Methods of fixing keels to hulls?

Discussion in 'Sailboats' started by Omeron, Apr 26, 2007.

  1. Omeron
    Joined: Feb 2007
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    Location: Istanbul

    Omeron Senior Member

    Recently, we seem to hear more and more of foil keels with lead bulbs,
    parting with hulls with grave consequances.
    Also,there seems to be little discussion or innovation regarding methods
    of fixing such keels to hulls in a more secure way.
    Hence my questions;

    What are the methods currently used today?
    Is any method superior to all others in all respects?
    Do you think there is room for a new method?,improvements?

    To me an ideal method would incorporate the following,

    The keel of the boat (Hull) would incorporate a strong point, built as part
    of the hull structure and protruding outwards for the foil and bulb to be
    attached. This part would be built in such a way that it would not meant
    to be removed from the hull at any stage of the boats life.

    This means that, if you ever manage to damage this strong attachment point, you have literally managed to split the boat in half, and destroyed the entire hull.

    The design of this protruding part, maybe 10 inches or so deep, would
    incorporate a rail, guide,or anyting else, onto which the foil would be
    sliding and fixed.

    If you ever happen to receive a strong enough impact, this attachment,
    by design would be expected to fail, and let the keel part with the attachment point, leaving the hull undamaged.

    To me, the benefits would be,

    You can easily detach keels from the hulls,

    If the attachment system is universal, you can also slide in different
    keels for experimenting.

    You can perhaps slide your keel a little forward or back to achieve perfect balance.

    Hull would always be watertight, and you never need to worry about removing keel bolts etc.

    Since the cruicial points are well exposed, inspection would be easy.

    If the keel fails, you know that it wont be ripping the bottom of your hull, and sinking your boat in no time.

    Perhaps a lower profile design inside the boat, improving headroom.

    Any views on this, and reading material regarding methods of fixing keels to hulls greatly appreciated.
  2. rayk
    Joined: Nov 2006
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    Location: Queenstown, NewZealand.

    rayk Senior Member

    Welcome Omeron.

    My particular pet is durable displacement yachts.

    A long keel root that reinforces the hull, instead of being a stress point.
    The 'foil' between the root and the ballast should not be a 'weak link'.

    Cheap and light seem to pop up a lot these days. Bolting on fins and then bolting on a lead lozenge looks to be the fast way of doing things now.
    What I think is cheap manufacturing process's is touted as the advance of science.

    I like your keel stub line of thought. However that reinforcement is usually in the floors of a fin keeler. Imagine the hull is a mirror, then your external reinforcement can be seen inside the hull.

    What type of boat would you like to draw?
  3. Omeron
    Joined: Feb 2007
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    Location: Istanbul

    Omeron Senior Member

    Keel Stub is a good way of describing what i had in mind.
    I am working on a custom, 39 ft performance cruiser. Strip planked,
    with a displ. close to 6000 kg, of which 3000 kg will be the keel.
    Therefore the keel/hull bonding is very important.

    Instead of relying on few bolts, i thought a large s.steel plate inside the hull,
    and by the shape of the hull, spreading the load over a large area,with a permanantly welded stub would be a secure, fix and forget method.

    Also, if you want to transport the boat by land, detaching the keel would be a job taking minutes rather than attempting it and not knowing whether you can put it back without shearing the bolts and what not.

    One other advantage i can think of ,is, if you ever get grounded and stranded, you can externally unlock the attachment, leave the keel, save the boat, and retrieve the keel later.
  4. rayk
    Joined: Nov 2006
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    Location: Queenstown, NewZealand.

    rayk Senior Member

    How about gluing timber into the hull instead of a large stainless plate? Ring frames, floors, longitudinal girders...
    Might work out better.

    Removing a 3000kg keel is no mean feat. This is something you dont want to do very often. Conveniently unlocking the ballast will add weight and complexity to your 6000kg performance cruiser. Maybe on a smaller trailerable keeler it would be practical.
    Being grounded or stranded on a 39' 6t boat would require some careful thought on the strength of your keel. You dont have much material to play with. Maybe you will have to use bolts and design a lightweight grid under the sole that will transfer stress up into the hull.

    How far along the design spiral are you?
  5. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    A deep tapered socket would be nice for interfaceing a deep fin & bulb or carrying the keel fabrication through to the deck would be even better- the Jon Sayer built "True Blue"? had such a system I beleive & carried John Adams? to victory in 50' class around the World/Southern Ocean etc- simple & strong is often the best
  6. Omeron
    Joined: Feb 2007
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    Location: Istanbul

    Omeron Senior Member

    Actually, i am not a naval architect,and not doing it professionally.
    I am so fed up with all the modern designs, I am tying to create a design for myself, and trying to put together all the aesthetic values my brain collected over the years, as well as some ideas which i think would work.

    The boat i have in mind is a cross between a six meter and a more modern design. Low freeboard, slight tumblehome, moderate overhangs, nice sheer, varnished mahogany, self tacking jib, modern rig,flush teak decks, minimum interior etc.

    I am completing a model of it. And when the time comes, hopefully a professional architect will do the proper drawings and the engineering of it.

    Headroom inside is critical as i want her to sit low and graceful on the water. Therefore, i do not want to waste precious little headroom in joining the keel to the hull.

    This is one area i feel totally illeterate, but also nervous.
  7. Crag Cay
    Joined: May 2006
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    Crag Cay Senior Member

    Hi Omeron,

    Waikikin has mentioned the most comonly used method for what you have in mind. I remember a few years ago one of the 'Victric' race boats (III or IV) was about this sort of size and had its own dedicated flat truck trailer to move it around between regattas. They would drop its keel off each time to get the boat lower on the trailer for towing.

    Have a look at 'Cathrine' that has just been launched and built by John Corby. ( ) It might be along the lines you are thinking about.

    Edited: Don't worry if your sence of easthetics does not appreciate the wheel steering on Cathrine. This was the owner's request as he has only limited mobility and found this arrangement more suitable, if a little 'clunky' to the eye.

  8. Omeron
    Joined: Feb 2007
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    Location: Istanbul

    Omeron Senior Member

    Hi Crag Cay and waikikin;

    Funny you mention ' Cathrine',

    I was examining the pictures of her closely, as she is somewhat along the lines of what is brewing in my mind. And in fact i commented on her in SA.

    My design is somewhat closer to a 'yacht' than a day sailer. A little bigger,heavier, stiffer,and somewhat more purposeful and masculine.

    But in essence, it is aimed in the same direction as far as provoking the
    same imagination of long missed lines and smell of a graceful boat, only to be seen today in much larger yachts of multi million dollar league.
    (wow it was not easy to finish this sentence for a non english speaker)

    I found that it is extremely difficult to take the lines of the past and blend that with more modern details.

    What i didnt agree with 'Cathrine' was funnily not the wheel steering as most people thought. For me, it was the near straight flaring out topsides,VOR style,un matching mahogany veneer, interior, and lacking details such as
    exposed gunwale fitting attachments, furling gear etc.

    I always believe God is in the hidden details.

    If you are out to challenge such a marginal design exercise,and leave the mainstream, it is impossible not to make mistakes or do things others would not agree.

    It is like reminding a masterpiece of a movie. I remember a still which was unforgettable, and somebody else remembers another.

    This is called hi jacking a thread by yourself, (with a little help from others.)

    Well, since i have gone so far, i might as well mention another nightmare of mine about this design.

    Under no circumstances, this boat is going to sit high and dry above the waterline. I think nothing destroys the total image of a boat than the freeboard, sheer, and what lies above the deck.

    If one needs more cubic space per $$s to live comfortably, there are less
    challenging options like buying a condominium.

    I am going nuts to find out whether an inch of more freeboard would destroy
    the whole design. And if i could, i would make a mock replica just to see how it would sit on the water.

    Well, there are still many a mental disorder undiscovered by medicine!!!

    Thanks for bearing with me.

    BTW, i am a Turkish national, living in Istanbul. Most of you will find it
    difficult to even visualise where that is. We happen to share the Agean Sea with Greece and also have coasts on the Mediterannian, Black Sea and the Marmara Sea.

    Anyone of you intending to visit this part of the world, I would be most happy to meet, and be a host in Istanbul.
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