Amel SM - Bolted on keel?

[rslifkin]

Originally Posted by Manateeman

They actually feel sorry for owners of bolt on keel boats who have no idea that bumping the bottom might wipe out their cruising budget.
You need not loose the keel to sink.

As an interesting point, the only fin keel boat I've personally known to be written off in a grounding (38-ish foot Tartan, but can't remember which model) didn't lose the keel. It actually peeled the hull apart slightly at the front of the keel and pushed the aft end of the keel up into the hull. The boat made it into port unassisted (fairly short trip), but insurance wrote it off.



In other words, the keel attachment was fine, but the hull itself failed due to the amount of force involved (6+ kts into an immovable rock). A different keel type would likely have suffered different damage, but unless you repeated the experiment with a substantially stronger boat, the damage would still have been severe.

[Wings888]

If you're going to limit yourself to encapsulated you'll not have much to choose from. As pointed out, failures are usually from previous damage. Access to the keel bolts for inspection IS something to consider. One of my boats had the engine over the bolts. It had to come out to properly inspect/tighten the bolts after a grounding. $$$ Our current French boat has bolts that can be backed out for inspection and replaced if needed.

[Bowdrie]

Originally Posted by PerfectPirate

The bolt-on keels from that era were structured differently from modern-day mass-production boats. Instead of presenting a rounded, fairly flat bottom onto which a rigid cast-iron structure is bolted, those past builders actually went through the more labour- and cost-intensive process of moulding a hull with a proper bilge and a keel stub projecting down from the bottom of the boat. Even with the more modern-looking bottom profiles, such as on a CS-30, there is a moulded keel stub. These stubs were laid up with reinforced fiberglass cross-sections much thicker than the rest of the hull and further reinforced with Lyasil bundles (or similar material) at the points where keel bolts came through. This is a much more robust structure that the vaunted internal grids used by modern mass manufacturers. In the event of a grounding, the shock load is carried through the entire hull/keel flange and then distributed through the entire hull, as opposed to severe point-loading of the hull at the front or back of the keel casting, which is what happens when you bond a narrow rigid component (the keel) to a flat section of a flexible component (the fiberglass bottom).

So true, and quite germane to any discussion of keels.
I might also add that the "old style" structures were much more likely to use a defined "ballast keel" that was bolted on, (look at an early S&S Swan, the bolted-on keel is similar to a wood boat of the period,) rather than something more akin to a wide helicopter blade that's hung under the "canoe body" of the hull.