Realistic scantilings

Discussion in 'Metal Boat Building' started by Arvy, Jan 13, 2008.

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  1. Arvy
    Joined: Jun 2005
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    Arvy Senior Member

    Hi all,

    I know crossposting isn't the way to do things, but as I didn't get any response to my questions in the Class society subforum, so I thought, maybe more people in this subforum can answer these.

    Sorry for crossposting!

    I am still puzzled with the germanische lloyd rules. I am designing a steel 40 ft sailing yacht, and right now I am working on the framing.

    I have decided to use transverse frames with a spacing of 400 mm, and longitudinal stringers with a spacing between 250 and 350 mm (max is on maximum beam, becoming closer to the aft and fore.

    Using the formulas in the rules (GL for vessels <24m) I get the following (for the first frame)
    Longitudinals: a section modulus of 2.39 cm^3 wich would lead to a flatbar 40x8 or 60x5 (mm)
    Transverse webframe: a section modulus of 3.1 cm^3 which could be achieved with a L of 60 x 40 x 4. (mm)

    I find the stringers extremely large sized compared to the webframes. When I would make the slots for the stringers in the webframes, I would nearly have to cut them through.. bending the stringers in a fair way will become rather difficult I think.

    Can anybody tell me if these scantlings are realistic? I don't want to use an L or T for the stringers.

    Or is it with GL that you can either use transverse of longitudinal framing? And when using longitudinal framing, the sectionmodulus is calculated without taking the transverse frames into account?

    Or did I misinterpret the unsupported lenght? I used lmin in the formula in table 1.43 (page 1-80). In my case the real unsupported length = 0,4 m and lmin = 0,815m more than twice the real length. The rules don't make clear if I should use lmin or the real unsupported length, so I used lmin to be safe.

    For the webframes I used the formula in table 1.44 (page 1-80). Beside this formula there is also a formula in table 1.42 to calculate the section modulus of transverse frames.

    I just can't figure out if I use the right formula or not. Can anyone help me with this?

    Grtz,
    Arvy
     
  2. Thunderhead19
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    Thunderhead19 Senior Member

    Have a look at Dave Gerr's book Elements of Boat Strength. There's some scantlings in there that should bring you closer to the real requirements of a 12m vessel. There are also some dusty old volumes from the American Bureau of Shipping that they don't publish anymore. You might be able to lay your hands on a copy of the appropriate one.
     
  3. Arvy
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    Arvy Senior Member

    Hiya,

    I did already look at the Dave Gerr book, it is an ok book I think, but I have a problem with his framespacing. In my case Dave Gerr suggest that one should use 325 mm and this is something that I really don't want. I would like to use 400 mm. But I think I have figured it out already :D

    Still thanks for the reply!

    Grtz,
    Arvy
     
  4. Brent Swain
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    Brent Swain Member

    Scantlings

    I have been building origami steel boats with no transverse frames since 1980 with no problems. Over 200 of my designs have been built, and have crossed most oceans, including the NW passage and several circumnavigations.
    Using shape and the structural continuety of steel lets you drastically reduce the need for framing . I've reduced the time to tack together a shell( hull , decks, cabin, wheelhouse, keel, cockpit,) to less than 100 hours for a 36 footer. My book is a guide to the proccess.
    Too much steel boat design is a direct copy of wooden boatbuilding methods, which do nothing to take full advantage of the properties of steel. Many of the stuctural bits and pieces in traditional steel boatbuilding are structuraly redundant.
    They refuse to recognize the phenomenally strong fully welded longitudinal bulkheads that decks , chines, keels, tank tops, etc consitute, and what they contribute to the structural strength of a steel boat, making transverse frames structurally redundant, in boats under 50 ft.
    Brent Swain
     
  5. Arvy
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    Arvy Senior Member

    Hi Brent,

    Thanks for your reply. I haven't looked into this building method, but to me it sounds a bit scary, but this is probably a lack of knowledge. You mentioned you have written a book about the subject, could you tell me the title of it?

    I just try to follow the rules by the class societies so that I am certain that in the case I need to have the vessel classed that it will get classed. How do the origami steel boats get classed by the societies as they don't follow their rules?

    Grtz,
    Arvy
     
  6. Brent Swain
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    Brent Swain Member

    Scantlings

    Gerr , having stated in a recent article in Sail Magazine, that all steel boats will lose a given amount of hull thickness every year ,regardless of how well they are painted, has a serious credibility problem.
    Brent
     
  7. Brent Swain
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    Brent Swain Member

    My book is called "Origami Metal Boatbuilding a Heretics Guide"
    I sell it by mail order .
    Over 200 of my origami designs have been built ,and they have done everything from circumnavigations to a single season passage thru the NW passage . They have survived everything from 16 days pounding on the west coast of Baja in 12 ft swells to pounding across 300 ft of Fijian coral reef ,to a collision with a freighter in Gibralter, to hurricanes , with no structural dammage. Their structural integrity has been well proven many times over , beyond all reasonable doubt. It is simply a matter of time before origami methods become the standard way of building small caft out of metal, altho dinosaur methods will still prevail amoung a few holdouts.
    Brent
    brentswain38@yahoo.ca
     
  8. Dutch Peter
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    Dutch Peter Senior Member

    There's no need in classing a 40 ft boat, but if you want to charter with it you might need a Hull Certificate. This is a statement that the construction was approved and build in accordance with a Class societies rules.

    As Class societies make these rules themselves, they can also dicide to accept alternative arrangements and calculation methodes.
     
  9. Bijit Sarkar
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    Bijit Sarkar Naval Architect

    I hope while computing the Z value for your stringer, you are taking into account the attached plating. You are supposed to compute the section modulus with attached plating of half frame spacing extending each side, if I remember correctly.
    That should give you a much more realistic size of stringer.
     
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  10. Arvy
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    Arvy Senior Member

    Hi Bijit,

    I am taking the attached plate into account, I have sent German Lloyds an email to ask them this as it wasn't immediately clear. They sent me an other part of the rules where this was stated. (it is half the frame spacing on each side of the stringer).

    After applying this I have a much more realistic value (which is somewhere near what I am remembering from the past).
     
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  11. lazeyjack

    lazeyjack Guest

    if you visit my gallery , you will see a 40 foot sailboat with transverse frames. built to and under Lloyds, there are no stringers and the frames are at 400
    Brent stop knocking yourself out, you beat the same ole drum over and over In many ways I agree BUT certification bodys are a whole lot smarter than you or I
    Most of us want to create a thing of beauty and test our skills, I bet you 5000 bucks you could NOT build the old way, can you wheel stretch, form? from your posts I doubt, but you are entiteled to expand upon your views, however dont try ram em down peoples throats eh, Have bonjour mon ami, I like your Alpha male, style:))
     
  12. Arvy
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    Arvy Senior Member

    Hi Lazeyjack,

    Nice pictures you have in your gallery. Was the m40 built to german lloyds or lloyds? I would like to use only transverse frames at 400 framespacing too, but somehow I get such a large scantlings that I don't quite trust them. Maybe I should recalculate them. Right now I am working on longitudinal framing and webframes at 800mm, but I would like 400 better. Well, I will do a quick recalc.
     
  13. lazeyjack

    lazeyjack Guest

    lloyds, deep floors fully welded 6mm plate, from my memory 60x40x6 t section, overlap your sections 2.5 times into floor, folding floors for flange is a real time saver i am not a navel arch. I do things from experience and they seem to pass plan approval, so if you are working with cut frames I spose you sizes are going to go UP
     
  14. Landlubber
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    Landlubber Senior Member

    Origami boats would not pass any class survey!
     

  15. Brent Swain
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    Brent Swain Member

    scantlings

    Friends had charter boats built to Canada Shipping Act certification using origami methods, no transverse frames. The Canadian government inspectors , when they were told that they were origami boats said "We are familiar with the method and have no problem with it." The boats passed with flying colours.
    I think the survival of my boats for 16 days of pounding in 8 ft Baja surf , a single season passage thru the NW passage, a pounding across 300 yards of Fijian coral reef, a collision with a freighter in Gibralter , etc etc, all without serious damage, are far more relevant than the approval of a desk bound bureaucrat who has never sailed anywhere, never owned and maintained a steel boat for any serious length of time, or never got his hands dirty building one.
    Transverse frames greatly increase the chances of a boat being holed on sharp rocks . They are a net liability in boats under 50 feet. When a BC ferry grounded east of Bella Bella ,the only holes were right next to the frames.
    Lloyds only approves stainless for keel bolts , which are guaranteed to corode badly in such an environment. I challenge anyone with a Lloyds or any other approved wood or fibreglas sailing craft to a demolition derby against one of my unapproved origami boats. So much for Lloyds, etc.
    I built my first boat using old fashioned dinosaur methods , frames set up on a jig , stringers laid along them , then plated. What a total waste of time and effort. Thankfully I had enough steel fabricating experience to relise what a waste of time it was, and was niether masochistic enough to continue this foolishness, nor sadistic enough to impose such slavery on others wanting steel boats .
    Brent
     
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