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

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

  1. gonzo
    Joined: Aug 2002
    Posts: 14,449
    Likes: 640, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Getting the voodoo out of boat scantlings, it is a cookbook approach in many ways. Scantlings are simply dimensions required for different parts of the boat. You get the minimum standards by whatever rule you use. Other parts of design, whether naval, aircraft or home, requires experience and common sense. Also, a sense of aesthetics, which is another subject of endless debate.
     
  2. TollyWally
    Joined: Mar 2005
    Posts: 774
    Likes: 26, Points: 0, Legacy Rep: 423
    Location: Fox Island

    TollyWally Senior Member

    Not to state the obvious but nearly all failures in this modern world have been engineered by fully qualified licensed engineers. At it's core, modern engineering relies on opinions backed up by lengthy equations that "prove" mathmatically that the opinions are valid, usually after extrapolating the data from a limited series of laboratory testing. It does not always represent real world best practices which are often "overbuilt, over budget".

    Elegant engineering is a beautiful but rare creature, solitary individuals in a herd of medicrosy. I don't wish to offend any engineers here but rules of thumb that result in moderately overbuilt structures certainly have their place in the world.
     
  3. ancient kayaker
    Joined: Aug 2006
    Posts: 3,497
    Likes: 146, Points: 0, Legacy Rep: 2291
    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    Rubbish! Where on Earth did you get that statistic?

    My point, which seems to have been missed, is that the keel attachment is one of the simplest, as well as most important tasks in boat design, no big challenge to determine the forces at work, the properties of the materials used, and the effects of age and use.

    My question did not get answered either: is it a real problem or are there just a very few isolated cases that get attention precisely becaue of the perceived simplicity?
     
  4. TeddyDiver
    Joined: Dec 2007
    Posts: 2,578
    Likes: 120, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Just my opinion but on this TollyWally nailed it..
    The difference with aero and naval engineering comes from the fact that in the naval environment the max loads met and their frequency are merely estimated with educated quessing, or known also as rules of thumb (or adequate safety factor in a scantling rule). For aeroplanes landings and pressure loads which are a couple of the main stresses for the construction are very predictable.. Thou a boat can be built to take the worst possible pounding for 30 years but then it's defineatly overbuilt..
     
  5. MikeJohns
    Joined: Aug 2004
    Posts: 3,192
    Likes: 206, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    Unless it's a Tasmanian coastal fishing boat, in which case it will be underbuilt :)
     
  6. Guest625101138

    Guest625101138 Previous Member

    Terry
    Small commercial and pleasure boats are a long way behind aircraft in terms of the engineering detail in the design.

    High speed cats built in Australia as recently as the 1980s were under continual repair. In some examples boiler makers were doing repairs whenever they were not at sea.

    I have seen crack interception in aircraft frames but not daily crack repairs. I have also seen some corrosion in galley and toilet framing but these areas are known problems and subject to timely inspection - at least in most instances.

    The only large ships I have seen closely during construction were submarines and the detail on these were very good. Even to the point of weighing the butts from welding rods so they knew the weight of everything that went into each assembly. I expect large bulk carriers are designed in considerable detail as any weight saving usually reduces cost. I know they have tight limits on loading to prevent hogging.

    I do know the maintenance on some large ships is deplorable - way behind most commercial aircraft. I know of instances where ships have not been permitted to sail because bulkheads are rusted through.
     
  7. Ad Hoc
    Joined: Oct 2008
    Posts: 6,565
    Likes: 586, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    AK
    ".As a retired engineeer, some posts in this thread leave an impression of a cookbook approach to boat design similar to the build-to-code approach used for housing construction.."

    This is because most of the design/structural design is done by non-structural engineers/naval architects. It is as you say, a cook book approach. But on a 5m run about...in reality one doesn't really need to be, but the desire to go bigger or to say "I can now design", after designing/drawing a 5m boat/model, is overwhelming to many.

    Since, your comment about:
    "..is that the keel attachment is one of the simplest, as well as most important tasks in boat design, no big challenge to determine the forces at work, the properties of the materials used, and the effects of age and use.."
    is spot on. If one is a professional trained structural engineer/naval architect, these things are a doddle. This is a simple calculation that would take just a about half an hour or so checking and validating.

    But, in the small boat market (which is ostensibly 'private' not public), there has been no call for "professionalism" with regards to what is being designed or built. Since why bother..it is only a 5m boat after all...However, it is only the increasing numbers of accidents and sadly the occasional death, that has lead to the every slowly increasing need for this "market" to be come more accountable and ergo professional. That is why codes like the ISO and RCD etc are being introduced and becoming mandatory.

    The "rules/regulations and methodology/practices" that are slowly being adopted, are nothing to "us" in the commercial market. It is the only way we can design boats. It is very strict...doesn't eliminate all errors/mistakes though (nothing can since most accidents are human error), just mitigates a high percentage of them. Which is why you get the likes of me, and a few others, cringe when amateurs sprout XX YY and ZZZ saying they know so much, just because they they have drawn/built a small 5m boat, they think they know design!

    A 5m boat, is as you rightly point out...just cooking by numbers. But one doesn't need a nuclear warhead to crack a nut!..ergo, it ain't difficult to do on a 5m boat. But try taking that same approach, cooking by numbers, on a 50m HSC 40knots 400 passenger boat.....what is that about the elephant in the room???!!!!
     
  8. idkfa
    Joined: Sep 2005
    Posts: 329
    Likes: 6, Points: 18, Legacy Rep: 79
    Location: Windward islands, Caribbean

    idkfa Senior Member

    "Not to state the obvious but nearly all failures in this modern world have been engineered by fully qualified licensed engineers ..."


    so true, yet funny how the engineers seem oblivious to this!
     
  9. dskira

    dskira Previous Member

    And all the wonder they did which we use everyday and make our life easier and more safe and comfortable.
    It is funny how peoples seams oblivious to this
    Cheers
    Daniel
     
  10. Crag Cay
    Joined: May 2006
    Posts: 643
    Likes: 49, Points: 0, Legacy Rep: 607
    Location: UK

    Crag Cay Senior Member

    That is factually incorrect. At the outset of the introduction of the RCD, we repeated ad nuseum at all the DTI / RINA / trade association sponsored conferences, that concerns about boat safety were NOT the driver for the RCD. The legislation was enacted to allow free trade within the EU and nothing has changed since then.

    The most oft-cited 'structural' issues with boats have been with race boats that are specifically excluded from the requirements of the RCD. Their structural requirements have not changed in that these were either race specific (eg Whitbread / Volvo) or more generally by the requirements of the ISAF OSR. The complication was the termination of the ABS plans approval scheme for smaller boats. The only workable replacement has been (will eventually be) compliance with the ISO structural requirements, but this is driven by self regulation within the racing world and it's wrong to muddy the water by suggesting this has anything to do with the RCD. Obviously if you have a production cruiser - racer that is RCD compliant, it's an easy way to prove you are OSR compliant.
     
  11. Ad Hoc
    Joined: Oct 2008
    Posts: 6,565
    Likes: 586, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    C.Cay

    Can you state what you mean by "factually incorrect"..???
    What facts are these??..I am on one of the MCA committees, these "facts" are new to me..please explain?

    Since the RCD states:
    "..these guidelines are intended to promote the free movement of goods in the EU/EEA internal market having been presented to Member States’ government experts, industry, notified bodies, users and other parties for comment..."
    ok, but goes on to say
    "...but it is not binding in the same sense as legal acts adopted by
    the Community...The legally binding provisions are those transposing the directive into the national legislation of the EU/EEA Member States."


    A very detailed report was conducted to evaluate all these rules, and the findings all point to increasing safety and risk management, even though hard factual evidence did not always wholly support it.

    The report starts by noting from the outset:
    "..Perhaps unsurprisingly, therefore, this research identified wide variations in the detail of mandatory safety standards applied. However, within this variation there is evidence of a move internationally towards tighter regulatory control on the maritime recreational sector. In many cases, it appears the individual regulator is becoming increasingly prepared to intervene through legislation, this possibly reflecting changing societal values towards recreational vessel safety risk..."

    And quotes a few examples, such as:
    "..Spain, for example, suggests regulations introduced in 2002 were needed to address the impact of increasing numbers of recreational vessels, increasing power and the risk this presented to other marine users, particularly swimmers..."

    and also

    "..This would appear to be equally true of the Eire Maritime Safety Act 2005, whose purpose is to strengthen the law against improper use of mechanically propelled personal watercraft (e.g. jet skis) and other recreational craft. The Dáil Éireann debate as reported had little supporting technical detail, though it had near unanimous cross-party political support for the legislation: “Everyone agrees there is a need for improved legislation on maritime safety.”..

    then notes:
    "..However, the UK is apparently alone amongst the countries reviewed in not using nationwide regulation as part of a recreational vessel risk management strategy.....In individual cases the data may be imperfect, but given that fatalities are generally supported by Coroners' reports in all countries considered by the research, as a body of evidence, it does provide a strong message for the UK to evaluate and similarly utilise this as a data source."

    and then summarises with:
    "..Some countries can record a net reduction in recreational risk, even in locations where sea conditions may (roughly) correspond to those of UK. The research has though identified that some local decision-makers in the UK see the need to directly intervene in recreational vessel activity, and are doing so..."

    The RCD began as "risk" of movement between member states of boats, in terms of commercial costs etc. BUT, when the rules were slowly being adopted, as noted above, the risk to the commercial market argument was being outweighed by the risk management systems and procedures of using the boat, by those that ahve to enforce the legislation...

    This is borne out in one of the conclusions:
    "..The evidence suggests nations which regulate recreational vessels primarily through legislation, do secure a reduction in risk.."

    So while to some these codes may appear to to allow free movement between member states, the ground swell of opinion is that it is to "enforce" a more risk based approach to recreational boating by the use of legislation to counter any increase in accidents, real or otherwise..
     
  12. gonzo
    Joined: Aug 2002
    Posts: 14,449
    Likes: 640, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    The thread being about Gerr's book, I think it is good. He clearly limits the application of his method, and within its limits no one has pointed out any major shortcomings. The scantlings are conservative, and there is nothing wrong with it.
     
  13. Crag Cay
    Joined: May 2006
    Posts: 643
    Likes: 49, Points: 0, Legacy Rep: 607
    Location: UK

    Crag Cay Senior Member

    Factually Incorrect?

    Okay, here goes. The discussion is about design and the engineering of boats. You said (admittedly whilst contradicting yourself):

    "But, in the small boat market (which is ostensibly 'private' not public), there has been no call for "professionalism" with regards to what is being designed or built. Since why bother..it is only a 5m boat after all...However, it is only the increasing numbers of accidents and sadly the occasional death, that has lead to the every slowly increasing need for this "market" to be come more accountable and ergo professional. That is why codes like the ISO and RCD etc are being introduced and becoming mandatory"

    and I highlight " . . it is only the increasing numbers of accidents and sadly the occasional death, that has lead to the every slowly increasing need for this "market" to be come more accountable and ergo professional. That is why codes like the ISO and RCD etc are being introduced and becoming mandatory"

    I believe you are suggesting that the introduction of the RCD was driven by "the increasing numbers of accidents and sadly the occasional death" and therefore the design and construction in the small, recreational craft market was in need of being "more accountable and ergo professional".

    Well, this was not so. The was at the time no mechanism within the EU for a directive to address this issue, even if those reasons had been cited (which there weren't). The only mandate for the initiation of the RCD was normalisation of trade.

    There were regulations brought it around that time, that were indeed in response to deaths and accidents, but these were 'Codes of Practice' and related to charter boats and Sail Training Vessels in particular, but these have all been within the commercial, not leisure arenas. The difference between to two types of legislation can be seen by who has authority over their implementation; the MCA inspect and pursue non compliance of Codes of Practice, whereas it's the Trading Standards Officers at council level that are responsible for the enforcement of the RCD.

    At national level within the EU, the RCD has indeed been drawn into local initiative around marine safety. But whether Ireland has seen a decrease in Jet Ski accidents since they have enacted controls has nothing to do with the RCD. I have yet to see any research that has attributed any increase in boating safety SOLEY by the enacting of the RCD legislation. That is, an increase in safety that is directly attributable to their design and construction and subsequent Categorising of recreation vessels as A-D at the moment they are first placed into the market.
     
  14. Ad Hoc
    Joined: Oct 2008
    Posts: 6,565
    Likes: 586, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    C.Cay

    It is a contradiction that i highlight, as also noted by the report.

    I have sat on endless MCA meetings where a new piece of legislation under the EU banner for "harmonisation" and ease of "cross border" movement has been brought in. Is the first thing that we debate, well, i can now sell my boats to Italy with no problems, or go an buy a cheaper boat in Greece??

    No.
    Always it has been able, risk and mitigation of the perceived risk, not from a financial position of ease of movement either. Often the committee, have had to investigate the implications of the new piece of legislation sometime expending unnecessary amounts of money, just to gauge the implications of the risk. One i recall a few years ago was the "Vibration" directive, 2002/44/EC, the debate on the implications for HSE, amazing!!!

    It does not matter whether there has or has not been a decrease in accidents, even though some states report a down turn once implemented. It is the social and public perception of such.

    For example. When the MCA finalise their endless reports and various bits of new code with statements thus:
    "..The purpose of the Marine Equipment Directive is to enhance safety at sea and the prevention of marine pollution through the uniform application of the relevant international instruments relating to marine equipment for which EC type approval safety certificates are issued..."

    You still think it is about the notion of "ease of cross border movement"..????. That is what it may says on the cover, but in reality it is far from the truth.
     

  15. Crag Cay
    Joined: May 2006
    Posts: 643
    Likes: 49, Points: 0, Legacy Rep: 607
    Location: UK

    Crag Cay Senior Member

    I'm sorry, but this is very muddled.

    The Vibration Directive has nothing to do with the RCD, it's a act to protect 'workers' across all industries. It was indeed driven by compensation concerns as the payouts for coal miners / road workers and other pneumatic drill users with white finger syndrome is (IFAIK) still to be determined, but will be vast! That's why the HSE was involved, because it relates to people 'at work'. The HSE has no involvement whatsoever with the RCD.

    Again the MED is a commercial 'work' directive. Completely separate from any requirements of the RCD. Admittedly, charter yachts are included, but they are now considered commercial craft.

    The underlying premise of much of this thread has been that, in the past, non NA boat designers used 'cook books' like Gerr's to produce boats that have caused a "number of accidents and sadly the occasional death". And this sad situation has been rectified by the introduction of the RCD and similar (ie, standards pertaining solely to the design and construction of recreational craft).

    To advance this premise you need to give evidence of the rate of these accidents before the RCD and the percentage reduction which can be solely attributed to its introduction and not any other factors that may have been introduced concurrently, such as restrictions on use of vessels (Spain), licensing of jet skis (Ireland) or speed limits (UK), for example.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.