Origami steel yacht construction

Discussion in 'Metal Boat Building' started by origamiboats, Nov 30, 2001.

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  1. peter radclyffe
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    peter radclyffe Senior Member

    i love it,
    so, as the full size boat is built to 1/16 th of an inch tolerance , side to side,
    what is the scaled down tolerance for the model
     
  2. Pierre R
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    Pierre R Senior Member

    He also admits that he has no control over what goes into the hulls once he leaves so how does he know they match the models?
     
  3. LyndonJ
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    LyndonJ Senior Member

    Yep
    Although to be fair no designer ever has.
    Look at all the production boats that have supposed decent stab curves, then the owner adds furlers, gensets dingy outboard extra fuel and on and on. Then a incline test shown a very poor stability, just cause they didn't count it.

    A decent designer includes everything possibe from scratch and an allowance for even extra gear on deck within the target stability. Ye gods, even the dry paint goes into big vessels.

    But Brent's never done a weights and moments, he wouldn't know quite where to start. Also they've never done an inclining test either.

    Only the model.
     
  4. junk2lee
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    junk2lee Junior Member

    I'm glad that this is a "simple"thing.
    and that's what I was thinking too.Being origami and -well,say aluminum gutter flashing?cardboard? ..it wouldn't have to be perfect per scaled mass IF the plate thickness of the full sized hull were well-enough known and other adjustments were made to cg (like a standard engine etc.)-There are the rigidity problems so some folded cardboard set athwart or whatever...oh, it can't be exact without plans!but darned near,I bet.

    I have done similar with cereal box cardboard a couple of times for friends building a boats but they just wanted the waterline and trim of the hull when launched and lbs per inch immersed.They had the plans,and I calculated the weights from known plate or wood thicknessess by interpolating the areas of the model and plans to steel and wood(because I had the areas of sheet metal now, including the framing,deck plus his input ...and the wooden mast weights and their cgs were not a problem either .It worked fine.I remember using lead fishing weights,and water measured into plastic bags.but this was just about the waterline ,really.
    cg isn't a problem really.It can be found by hanging the model boat from a string maybe with a light plumb bob hanging on it to give a line to mark...Or balance the hull on pins and other ideas you get as many lines as you can,then where the intersect is cg...when weights are added(they have to be glued)same thing...just have some small ones with an eye to fiddling a bit....ideally,when cg is found the model is neutral when hanging FROM cg.no predilection of bow down or roll etc.There'd have to be a 'hatch" in the deck

    A spring scale sounds too easy!but of course,now the model must be somehow "held"?and the axis is "dynamic".Is that tricky?
    Or cut through it and just haul her down !
    because really,a very big springscale could be used on the real boat that'd have an inclinometer..Easier, a known weight pulleyed to masthead,all statically resolved after the fact per the inclinometer, and really no danger up to rail-down -after that it's up to the volunteer boat to say "Uncle"!(or sign a release!haha)
     
  5. LyndonJ
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    LyndonJ Senior Member

    Junk
    These days you put the hull shape displacement and CG into a computer program. It does a very accurate job much better than a physical mode, you can vary any parameter you want and get an instant solution.

    Make the cabin top out of 5mm rather than 4mm ....wham there's the GZ curve. Many of the NA's it this thread here would run a model for free for Brent.

    On a full size boat it's called an inclining test. It's done by moving weights around and looking at the heel angles. It shows if the initial GZ curve is correct or not but doesn't really predict AVS.

    Whatever you do you still need the CG of the vessel as designed. For that you need weights and moments. Most designers would do a W&M for the ship and one for the model. They might even match inertia for seakeeping.
     
  6. peter radclyffe
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    peter radclyffe Senior Member

    rubbish,
    make it of steel with dodgy welds, or its not even near
     
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  7. Ad Hoc
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    Ad Hoc Naval Architect

    I don't wish to contradict, but this is not so.

    The design MUST know. Period.

    The deisgner must make allwowances for items which s/he cannot obtain easily in the begin of the deisgn phase and also cater for the worse case scenario. Not doing so, is negligent.

    It is, as you have rightly noted, finally confirmed with the Inclining experiment. This estbalishes the KG.

    All worse case scenarios are then run to confirm where is the max KG to remain 'safe'. This KG value is then used as the guide for the owner/operator, with regards to loading up the boat.

    Brent, has no zero control, he has pointed this out. Thus he doesn't even know how the boat "should" behave, prior to an inclining experiment, ie what limits of resverse stablity there are under varying sea and loading conditions. This is compunded, because he does not conduct an inclining expt to locate the KG and also provides no guidance to those building them about the max KG, because he washes his hands of the client once he has their money.

    Thus he builds a simple model that bears no relationship to the final boats VCG and LCG, and indeed the shape too, since all are different.

    To go to sea, especially offshore in such a boat, with zero data regarding the stability, is puting your life in danger.
     
  8. junk2lee
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    junk2lee Junior Member

    Thanks,LyndonJ and others where pertinent..you've kept me busy looking up the acronyms!and brought me down a bit to earth.......sure,I was looking for something fast and easy-even the the good ol' get-her-rolling and time-the-period?that I can do on my good ol' Sharp EL5120(a plug for my friend!)Maybe Brent will lend me his model and plans and I can develop some figures that would be make a reasonable discussion.I don't know if this can be done and anyways I won't bother if the forum carries on with the angry backnforth on both sides...maybe I can translate for Brent!

    I wouldn't expect any wild suprises-do you?because this hull shape isn't radical,anyways,is it?I do get that people here expect a more forthcoming attitude and I see the merits of their case but a Buoyant,not-over canvassed and Lead-ballasted boat to boot should not draw such heat.A junk-rigged solid-wood masted canoe or catamaran might get me excited but not this.
     
  9. Tad
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    Tad Boat Designer

    Rolling a model over tells you nothing about the full scale boat's stability. Flotation (displacement) and VCG of the model do not come close to real life.

    With so many boats built there is no need to calculate weights and centers. What needs to be done is measure the flotation and do a simple inclining test on perhaps three different boats. Stability can be run for a range of displacements and VCG's.

    These boats are not deep draft, not heavily ballasted, of steel construction including deck and deckhouse, and some have steel masts. The VCG will be quite high, well above the waterline. Range of positive stability will probably be in the 90-110 degree range.....not 175 degrees.....
     
  10. LyndonJ
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    LyndonJ Senior Member

    It should draw a lot more heat. Come on man this guy is lying about the most significant thing that ensures your survival. All the crap about collisions and ignore what the sea itself can do to you :!: :!:

    You'd be safer in a just strong enough thin plywood boat with good stability than a steel one with poor stability.

    Bouyants got nothing to do with it, it's the shape of the heeled sections and the centre of mass.

    As Tad said these are steel boats without deep draft, the CG will be a lot higher than you imagine or BS would like to admit.

    For anyone going offshore the stability range and the length are really important, the smaller the boat the more stability it needs to be considered safe.

    The crime is to lie to the clients about stability. About it's range and about how it was derived.
    Those claims are just intentional even criminal fraudulent practice that would see any other 'design firm' in deep trouble. The first time there's a fatality then you'll see a proper and thorough investigation.
    I'd say any designer that could be shown to have falsified the stability data is guilty of manslaughter.

    That's the nasty reality of that origami con. Build these boats they are stronger (not), cheaper( not really), and more stable( definately not) than anything else:rolleyes:

    So if you were a thinking man wouldn't you choose a design that was scantling approved, had a good properly derived stability prediction and so what if the hull took a few weeks extra to build. You'd get safety, strength resale value and an honest designer who didn't lie about calcs he appears unable to do.
     
  11. MikeJohns
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    MikeJohns Senior Member

    Junk2Lea

    Stability is worth the 'heat'. It's the holy grail of boat design and operational category for good reason.


    Yes the designer should make allowances for all the extras that might reasonably be expected. Sadly that's often neglected on production sailboats published GZ data. Often the requirements for commercial survey and an inclining test end up with a sheltered or semi sheltered water category. small and even big (when light displacement) sailboats are particularly bad for this, all the extra gear not counted initially ends up well above the waterline.

    For Brent to lie about stability is like your car manufacturer lying about having conducted a crash test and falsifying the results. To say this stabilty issue doesn't deserve the 'heat' is naive.

    This is a blot on the designers record that will never be spun away with anecdotal tales.
     
  12. junk2lee
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    junk2lee Junior Member

    How so,Tad?I think there are differing opinions some posts back.My model would duplicate VCG and buoyancy to scale.I couldn't build so well as to make a model that would act properly sailing in a wave-tank as in distributed scale weight but just to heel it over it should be ok wouldn't it?-I mean if stability were borderline it'd show up well enough to give pause.

    I agree,of course.
    Absolutely agreed.
    and ...
    true and true too often.Dinghies,motors,sails in the foc'sle,stoves and such and more.

    I agree,of course.But I say,again,why the heat?Why these disappointing rants just when a little progress is made?Is it against Brent or the boat?If nobody will bother to model her,Can you show me another boat similar to a Brent boat that fails a stability test?That be another argument but at least there'd be some meat in it instead of "it's a bad design because Brent's a Pugnacious B***er who don't do his homework" and all that...But the boats abide.

    Well,even if I didn't know Brent,I'd never agree that the good boat that I did sail was UNSTABLE.Single-keeled Mungo had GOOD stability.The boat was not driven over-hard by me because it's stupid to sail with the cabin windows underwater but on the occasions she was,by force , driven down,she gained strength as a cruising sailboat should.I see this won't carry weight in this court because you want figures and they're the only evidence you'll accept.Ok,I don't know that much about the bilge keels and I'd be interested in a comparison and such ,as I am about steel construction and the various lessons thereof I'm learning ,but to begin with a supposition of instability is ridiculous.
    The Mungo isn't "anecdotal". I sailed her.I'm a "witness".As to grounding,that I was not there.So that's an anecdote if YOU or I give it as "evidence".But,if I were to produce all the characters in a so-called "anecdote" as witnesses,what would you then say?
     
  13. SheetWise
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    SheetWise All Beach -- No Water.

    Anecdotal evidence is any evidence based on personal observation or random observations -- as opposed to scientific analysis. Anecdotal evidence, by definition, cannot be analyzed.

    It's not meaningless -- it simply cannot be analyzed.
     
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  14. junk2lee
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    junk2lee Junior Member

    Ok,I'm corrected fair enough but it's still Ridiculous.and,from wikipedia,"Unlike anecdotal evidence the reliability of accounts of personal experience is normally capable of assessment for legal proceedings." which is the sense I'm after...ie:if I say" I saw Sheetwise spill coffee on your keyboard" that's acceptable but if I say ,"someone told me Sheetwise spilled coffee " that is not.
     

  15. pdwiley
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    pdwiley Senior Member

    Nobody CAN model Brent's 36' design because Brent won't release the lines & offsets to anyone so it can be done.

    Get Brent to provide the data and THEN you can legitimately complain about people not doing it and complaining anyway. Until then, the modelling (or lack of it) responsibility is squarely in Brent's court.

    Hassle him to release the data rather than complaining here about people asking for that information.

    Honestly it's tempting to take up a subscription (I'd kick in $100) and get someone to buy a copy of the plans just to get this done. No point in my attempting to buy them, I suspect it'd be a NO SALE.

    PDW
     
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