Encapsulated Keels V bolt on Keels

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joha

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Hi

Just wondered what the pros and cons are regards encapsulated verus bolt on keels. My own thoughts are that an encapsulated keel should give less problems in that you don't need to worry about keel bolts failing, but it can't al be good news, and I suppose they only suit boats with traditional underwater lines.

Any thoughts would be welcome.

Jh
 
I think the trouble with encapsulated keels is that you can get water between the iron and the GRP, which expands when it freezes (of course) and then weakens the fibreglass. And then you have a tiny bit more space for more water to get in net year, and after many years, it's a bit wobbly. Not saying it happens to every encapsulated keel.

You're right that traditional underwater lines (i.e. not a deep fin, but a long, shallow ballasted bit on a V shape hull) puts much lower loads on it.
 
Very unlikely to get any water ingress into what's effectively a solid structure, except through external damage. Trad shapes are also more likely to be using lead than iron, so no rusty problems.

Disadvantage - higher wetted surface area = more drag = poorer performance (all things being equal) and long(er) keels usually mean somewhat idiosyncratic performance when going astern.

Advantage - generally a better engineering solution when it comes to absorbing shock loads, and (usually) better for drying out alongside, tho' that's more a function of keel shape than encapsulated or not.
 
Like many things in life, it is not usually a simple comparison. Keel bolts are one of the discriminators but the whole boat tends to be involved. If you are simply comparing something like a wooden Folkboat with its bolt on lump of iron with a CO26 with its encapsulated iron stampings then the keel attachments are minor compared with wood v plastic. If it's comparison with a fin keel then encapsulated keels tend to be of the longish variety which offers different handling characteristics (specially in astern), they also come with deep bilges (often wet), less commodious accommodation, less form stability and on it goes.
 
My keel is encapsulated. The down side: -

1. As has been mentioned above it is a big lump and not the most hydrodynamic shape.

2. The reverse prop wash gets directed to one side of the keel (stbd in my case) because the trailing edge of the keel is a flat 6", hence the flow from the port side of my propellor gets diverted more favourably to starboard instead of having some chance of passing down the port side of the keel

3. The bilge is deep and if you have tanks in there a complete pain to keep clean. Condensation and crud that ends up in the bilge, soon builds up. Getting the crud out is awkward.

4. For the same reason above retrieving dropped things is a hassle.

5. Be careful of mounting underwater things, such as seacocks and paddle wheels. The hull can be relatively, exceptionally thick quite far from the encapsulated keel.

6. Almost no chance of knocking the keel off and blissfully sailing on i.e. if you are going to damage it structurally then it will be seriously damaged. Not a cut and shunt job to put a new one on. This downside is dubious.

7. You may find that there is a built in drip pan under the engine. This sometimes means that there is a dead volume in the bilge which is neigh on impossible to access as the fixed sump covers it and the tanks are in front of it. Everything you loose will be in there.

8. More anti foul paint, more hull scraping, more hull.

9. When drying out the flat area is more likely to sit on half of a stone and slice a chunk out the foot. The fin just pops to one side.

10. The effect of turbulence on under water instruments can be more than a fin.

That's how I see the down side from my experience with fins / encapsulated keel yachts. Note that the above are not reasons to eliminate an encapsulated keel.

I am aware of some water issues in an encapsulated keel but have no experience of this.

Hope this helps,

BlowingOldBoots
 
The hull is aTrident voyager (the one with the pilot house) the engine sits below the saloon sole and the the bilge is sealed below it, nice and clean and dry and flat so a drip tray could be placed under the engine for oil changes etc, the calorifer et al lives in this quite large space and access to the engine is very good as you can kneel on the flat area that seals the ballast to work on it, I have driven long keeled boats before so am aware of the handling issues, The tanks are not in this space but are on port and starboard between the back of the wheel house and the cockpit lockers effectively creating the bridge deck.
J
 
My Verl 27 has an encapsulated keel (Lead pellets inside). If you looked at the keel you wouldn't think it was encapsulated, it just looks like a fin keel, you know, sort of fin keel shaped.
Photos of the boat out of the water are on an old web page here:

http://www.western-horizon.co.uk/boat_details.php?boat_id=181

Having got as much sailing in as I could since I bought the boat, I love the way she sails and cannot see a downside to a keel like that.
 
I suspect the most significant downside is the cost of manufacture.
When fitting out a hull with an encapsulated keel everything has to be carried up and work is at a high level.
Where the keel is bolted on almost at the end of the production run significant man hours have been saved.
Hence manufacturers switching to bolt on keels.
Personally I love encapsulated keels.
 
joha said:
Hi

Just wondered what the pros and cons are regards encapsulated verus bolt on keels. My own thoughts are that an encapsulated keel should give less problems in that you don't need to worry about keel bolts failing, but it can't al be good news, and I suppose they only suit boats with traditional underwater lines.

Any thoughts would be welcome.

Jh
Click to expand...

It is mainly good news.
The main drawbacks to a lead encapsulated keel on a cruising boat is production cost and lack of choice.
 
Encapsulated keeels went out of fashion because they are not suitable for modern hull and foil shapes. They are difficult to build properly because of the depth of cavity restricting the ability to lay up a sound laminate. Many hulls were made in a split mould to avoid this adding cost and complexity. "cheap" versions used steel punchings in resin for ballast - fine provided the laminate keeps the water out - but I have seen a couple of examples of the consequences of failure. Not a pretty sight.

However the vast majority were well built because they were expensive boats and if that hull form appeals to you it probably better to have an encapsulated keel than external ballast and keel bolts.

So the question with a Voyager is not whether its keel has advantages or otherwise over a bolt on keel, but whether it is still sound. So close inspection for damage to the leading edge and base and possibly the laminations in the bilge over the ballast.
 
Another point, although not necessarily dependent on construction type: Encapsulated keels tend to have a raked leading edge help to raise the boat out of the water if it hits something solid and hence reduce shock loads in the hull and keel. The more verticle leading edge keels, whether they are bolted on or not, tend to transfer much greater loads into the hull structure (especially if cast iron rather than lead) , and hence these boats are more susceptable to damage on grounding.

As with all things, the choice between keels depends on use. Whichever is chosen, the supporting structure within the hull should be able to distribute the keel loads during service and grounding without damage.
 
In summary then, encapsulated keels are available in both long keel and fins but not the modern racing styles - girder and torpedo type. In general, a lead keel is better than ferrous stampings as it won't rust if the laminate leaks and it is denser giving more righting moment for a given size. The real downside for me is that I daren't use a cheaper half tide mooring as it risks wearing through the bottom of the keel.

My boat is a fin and skeg design with an encapsulated lead keel: http://s780.photobucket.com/albums/yy87/rob2hook/?action=view&current=RobandMojo10.jpg

Rob.
 
rob2 said:
In summary then, encapsulated keels are available in both long keel and fins but not the modern racing styles - girder and torpedo type. In general, a lead keel is better than ferrous stampings as it won't rust if the laminate leaks and it is denser giving more righting moment for a given size. The real downside for me is that I daren't use a cheaper half tide mooring as it risks wearing through the bottom of the keel.

My boat is a fin and skeg design with an encapsulated lead keel: http://s780.photobucket.com/albums/yy87/rob2hook/?action=view&current=RobandMojo10.jpg

Rob.
Click to expand...

Nice looking boat!
 
I'll second that, drop keel version would be interesting to look at also. The scaffolding cradle looks interesting although I think I would also have made it so that the boat actually sits on part of it making it more secure i.e. have another length front to back that the keel sits on.

Just done a search - very nice and nice pedigree with a very reasonable price!
 
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joha said:
Hi

Just wondered what the pros and cons are regards encapsulated verus bolt on keels.
Jh
Click to expand...

A keel has two functions - first stability and secondly as an aerofoil. The first is largely unaffected by whether the keel is encapsulated, at least until you start comparing with deep draft or bulb type keels, neither of which can really be done in encapsulated. As an aerofoil, an encapsulated keel is inefficient - too fat, too long and not deep enough.

Even in engineering terms I dont see a benefit. Keels hit things, or at least my keels do. I'd rather hit things with an iron keel or better still a lead one than with a relatively thin skin of grp.

Lastly, I dont like the idea of things happening that I cant see between the encapsulated metal and the skin. Its bad enough with sandwich decks.
 
Zagato said:
I'll second that, drop keel version would be interesting to look at also. The scaffolding cradle looks interesting although I think I would also have made it so that the boat actually sits on part of it making it more secure i.e. have another length front to back that the keel sits on.
Click to expand...
Thanks for the complements. Of course that's why I posted pics of her freshly painted on launch day. Incidentally there is another Weston with encapsulated keel for sale, "Catnap".

The pics of "Joker" are the first lift keel model built, subsequent boats had a standard skeg fitted so less drag. I know of three lift keel boats and have heard stories of one twin keel being built, but haven't tracked down the boat.

I agree about putting more cradle members under the keel, it was intended to have a longitudinal pole either side of the keel. The ground in our yard is very hard - I know, I've dug into it with a pickaxe - impossible without.

Rob.
 
Encapsulated Keels

Just a feew generalised thoughts in rambling form.
The question of course is very generalised and many have regarded encapsulated keels as the large long keel hull. This because so many cast iron keels have been built bolt on onto fin keel designs. I guess in practice that is the majority situation.

However my lift keel on 21fter is encapsulated lead in a very nicely shaped foil which is quite deep when down. The Hull has a dinghy like flat bottom with foil extending to which I attribute the excellent windward performance.

IMHO the long keel low aspect ration keel of older designs is very poor on keel performance lathough granted for a bigger boat you can not have a correctly proportioned deep keel so to get enough keel area you get a low aspect ratio.

I have been dismayed at so many friends whose cast iron keel is rusty and so sheds the a/f paint. Treatment is difficult and often short lived. I think the best would be cast lead keel with strengthening alloys in the lead.

I don't hold with the idea that a swept back or sloping leading edge makes grounding or crashing into rocks any more gentle. I think most fin keel boats have a keel sloping aft to enable the boat to sit on the keel when a straight down keel would leave the boat very stern heavy. A straight keel should be a little better in performance.

So if the op is buying a boat. probably the bolt on cast iron keel is going to be a better performer. A bolt on lead keel would be far better. If the only encapsulated keel boats you find are long keel types then I would go for bolt on cast iron. However expect all sorts of heartaches with superficial rust.
good luck olewill
 
Bosun Higgs said:
Lastly, I dont like the idea of things happening that I cant see between the encapsulated metal and the skin. Its bad enough with sandwich decks.
Click to expand...

Something like this

30a5bop.jpg


Amazingly, it was relatively 'cheap' to remedy.
 
Bosun Higgs said:
A keel has two functions - first stability and secondly as an aerofoil. The first is largely unaffected by whether the keel is encapsulated, at least until you start comparing with deep draft or bulb type keels, neither of which can really be done in encapsulated. As an aerofoil, an encapsulated keel is inefficient - too fat, too long and not deep enough.

Even in engineering terms I dont see a benefit. Keels hit things, or at least my keels do. I'd rather hit things with an iron keel or better still a lead one than with a relatively thin skin of grp.

Lastly, I dont like the idea of things happening that I cant see between the encapsulated metal and the skin. Its bad enough with sandwich decks.
Click to expand...

In aerofoil terms a long fin keel is like a 130 % genoa as opposed to a deep short chord keel that could be compared to a jib. Horses for courses: it depends on what boat it is attached to, and what you are doing with it.

Theres nothing 'relatively thin' with a lot of encapsulated keels .... or rather integral keels, which is what I believe the op was talking about. A true encapsulated keel to my understanding is an ordinary bolted on keel with a grp skin. The integral keel is effectively a structural grp moulding that is integral with the hull moulding, the ballast is placed within the moulding and usually 'encapsulated' in place with resin. In my experience these integral keels have substantial solid grp shoes and leading edges. The trailing edge is usually solid grp too for at least 30cm or so. The ballast is usually placed in the bottom of the moulding, and forward. Some of the aft part of the keel moulding will incorporate a deep sump for the bilge to keep any bilge water away from the stores and furniture.

As for hitting things with keels, in engineering terms, it is better to use the impact energy to raise the boat out of the water and to flex the grp hull over a large area than to come to a sudden halt with large stresses radiating out through the relatively small supporting grillage or floors. With both types of keel the boat would pitch forward and use up some energy that way. Theoretically of course you can of course design a structure to withstand any grounding load no matter what design of keel you use.
 
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Avocet has a long, encapsulated (integral) keel. She was laid up in two halves, as hs been said. That meant the ballast was put in after the two halves were joined together - lead and resin. I've not had any problems with water ingress and I've had so much water on the INSIDE of the boat on two occasions, that the floor boards were floating!

There's a deep sump in the aft section, and yes, everything you ever loose will be in there - but it's realtively easy to get at....

....once the engine is out!

Aside from never worrying about keel bolts or rust (which is great!) Avocet's keel shape is such that when you DO run aground, you just send a couple of crew to the foredeck and she nearly always sides back off the way she came. Of course, it helps if you only ever run aground on soft mud (of which there is an abundance in Morecambe Bay)! I admit that last quality is more a function of keel shape than whether or not its encapsulated, but the two often go hand-in hand. Likewise, I never worry about slamming in heavy seas or "slapping" at anchor. The GRP is MUCH thicker at the leading edge than one might imagine, and is backed up by a solid block of resin and lead. Probably not as easy to damage structurally as a bolt-on cast iron one, to be honest.

PICT0024s.jpg
 
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