Who's qualified to do "detailed engineering analysis"?

Discussion in 'Boat Design' started by TealTiger, Feb 3, 2012.

  1. TealTiger
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    TealTiger Junior Member

    Man I love the book Boat Strength! Read it several times through, own two copies, and made spreadsheets that showed me how everything was related to and changed with 'spec's'. Kinda come full circle though. I've done the GA and approximated a lot of the design for a 40-60 foot ocean cruising cat but now want to see if it's viable in a new material (let's say bamboo reinforced concrete ;) The book doesn't cover multihulls, or non-standard materials. I need to first find out what type of person I am looking for, before I look for them :) Any comments, questions, or suggestions would be appreciated.
    Thank you.
     
  2. Petros
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    Petros Senior Member

    I am a licensed professional engineer with 30 plus years experience in aerospace structures, aerodynamics, as well as spent most of my career designing land based structures (buildings, retaining walls, towers, bridges, tanks, etc), and with a fair amount of marine and automotive experience as well. I am familiar with wood, steel, aluminum, concrete, and fabric structures using a variety of bonding or fastening methods, with some limited experience with composites.

    Depending how complex your structure I could do the analysis you need, but if it is a completely new design you are talking about a pretty costly analysis. Also, the problem with unconventional materials is we need a reliable basis for how these material behave under the load conditions we expect to encounter on the design. Some of those questions can be answered with some testing of samples of materials if there is no published data, but you have other considerations that take time to determine. like fatigue life, resistance to rot or decay, moisture intrusion, bond durability, etc.

    Concrete is not water proof, and bamboo will not bond to concrete reliably. So even if you could get a bond, moisture intrusion will eventually break down the bamboo. There are reasons these materials are not used to make structures that are expected to last a long time.

    I can not see how concrete and bamboo composite could ever work reliably together. Even to get steer bars to bond to concrete it has to have ridges on the bars to keep it attached. Also concrete does not tolerate much flex at all, while bamboo will take quiet a lot, this kind of incompatible materials will only crumble away as it is loaded and unloaded in repetitive cyclic loading even if far below its tested strength.

    Laminated Bamboo primary structure might have applications in hull structures, if it can be treated to resist rot. It would be interesting to make woven or laminated sheets of bamboo that could be used like plywood, or even better, cold form it in strips over a mold. It would be labor intensive, but so is most traditional boat building. Except you have the added task of gathering the raw materials and preparing it to make the beams, ribs, stringers and sheets you need.

    Of course that means finding a suitable adhesive; epoxy, polyurethane, or perhaps reprisinol or Tightbond 3. The strength to weight ratio of bamboo is not too favorable compared to other woods, nor its rot resistance. But if it your goal is to use low cost materials, and a suitable and acceptable adhesive can be found, and an acceptable way to make it more rot resistance can be found, it can be done.

    If your intent is to use low cost materials to prove it can be done, there are lots of way to accomplish such an undertaking. Concrete has limited applications in smaller private vessels, in larger commercial vessels it can be made to work but there has not been a large whole sale shift to concrete for building barges and cargo vessels. There are economic reasons.

    What design did you have in mind? Typically you would design the hull around your intended use, and the structural engineer will determine structural details; fasteners, beam sizes, hull thickness, etc. I would choose a proven design if your intent is to experiment with new materials or construction methods. Just as I would recommend you choose proven materials if you were experimenting with new hull designs. Too many changes at once means you double your risks and will not likely have a successful design.
     
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  3. Richard Woods
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    Richard Woods Woods Designs

    There is a HUGE difference in every respect between a 40ft cruising catamaran and a 60fter.

    If you are optimising the design, then if you are looking at a 40fter and a 60fter you will be wanting to use them for different purposes. A 40fter is plenty large enough for a family ocean cruiser. A 60fter is only really sensible for skippered charters. So what are your plans for the boat?

    I think it would be too much of a gamble to try building a large boat in such a new untried material. Remember also that building the shell is not the whole story. You still need to fit it out and I suspect the inside finish of a concrete boat, even reinforced with bamboo will remind you too much of a prison cell.

    So you'll need to fit out the interior in other materials. And as I recall, one of the problems with conventional ferro boats is the difficulty of attaching the interior to the shell.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
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  4. Ad Hoc
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    Ad Hoc Naval Architect

    A naval architect!
     
  5. DCockey
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    DCockey Senior Member

    One of the significant challenges with the structural analysis of a dynamic system operating in a varied enviorment is deciding what sets of loads to use. It's simplier if the system is being designed to a particular set of rules and/or requirements that specify the load sets and there is confidence that those load sets are applicable and sufficient for the particular design and its use. Of course that is effectively depending on the knowledge and judgement of who ever developed the rules and/or requirements.

    What load sets to use is different knowledge and judgement than building the structural model, running the analysis and plotting the results, though knowledge of both together will result in a more efficient and better analysis. In another industry I've seen folks who are excellent at modeling and analysis as long as someone else tells them what loads to use.
     
  6. michael pierzga
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    michael pierzga Senior Member

    you should first contact a materials engineer specializing in bamboo concrete structures then forward this data to a multi hull friendly Naval architect with experience designing concrete bamboo boats. .
     
  7. PAR
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    PAR Yacht Designer/Builder

    Ignore Michael's request and hire the best Na you can. You clearly need a custom design.
     
  8. TealTiger
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    TealTiger Junior Member

    Dear Mr. Woods,
    My apologies. I should have been more careful. The concept is a conventional 40' for, as you note, a family ocean cruiser. The length range I gave was for that same boat in 8:1 and 12:1 versions. I'm sure I sounded a bit flakey, but hope I didn't waste your time.
    Agreed and fwiw, I'm not really interested in bamboo reinforced concrete; just came to mind as an example. The material I'm interested in are more conventional, well documented, and already used, but in different ways.
    Thank you.
    PS I though I was 'subscribed' to this tread and that nobody answered. I only saw these because I came back to reformulate a post. Thank you for answering.
     
    Last edited: Feb 26, 2012
  9. TealTiger
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    TealTiger Junior Member

    Dear Ad Hoc,
    Is a naval architect more appropriate that a Marine Engineer, if the design is done and I just need scantlings? Could any NA straight out of studies do it, or would they have to have a certain amount of experience?
    Thank you.
    PS I though I was 'subscribed' to this tread and that nobody answered. I only saw these because I came back to reformulate a post. Thank you for answering.
     
  10. Richard Woods
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    Richard Woods Woods Designs

    A "Marine Engineer' will typically deal with the services on a vessel - engine, plumbing etc

    a "Naval Architect" may or may not actually design vessels. He may instead be a stability specialist, for example

    a "Yacht Designer" should be able to design all aspects of a design. But may subcontract detailed work to a naval architect or a marine engineer

    Hope that clarifies the different professions

    Richard Woods of Woods Designs (trained as a naval architect, but calls himself a yacht designer)

    www.sailingcatamarans.com
     
  11. TealTiger
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    TealTiger Junior Member

    Dear Mr. Cockey,
    That sounds like good advice. Thank you. Do you think the load sets on a 40' family ocean cruising catamaran are 'well defined' as so many have been made. Or is that knowledge locked away as proprietary info of the firms involved?
    Thank you.
    PS I though I was 'subscribed' to this tread and that nobody answered. I only saw these because I came back to reformulate a post. Thank you for answering.
     
  12. TealTiger
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    TealTiger Junior Member

    Dear Mr. Pierzga,
    I think the materials I'm considering are well know but I'll keep a materials engineer in mind. Otherwise, back to the NA, I see. Btw, if you're being cheeky, well done :)
    Thank you.
    PS I though I was 'subscribed' to this tread and that nobody answered. I only saw these because I came back to reformulate a post. Thank you for answering.
     
    Last edited: Feb 26, 2012
  13. Ad Hoc
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    Ad Hoc Naval Architect

    You need an experienced NA.
     
  14. TealTiger
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    TealTiger Junior Member

    Dear Mr. Riccelli,
    I think I understand the wisdom behind your recommendation. Unfortunately, I doubt I'll be able to pay up front. I'm hoping to split a business with anyone who can check the strength of the materials and spec's I've chosen. The relatively low casts of the materials and their construction should allow a lot of 'wiggle room' within which to get it right. I understand it will be a lot of work, but it wouldn't be out of pocket and might hopefully appeal to someone, new, curious, or ambitious.
    Thank you.
    PS I though I was 'subscribed' to this tread and that nobody answered. I only saw these because I came back to reformulate a post. Thank you for answering.
     

  15. TealTiger
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    TealTiger Junior Member

    Dear Mr. Woods,
    That does help clarify, and puts some of the other comments into perspective.
    Thank you.
     
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