Welding the skin to the frames demystified

Discussion in 'Metal Boat Building' started by M&M Ovenden, Aug 31, 2008.

  1. Brent Swain
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    Brent Swain Member

    Welding skin to frames.

    Talking of hogging and sagging , shows an abysmal naivete when discussing small boats. To hog the deck plate has to stretch longitudinally , not likely with a material with a yield point of 45,000 psi. To sag the hull plate would have to stretch logitudinaly. To twist it has to stretch diagonally. This points out the abysmal foolishness of trying to justify transverse framing in boats under 50 feet. How do transverse members haver anything to do with decks or hull plates stretching logitudinally, or diagonally?
    When you can get a very attractive sailing hull in 1/10th the time effort and expense, that sails better and faster , there is no justification for doing it the slow and expensive way.
    Brent
     
  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Brent

    So when a small boat, let say 10m yatch or a 10m "speed boat", is in rough weather. The forefoot/bow is exposed owing to the large seas coupled with the speed of advance of the boat relative to the waves. When the bow then plunges back into the sea, if the sea state is a short sharp irregular sea, as often encountered in coastal waters, the bow is momentarily supported by the wave and the so is the stern.

    This is a classic sagging moment.

    I once got very very wet out on a 8m run about on sea trails in 2~3m seas doing 30knots, just like this....very very bumpy, but great fun.

    The application of the load hogging or sagging has nothing to do with hull material. If you selected wood, for example, does the boat suddenly say...oh, I'm made of wood not steel, so i no longer am in a sagging/hogging load case...er, nope! Would it change if the hull was made from switz cheese, er...nope....so what about from steel/ally...er...nope. The moment is a function of the hull length, sea state, speed etc...has zero to do with the hull material.

    But, what stresses you expect in the boat owing to the hogging/sagging or indeed any applied load, is a direct function of the hull material.
     
  3. Guest62110524

    Guest62110524 Previous Member

    what nobody has bothered mention, is when an unframed boat come on the wind, the rig is under enourmous tension, Swains boats must have a very small underpowered sail plan.
    I have been on boats without adequate framing, and what happens is, the doors will not close, they jamn, the glue on the wood cracks and so on
    Actually I think many of you are not sailers at all, despite claims to the contrary, or you would not make these outrageous statements
     
  4. welder/fitter
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    welder/fitter Senior Member

    "what nobody has bothered mention, is when an unframed boat come on the wind, the rig is under enourmous tension..."

    Interesting point, when one considers the flexing with no knees or the saddling with transverse framing(knees) in this area alone. The alternative to this would be that the hull-deck joint must take enormous loads, even more so than it already does.

    "I have been on boats without adequate framing, and what happens is, the doors will not close, they jamn, the glue on the wood cracks and so on..."

    I think that the bulkheads on the frameless boats become the frames - attached to hull by tabs - so one is then relying on the plywood bulkheads to take the load? Or, once again, the hull-deck joint, combined with transverse deck framing & deck plating take the loads, but twisting of hull? Brent will have to straighten us out on this one.

    'Actually I think many of you are not sailers at all, despite claims to the contrary, or you would not make these outrageous statements"

    How you sometimes manage to fit the other foot in is what amazes me.:rolleyes:
     
  5. Brent Swain
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    Brent Swain Member

    Welding skin, etc

    River boats dont let frames touch the hull skin because if they did that is where the holes would be punched in. Pollard makes this point in his book. That is the only place where the BC ferry Queen of the North was holed in Gunboat pass.
    Instead of gussets which only have a short reach down the topsides, I run a sch 40 pipe from the inside corner of the cabin side to the chines. This triangulates the corner. The cabinsides are a beam on edge supported on top by the cabintop and on the bottom by the decks. To distort the decks would have to be compressed on edge. You can tell how much give there is in your rig by how much slack there is in the lee shrouds driving hard to windward. The lee shrouds on my boats are as tight with the rail buried as at the dock.
    Some one again made reference to large ships, completely missing the point that I have made so many times that it is the for and aft curves of the topsides on a sailboat that take the place of transverse frames. frameles doewsn't work for l flast topsides.If I were to say here that the sun rises in the east some half wit semi illiterate would respond with"NO Brent you are WRONG. the sun does NOT rise inthe WEST."
    There are adult literacy courses available for such people .
    Comparisons have been made with German battleships. The idea that smal sailing crag ft should be built to German battleships is the reason that the myth persists that steel boats under 40 feet are not practical. If we followed their logic , steel boats under 150 feet would be impractical. I only design to 40 feet, Beyond that is speculation altho several frameless origami boats wiht Canada Shipping surveys for opasseger boats have been built.
    If I wanted to build ugly boats I'd build the ones with the chine visible in the water with ugly chines extending right to the ends instead of smooth rounded , seamless origami ends with no chines visible.
    Brent
     
  6. apex1

    apex1 Guest

    Yes Brent, by yourself........................:

    And do´nt call people illiterate that might be able to speak more languages than you can enumerate. (and produce less typo´s in a foreign language than you in your mother tongue)
    Regards
    Richard
     
  7. Dudley Dix
    Joined: Sep 2005
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    Dudley Dix Designer

    This thread has become little more than a series of personal attacks and of little value to followers of the thread. I see insult in some posts, resulting in angry responses. The same opinions appear over and over again.

    I want only to make some observations and am not going to enter an argument over nor make apology for my opinions. If you disagree with them then so be it, that does not mean that you are right and I am wrong.

    1) What has been proven to work in use is valid basis for future design.

    2) Houses are not designed with the same structure as tower blocks nor a Piper Cub with the same structure as a jumbo jet. Why should a small sailing boat be designed with the same structure as a battleship? Yes, loads increase disproportionately as size increases, so the structure of a small boat cannot be scaled up to a much larger sister. That also works in reverse, so don't expect to see the same structure in a small boat that is needed for a ship or a submarine.

    3) Yes, construction material does affect the behaviour of a sailboat's hull under sailing loads. A welded steel hull is dimensionally much more stable than a carvel wood hull, or a GRP hull for that matter.

    4) Yes, the bulkheads of a frameless steel hull do act as frames but they support the stringers and the stringers support the skin.

    5) I have steel designs up to 38ft that have no tranverse ring-frames. Stringers are supported by bulkheads. Some of these boats have been sailing 20 years and continue to do successful trans-ocean trips. They do so with doors continuing to open and close, a problem that is more likely on GRP boats than those of metal.

    6) Hull distortion is not the only reason for slack leeward rigging. Stretch under tension in the loaded windward rigging will relieve the pre-set load in the leeward rigging, as will compression in the mast. Bending the mast to de-power the mainsail also has a big effect because the bent length of the mast is less than the straight length.

    7) The van de Stadt design office is very well respected worldwide and has supporters among those posting on this thread. The steel Stadt 34 design is frameless, with very little welded internal structure. If you reject frameless construction then this design must be included, despite having proven itself through many thousands of miles of safe voyaging.
     
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  8. TollyWally
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    TollyWally Senior Member

    Well said Mr. Dix. The exchange of knowledge is facilitated by more civil discourse.
     
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  9. Wynand N
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    Wynand N Retired Steelboatbuilder

    Dudley, if I may quote old Meatloaf; "I couldn't have said it better myself..."

    Thanks for your input in this thread - some probably took it to heart, others not, but hey, we are a democratic society ;)

    As a parting note and without being biased, I have yet to see a Dix steel boat fail structurally and that in my book, based on more than 25 years of his boats being built all over the world, says it all about his designs, engineering he puts into them and method of construction. Why fight the facts?
     
    Last edited: Mar 16, 2009
  10. Brent Swain
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    Brent Swain Member

    Welding skin to frames

    I was told that when cutting torches were first introduced to shipyards, the luddite workers snuck them out and threw them in the harbour, for fear they would cost jobs. When advancements in boatbuilding technolgy reduce the number of hours a yard can charge for a hull and deck by 90%, one can expect the same reaction by those boatbuilding luddites with a big financial stake in holding the clock back.
    The decks and cabinsides on my 36 have a yield strength of over 420 tons. Wood , instead of a strength of 60,000 psi ,has a strength of 1500 psi. No, they are not the same. Believeing that a 9 ton yacht being bounced around will put a load of over 420 tons tension on the decks is like believing that the Flintstones is a documentary. Resistance to twisting is in the same magitude.The hull, being 3/16th plate, is 50% stronger, not counting the topsides, or the keel web and skeg, on a single keeler.One has less chance of such decks stretching longitudinally than of being hit by an asteroid. So do critics of origami boats have asteroid collision on their boats? Wanna buy some?
    Herreschoffes rules talk about putting in diagonal bronze strapping to avoid hogging and sagging. Is someone suggesting that a steel topside is less effective that 4 inch wide strapping? The whole topside is a diagonal strapping, any direction you choose.
    The chines are structurally, massive logitudinal angle irons. Tying the cabinsides , beams on edge , to the chines with sch 40 pipes is far more effective in supporting the decks that any number of short gussets. You need two on each side. I put one under each side , by the mast , altho with no ports nearby it is not structurally neccessary for it to be directly under the mast. The aft ones can be anywhere convenient . It can be hidden behind a bulkhead , or under the back of the cabin if that suits you.
    One always has the option of saving a huge amount of time by building larger boats using origami methods, then putting in whatever frames you feel comfortable with, after the seam welding is done. However , once the skin is together it becomes self evident what supports what and how irrelelevant transverse frames become.
    Skeptics can educate themselves by simply building sheet metal models of origami boats , then try bend it without the decks on, then with the decks on etc etc . What supports what becomes self evident. Most won't ,because it will clearly display the foolishness of ther skepticism.
    I don't just sit around in a comfortable office drawing pretty pictures of boats. I have sailed my 31ft origamiboat to Mexico and back and two trips to Tonga and back, the later involving 4,000 miles of beating to windward against the trades, the last trip being non stop, Tonga to BC. Nothing budged .
    If a hull speed colision with a steel barge, a log boom at 14 knots, a sunken barge, a freighter , etc etc, haven't moved anything on my boats then its safe to say that not much will.
    Peter D Wiley gave a clear example of the type of deception and distortion it takes to cook up fault with origami boats, when on another site he posted a comparison with the weight of his "38 ft Saugeen Witch" with my 40 ft design. The Saugeen witch is a 34 footer with ten ft beam. It's only 38 ft if you count the bowsprit. It's like me putting a ten ft bowsprit on a 36 footer then comparing it's weight with a 46 fooer with no bowsprit. my 36 footer is a much larger boat than the Saugeen witch . My 31 is roomier. My 40 footer is huge with nearly 12 ft beam, and no comparison with a Saugeen witch..
    Brent
     
  11. MikeJohns
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    MikeJohns Senior Member

    I agree it is much better to be civil.

    Much of this is actually defensive, Brent starts on the attack often vehemently eg .... "The abysmal foolishness of trying to justify transverse framing in boats under 50 feet" In other threads it's been 55 feet and I seem to remember once even 60 feet.
    Structural bulkheads are always considered transverses and this has been made clear enough in the past, but the whole “frameless design” term is really misleading it just means transverse and longitudinal support and stiffening is achieved by integral design, allowance for chines , curvature, tank walls, bulkheads, keels cabin top sides/ends etc as we all do.

    Unfortunately Brent tends to have a habit of condemning other peoples designs, invoking a series of questionable reasoning and then jumping needlessly but vocally to the defense of his 26 and 36 footers whilst driving any discussion into some very questionable and even entertaining arguments. Although people get very frustrated with him it should probably be taken more as round table banter rather than a bar room brawl. Such is his personality.

    Small steel boats are very strong whilst as they get larger that great strength diminishes and ships are comparatively weak. Relating any small boat design to ship design is a complete fallacy. It was actually Brent who introduced battleships (and gas bottles) the submarine was just a corrected corollary of the gas bottle.

    What has been proven to work is something that must be considered within a carefully framed reference. The problem with leisure boats is ascertaining just what conditions and duty levels the boats have endured. As I said before, the scantling societies do consider all this in detail, the point being that nowadays we have collated enough data to predict just what factors of safety we need and in which parts of the vessel. Any class society or body will reject what they consider a deficient construction even if it and its sisters have managed to circumnavigate the world time and again. Blue water design is for worst case scenarios which will seldom if ever be experienced so I would use this argument with provisos.

    The Van de Stadt design office generally designs to GL, these rules are quite specific on just how frameless you can make a metal boat. The Dutch have been building both frameless and “origami” steel construction since around 1947 and have always been at the forefront of small steel vessel innovation. Van de Stadt has always been very happy to discuss design and to provide details and calculations, in other-words a professional approach from a gentleman. Van de Stadt’s designs go into survey here without much fuss and they have a clear honest and open approach.

    It’s always a hard call on a forum to know whether to add a post as a note of caution to someone who has searched for the subject to educate themselves or to leave what is obvious to most of us here unsaid. Generally it’s worthwhile to add clarification and prevent dubious ‘facts’ from becoming urban myth. eg .... "The abysmal foolishness of trying to justify transverse framing in boats under 50 feet" This position is what Brent should be defending not jumping back into the 26 footer for a series of anecdotal collisions.
     
  12. apex1

    apex1 Guest

    Mike
    thank you, you brought it to the point:

    >>>>>It’s always a hard call on a forum to know whether to add a post as a note of caution to someone who has searched for the subject to educate themselves or to leave what is obvious to most of us here unsaid. Generally it’s worthwhile to add clarification and prevent dubious ‘facts’ from becoming urban myth. eg .... "The abysmal foolishness of trying to justify transverse framing in boats under 50 feet" This position is what Brent should be defending not jumping back into the 26 footer for a series of anecdotal collisions.<<<<<<

    And I agree, for most of us it stands to reason, just to ignore Brents promotion campaign. But sometimes it´s hard to stay sober if the drum is beaten too aggressiv.
    Regards
    Richard
     
  13. welder/fitter
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    welder/fitter Senior Member

    Perhaps, everything that needed to be said about welding the skin to the frames was covered in the first two or three or four pages? What part of "welding the skin to the frames demystified" involves the pros & cons of frameless boats? No part. I am, actually, curious as to whether the load on hull-deck joints are greater on frameless boats, but that belongs in another thread.

    I am sure that there are many great frameless designs in the world. If a thread regarding these hasn't already been started - which I highly doubt - perhaps, now is the time, by those interested?
     
  14. Brent Swain
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    Brent Swain Member

    Welding skin to frames

    You are absolutely right. The term frameless is misleading. Origami boats are longitudinaly framed. Hull to deck joints are more than a frame, but a huge fully welded steel bulkhead, as are chines , centreline and welded in tank tops. So is the single keel , skeg, and web conecting them along the centreline. The distance between these super strong structural members is relatively short, and supported by longitudinal angle stringers , on which any load is taken in compression on end, rather than the simple bending load on a transverse frame.
    Any designer can learn a lot about metal and how the loads are taken, by building a sheet metal model and experimenting with it.
    I respond to attacks on origami boatbuilding methods. I attack when attacked. I respond to the elitism in boat building, by methods that will deny many the opportunity to own a good steel boat, using the most modern and efficient building methods.
    I respond to attempts to slow down steel boat development to a pace that the most backward can keep up with, at the expense of the advancement of metal boatbuilding , cruisers and the realisation of their dreams. For that make no apology.
    No, there is no justification for continueing with methods that take ten times as long with poorer results.
    Brent
     

  15. pdwiley
    Joined: Jun 2008
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    pdwiley Senior Member

    Actually Brent you need to do the remedial reading.

    I have a set of plans from Tom Colvin for a 38' Saugeen Witch.

    Let me repeat that bit - 38'. That's LOD, Brent, not including the bowsprit. It's a stretched Witch displacing 15200 lbs.

    I didn't compare it with your 40' design, I compared it with your 36' design. If you don't like the comparison that's not my problem. Your 36' design displaces some 2,000 lbs MORE than the 38' LOD Witch, on your own figures.

    Your 40' design displaces *tonnes* more than Tom Colvin's 'GAZELLE' design, on your own figures, and the GAZELLE is 42' LOD. That's what I compared it to. I'm away from my library at the moment so I can't recall what the displacement of your 40' design is but it's way more than the GAZELLE.

    The hull plating for your 36' and 40' designs weighs nearly 8 kg/m2 MORE than Tom's designs, in the most favourable case for you - Tom's designs built with 4mm plate rather than 3.5 or 3mm. How many square metres of plate in those hulls of yours?

    Your designs are NOT frameless. There's as much framing in your deck supports as there is in a Witch deck. You have heavier floors than a Witch. You have to add a lot of tabs to the hull plate so as to attach an interior. All that steel adds weight but in the case of the tabs, it doesn't necessarily add strength.

    The point I was making is, your claim that framed designs weigh more than origami frameless designs, is ********. They don't, necessarily, and claiming that they do is just a sign of wilful ignorance of readily discoverable facts.

    I won't bother waiting for you to retract anything because you never do.

    PDW
     
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