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Encapsulated Keel?

18K views 41 replies 12 participants last post by  Brent Swain 
#1 · (Edited)
Saw this Ericson in the yard the other day. I'm under the impression Ericsons have encapsulated keels and was struck by the narrow profile of this one. If this keel is encapsulated, it's hard for me to believe the narrow profile of the FRP could take the lateral stress induced by the led while heeling. How does it work? Does the lead become a structural component? What would the ratio of lead to FRP be 3/4 down the keel? How day do dat?
 

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#3 ·
Our Albin Ballad has an integral keel. Even with a 47% ballast ratio, all the lead is in the bottom 32" or so. Which leaves more room for structural FRP & flooring up high, where the stresses are. Think of it this way: the farther down the keel you go, the lower the leverage on the assembly. At the very tip of the keel, the glass only has to support the lead right at that level. Move up six inches, the glass has to carry its lead plus the weight plus the moment arm created by the lead below it. Up another six inches, the glass has to support its lead plus the weight plus the moment arm of the 12" below it. And so on. The trick is to run out of stress (lead + leverage) before your FRP runs out of strength. :D This is a calculation NAs are quite capable of making.

The difficult aspects come from dynamic loading, which is always a fudge, and in achieving good layups inside a deep, narrow keel or skeg. I haven't heard of too many encapsulated keels tearing off, so presumably they got it approximately right.:)
 
#4 ·
Look in the bilge under the cabin sole... if there are keel bolts then it's a bolt on keel. Tap on the outer surface of the keel.. are you hitting (painted) metal or fiberglass?

I'm sure it's a lead keel, and I was under the impression that that model has a bolt on keel but not positive.
 
#7 ·
If replying to my post.... The Ballad keel is most certainly integral -- no bolts. You see the light streak running down the keel in this photo?



That's the drain plug in the aft keel sump. The lead ballast starts just below that line.

The Ballad's lead was supposedly laid in place as formed ingots, not hot-poured as with some Morgans. Which method I agree sounds horrible, but many many boats have poured lead keels & again, very few have fallen off. For every example of an integral keel failure you can toss out, Brent, I'll match you with a bolt-on keel failure.;) There's no surety your Auckland boat would not have lost its keel -- and perhaps its stub -- had it been bolted on. Either attachment method is fine if the engineering was sound and the layup done properly. Jeremy Rogers built Contessa 32s with integral keels. Not a weak boat.
 
#5 ·
Don't know the details of your boat but you can think of it somewhat like a cored hull. Depending on tack one skin is in compression and the other extenson. If glass lay up is not on bias of forces it can easily handle loading. Also some boats use various sub structures to transfer loading to grid structure (stringers etc.) inside hull. Very rigid and strong if done correctly and no issue of keel boat corrosion or metal fatigue concerns. ?Is it an erickson made by PSC. They made great strong boats.
 
#6 ·
I once saw a fibreglass boat hauled out in Auckland, which had had an encapsulated lead keel. It hit St Heliers reef, the fibreglass around it had broken, and the lead sunk. The boat floated to her haulout . You could see the neatly broken line, where the fibreglass had cleanly broken around the profile of the lead. Only the fibrglass which was put over the lead had stopped her from sinking.
I'd want a bit more than the fibreglass holding the lead it. Pouring molten lead into fibreglass has to effect the glass.
 
#8 ·
I have done many internally ballasted, "encapsulated keel" or "integral keel" boats. I've done a similar number of bolt on lead keels. Either way done correctly is fine. I like bolt on from a designj perspective because it gives me a free hand in shaping the ballast. With an integral keel you shape and foil distribution has to be suxch that you can pull the boat from the mold. Ionce poured hot lead into an integral GRP keel on my own half tonner. It worked fine. That boat is still around.

Once again, generalizations about a keel type are silly. If the boat is well designed and well built either an integral or bolt on keel will be fine. With all my designs with integral keels I cannot think of one that has had a keel problem and I would estimate I'm talking about over 2,000 boats. Maybe there has been a few but I have never heard about them.
But, when there is a problem like a keel failure I am usually one of the first to be called.
 
#12 ·
Regards the OP's question, and with reference to Outbound's point about the keel as core-box: I found details in the manufacturer's handbook on our boat. The layup thicknesses are 8mm topsides, 10mm below waterline, 25mm (1") at the hull/keel transition, and a mere 6mm down the keel sides. I'm not sure if NAs include whatever structural properties the ballast may exhibit in their calculations, or if they just treat it as a generic, non-compressible core material & focus all their attention on the FRP skins. *shrug* Whatever methods they use/used have proven adequate -- it's astounding how few recreational or cruising boats drop their appendages.:)
 
#13 ·
Good question for Bob. Haven't a cue. Just thought most of the lateral loading would be at or near the canoe body appendage transition and would note skins are 1" thick there. Seems you're probably right-antimony hardened Pb should have some structural benefit.
 
#14 · (Edited)
"In layperson's terms"?
I would say great. There are impact loads and there are bending loads. Imagine you have your chute up and it's blowing. You do a round up and are knocked down say 90 degrees. The chute collapses and the boat begins to right itself. The chute starts to fill and fills with a bang that shakes the boat and because you have rounded up the chute is still luffing so it fills and dumps several times each time with a big "bang" is not the right word maybe "huge thump" is better. This filling and dumping shakes the entire boat and with the boat still pretty much on its side the lateral forces on the keel joint are great. I could lie to you and say there was a precise way of calculating that but there is not. At least not with the tools the typical yacht design office has. We can guess and we can use safety factors. We can try to simulate it on paper but it's hard to replicate the dynnamics of what happens at sea. We can use CE regs to insure the keel meets those requirements. We can use LLoyds or one of the other certification bureaus scantling standards. I would not include any benefit from the lead or iron ballast in the calculations as there is no way of being sure the skins are bonded to the ballast completely. There is always a possibility that you are going to do something with your keel involving wind, waves and rocks that the designer did not have in mind and that is regardless of whether the keel is bolted on or integral with the hull. The best insurance is plenty of deep and strong floors in the way of the keel with an extra strong floor right at the trailing edge so if you impact the leading edge hard you will not drive the trailing edge up through the hull. I once hit a rock pretty square at 6.5 knots with a bolted on keel. It got very quiet on board for a couple of minutes while we checked the bilge area for damage. There was none. We did put a softball sized divot in the leading edge of the keel though. That was on NIGHT RUNNER a cold molded boat. My AMATI, another 41'er composite build with a high aspect ratio, deep bolt on fin/bulb keel hit a rock hard and managed to break a couple of floors but it did not take on water and had no hull skin damage. We beefed up the floors when it was repaired.
 
#15 · (Edited)
Keep in mind, and I'll speak for the way I do it knowing that most designers do it this way, I'm certain there must be exceptions. If you use ABS or LLoyds or any other certification bureau you will chose your laminate thicknesses from their scantling rules based on the dimensions of the hull. LLoyds and ABS are particularily conservative. The rule will give you a thickness for the keel shell lam. But the way you physically layup the boat on centerline is to take the laminate from one side and wrap it accross the centerline essentially doubling the centerline laminate so you don't just have a lam butt joint on centerline. This is pretty standard practice. That's why a Valiant 40 is an inch thick on centerline. And because we are talking about an area well below the VCG of the boat there is little impetus on a cruising boat to go light.

If this structural stuff interests you try this:
Google "the front fell off".
 
#17 ·
"The Front Fell Off" was priceless. They had me completely taken in until the "no cardboard or packing tape" part. I thought the guy was just your basic condescending idiot bureaucrat until then.

Monty Python never did better. :D
 
#21 · (Edited)
My Ericson 39b has encapsulated lead. recently I had to do a repair of an old repair due to the keel being put down on the edge of a sleeper cracking the old repair. what I found was the glass was at least 1" thick at the sides and nearly 2" at the foot. the lead did not touch any part of the skin but was supported all around by large blobs of bog. I could only see the bottom 15" inside the keel the top of the keel is glassed over as is the leading edge of the bilge behind the lead.
 
#25 ·
Alex:
It's a long story.
But there was a time, you were probably a kid, when designers had this idea that for a keel to be efficient it had to have "eliptical loading".

Say that twice, eliptical loading. Good.

This meant that the loads on the foils ( and I probably have this a bit off) had to describe in a vertical plane an eliptical curve. I could draw it for you.

The idea was that the drag of the keel would dissipate towards the tip reducing the tip vortex ad it's accompanying loads.

This "eliptical loading" gave way to keels with plan forms that features curved leading and trailing edges. Sort of an eliptical shape to the planform. But this really had nothing to do with eliptical loading. You could achieve eliptical loading with a highly tapered keel with straight leading and traling edges. Eliptical edges were of a red herring. But people bought into it anyway and the weird thing is that it did have some benefits apart from eliptical loading. If you reduced the root foil you could reduce the interference drag of the keel, i.e. where the fin meets the hull. Keep in mind that the perfect keel was not attached to the boat.!!!!!!

Short story is we had a series of keels with that highly taered shape. I used it myslef on the Nordic boats. It made sense. But it did put the VCG pretty high up on the fin. But the damn boats sailed really well.

Now we know better. It's better to get the VCG of the keel as low as possible, make the bat stand up and take advantage of the sail plan.

Phases and trends:
Yes, we went through quite a few. Some worked to some degree and some were bogus. But in the end we learned ( some of us) a little bit more about what makes a boat go.

Does that make any sense?

I have to go now. I'm certain there is someone I need to be rude to.
 
#26 ·
Thanks, that does more or less make sense, and gives me more to search on. I really appreciate you hanging around here (and on sailing anarchy) and providing context, design history, and sharing your thoughts on sailboat design.

I've been trying to wrap my head around different keel plans (not fin vs full, but different designs of fin keels and different B/D approaches) and how they affect sailing ability. This comes from seeing how differently my Pearson 28-2 (low B/D) and a friend's Yankee 30 (high B/D) sail even though both have the same LWL and close SA/D. His boat is over 2000lbs heavier, and almost all of it is in the keel. The mast is 4' taller to make up for that. It's interesting seeing how my boat gets pushed around in following seas, while his extra weight keeps the boat on track. Speed and performance wise they feel quite similar.

Researching those differences has lead me down many other tracks and paying attention to things like odd Ericson 38 keels.
 
#37 ·
Thanks, that does more or less make sense, and gives me more to search on. I really appreciate you hanging around here (and on sailing anarchy) and providing context, design history, and sharing your thoughts on sailboat design.I've been trying to wrap my head around different keel plans (not fin vs full, but different designs of fin keels and different B/D approaches) and how they affect sailing ability. This comes from seeing how differently my Pearson 28-2 (low B/D) and a friend's Yankee 30 (high B/D) sail even though both have the same LWL and close SA/D. His boat is over 2000lbs heavier, and almost all of it is in the keel. The mast is 4' taller to make up for that. It's interesting seeing how my boat gets pushed around in following seas, while his extra weight keeps the boat on track. Speed and performance wise they feel quite similar..
Going off topic, but as a Yankee 30 owner, it's my impression that the main advantage of the skeg mounted rudder is stability in following seas.
 
#29 ·
Simon:
We use "bog" over here too.

Alex:
I'm not sure what you see in handling differences in a following sea with your Pearson and the Yankee have anything to do with displacement. I think it may have more to do with the fact that they are very different hull shapes. Very light boats can track beautifully.
 
#30 ·
My Pearson 28-2 tends to get pushed around quite a bit in following seas (not even overly big ones, just the ~2 foot wind waves that we get in Puget Sound). If we get the right sail plan it will start surfing, which keeps it better under control (and brings up the speed). It can get quite tiring going downwind in over 20 knots of wind.

The Yankee 30 tracks a whole lot better and seems to sit in the waves rather than climbing over them in the same conditions. The ride is smoother and easier. We sailed from Eagle Harbor to Shilshole side by side a couple of months ago and it was very obvious.

I had guessed that some of this might have to do with his boat having a lot more ballast (BA/D is close to 50%, vs about 33% on my Pearson) and having the ballast lower down. The Y30 has a deep bilge with the lead hung down low. My Pearson has a thin bolt on keel with a very shallow bilge, so the weight is higher up.

I'd think that the Yankee's extra weight would hurt it in light airs, but he seems to do okay there too. There is a lot of extra sail area to make up for the extra weight, so the SA/D is about the same on both boats (a little under 17...squarely in the cruising not racing range).

I haven't looked at enough boats out of the water to really understand hull shapes very well. Is there a book that you'd recommend for someone trying to understand the basics? The boats are very obviously different there, the Yankee has a much longer keel (though still a fin) and a big skeg where my Pearson has more of a fin keel and a spade rudder.

I quite like how my boat sails in general, this is just one big difference that I noted.
 
#31 ·
You are correct Alex. We can't talk hull shape differences without including displacement. But beghaviour in waves my have more to do with initial stability than it does with the high heel angle benefits of more ballast, lower down. Your two boats are almost polar opposites in terms of hull shapes. The Yankee's speed in light air may have to do with wetted surface and sail area/wetted surface ratio. Ted Hood did a string of IOR boats that were deep and heavy and renowned for their speed in light air. The Yankee 30 wads an IOR era boat and say whaty you like about the IOR (or better yet read my article in GOB several months back on the IOR) but IOR boats performed very well in light air.

It could be something as simple as the fact that maybe the Yankee has better sails.

There are a lot of books on yacht design but the one book I think stands out is Steve Killing's book YACHT DESIGN EXPLAINED. I also go into quite a bit of design theory in my own book YACHT DESIGN ACCORDING TO PERRY. There is also a lot of design wisdom in Chuck Paine's beautiful book.
 
#32 ·
My boat was all over the place in a following sea on the upper chessy a few years back. I was exhausted by it at by time we reached the bridge.
I like my boat and the low maintenance of the encaped keel, but there just something comforting about seeing BIG Bolts. which my boat doesn't have. I think all the other O30s had bolt ons.
 
#33 ·
I would think just the opposite - I've seen so many corroded keel bolts that the absence of them would be a comfort.

Just look at what I pulled out of my old Columbia 43 - that mess was actually still holding the 10,000 Lb keel on without a leak. :eek:
 

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