cheeky rafiki

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

  1. peter radclyffe
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    peter radclyffe Senior Member

    quote from bulbhunter sailing anarchy

    The crew reported taking on water in their last communication - any decent level of water in the hull at the time of the keel finally exiting the scene would contribute to the boat rolling over the second the keel let go. The only way the crew may have kept the boat right side up is if they knew that the keel was going and they shed the mast in an attempt to keep the hull right side up when the keel let go. I highly doubt any racer cruiser production hull will give you enough time to drop the rig in rough conditions once you realize that the keel is peeling the hull skin laminate free and getting ready to drop off.

    This has been discussed at length with some prior losses similar to this where the keel tore free and in every case regardless of collision history etc the keel was mechanically fastened to the hull skin between the grid stringers meaning the whole point of the structural grid in the hull had the largest most stress full object unattached and simply bolted to the hull skin between the grid stringers.
     
  2. peter radclyffe
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    peter radclyffe Senior Member

    quote drew

    The 40.7 I used to race on had no bilge, the keel mates directly to the bottom of the hull, no sump, thru the hull into a grid system which appeared to be attached to the hull with some type of super adhesive. When they ground hard, the grid system breaks away from the hull by design (I was told).

    How do I know this? I was on the boat when we hit ground at at or near hull speed. Mucho dinero to fix correctly. Bene was involved directly with yard when it was fixed. I was at the yard when the keel was reattached and also during some of the repair work. The grid system seemed robust and allegedly designed to do exactly what it was supposed to when grounded hard.
     
  3. peter radclyffe
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    peter radclyffe Senior Member

    does anyone have a link to
    1. beneteau 40.7 hull construction
    2.what classification society
    3. who insures these boats

    thank you
     
  4. peter radclyffe
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    peter radclyffe Senior Member

    Here's a Beneteau 40.7 in from France. Custom Offshore is not a Beneteau dealer but her owner arranged for the yacht to be drop-shipped directly to our yard upon import for full commissioning. Here we installed her instruments, keel, applied a Baltoplate bottom and assembled and stepped the rig. The yacht dealer�s service manager spent a day at our yard to give their blessing to the job done as well as meet factory warranty requirements.


    Custom Offshore Yachts, Inc. image
    Here the keel of the 40.7 is being setup for attachment to the yacht. The small red line visible on the back of the keel�s trailing edge is the flash line from a rotating laser used to guaranty proper alignment of the blade to the hull. We�ve found that having the keel on straight is pretty key to balanced upwind performance.
     
  5. peter radclyffe
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    peter radclyffe Senior Member

    photo

    [​IMG]
     
  6. peter radclyffe
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    peter radclyffe Senior Member

    photo

    [​IMG]
     
  7. peter radclyffe
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    peter radclyffe Senior Member

    quote bulbhunter s a

    Few years back while boat shopping I was looking at production boats and how the keels were being attached to the flat bottom hulls of the more modern production boats. The newer production boats really don't have much of a sump or heavily built up structural hull sump area where the keels are attached, The heavily built sumps have slowly morphed into a flat hull bottom or very close to it where the keels have been bolted between the hull stringers I recall reading in another forum some place when the A&M boat lost its keel that a few folks with pretty good build back ground explained that in many cases the production builders consider the bonding strength between the stringers and the solid laminate hull area to be acceptable to support the keel. However as several pretty savy materials folks pointed out cycled loads over time from the keel can dramatically impact the bonding and glass structure where the keel is bolted. Add any minor lay up flaws or bonding agent flaws that impact strength even slightly and you have a added risk of the hull strenth vs keel loads not being up to the task especially in harsh rough conditions

    I really hope they find these guys and these sailors come back and demand that production builders re evaluate how they build these boats. I only know of one major production builder today that mechanically fastens keels to the physical structure grid inside the boat. There may be more doing it today than last time I researched it but at that time Elan was the only big production builder doing this.

    I really like the idea of the swing keel, and rudder posts behind a proper bulkhead approach that many of the smaller more performance focused builders are doing like Pogo. The swing keels sadly have far far far more structural effort going into the hull than the fixed keel boats today. I know which I would prefere to have if I were dropping big money on a boat I were doing lots of open ocean miles on.
     
  8. peter radclyffe
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    peter radclyffe Senior Member

  9. peter radclyffe
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    peter radclyffe Senior Member

    quote s a, trickypig

    know of two loose keels in that time and both were caused by under torqued keel bolts when the keels where attached. One boat had been raced hard offshore for several years and then had it's keel removed and reattached; within weeks they had a loose keel issue. The second loose keel came when we used a different yard to commission a boat and it was obvious they had not consulted the Beneteau factory's specification on keel bolt tightening.

    Once a keel is loose I'm thinking the failure (from metal fatigue in the bolts) would come more quickly then expected.
     
  10. peter radclyffe
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    peter radclyffe Senior Member

    quote i bystander

    6924, on 20 May 2014 - 15:14, said:
    There should be significant redundancy in the design - like a factor of safety of 10 instead of the typical 2-4 factor. This is to account for sloppy yards down the road. Keel bolt torque is BTW not a exact science. Plenty of rough assumptions and guesswork there.
    Bene has a deep bench of Engjneering talent. so one could feel confident the failure is unlikely to be a design flaw.

    The problem is not the safety factor. It is in calculating the dynamic loads that you need to base those safety factors on. "Rile of thumb scantlings are generally based on years of fat keels bolted to an overbuilt sump with each bolt capable of holding the static load of the keel. Put this 8 or so bolts in tension and the subject it to bending moments in every angle of the X and Y axis. Run it aground and put them in a bit of shear. Then take them off shore and drop off a few waves at 25-30 degrees of heel...for 4-5 days.

    For more modern performance oriented boats, you narrow the section, get rid of the sump, lower the VCG and the old rule of thumb no longer apply. IIRC, someone put a bunch OG strain gauges and accelerometers on a maxi canter a few years ago (post Rambler I think) and the loads were significantly higher than their worst case estimates.

    Rig loads are pretty easy to calculate and, like sheets, stretch is more of an issue and ultimate strength is not generally an issue. Pure strength, fatigue or static is a lot harder because load predictions are crazy hard. ABYC and CE standards and the inspectors and engineers needed to meet those standards really fall back on rules of thumb and imprecise load estimates.

    There are ways to install keels that don't rely on bolts in tension and a few square inches of resin starved layup to last but they are expensive to build. We see a lot of keel failures (and for most of us, one is one too many) but in the big scheme of things, it's not a lot. It will take underwriters and certification authorities to demand engineering standards that are a lot more robust than we have today to drive a change. Most boats out there are fine for their intended purpose but in section, VCG and attachment, we have pushed to the edge and it only take a chain of a couple of events to cause failure. In 1992, Mike Plant died after an iffy design (bulb attached by bolts threaded into a pale bonded to the bottom of the fin) had two soft groundings in mud and then ran into rough weather on a translant. When she was ultimately found inverted, the bulb was gone and the threaded plate that the bolts were set into had separated from the fin. We haven't learned a lot since then.
     
  11. peter radclyffe
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    peter radclyffe Senior Member

  12. peter radclyffe
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    peter radclyffe Senior Member

    if i understand it correctly, these boats keels can be bolted off and on by anyone, skilled or unskilled,
    if this is so,
    please correct me if it isnt, i am trying to find the facts
    how can these boats then be classed under survey as ocean racers
    and
    they are then painted underwater in a really cool color man
    so cool that it is almost for S A R to see
    instead of orange,yellow or red or something bright and obvious that can be seen
     
  13. SukiSolo
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    SukiSolo Senior Member

    Thanks for raising the news of the Cheeki Raffiki. Here in the UK this has been quite a big news story. Let us hope they find her missing crew soon. Thanks to the US Coastguard and all others resuming searching for the crew.

    One of the crew Andrew Bridge was a local who sailed in a Cadet at my current Sailing Club. The BBC were down yesterday at the Club, interviewing his mother and brother and filming it live for the main news channel and regional South Today programme. All at the Club are hoping to hear good news soon.

    http://www.bbc.co.uk/news/uk-27497974

    These guys have the skills to survive and the kit, I hope all sailors everywhere will join in supporting the search and hope the crew are found alive and well.
     
  14. peter radclyffe
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    peter radclyffe Senior Member


  15. peter radclyffe
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    peter radclyffe Senior Member

    [​IMG]
     
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