Best way to attach a keel

[pmagowan]

The way the designer specified

Or are you planning to design your own boat as well as build it? Personally I have some ideas of the type of boat I'd want in this situation, and a million and one ideas for details, but for the actual hull and rig design I'd be approaching an experienced naval architect with a track record of similar types rather than investing all my money and ten years of my life building my own unproven first attempt at a design.

Pete

Yes, I am designing the boat, foolhardy or not. I am reading a lot about naval architecture and boat design, obviously. There are also some online lectures from the training colleges. I am going to give it my best shot and I am reasonably confident I can design a boat that looks good and performs adequately. I have the appropriate cad programs that analyse things and I am learning their intricacies. I have a fundamental opposition to buying a design from a NA. The whole point of this project is DIY. I may get a NA to have a look over my design before I commit.

 

[prv]

His challenge is going to be to design the supporting structure, but again the RCD includes scantling rules for different methods of construction. If (as one hopes) he is sufficiently technically minded to follow the rules he can design it himself and then get it checked by a third party as required to obtain the CE mark.

Oh, I have no doubt at all that he can design something that's safe, structurally sound, and works in a technical sense. How the keel is attached isn't the issue; I guess I'm drifting the thread a bit. But we all know there's a lot more to designing a good sea boat than just making sure it floats and doesn't fall apart. Does the RCD say anything about good sailing performance (at your chosen trade-off between speed, comfort, and ease of handling), or a sea-kindly motion that has you comfortably deciding to spend an extra day on passage rather than dashing into the nearest available port to put an end to being thrown around and tipped on your ear? These are the things I'd expect a good designer to bring to the project.

A skilled amateur might get it right too if he's lucky, but it's a hell of a gamble with all that time, effort, and money and you won't know if you got it right until it's far, far too late. As it says near the front of one of my boatbuilding books, it costs the same to build a bad design or a good one, and the cost of the designer is a tiny proportion of the build cost. That makes building anybody's first design as your once-in-a-lifetime full-size yacht project far too big a risk to my mind.

Pete

 

[prv]

Yes, I am designing the boat, foolhardy or not.

Well, in that case I wish you (genuinely) the best of luck :encouragement:

I hope we get to watch the project progress over the coming years - I love reading boatbuilding blogs like http://www.odysseyyachts.com/Odyssey_Yachts/BUILDING_BLOG/BUILDING_BLOG.html .

Pete

 

[doug748]

However, it was not like that because it was necessarily "better" - just that the tumblehome meant that it need to be moulded in two halves and it is easier to mould the keel shape in this way, join the two halves together and fill the hole woth ballast, rather than build a structural framework inside the hull to take a bolt on keel.

As ever design and construction is a compromise and the keel is the consequence of construction which is a consequence of design. As soon as design (and rules) changed the shape of hulls, construction methods and keel designs changed.

As you say, nothing is better in the absolute sense. There are plus and minus points in all of these things.
Bolted on iron keels are in vogue, cheap to produce and fill a need; you can have a very thin deep one. However we also know they are vulnerable to spectacular failure, rust externally, leak, become loose, corrode at the interface and the majority do not contribute stability in the most efficient way. The screwed fixings have a similar list of problems of their own.
The first owner is not likely to be greatly interested in these long term maintenance problems.

I have no idea if the photographed boat was made as you say.
Tumblehome does not mean that a boat has to be made in two parts nor does it dictate a moulded keel. Australian UFO 34s had a keel bolted to the stub
Boats are made in two bits in order to reduce tooling costs. If the original manufacturer had confidence in a long run of production, he would invest in a split mould at the outset and make the boat in one bit.

 

[lw395]

Oh, I have no doubt at all that he can design something that's safe, structurally sound, and works in a technical sense. How the keel is attached isn't the issue; I guess I'm drifting the thread a bit. But we all know there's a lot more to designing a good sea boat than just making sure it floats and doesn't fall apart. Does the RCD say anything about good sailing performance (at your chosen trade-off between speed, comfort, and ease of handling), or a sea-kindly motion that has you comfortably deciding to spend an extra day on passage rather than dashing into the nearest available port to put an end to being thrown around and tipped on your ear? These are the things I'd expect a good designer to bring to the project.

A skilled amateur might get it right too if he's lucky, but it's a hell of a gamble with all that time, effort, and money and you won't know if you got it right until it's far, far too late. As it says near the front of one of my boatbuilding books, it costs the same to build a bad design or a good one, and the cost of the designer is a tiny proportion of the build cost. That makes building anybody's first design as your once-in-a-lifetime full-size yacht project far too big a risk to my mind.

Pete

I tend to agree.
There are hundreds of perfectly adequate designs covering the spectrum.
So unless you are pushing the boundaries, or genuinely have requirements that are not addressed by previous designs, what is the up-side?
First prototypes of new designs often get significantly modified as a result of early experience.

I design stuff for a living, electronics not boats, but I suspect the 'right first time' mantra is equally unlikely to go well in boats.
We take many man-years of experience, do a lot of simulation, design things fairly rigorously, etc etc, but most designs go through a prototype phase and at least one major revision before being good enough to sell.
A yacht is a pretty complex system, with many inter-acting systems.
I think it might be like my German friend said about houses, you need to build at least three, the first one you will sell to your enemy, the second one you can sell to a friend, the third one will be OK!

 

[PaulMcC]

As you say, nothing is better in the absolute sense. There are plus and minus points in all of these things.
Bolted on iron keels are in vogue, cheap to produce and fill a need; you can have a very thin deep one. However we also know they are vulnerable to spectacular failure, rust externally, leak, become loose, corrode at the interface and the majority do not contribute stability in the most efficient way. The screwed fixings have a similar list of problems of their own.
The first owner is not likely to be greatly interested in these long term maintenance problems.

I have no idea if the photographed boat was made as you say.
Tumblehome does not mean that a boat has to be made in two parts nor does it dictate a moulded keel. Australian UFO 34s had a keel bolted to the stub
Boats are made in two bits in order to reduce tooling costs. If the original manufacturer had confidence in a long run of production, he would invest in a split mould at the outset and make the boat in one bit.

This is really interesting as I hadn't thought about whether or not my UFO was build in two pieces. From the look of it I would say not. The hull has a chine down the centerline however internally there is no sign of any discontinuity down the centreline. I guess it's possible that an extra layer of GRP was added all over the inside after two halves were joined but I can't see any evidence of a 2 stage construction. Would there be any clear indicators?
I have to say as an owner (as opposed to a builder) having an encapsulated lead keel is great. It's just less to worry about. Far less maintenance concerns.

 

[pmagowan]

Oh, I have no doubt at all that he can design something that's safe, structurally sound, and works in a technical sense. How the keel is attached isn't the issue; I guess I'm drifting the thread a bit. But we all know there's a lot more to designing a good sea boat than just making sure it floats and doesn't fall apart. Does the RCD say anything about good sailing performance (at your chosen trade-off between speed, comfort, and ease of handling), or a sea-kindly motion that has you comfortably deciding to spend an extra day on passage rather than dashing into the nearest available port to put an end to being thrown around and tipped on your ear? These are the things I'd expect a good designer to bring to the project.

A skilled amateur might get it right too if he's lucky, but it's a hell of a gamble with all that time, effort, and money and you won't know if you got it right until it's far, far too late. As it says near the front of one of my boatbuilding books, it costs the same to build a bad design or a good one, and the cost of the designer is a tiny proportion of the build cost. That makes building anybody's first design as your once-in-a-lifetime full-size yacht project far too big a risk to my mind.

Pete

The good thing is that I am not designing anything revolutionary. It will be quite traditional as my main requirement is a rugged boat. I am not into racing but I obviously appreciate good performance. It needs to be a 'blue water' boat, whatever that means. I will be designing and building a number of smaller projects first to see where potential problems are.

For construction I like the idea of the mix of modern and old. I will be using a lot of wood but with modern epoxy and fibres I will 'cure' some of the problems of dimensional stability and rot that wood can suffer from. I plan to build a CNC machine in my, currently being built, workshop. This will allow me to spend more time on the design in the knowledge that a clever computer will do a lot of the work when it comes to construction.

I love DIY and this project is partly to provide me with a never ending supply of it. I want to cast my own keel and many metal fittings, design and make my own anchor and use some of my own trees in the joinery.

Once it all starts happening I will probably make a blog or a website. It is pretty boring stuff at the moment with research and CAD. Of course I will continue to use this forum as a font of all wisdom

 

[prv]

I think it might be like my German friend said about houses, you need to build at least three, the first one you will sell to your enemy, the second one you can sell to a friend, the third one will be OK!

"Build one to throw away - you will anyway" is a longstanding idea in the programming world, though rarely followed.

I think the "three houses" idea matches my experience of boat refits. I'm within sight of finishing my second - it's better than the first, and I'm generally happy with it, but I know there are bits I could have done better and if I do a third boat it will be better still. Obviously it's hard to say from this position, but I think after that it would start to get into diminishing returns.

Pete

 

[pmagowan]

The encapsulated keel has a lot going for it. You don't need to worry about it falling off and you don't really need to cast it in lead as you can use ingots. However, I am erring towards the bolt on lead keel as this is probably more suited to hydrography by impact. I would worry about the grp getting damaged with an encapsulated keel. My own boat has a cast iron keel with bolts and we removed one to check it after its 50th birthday and all was fine so it seems to be a robust solution. I will look up the bolts that Vyv had discussed in a previous thread that have an indicator on them to show if tension has been lost.

There is still the question of a flush mount or a female socket.

re prototyping. With CNC building it would not be hard to make a scale model to test, although the computer programs seem to do this for you anyway, within their limits.

 

[prv]

There is still the question of a flush mount or a female socket.

Ariam has a remarkably narrow (thickness port to starboard) iron fin with a wider bottom (not quite a bulb shape, but same idea). The top flares out to a flange about a foot wide, and this is recessed into a shallow box formed into the hull. We're very happy with the strength of this arrangement. We did have the keel removed a couple of years ago to cure a slight weep around a keel bolt (a potential problem for any attachment method involving bolts) and even after removing all the bolts it took a skilled yard, who had done it before, half a day to actually separate hull and keel. They had to cut several holes in the hull as places to anchor long crowbars, so that six large men could lever the joint apart. I was at work, but my dad was present to observe - before starting they advised him that he might not want to watch what they were about to do!

If using a bolt-on fin, I would definitely do something like this. I can't see any downside except perhaps increased cost to mould the socket, which isn't a big deal to a one-off home builder.

My own fantasy blue-water design would be metal (I have two different designs to different philosophies, one steel and one aluminium), which strongly lends itself to "encapsulated" type keels without some of the problems of doing it in GRP.

Pete

 

[Tranona]

As you say, nothing is better in the absolute sense. There are plus and minus points in all of these things.
Bolted on iron keels are in vogue, cheap to produce and fill a need; you can have a very thin deep one. However we also know they are vulnerable to spectacular failure, rust externally, leak, become loose, corrode at the interface and the majority do not contribute stability in the most efficient way. The screwed fixings have a similar list of problems of their own.
The first owner is not likely to be greatly interested in these long term maintenance problems.

I have no idea if the photographed boat was made as you say.
Tumblehome does not mean that a boat has to be made in two parts nor does it dictate a moulded keel. Australian UFO 34s had a keel bolted to the stub
Boats are made in two bits in order to reduce tooling costs. If the original manufacturer had confidence in a long run of production, he would invest in a split mould at the outset and make the boat in one bit.

First thing, long term problems are not inevitable with bolt on keels - typical sweeping statement that ignores all the other variables.

Second, the split mould method lends itself to the exact same shape as described. The hull is laid up in the two halves, then joined together. That means it is possible to lay the hull on its side which makes laminating easier and particularly in keel pockets allows the layup to be consistent. The two halves are them joined together and the ballast inserted, followed by the mould being split to extract the hull. Not possible to build a hull with tumblehome in a one piece mould because you can't get it out!

Expect the Australian hulls were moulded in a split mould for the same reason, but the join on the keel line would be different to incorporate the structure to take the keel loads. So tumblehome does need a split mould, but split mould does not necessarily mean an encapsulated keel. However, many boats of the period (and just before) had slack bilges and deep keels, being GRP versions of designs for wood, where a split mould was useful for ease of layup and formation of an encapsulated ballast keel.

 

[Tranona]

This is really interesting as I hadn't thought about whether or not my UFO was build in two pieces. From the look of it I would say not. The hull has a chine down the centerline however internally there is no sign of any discontinuity down the centreline. I guess it's possible that an extra layer of GRP was added all over the inside after two halves were joined but I can't see any evidence of a 2 stage construction. Would there be any clear indicators?
I have to say as an owner (as opposed to a builder) having an encapsulated lead keel is great. It's just less to worry about. Far less maintenance concerns.

Yes, exactly what you see - the external line where the join is. As i described elsewhere, the two halves are bolted together and the join laminated over internally so you won't see anything from inside. one of the challenges of this method is to ensure that you disgiuse the join as much as possible. Difficult on the boats I was involved in building using this method as the two half moulds were not symmetrical! Not sailing boats by the way.

 

[pmagowan]

Ariam has a remarkably narrow (thickness port to starboard) iron fin with a wider bottom (not quite a bulb shape, but same idea). The top flares out to a flange about a foot wide, and this is recessed into a shallow box formed into the hull. We're very happy with the strength of this arrangement. We did have the keel removed a couple of years ago to cure a slight weep around a keel bolt (a potential problem for any attachment method involving bolts) and even after removing all the bolts it took a skilled yard, who had done it before, half a day to actually separate hull and keel. They had to cut several holes in the hull as places to anchor long crowbars, so that six large men could lever the joint apart. I was at work, but my dad was present to observe - before starting they advised him that he might not want to watch what they were about to do!

If using a bolt-on fin, I would definitely do something like this. I can't see any downside except perhaps increased cost to mould the socket, which isn't a big deal to a one-off home builder.

My own fantasy blue-water design would be metal (I have two different designs to different philosophies, one steel and one aluminium), which strongly lends itself to "encapsulated" type keels without some of the problems of doing it in GRP.

Pete

I understand the attraction of metal but it doesn't do it for me. It strays too far into the magical world of electricity and magnetism. Also, composite materials get a better strength to weight ratio than steel and better fatigue resistance than aluminium. I want to do some high latitude sailing and grapple with ice and metal seems to win here but I am considering temporary bow platings.

 

[prv]

I understand the attraction of metal but it doesn't do it for me. It strays too far into the magical world of electricity and magnetism. Also, composite materials get a better strength to weight ratio than steel and better fatigue resistance than aluminium. I want to do some high latitude sailing and grapple with ice and metal seems to win here but I am considering temporary bow platings.

Yep, nothing's perfect

Electrical voodoo is a concern for aluminium, but people seem to manage. I'm relaxed about such things for steel, there's an awful lot of experience of steel workboats and fishing boats out there and that's the world I'd be looking to emulate for that boat.

A big part of the appeal of metal for me is the ability to weld everything to the hull and deck instead of drilling holes in them, and thus avoid leaks. A seamless shell except for deliberate (and well designed) vents, hatches, and skin fittings is a good thing. I've never managed to completely eliminate leaks from above in a GRP boat.

As for weight, I am by nature not a "travel light" sort of person, and even less so on a self-sufficient blue water boat. So my hull design would assume a fairly heavy displacement as a starting point - it's inevitably going to happen anyway, so the design might as well be optimised for it rather than struggling against it. The simpler steel design (which is the older and more thoroughly worked out in my head) has a large, low-aspect-ratio sail plan, somewhat inspired by sailing cargo vessels of the past, so that substantial weight needn't mean slow speed (though it probably won't be fantastic to windward). In those circumstances, a bit of extra weight in the hull doesn't matter as much as in a lighter and more "yachty" design.

But I can also see the benefits of your high-tech wood/epoxy technique, and indeed I can see benefits in traditional wood and in GRP. There is no single wonder material that's obviously the best, it just depends on the tradeoffs for a particular project.

Pete

 

[pvb]

Not true actually.Andrew Simpsons boat has a glued on deep fin.The hull is cedar strip and the keel is composed of an outer GRP shell holding a lead inner part .The bottom of the boat has a GRP stub flanged on top that is glued on from within the hull .To that the GRP/lead keel is glued in a male female fit.The glue was a special high performance epoxy with an astronomical shear strength,can't really remember which make.It was all in PBO at the time.

That's not really "glued on" though. All the strength in that arrangement comes from the flange on the GRP stub, sitting inside the hull.

 

[pmagowan]

Hopefully the composite material will achieve a similar watertightness as steel would for the decks. My welds will be made up of epoxy/fibre! I like wood so I am working from there really, incorporating modern materials to make up for woods weakness'. I have been watching a massive home-built steel boat on youtube called SV Seeker. It has been an interesting build and I can see why it would be preferrable for a work-type boat.

Well, I will have plenty of time to mull things over as I am going to be off sailing for a week or so in my old leaky wooden boat.

 

[prv]

Hopefully the composite material will achieve a similar watertightness as steel would for the decks. My welds will be made up of epoxy/fibre!

That's interesting - how do you attach a block or a cleat with epoxy? Obviously lighter stuff can just be glued on with a runny filler mix, but I'm not sure I'd trust that for an anchor cleat, a halyard turning block, or a block for a jib sheet.

I have seen a design for building shroud chainplates from epoxy and kevlar integral with the hull, but it was pure speculation, hadn't yet been done at the time.

Pete

 

[30boat]

That's not really "glued on" though. All the strength in that arrangement comes from the flange on the GRP stub, sitting inside the hull.

Yes that's true but there are no mechanical fastenings involved.Come to think of it the same strength might have been achieved by simply laminating the keel to the stub.But I could be wrong...

 

[lw395]

That's interesting - how do you attach a block or a cleat with epoxy? Obviously lighter stuff can just be glued on with a runny filler mix, but I'm not sure I'd trust that for an anchor cleat, a halyard turning block, or a block for a jib sheet.

I have seen a design for building shroud chainplates from epoxy and kevlar integral with the hull, but it was pure speculation, hadn't yet been done at the time.

Pete

You bolt the block to a pad of some sort.
You epoxy the pad to the deck.
You only need the epoxy to be as strong as the deck you are bolting it to.

alternatively take a look at some high performance dinghies. Things like kicker attachments may just be carbon threads radiating into the structure.

 

[lw395]

....
As for weight, I am by nature not a "travel light" sort of person, and even less so on a self-sufficient blue water boat. So my hull design would assume a fairly heavy displacement as a starting point - it's inevitably going to happen anyway, so the design might as well be optimised for it rather than struggling against it. The simpler steel design (which is the older and more thoroughly worked out in my head) has a large, low-aspect-ratio sail plan, somewhat inspired by sailing cargo vessels of the past, so that substantial weight needn't mean slow speed (though it probably won't be fantastic to windward). In those circumstances, a bit of extra weight in the hull doesn't matter as much as in a lighter and more "yachty" design.

....

Pete

If you want to take x tonnes of stuff with you, you can either have a lightweight 40ft boat or a heavyweight 30ft boat. The former will be a lot faster.
If you are serious about blue water, they don't charge by the metre out there.

I have spent enough time going slowly at an inefficient tacking angle to prefer fastish boats that point well.
Other people may have different views, but IME people with heavy sailing boats that don't point spend a lot of time complaining about the cost of diesel.

But my thoughts are not much help as I can't afford a new big boat anyway and if I could, I might be more relaxed about the cost of motoring up wind?