Design Life

Discussion in 'Boat Design' started by issac82, Aug 27, 2009.

  1. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The term design life is not appropriate here. It is used whenever someone designs a device and has to make decisions about materials, bearing sizes and permissible temperatures and other conditions. In that case there is also statistical data, like MTBF (mean time between failures) for the components used.

    You do not design GRP to live a certain time, but you could design a boat to survive a certain impact, a maximum engine weight or a number of passengers. GRP like it is used now doesn't differ much from what was used 30 years ago with the exception of the bonding of glass strands when they discovered that certain materials were prone to osmosis. No sane person will use a material for a boat that is completely destroyed once seawater comes into contact with is. It happened in the past, but that was an expensive error.
     
  2. ancient kayaker
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    ancient kayaker aka Terry Haines

    Damage can be repaired, although some materials are easier than others. It is understood that an engineered material may be improved over a period of time but nothing lasts forever. If a material is subject to degradation over a period of time tht is an important issue and the information should be made available.
     
  3. Willallison
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    Willallison Senior Member

    Ok - seems our more complicated responses arent getting the message through, so I'll go back to my original (somewhat fascetious, I admit) answer.

    It depends....
     
  4. FAST FRED
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    FAST FRED Senior Member

    GRP is almost always strong enough , the hassle is it is hard (either engineering or thickness/weight) to get stiff enough.

    The early boats were really stiff , and seem to have unlimited lives.

    Later thin wiggle wall boats are not worth considering long term.

    Some not even short term.

    FF
     
  5. ancient kayaker
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    ancient kayaker aka Terry Haines

    Good point. My last post was too simple also.

    As a former engineer, I could safely assume that a mechanical designer selected a material for a specific application knowing the capabilities of the material such as resistance to thermal, mechanical and other stress factors and susceptibility to fatigue failure. This is hardly news - all part of an engineer's life and responsibilities to client and society.

    The stresses that can be applied to a boat are known from centuries of experience with wooden boats. The characteristics of the material are also reasonably well known, although it is impossible to be totally accurate with a grown product.

    So where are we in the small plastic boat design field? Are the characteristics of resin/glass/carbon composite materials that have largely replaced wood sufficiently known? How long is a modern boat likely to be safe, if indeed it was safe to begin with?

    Synthetic composite materials have been around for over a half-century. Surely by now values can be put on such important characteristics as fatigue life and loss of strength due to environmental conditions and simple passage of time? If not, then I have to agree with fast Fred; a plastic boat, like a car, is a sometime thing; better to toss it than fix it.
     
  6. amateur mariner
    Joined: Feb 2009
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    amateur mariner Junior Member

    can somebody tell me that does HSC rules tell us about the maximum stress encountered by the yacht depending on the type of boat
     
  7. joz
    Joined: Jul 2002
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    joz Senior Member

    Richard and Others

    The Article is in a magazine called Yachts International Jan 09 Edition (not Professional Boatbuilder my mistake) Page 158 to 160 and the title is called Fibreglass Boats: Here Today, Here Tomorrow. on recycling old GRP boats into new ones.
     

  8. joz
    Joined: Jul 2002
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    joz Senior Member

    Richard and others

    An update please read this article from Eric Sponberg on Recycling Old Boats, its a 13 page PDF to which is at http://www.sponbergyachtdesign.com/RECYCLING DEAD BOATS.pdf


    I hope this helps.
     
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