which was enough to crush the encapsulation and drive the ballast up through the water proof membrane and dislodge the tank above.

With a Daggerboard a well engineered scabboard has a hard rubber crush block that absorbs much of the force of an impact rather than distributing the impact loads into the hull. Again the water tight membrane is not exposed on impact.

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