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Discussion Starter · #1 ·
I''m shopping for my first sailboat (fast coastal cruiser) and ran into a boat with an encapsulated keel. All others I''ve seen were bolted on. What are the potential advantages/drawbacks for performance and structural integrity? The boat is a Dehler 35 Optima.

Thanks, Art
 

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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 be lower 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 elese where on the boat.

I am surprised that the Dehler has an encapsulated keel. Most of their boats have a bolt on keel.

Good luck
Jeff
 

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Discussion Starter · #3 ·
Right you are Jeff_H, this Dehler 101 has a bolt-on iron keel. The owner and broker thought it was encapsulated(!?). The table post must be unbolted to remove the right floor panel to even see the bolts, which were in pristine condition.

Thanks for your detailed response on this issue, as well your responses to many queries on this board. I am relatively new to sailboats and sailboat systems, and I really appreciate your well balanced, well informed input.

Art

San Diego
 

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Discussion Starter · #5 ·
Jeff,
With all due respect. When you wack into somthing with a external ballasted boat,
nine times out of ten (if not ten times out
of ten) the boat will have damage to the
leading and trailing edge fillet , not to mention the damage caused by the "fulcrum and lever" effect caused by the
keel trying to yank the keel bolts through the floor (and that lets water in).

The worst that can happen to a internally ballasted boat is that a little water gets
into the ballast area.At the end of the season, when you normally haul out,
tilt the boat to the stearn drill a couple of holes aft in the tip chord and in the spring
simply patch up the holes that were drilled in the fall. No water in the boat, no
extensive fiberglass repairs and no emergency haul-outs and no keel bolts to replace every ten years or less. Iam a profesional fiberglass repairman and have never in the twelve years Ihave been in this buisness saw or heard of such damage to e-keels like you have fore mentioned . Its true some builders have thrown junk in and covered it with cement.Do a little reasearch, you will find out what builders did this.I will trade
a tenth of a knot for an the security of an encapsulated keel any time. In fact,
I already have

Dennis L.
s/v Pangaea-Buzzards bay
 

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It is very hard to do proper glass work in the tight confines of a keel stub. The glass work that I have personnally repaired in that area has been really poor almost by necessity. The leverage of a hard grounding does not go away when you hit hard just because there is a skin between the keel and the rock. Instead the ballast gives the rock something hard to push against and the comparatively thin membrane above the ballast has to absorb all of that leveraged load.

So, having owned a Pearson Vanguard that had an encapulated keel that hit a rock at not a terribly high speed and had the encapulation readily crush, driving the aft end of the ballast through the comparatively weak membrane above the ballast and dislocating the water tank. And after trying fruitlessly to get a decent repair and never being able to get a bond between the ballast and the encapsulation shell, I can readily assure you that a lot worse can happen than,"The worst that can happen to a internally ballasted boat is that a little water gets into the ballast area." You can end up with a boat that cannot be repaired.

Jeff
 

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Discussion Starter · #7 ·
Jeff,
Are you trying to say that you think internally ballasted boats take ground better than externally
ballasted boats?
How fast were you going????
I dont dispute this happened to your Vanguard. They were built in a time when builders did not know alot about this material. Since the late sixties these relativly weak areas have been realized
and this acurance simply does not happen anymore because these areas are now heavily fortified because it is a very difficult area to work in. Furthermore,
a boat with a deep full modifided keel has its ballast very low in the keel. It would be hard to repair at any rate. But as I stated before, this problem has been delt with.
What do you think would have happened to the ex- ballasted boat in the same circumstance???. ex- ballasted boats require maintainance int ballasted
boats simply dont. Ex- ballasted boats do not take a collision well at all.And as far as speed, how much do you really benifit? A tenth, maybe two tenths of a kt?
My good friend had a Sabre 34 deep draft and I would beat him nine times out of ten. The truth is that with a well designed boat there really is not much of a difference,if any, at all. (Unless your talking about a racing sled)
The external ballasted boat came to pass simply because of the need for speed- and thats not a bad thing...
...just dont hit any thing.

Dennis
 

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I am not sure what the photos indicate about bolt on or encapsulated keels. The keel stub failed at the hull above the keel joint and not at the keel bolts or athwartship frames. This is an area of the boat where a failure could have occured with either a bolt on or encapslated keel. In some whats a bolt on should do better in this kind of situation since a properly engineered bolt on keel has a lot more structure (athwartship framing) than an encapsulated keel. (That athwartships framing in one of the disadvatages of a bolt on because it prevents having tanks in the bilge as easily as you would with an encapsulted keel.

This accident was actually pretty widely discussed on the internet a while back. It is my understanding that the failure occured in an area actually above the keel joint where there was a large section of rotted core thought to have been possibly damaged in an earlier grounding.

In any case, it is a very dramatic set of photos and I am really glad that all escaped without major injury.

Jeff
 

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(This is a long one)

It''s not too hard to explain how I can keep on saying bolt on''s are equal to an internals. Lets start with the basics, niether bolt on keels or encapsulated keels are inherently stronger or weaker. It all comes down to how any given example of each is actually engineered. They each have to deal with a variety of loads they both have to spread these loads out into the hull and they both have to deal with the trauma of a heeled boat dropping off a wave or running at speed into an immoveable object.

If you look at the way side forces work, the maximum force occurs where the keel stub hits the hull and not necessarily where the ballast meets the hull. The keel is a simple cantilever and maximum bending moment occurs at the fold in the hull where it turns down toward the keel. What happens structurally at the bottom of the keel is almost irrelevant to the discussion.

So it is that the area that turns down into the keel needs to really have a lot of strength and that area needs to be reinforced to distribute the loads out into the hull. In a properly designed hull, there are a series of athwartship frames that take the load out into the hull and often there is a longitudinal frame that distribues these loads fore and aft. It does not matter whether we are talking about a bolt on keel or an encapsulted keel, these framing elements are critical to achieving the necessary strength in this area of the boat almost no matter how thick you make the fiberglass.

And these athwartship members have to be connected to the ballast keel so that they take the sideward moments (bending forces) from the ballast keel and connect them to the rest of the hull.

Here''s where it gets harder (but not imposible for an encapsulated keel). If you visualize a boat with an encapsulated keel at an extreme angle of heel, the weight of the ballast keel has a lot of leverage pushing against the sides of the encapsulation. The high side of the keel where the ballast ends is trying to pry the encapsulation away from the ballast. All that glues the ballast to the encapsulation typically is a polyester resin slurry. Polyester resin is not a great adhesive especially to lead or iron, and so oved time that adhesion fails.

You might think that is no big deal. The ballast is in there and where can it go. But lets go back to our earlier discussion. As I said earlier it is critical to transfer the side loads from the ballast to the athwartships frames. In a properly engineer encapsolated keel, this is done through a series of bonds.

To explain, once the ballast keel is ''glued'' in place in the fiberglass keel cavity, the top of the keel is glassed over. Normally this layer is pretty thin and is only intended to keep water out of the keel and if there athwartships frames, provide bonding for the athwartships frames. Then the athwartships frames are bonded to this membrane. Done right and still intact, the ballast transfers its loads to the sides of the keel cavity, which transfers most of the loads to the athwartships frames through the membrane at the top of the keel. And there in lies the problem, once the bond between the F.G. keel and the ballast has loosened the ballast is prying the top of the keel membrane away from the side of the keel cavity and with that goes a weakening of the athwarships connection to the hull.

Walk around most any boatyard with a lucite hammer and tap out the area about 6" to a foot below the top of the ballast on any older boat with an encapsulated keel and you will find that many, if not most, have a void in this area.

Making this problem worse is that this is an area that is next to imposible to repair because once water gets in there (and it does) it is very hard to re-establis a connection between the ballast keel and the hull.

Now then run that boat aground. There''s a couple things at work here. First of all, it is very hard to do a proper glassing job at the bottom of the keel. You are laying up glass in a narrow cavity that a person really can''t get into very well. Although there are lots of tricks to doing the work in these tight areas, having repaired quite a few of these in my day, the glass work at the bottom of keels is very heavy, from the laps in the cloth, but not very sturdy. There are usually large lenses of unreiforced resin and sections of dry cloth.

When you run aground hard, the force generally crushes the cloth and drives the ballast upward against the membrane to the top of the keel and the athwardhips frames and pulls downward at the forward end of the keel. Now you have a leak. Maybe small maybe large, but not one that can be easily repaired to full strength,

So now for the other side of the story. In the case of a bolt on keel you really do have greater maintenance. The fairing materials tend to be short lived. This is a pain in the neck process and even using epoxy it has to be done every 7 to 10 years. (That said it is no worse than fixing blisters that come from moisture trapped between the keel cavity and the ballast working its way out through the not so great glasswork in the keel cavity. But not every encapsulated keel boat gets blisters while every bolt on keel boat sooner or later needs refairing.)

At some point, on most production boats with bolt on keels the SS keel bolts need to be replaced. (I have never understood why for just a little more cost the boating industry does not use Monel Keel bolts but that is another story)

When we talk about the strength of a bolt on keel we are really discussing depending on the ability to make a mechanical connection vs than a glued connection. I''m a mechanical connection kind of guy. Also The stub is generally shallow enough that you can get really good glass work and the overlaps occur so that you have the thickest amount of glass where you need it most, right at the top of the keel. Often, on better built, low volume boats, the athwartships frames are often glassed right in as the hull is being laid up. (On less expensive boats and mass produced boats the frames are generally molded separately or as part of the liner and glassed or glued in.) The keel bolts then pass through the outward turned tabbing or flanges on the frames making a solid mechanical connection.

In the same grounding as above, the metal (especially lead) absorbs much of the shock of the impact before ever distributing the loads to the keel bolts. The bolts have to distribute all of the loads in a compact area. Here is where engineering is critical and why there is nothing worse than a poorly engineered bolt on keel, and nothing better than a properly engineered one. In that impact, the aft end of the keel pushes up. In a properly engineered bolt on keel, that upward force is distributed through a solidly engineered frame at the aft end of keel which carries the loads into a wide area of the boat. Often there will be a bulkhead (seat face or other cabinetry) or massive longitudinal member tied to this frame that distributes the loads fore and aft, and a athwartships bulkhead that distributes the loads into the hull and deck. (That same structure should be there in an encapsulted keel but it absolutely needs to be there on a bolt on.)

At the forward end of the keel there needs to be a similar frame as well. This is the frame is perhaps easier to engineer. It only needs to have sufficient bearing area to not slice down through the hull and to withstand the withdrawal forces of the forward keel bolts. Lastly there is shear but that''s the easy one. All it takes is enough surface area on the bolts and enough bearing plate area to prevent the bolts from acting strictly in single sheer.

Of course a proper bolt on keel requires better engineering and is probably a more expensive keel to build. The keel casting must be made carefully. The bolts, and bearing plates are expensive. Great care must be taken in boring the holes for the keel bolts and there is a lot of labor and handwork in fairing the keel.

This is why a lot of manufacturers take the short cut of doing an encapsulated keel. This is especially true of smaller production yards where the cost of precision tooling a keel casting can be exessive.

In the end it is a trade off between the maintainable and the low maintenance. Encapsulated keels are low maintenance until they can no longer be repaired.

To address your final line, while it is true that the keel cavity is integral with the hull, the ballast in not integral with the with the keel cavity. There it comes down to whether you trust an not extremely good glue (polyester resin) or mechanical fasteners.

(Heck, once upon a time, wooden boats had internal ballast, but they went to bolt on keels for the same reasons outlined here.)

For those of us, like myself, who tend to own older boats, I would think that the ability to repair a bolt on keel far outweighs the potentially lower maintenance of an encapsulated keel.

At least that''s how I see it.
Respectfully,
Jeff
 

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Discussion Starter · #12 ·
I''m a reasonable man Jeff , and Your starting to
make a little sence to me about keels.
I''ll do some reaserch.
I''m also going to take my little hammer and tap on alot of internal keel skins.
Now I''ve got to get some sleep.
I''ve got a busy day tommorow.

Dennis L.
 

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Discussion Starter · #13 ·
Jeff,
You brought up a good point as to the benefit of using monel as the material for keel bolts. Why don’t boat manufacturers do it?

For that matter, have you ever seen monel rigging - either cable or rod type?
Is cost the main factor? Some propeller shafts are made of monel, why not other items?

I suppose the real problem with keel bolts is the old ‘out of sight, out of mind’ problem. If the head of the bolt looks clean and shiny, then the rest of the bolt looks the same, right?

Bob….
 

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Discussion Starter · #14 ·
Check this site out.

It makes an argument for an integral keel, but the boat is made of steel, not fiberglass.

I don’t think you could do the same thing with a fiberglass boat.

http://www.yandina.com/Hugo.htm
 

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That''s Colin''s boat. Last time I saw her she''d just been sold and was sitting down in Beaufort, N.C. In a boat that big, steel really comes into its own but if you built a fiberglass boat as heavily as she is built you would have pretty similar strength.

As to her keel, it is actually bolted on and not integral. Internal ballast had pretty much died out in better built steel boats by that time.

Jeff
 

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Discussion Starter · #17 ·
Being a metal designer and fabricator for nearly thirty years, I can say that if there was a truly ideal application for a bolt on,
it would be here.Steel against steel held together with steel.Virtually no give.VERY
strong.

Dennis L.
 

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Discussion Starter · #18 ·
Hi Dennis,

You look like the guy I need to talk to. I''m looking at a Dufour 35 that apparently had a serious grounding in the late 80''s. The bottom of the glass keel was trashed. More significantly, the rear keel-hull join area was also significantly cracked. Finally, the collision must have really been forceful because most of the internal liner was separated from the hull and at least one engine stringer was cracked.

Supposedly all this was fixed and the boat is still afloat and in very nice condition. But I have to confess to being a little nervous about how well something like this could be repaired.

Got any thoughts or advice?

Many thanks,

Steve
 

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Discussion Starter · #19 ·
hansville,
The main concern is that all areas of the damage were fixed properly. For me to say that it was, I''d have to survey the areas myself. Look the effected areas outside around the keel. Do you see any cracks? Look at the areas inside in the keel stub and the areas that have been re-tabbed. Any delamination? Any cracks? Do you plan to have the boat surveyed? You absolutly should and
(because it does sound like a bad collision) mabey get a second and even a third opinion. Also, because the engine
stringer was cracked and repaired, check
the engine and shaft alignment at the stuffing box and at the cutless bearing.
If the ballast is internal, sound around the ballast with a sounding hammer if voids are preasant drill a 1/4" hole at the bottom of the void if water is there it should be dealt with(I''ll explain later if need be). Then drill a few 1/2"
holes at the lowest part of the underside of the keel to find out if there is any water trapped inside. If the repair was done correctly,there wont be. If there is, this should be delt with. (I''ll explain later if need be).
Find out were she was repaired. Look at the records.
Finaly, I would be very cautious about a boat with the level of damage youve explained because so many boatyards out there will do fast but substandared
work to keep laber costs down below the
estimated repair cost. The main thing is,
have the boat surveyed by a reputable
surveyer.
Hope this helps.Good luck.
Dennis L.
 
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