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post #37 of Old 06-01-2019
Jeff_H
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Re: Looking to purchase- advice

Quote:
Originally Posted by john61ct View Post
Encapsulated keel without any bolts at all even better no?
No.... while bolt on keels require maintenance over their life span, they can be maintained pretty much forever. The problem with the way that most encapsulated keels are constructed, they count heavily on the bond between the ballast keel and the encapsulation envelope. Over time that bond breaks down and when it does the forces increase where the the hull turns down into the sump of the keel.

In a bolt on keel, by necessity, those forces are resisted by transverse framing that are an integral part of the structural engineering of the boat. But very few boats with encapsulated ballast have any internal framing in the keel area.

The net result is that without internal framing and without the bond between the ballast and the encapsulation envelope, the turn down at the keel flexes more and so fatigues more, and therefore more rapidly loses strength to resist a grounding.

Because of the way that the ballast is bonded to the envelope, once that bond is broken, there is no good way to reliably reestablish a proper bond.

This problem is exacerbated by the way that encapsulated keels were typically constructed. Typically the ballast was inserted into the encapsulation and then a slurry (polyester resins with a thickener) was poured into the cavity over the ballast with the hope that gravity would allow the slurry to the bottom of the envelope and fill any voids. That almost never worked in an ideal manner.

The slurry itself was lose-lose situation. If the slurry was thickened too much it would not flow, and if not thickened enough the unreinforced resin was brittle and had very little strength. Making matters worse the bond was by necessity a secondary bond.

Further complicating things, on most encapsulated keels the membrane between the top of the ballast and the sump was not structural, consisting merely as a couple layers of cloth solely intended to prevent water seeping into the voids between the ballast and the encapsulation.

Lastly, it is important to understand that encapsulated keels were done as a cost savings method, rather than as a better way to build a boat. Then they were marketed heavily in manners that didn't focus on the life cycle of the boat, and that marketing has informed the court of commonly held opinions. But as these encapsulated keel boats age, they reach a point where their strength is somewhat suspect and are showing up increasingly being totalled in what should have been a minor grounding.

Jeff


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Last edited by Jeff_H; 06-01-2019 at 12:16 PM.
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