cheeky rafiki

Discussion in 'Stability' started by peter radclyffe, May 21, 2014.

  1. fcfc
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    fcfc Senior Member

    I would say 99.9% of beneteau or bavaria owners exactly know why they have bough this kind of boat, instead of a nautor swan, X yacht or other brand.
    It would be foolish for them to expect the same use and life.

    And for chartering, chartering for a summer holiday for a family in the med is not the same as chartering for the Fastnet, then in winter, chartering for atlantic crossing, then chartering for antigua racing week, then chartering back atlantic crossing.
     
  2. powerabout
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    powerabout Senior Member

    a osmosis filled x yacht lasting longer than a bendy?
     
  3. Nick.K
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    Nick.K Senior Member

    What practical modifications would you make / recommend to prevent this kind of failure?
    It looks likely that the single keel bolts were fatigued to the point of failure, but is it possible that the single skin hull under the backing plates was also heavily fatigued and only at a fraction of the original calculated strength? For inspection, the actual hull skin is not visible from inside the boat because of the floor pan moulding and the external surface is not generally visible and is covered in antifouling in any case.
    Is it the floor pan moulding which is giving the impression of a cored hull in the photos?
    There is some talk of leaks when the backstays are tensioned, given that the 40.7 has a keel stepped mast this would seem to indicate that the area is not sufficiently stiff.

    There were about 800 40.7 built (according to one site I looked at) but very many other similar types of boat which are getting to be around twenty years old but may easily have another twenty years of practical life.

    For those like me who unfortunately can't choose between a new Swan or a new Beneteau...but despite this would still rather not drown and rather not hear of others drowning...

    A simple practical measure could be to replace the keel bolts and then in place of the backing plates use a fabricated channel (8mm SS?) that would come up the sides of the internal reinforcement until the cabin sole level and be bolted through the sides of the reinforcement in several places. The reinforcement could be resin filled in the bolting areas. This would distribute the forces over a wider area of hull surface and through bolting of the channel would give some measure of reserve if the hull skin fractured. It may also reduce the rate of hull flooding in the event of a fracture.
    Would this work? Other suggestions?
     
  4. fcfc
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    fcfc Senior Member

    Suggestion : Wait for the MAIB report to be published. You will get full technical explanation of what and why it happened made by very knowledgable people.

    http://www.maib.gov.uk/latest_news/cheeki_rafiki.cfm
     
  5. MikeJohns
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    MikeJohns Senior Member


    Bavaria's Match 42 was a classic case of inadequate design. After the death following the keel falling off, the root cause failure analysis was damning of the design. It had certainly failed to meet the newer OSRY with a solid laminate thickness of only 12mm in way of the keel attachment.

    Every existing boat was modified promptly with a significant beef up of the laminate. On inspection many if not all the boats that had been used showed damage that would have inevitably lead to failure. Not just cracking of the hull but complete separation of the stiffeners from the hull as well.

    The problem I see with many failures that should have served as a prior warning is that they are buried by the dealership/manufacturer in a confidentiality clause attached to a payout. It's only when someone dies that we get full public disclosure.
     
    Last edited: Jun 7, 2014
  6. Dick Flower
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    Dick Flower Junior Member

    Maybe Beneteau should stick to building mobile homes. At least they don't usually sink when something fails.
     
  7. powerabout
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    powerabout Senior Member

    Is the yacht going to be salvaged?
    If not the MAIB wont be able to say much
     
  8. SukiSolo
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    SukiSolo Senior Member

    The hull (Cheeki Raffiki) was GPS tagged by the US Coastguard. I have no information as to whether it is intended to be recovered. It is of course now itself a hazard to navigation of small vessels in the N Atlantic. A 35' er was sunk off Portsmouth some years back after colliding with a domestic fridge thrown in the sea, imagine hitting a 40' hull with a 30'er..at night in a big sea..

    I am pleased to say quite a few people have signed the Book of Condolences at my Club in memory of Andrew Bridge (one of the four lost) and it is possible that the Cadet Class may have a Championship race partly named in his memory.
     
  9. RHP
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    RHP Senior Member

    Mike, wow betides any subsequent buyer in 10 years when the stories have been forgotten and the poor fellow sets sail across a stormy sea for the first time. It doesn't matter whether every yacht of a particular model was updated, the designer has 'most likely' used 12mm thick laminate before on earlier or subsequent designs and these must also be checked for similar symptoms.

    Manufacturers churn these boats out without regard to end of life disposal nor, it seems, the concept of responsibility for suitability of purpose when the owners most depend on it, when facing testing conditions.
     
  10. powerabout
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    powerabout Senior Member

    I guess the gulf stream will send it toward the UK eventually
     
  11. JosephT
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    JosephT Senior Member

    RHP you have a very good point. Looking through the comments and history of the transition to winged keels, it appears there is indeed a lack of a robust design standard for keel roots. No question the roots should be longer to distribute the loads better, and a more robust hull specification in the area of the keel root should be established. Any layman can examine the variety of keel roots and determine there really isn't a sound standard in place (at least one that is being honored internationally).

    Off the top, I would consider the following as basic design standards for a winged keel:

    • Keel root should extend from bow to stern to transfer loads through the full length of the hull
    • Keel through-hull bolts should attach to solid laminates (no honeycomb or form core laminates allowed) and should never be overtorqued.
    • Solid laminate keel root should be at least 4x the thickness of the hull layup and be able to withstand a test grounding at normal cruise speed.
    • Maximum torque specificationf for keel bolts should be specified on a highly visible WARNING lable.
    • Precise maintenance and inspection instructions of keel bolts should be provided by the manufacturer.


    These are just some high level thoughts that can be optimized further.
     
  12. JosephT
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    JosephT Senior Member

    As a tip for the engineering teams designing these keels some strain gages would prove very useful. In fact, considering it's common knowledge a keel failure could result in loss of crew it wouldn't be a bad idea to incorporate a keel failure detection system (with waterproof strain gages) as part of the delivered boat. Marine surveyors, delivery skippers, and vessel owners could inspect the system and have an easier time spotting faulty keels.

    Ref: http://www.hitecprod.com/pages/straingage_axial.html
     
  13. powerabout
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    powerabout Senior Member

    I think the issue might be cycles not over stress?
    Between which 2 items would you put the gauge, the keel usually takes a piece of boat with it so not there
     
  14. Nick.K
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    Nick.K Senior Member

    A few years ago a local 40ft fin keeler broke its mooring in strong winds and landed on the rocks. The owners insurance had unfortunately expired some days earlier, the weather didn't abate for a week and the boat bounced up and down until there was a massive hole extending about the full length on one side. She was underwater on the high tide. I bought her for one euro like that for the parts. It was a Scandinavian built yacht but I donĀ“t remember the type. The keel was lead, we had to work between the tides so I employed a large tracked excavator to break off the keel and load it for transport. I imagined that after fracturing the hull around the root (with the shovel teeth), the keel would more of less fall off...how wrong I was! The keel was bolted through heavily laid up FRP floors and eventually the driver succeeded in breaking it off by repeatedly lifting and dropping it. Even then the hull tore in half before and the keel still had a large piece of the hull attached.
    You don't often have a chance to destruction test a quality yacht (!) so it was interesting to watch and since then I have been convinced that keels should be bolted through the structure and in no circumstances just fixed to the hull skin...how is this possibly permitted?
    (The keel is end-on on the beach between the person on the left and the rear portion of the hull)
     

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  15. Steve W
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    Steve W Senior Member

    As a young boatbuilder 40 years ago in New Zealand we built quite a few light displacement cold molded wood sailboats and the structure supporting the keel, mast and rig loads were very elegant in their engineering in the way they transferred the loads out into the lightweight skin with no point loadings at all. In subsequent years it has always rather annoyed me this practice of bolting through the hull bottom with no floors to carry the loads out into the hull, sometimes you will see piddly little floors alongside the keel bolt pairs, not much more than a token gesture really. I personally think that boats were better engineered in the days before engineers got invoved.

    Steve.
     
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