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  #1  
Old 02-06-2008
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Keel Design

I was reading another thread which mentioned encapsulated vs bolt on keels. What's everyones opinion on the best keel design for a bluewater boat. I have leaned toward a lead keel bolted onto a frp stub molded onto the bottom of the hull. I believe Pacific seacraft does it this way. I don't really know the pros and cons of each. If you could have it either way, what would you choose, why? Thanks
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Old 02-06-2008
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An encapsulated keel, with molded lead ballast has the advantage of not having keelbolts or a keel-hull join. These are often problem areas on many boats, as seen in the Catalina "smile".

However, an encapsulated keel does have some issues that you generally don't have to deal with in terms of a bolted on keel, such as damage to the encapsulating fiberglass in the case of an impact or grounding. This can be a serious problem, since most metals expand as they corrode. While it is a bit less of an issue if the encapsulated ballast is lead, it is still a problem.

While an externally-mounted keel has some issues, a lead keel is far more forgiving in a grounding, since the lead will often deform and absorb some of the impact forces, rather than breaking something, like a steel or encapsulated keel will do.

The problem is that many designs don't properly spread the load of the keel bolts across the hull. If this is the case, any impact to the keel will result in a lot of damage.

Personally, I am against adding ballast to make a boat seaworthy... but then again, I sail a multihull.
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Old 02-06-2008
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This subject has been extensively worked over in prior threads such as this one what keel for offshore

You should use the SEARCH funtion to find them.
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Old 02-06-2008
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This was written for another venue but represents my take on encapsulated vs bolt on keels:

This is another one of those ‘no one universally right answers’ questions. In other words an argument can be made for either type of keel. (For the record, I personally strongly prefer a bolt on keel rather than an encapsulated keel.) Here’s the way I see it.

Bolt-on keels tend to offer more performance since the ballast must be cast and without the keel stub skin thickness tend to have a lower vertical center of gravity relative to the center of bouyancy. They also have significantly less wetted surface and frontal area making them theoretically faster on all points of sail. They are simple to repair and generally can be repaired satisfactorily no matter how bad the mistake.

On the down side they are more expensive to build; requiring precision casting, bolt hole drilling and a lot more hand fairing. They are higher maintenance requiring fairing every 10 years or so and new keel bolts at some point in the boat’s life.

Encapsulated keels are less expensive to build. There’s less labor and less precision required. Boat builders will often use less expensive forms of ballasting with encapsulated keels, such as iron or lead scrap cast in concrete, resin or other binder further reducing costs. If they are not damaged in a grounding, encapsulated keels are less expensive to maintain.

On the down side they are less efficient. Their real downside is the difficulty in doing a proper repair. Typically, in a hard grounding a number of things happen on an encapsulated keel. Typically the skin of the keel encapsulation gets ruptured and separates from the ballast. This allows water into the small cavities between the keel and the ballast and once wet it can mean the ‘beginning of the end’ for the boat as this permanently wet fiberglass blisters itself from the interior and the wet areas spread around the ballast. This is especially a problem on a boat that is hauled out for cold winters where freeze/ thaw cycles can really pry the skin loose from the ballast. The problem gets worse when the ballast contains ferrous materials. Here the ballast begins to rust and can reduce the ballast into a loose mass of matrix and rusting iron.

Beyond that, in a grounding the ballast is often forced upward as well. In an encapsulated keel the membrane of the hull is at the outside of the keel and the membrane above the ballast is often quite thin. In a bad grounding the ballast keel is often is pushed through this membrane causing a serious and difficult to repair damage and leak.

We grounded a boat with an encapsulated keel that we never could permanently fix for as long as we owned the boat. The problem would get worse with every year, spreading from a small dimple on the leading edge of the keel to an area that was much of the bottom and sides of the keel.


Lastly, it is very hard to lay-up the glass in the keel cavity. As a result the glass work in this vulnerable area of the boat is often inferior to the glass work else where on the boat.
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Old 02-06-2008
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Quote:
Originally Posted by snider View Post
I was reading another thread which mentioned encapsulated vs bolt on keels. What's everyones opinion on the best keel design for a bluewater boat. I have leaned toward a lead keel bolted onto a frp stub molded onto the bottom of the hull. I believe Pacific seacraft does it this way. I don't really know the pros and cons of each. If you could have it either way, what would you choose, why? Thanks
Lots of other folks responded while I was typing, so pardon any redundant comments below....

Snider,

If you are asking whether a bolt-on lead fin keel is preferable to a fin-keel with encapsulated internal lead ballast?

Some folks prefer internal lead ballast encapsulated within a molded fibreglass keel. The principal argument in favor of this arrangement seems to be that it avoids the need for potentially troublesome keel-bolts and their associated hull penetrations. Some also feel it is more robust in the event of collision with a submerged object or a hard grounding, believing that the overall keel design is stronger and will not experience point-load damage at the keel-bolts as an external ballast boat might.

Others prefer external lead ballast that is bolted to a keel stub. There are several arguments in favor of this approach: (1) In the event of collision or hard grounding, the lead is malleable and will partially deform, but can later be repaired. They would argue that a collision or hard grounding that would damage a properly designed keel bolt arrangement, would shatter and structurally damage an internal encapsulated ballast keel;

(2) Another advantage of the external ballast is that for the same draft the keel section can be designed with a narrower cross section, lower center of gravity, and less wetted surface, which generally provide better performance. This is because the thickness of the encapsulating fibreglass is absent from the cross-sectional measurements of the internal ballast boats.

For off-shore sailing, I am comfortable with a properly designed external ballast arrangement and prefer it, but I would not rule out a properly designed internal ballast boat (by properly designed I mean at a minimum that the ballast is cast lead).

Also, on the Pacific Seacrafts, yes, most of the Crealock-designed boats have bolt-on external lead ballast. However, the Crealock-designed Dana 24, as well as the older Morschladt designs like the PSC 25, Orion 27, and Mariah 31, and the Bingham-designed Flicka, all have internal, encapsulated lead ballast (and full keels).

Last edited by JohnRPollard; 02-06-2008 at 11:34 AM. Reason: spelling
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Old 02-06-2008
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The internal/external keel debate is endless. I would base my decision on the rest of the boat. Both types of keels have done everything you would ask for from a boat. I would only make this a prime consideration if I was buying the latest in sport boats. There seems to have been some challenges keeping the keels on in that genre of boats lately. Specifically the Clipper Race had to be stopped for loose keels. Bavaria Match 42, Maximus (Sydney-Hobart), Movistar (Vendee Globe). Just do a search on Google for "keel lost". Internal keels just don't fall off. That sounds like a requirement for a cruising boat.
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Old 02-06-2008
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A properly maintained external keel doesn't fall off either. Using the examples of racing boats, which are often very lightly built and much more heavily stressed than a cruising boat ever would be is basically pointless. You won't see modern racing boats with anything but externally fastened keels, since you can't make a modern high-profile, low drag fin keel any other way.
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Old 02-06-2008
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The keels on all those boats that I mentioned were "properly maintained". They were all brand new. Of course the racing crowd is pushing the limits but some modern racer-cruisers are suspect because of the failures in those high profile boats. Saying that "A properly maintained external keel doesn't fall off" is risky. They can and have fallen off. They likely will continue to fall off. Especially as these new boats age. Just something to consider. A bolt on keel is one more thing to inspect regularly. Like I said, look at the rest of the boat and its history. If one has had a keel come off, it will be known.
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Old 02-06-2008
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Plumper-

Might want to read what I wrote again.

First, the Bavaria Match 42 was a bad design, since the keel support structure was under-engineered from the start, and that was proven by Bavaria retrofitting additional reinforcing layers of glass to the structures on their boats at their cost. This doesn't qualify as a properly designed boat, much less one that is properly maintained.

Maximus and Movistar are both clearly racing boats... and as such, also fall under the rule of lightly built, heavily stressed... and are nothing like cruising boats of the same LOA.

If you could say the same thing about a properly designed, maintained CRUISING boat, you might have a point... but you obviously can't.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 02-06-2008
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My point exactly. They were built so the keels could fall off. What is to say that the rest of the Bavaria fleet doesn't have similar problems but, because they aren't being raced aggressively, one hasn't fallen off yet. Keel issues are even present on older boats, think of the C&C smile, the crack they always have where the keel joins the stub.
http://www.cncphotoalbum.com/doityou...mile/index.htm
Bolted on keels have and will continue to fall off on occasion. Age and dissimilar metals will just exacerbate the problem. That is why surveyors check keel bolts.
I'll stick with the idea that I would not choose the boat based on how the keel was attached. I would look at the rest of the boat and the history of that kind of boat first.
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