Keels and Keels Again!

Discussion in 'Boat Design' started by D'ARTOIS, Feb 9, 2006.

  1. Vega
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    Vega Senior Member

    It seems to me that most of the blame is on the builder. The original design seems satisfactory to me, even if the safety factor is a bit too narrow. The modification of the original design is a disaster and even worse, the fact that the owner never knew that the keel had not been built according to the designer drafts.

    Also worrying the fact that, having had knowledge that his drawings had been modified, the designer has not taken any actions.

    The report (drawings of the original and modified keel and a lot of interesting pictures):

    http://www.maib.gov.uk/cms_resources/Hooligan V - full report.pdf
     
  2. MikeJohns
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    MikeJohns Senior Member

    Vega

    The report says the designer;
    Confused Ultimate tensile strength with Yield strength in his calculations
    Didn't calculate the bolt tensions or bolt grounding loads at all
    Given a range of possible strengths of the steel ex-mill didn't specify any batch test and designed to the highest strength possible in the range.
    Used a factor of safety of only 2.0, but with his mistakes he achieved a FOS of just under 1.4 on the original unmodified design.

    Even if he got the rest of the design correct a FOS of 2 is woefully inadequate for a keel since it allows no decent long term fatigue allowance.

    I keep saying this.... in yacht structural engineering many designers are blissfully unaware of fatigue and simply do not design with it in mind as a significant criteria. It really concerns me.
    When designing to a minimum of materials the fatigue strength is more important than yield and should be the target criteria for your true long term FOS.

    I think as a rule of thumb the static cantilever load with a FOS of 3.5 to 4 should allow for long term dynamic load stress-fatigue with a steel keel (for a boat intended for use in a seaway).

    If we design to aircraft factors of safety in a less predictable higher load environment then we need the same sort of maintenance and inspection and replacement regime and skilled certified maintenance people. High tech big racing boats do this, they rebuild and inspect stressed components on a regular basis, commercial production run vessels don't have this luxury nor the diligent technicians. Consequently they make poor parent models for mass production.

    Keels break off because the designers do not properly design them for intended use, in this case poor design was compounded by even poorer construction and an apparently rather dim maintenance crew (when you look at those photo's). However construction aside the keel was going to fall off anyway because of the bolt issue. This designer (and how many others) needs his designs reviewed by a qualified body and it appears that this should be the case for every "officially approved design".
     
  3. fcfc
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    fcfc Senior Member

    Qualified body and officially approved design means that there are at least some officially recognised rules to check against.

    For now, for RCD and ISO, as of today, there is NO official rule for rudder, keel, mast and rig, and nearly all the propulsion system (gearbox, shafting, propeller ).
    For engines, the only things checked are tanks, some fire protection, exhaust sound and pollution.
     
  4. Guillermo
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    Guillermo Ingeniero Naval

    Roger to that, Mike. :)
     
  5. Guillermo
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    Guillermo Ingeniero Naval

    In fact that's why I've reccommended somewhere else in these forums not to use ISO 12215 for the time being, but Classification Societies' rules (and, agreeing with Mike, I'd add using sensible FOS when needed!).

    Interesting reading:
    An Assessment of ISO 12215 Small Craft Hull Construction with Classification Society Rules

    From there:
    "The first (stage of verification of the scantling requirements) compared category A craft scantling requirements with the scantling requirements of ABS, BV, GL, LR and RINA for six typical motor yachts and six typical sailing yachts over the parametric range of the standard. The scantling requirements of the standard were at about the lower one third level within the band of classification society scantlings for lengths of over about 12m. Below this length the scantlings of the standard were somewhat less than class society
    requirements.
    ...............
    The second and much later verification process compared existing craft scantlings with the standard.......
    The existing craft scantlings showed a very wide band of scantlings for the same craft type, length and speed; very much wider than the scantlings band for the five classification societies scantling requirements. This in itself confirmed that class society requirements had not been used generally for these existing craft.
    The results indicated existing craft scantlings to vary between being notably greater than to being less than the standard."

    Worrying.

    (italics are mine)
     
  6. Guillermo
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    Guillermo Ingeniero Naval

    Yet another keel failure I didn't know of:
    “We were sailing at 12 to 13 knots in steadily building breeze under full main and solent (our working jib) when two sharp BANGS sounded from down below. We did not slow as if we had hit anything, but the boat began to round up and lay on her side. With the mast and sails in the water, I climbed around the stern of the boat to look at the keel to see what had happened. The sight that greeted me was chilling . . . the lead bulb had snapped off of the keel strut. Everest Horizontal, the wonderful boat that had carried me so safely around the world, was crippled beyond my ability to help her."

    http://www.sailingbreezes.com/Sailing_Breezes_Current/Articles/July03/disaster.htm

    Cheers.
     
  7. sharpii2
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    sharpii2 Senior Member

    'brutal scrutiny'

    I can't believe that the manufacturer of HOOLIGAN's keel would take such redesign liberties. To me, this shows a serious flaw in the boat building industry, especially when it comes to subcontractors.

    I would hope that if I were one, I would submit any suggestions of redesign I might come up with to the original designer for approval.

    It also seems to me that this type of keel is a practical guarantee of trouble.

    Fine for pond sailors but very questionable for ocean sailors.

    If one must go through with having one, I would think its design and final construction would be subject to the most brutal of scrutiny which would include actual inspection by the designer subject to rejection should it stray one bit from the original drawings.

    And people wonder why the USA is packed to the gills with tort lawyers.

    Maybe the EU could use a few.

    Bob
     
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  8. Pericles
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    Pericles Senior Member

    Guillermo,

    Referring back to your post of 22nd September last year, in which you mentioned ISO 12215, I was reminded today I had saved an article in European Boatbuilder, which is linked below.

    http://www.ibinews.com/ibinews/ebb/tech_10.html

    Part 6 is relevant to keel loss.

    "Part 6 – Details of design and construction gives detailed requirements for both FRP and metal (steel or aluminium alloy) construction. It offers design guidance rather than detailed calculation methods. Amongst other aspects it covers:

    * l structural continuity and detail design.
    * principles of arranging suitable stiffening.
    * local reinforcement — e.g. in way of keels, engines, or highly-loaded fittings.
    * thickness of transoms in way of outboards or sterndrives.
    * docking, chocking or trailer loads.
    * fitting of appendages such as keels, shaft brackets.
    * hull-to-deck joints.
    * welding and rivetting of metal structures.

    This part is undergoing validation, and should be published fairly soon."

    It seems to me that common sense would dictate that one manufacturing defect and/or failure of keel bolts will have catastrophic effects on future sales. OTOH, common sense is not that common.:(

    I await Part 7 Scantling determination for multihulls, with bated breath. In the meantime, some other articles are below.

    http://www.ybw.com/ibinews/ebb/tech.html

    Regards,

    Perry
     
  9. Brent Swain
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    Brent Swain Member

    I think on that type of boat, running the keel right thru to the deck would be the only really safe option.
    Brent
     
  10. Guillermo
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    Guillermo Ingeniero Naval

    "Unlike classification society Rules, ISO 12215 does not require that the mechanical properties of the hull material be verified by testing. This is not so important for steel and aluminium but it could be significant for FRP hulls where the building process has a much greater effect on the material mechanical properties, noting that ISO 12215 uses the same design loads and design stresses as in classification society Rules.

    Another difference between ISO 12215 and class society Rules is that ISO 12215 has no requirements for verifying the in-service condition of the hull, or for approval of repairs in the event of damages.

    The classification process requires periodic surveys and damage surveys as a condition of maintaining class. In addition to operational safety these surveys provide valuable feedback on the performance of the vessels and on the Rules to which they were designed and built. Assessment of this feedback is an essential part of the classification society Rule development process.

    The final difference between ISO 12215 and class society Rules is that changes to the latter can be implemented on short notice whereas changes to an ISO standard take much longer time."

    http://www.eagle.org/news/TECH/Mari...ruction with Classification Society Rules.pdf

    Part 6 of the ISO 12215 standard is still in draft.

    Cheers.
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    More:
    "Theoretical prediction of fibre composites’ mechanical properties and behaviour is a tricky passtime. The theoretical model is often based on ideal assumptions and can often only be seen as either a lower or upper bound in an early design stage. Therefore the Standard has been developed partly on empirical or semi empirical methods, based on sample tests on GRP laminates and panels. This is definitely a strength, but can also be a weakness. Many boat builders might want to use the ISO standard as a design tool and do not have the proper equipment nor resources to perform extensive testing on laminates that are not included in the Standard. This renders the ISO a poor tool and even an obstacle for a small backyard boat builder."

    http://flygmac7.flyg.kth.se/msy/education/thesis/leygraf_jakob/leygraf.pdf

    Also interesting to read:
    http://www.hiswasymposium.com/pdf/2006/I. Campbell.pdf

    Cheers.
     
  12. rwatson
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    rwatson Senior Member

    The other factor after design is ongoing maintenance.
    I believe we had a hull failure here in Australia where a sold stainless steel fin snapped.
    I seem to remember hearing that during repainting, a labourer removing the old paint put a very small grinding mark right around the keel at the hull intersection. Some months of sailing caused stress fractures to develop along this grinding line, and it snapped off under load.
    Theoretically soundly engineered, but betrayed by working factors.
     
  13. MikeJohns
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    MikeJohns Senior Member

    Excalibur, built by 'Applied Alloy Yachts' designed by David Lyons, The keel was nicked accidentally with a grinder and welded to repair. The weld became a stress riser and the swing keel fractured in heavy weather, the fracture started from the weld. 4 people drowned 2 survived. One was trapped by his harness 2 were able to cut theirs and float free, the 3 trapped inside perished. The survivors were only rescued due to a personal epirb.

    Evidence suggested that the damage occurred when the keel was being fabricated but the courts couldn't get to the bottom of it.

    Stainless steel components require very careful design and manufacture particularly when highly stressed, only knowledgeable design accompanied by vigilant quality control and close qualified supervision of the manufacture will guarantee reliability. Also highly stressed immersed ss components must be painted with epoxy as direct contact with water accelerates fatigue.
     
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  14. rwatson
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    rwatson Senior Member

    Its useful to hear more details of that particular incident.
    It also re-inforces the requirement for proper maintenance programs and standards on keels.
    Some boat designs make it impossible to check keel bolts on a regular basis - a scary thought.
    Has anyone ever heard of built in keel stress monitors to warn against impending separation or failure ? I think this is available on some planes, to detect fuselage failure.
     

  15. Pericles
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    Pericles Senior Member

    This thread about keel flops, reminds me of the history of Porche cars, which are a triumph of engineering over flawed design. They stuck the engine in the wrong end and spent millions and millions to get it to work. :p Someone should have tapped the good Herr Doktor on the shoulder and whispered "Front wheel drive. Look at what M'sieur Citroen is doing!"

    In the time honoured phrase of Orwell's "Animal Farm" One hull bad, two hulls good. :p :p :p

    In the interests of safer boating, the EU has decreed that mono hull must be nailed to mono hull, so that only Catamarans may exist. This law comes into being on 1/4/2010 and failure to comply is 4 years in prison and and a fine of 100,000 EUros per hull.

    Pericles
     
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