The Elements of Boat Strength: For Builders, Designers, and Owners

Discussion in 'Boat Design' started by wardd, Oct 24, 2009.

  1. Paul Kotzebue

    Paul Kotzebue Previous Member


    Yacht designers use outside firms all the time. Companies like High Modulus and SP Systems provide structural engineering services, for example. Generally, states require a professional engineer's license to offer engineering services to the public. Most states exempt industry from this requirement, so boat builders do not necessarily have to be licensed to do their own engineering. A certified as built plan bearing the stamp of a professional engineer would have to be prepared by or under the supervision of a licensed professional engineer.
  2. Paul Kotzebue

    Paul Kotzebue Previous Member

    Now that ISO12215 is a requirement for ocean racing yachts built after June 2009, we are seeing the top U.S. sailing yacht designers implementing the European standards as well.
  3. Tad
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    Tad Boat Designer

  4. TeddyDiver
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    TeddyDiver Gollywobbler

    Good book for handy scantlings..
    Please bear in mind what Dave states in the introduction "This book was not written for specialist looking for the latest arcane developments in structural engineering.."
    My 2c
  5. marshmat
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    marshmat Senior Member

    (Disclaimer: I'm not trained as an NA or boat designer, rather, I'm an engineering physicist.)

    I find "Elements of Boat Strength" a useful starting point for figuring out, roughly, how a particular system of construction would work for a particular boat. Gerr's rule seems to yield quick, somewhat conservative estimates of appropriate scantlings for a boat of a given general size and configuration.

    I'm really not that comfortable using it for much more than preliminary or comparative analysis, though. I would much rather get an estimate of the actual loads, apply a suitable multiplier ("factor of ignorance" as I call it) to those loads, and select materials and sections to withstand the resulting forces. If the engineering justification for a particular set of rules isn't presented before me, I'm reluctant to use them.

    Having said that, if I were working on a fairly "normal" monohull design of "normal" proportions, I'd probably just use Gerr's rule, repeat with one or two "official" rules (BV, perhaps, or ABS), and use something a bit beefier than the most conservative of the results.

    The design I'm working on now, a power trimaran, is not within the scope of Gerr's rule and is subject to slightly unusual service conditions, so the engineering there is from first principles with some guidance from ISO and BV standards.
  6. Paul Kotzebue

    Paul Kotzebue Previous Member

  7. dskira

    dskira Previous Member

    Yes it is true that Gerr is very well knowne in the US. The Beatles are known worlwide. I will not put Gerr (which I admire very much) on the same name recognition as let say Olin Stephens.
    Gerr seams to write a lot and unfortunatly do not design much. It is a pitty.
    I find some designer is more well knowne because of the amount of writing they do than their design.
    But as usual it is my two cents. :)
    By the way I prefer the Lloyd's for wooden yacht and wooden ships. The century of Lloyd's experience in wood construction can't be ignored and certainly very unic.
  8. gonzo
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    gonzo Senior Member

    A typical American design, shallow and beamy will be overbuilt by Lloyd's rules. They were developed for narrow deep hulls. I can't think of any rule not based on scantlings or tonnage. Critizism of Gerr because he has a scantling rule doesn't make sense. His dimensions are almonst identical as if you use Herreshoff or Skene's rules.
  9. dskira

    dskira Previous Member

    Gonzo, I respectufully do not see why a beamy hull and shallow hull will be "overbuilt" with lloyd's. And what you mean by "overbuilt'. A beamy and shallow yacht or fishing boat? Lloyd's take care of both in different categories.
    I do not critisize (if you refer to me) Dave Gerr, I like is tutorial attitude, he knows how to share his knoweldge.
    McNaugthon also has rules, but never read them.
    As for the Herreshoff rules, interrestring but why so complicate. Skenes do not have rules to my knoweldge but Nevin yes. For Yacht and sailing yacht only.
    Sorry for my disagrement, if I mistake please correct me. I like to learn, it is always nice, as a good discussion.
  10. gonzo
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    gonzo Senior Member

    A sailing yacht built to ABS tends to be lighter than by Lloyds. I think they are overly conservative and taylored to local models. The interesting about Gerr is that the results are so close to Herreshoff's but easier to find. To me, that is a great vote of confidence. I believer that any designer would admit that Herreshoff was reputable and his scantling rules good.
  11. Ad Hoc
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    Ad Hoc Naval Architect

    "..Just a few questions please. Would all engineering be done by an in house NA?
    Do NAs use out side engineering firms ? Is some kind of certificate for an engineered product required ? Could I as a hobbyist get a certified as built plan from a NA or engineering co. ."

    In addition to that good summary above by Paul, I speak from the commercial field.

    The answer to your Q is 99% no. My colleague and I, at our previous company for example, did 99% of all the NA/engineering. That is what we are trained to do. By that i mean the obligatory degree and then btwn 5~10years minimum training. Then we can become "professional" NAs.

    The 1% is when we have either not had the time to finish off a project, or a specialist does it better than we can and in less time, since not our area of expertise. We have done this on 2 occasions to my recollection, over the past 15 years.
  12. Willallison
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    Willallison Senior Member

    The reason's for the move towards 'outsourcing' much of the scantling etc engineering are, I think, twofold.
    The first, and foremost, from the designers point of view is to limit liability.
    The second, which comes more from the builders perspective, is for marketing reasons. "...high-tech composite construction, engineered by H... M...", so the brochure reads....
  13. dskira

    dskira Previous Member

    Interresting since al lot of these very trendy productions boat with all the ISO on the world loose their keel, and cost an arm an a leg to search and rescue.
    Beside that I think we have two different discuussion, one for the commercial and one for yachts. The rules are not the sames, the ISO is a monumental stupidity for yacht under 24 meters. Now this EU rule is implemented differently in the different country of the EU. How beautiful. Irland is the most easy, Spain a torture. Go figure. You can even paid the VAT twice or three times. Grece has a new, illegal by the EU, taxe on yacht. They don't give a squat. The French don't accept the taxe paid in Irland, and so on. The ISO is even not knowne in Grece. They follow the rule of the drachme.
    A disaster of imbecility of pushpaper in Bruxell. Don't talk about EU Standars, they don't exist.
    For commercial it is more easy since we use a body of professional, with agencies. We know where we stand. Its is more easy in a way.
    I don't like regulation or standards (Awful word for a boat) because they are regulation they don't mean they are right, and I don't feel more important because I follow them. A yacht is a little more that that.
    Ok I am done with my rambling :D
  14. frank smith
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    frank smith Senior Member

    Thank you for that additional info.

    It seems to me that there are enough people around with the required credentials to allow a designer to put together a design and then have the necessary engineering done. After all Phillip Johnson was not a trained or certified architect , but did use other to do the engineering. I think in his cass it worked rather well.


  15. Ad Hoc
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    Ad Hoc Naval Architect

    "..It seems to me that there are enough people around with the required credentials to allow a designer to put together a design and then have the necessary engineering done..."

    This is how i currently get a lot of my work. I am called up by "others" to design for them. I just don't have the network or resources to go out and get the work I/we are independent.


    The ISO is an EU standard, it is just the enforcement and method of enforcement that makes it difficult. Just as in the US, each State has its own rules and method of enforcement for each State, which are different to the 'whole' country.
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