Welding a steel hull

Discussion in 'Metal Boat Building' started by Wynand N, Jun 23, 2008.

  1. Mastadon
    Joined: Jul 2009
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    Mastadon Junior Member

    CNC Worth It?

    what are the main advantages to having your boat cnc cut? Is the manual lay-out and cutting of plate a very difficult task? Do the advantages differ when building with aluminum rather than steel?
     
  2. Brent Swain
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    Brent Swain Member

    Laying out and cutting the plates is very simple and easy to do, both in aluminium and steel. CNC would simply shorten your building time from the time the steel arrived, and make for cleaner cuts, and thus possibly shorten the welding time ,slightly.
    You'd spend far more time than you would save ,doing all the CNC computer work for a one off hull.
    Brent.
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    If you also negotiate correctly, you save money by not paying for wastage too, which you would have cutting yourself. Also, if the cut-part is wrong, not your fault...you can claim for another....it is whatever you prefer and what is the main focus of hand-done compared to cnc-done which attracts you the most. For a one off small boat not much in it really...but many off, or a bigger boat, cnc comes into its own.

    PS.
    Yet again, another anonymous immature childish person hit me with more neg points, rather than discussing their petulant myopic behaviour in 'open'....what a total waste of space these childish people are! I suppose it gives them a kick from their otherwise dull mundane boring lives they live. Glad to be of service...keep taking the pills for the personality disorder :p
     
    Last edited: Aug 29, 2009
  4. Brent Swain
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    Brent Swain Member

    There is definitley a huge advantage in CNC for many boats being built to the same design. Even interiors could be pre cut to computer discs. This would result in hulls going together in a day. For the one off , it wouldn't be worth the time.
    Don't know what the childish rant in the PS was all about, but it obviously should be ignored with the contempt it deserves. I think the childish ranter was trying to impress us. Duhhh!!!
    Brent
     
  5. lumpy bumpy
    Joined: May 2009
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    lumpy bumpy Junior Member

    A couple of rattles chucked out the prams there.
     
  6. welder/fitter
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    welder/fitter Senior Member

    I think it would depend on the extra cost. As Ad Hoc points out, wastage is removed from your build costs, with the exception of limber holes, etc. .

    Other advantages are the lack of plate deformation, as compared to oxy-fuel cutting & nicely cut edges that don't require grinding.

    The materials for the M.V. "Island Sky", the newly built ferry for the sunshine coast, was delivered pre-cut. One disadvantage of pre-cut associated with that build was that there was no room for screw-ups. Due to a number of experienced steelworkers retiring or moving to Fort Mac, We had a few workers new to the drydock/shipyards & there were errors in design, the chief mistakes being that Vic. ship built the superstructure 6 inches too wide & the shrinkage of welding was not considered for the elevator shaft. An important part of any build is thinking ahead & recognizing potential problems before it is too late to correct them. You can well imagine that, the elevator shaft being midships & surrounded by the rest of the vessel, reworking the dimensions was a major undertaking.
     
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  7. welder/fitter
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    welder/fitter Senior Member

    Though I seem to remember Woosh mentioning something to me about these "points", I didn't know what it was about until I read this post & checked my own profile. Yeah, negative points left by some chickensh*t who won't leave their name is the act of a true coward, though not a surprise. I left a few positive points for those whom have made valued contributions, but have found that it is easier to ignore certain posters than to play their silly game.
     
  8. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    welder/fitter

    "..Yeah, negative points left by some chickensh*t who won't leave their name is the act of a true coward.."
    Its rather sad and pathetic really. I may not agree with everything that Brent says, but at least he has the courage to write in public his views/opinions. I didn't know what the points were either until pointed out to me too...not that i really care about my points (I have as many -ve's as +ve's)...i do follow the sad gits that hit negatives though...highly amusing and predictable. :)

    "..Other advantages are the lack of plate deformation, as compared to oxy-fuel cutting & nicely cut edges that don't require grinding..."
    One can also add, if done nicely, level lines and if thought out in advance enough, marking of the stitch sequence for the welds...saves a lot of time.

    The only thing to consider is how fast the burn speed is and hence the quality of the cut. Too fast and it'll leave rough edges which I've seen cause fatigue cracking. Fortunately nothing major, just and inconvenience which could so easily been avoided.
     
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  9. Wynand N
    Joined: Oct 2004
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    Wynand N Retired Steelboatbuilder

    Im in total agreement.
    I can understand when someone gets credited with a few points and the donor prefer to stay anonymous, that is real gentleman like.
    However, taking points from someone (which can get one of the board eventually) call for a different tack. If you are in disagreement with someone, why not have the balls and tell him straight out posting your grievance. If it has to be neg points, at least have the decency of leaving a name, and it can be persuaded by PM if it need to be private.
    Or are these chickenshi**ters afraid of tick for tack resulting in points taken off them as a token of goodwill?

    BTW, Welder/fitter is quite correct about CNC cut plates having no room for error, or can be supplied cut wrong. A common problem with this are accumulative errors can result in disasters, for example laying down frames, misfits etc. That is the very reason I dislike it personally and will never build a boat that way. Doing it the traditional way leave room to "hide" an error and can easily be fixed.
     
  10. M&M Ovenden
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    M&M Ovenden Senior Member

    Mastodon,

    To your question: “ Is CNC worth it?”, my answer is a big confident YES!

    I will first agree with others that, even though I am big on CNC, I would not get my plating NC cut. As already mentioned the cumulative error could lead to some nasty misfits. Saying that, it is done. I have visited a high end boat building facility that not only had all the boat NC cut but also had the plate NC rolled. In that shop the boats are also assembled on NC cut jigs and that even for some one offs...really crazy and amazing, but that's for the top of the line boats... for those who can afford it.

    For the common of mortals CNC is still very affordable and totally worth it. For a boat which would have been designed and modelled on a computer all what generating CNC files mean is to provide 2d drawings to a CNC shop. They should have software to nest and code those drawings. The real question becomes is it worth it to design and model a metal boat in CAD. There is no doubt in my mind, absolutely!...and the most detailed the better. Think about it, for every single little cut that will be integrated in the model (and further cut by laser, plasma or water jet) you will not need to measure, cut and clean. In my mind I much rather spend the time in the comfort of my office with the radio and a coffee than sweating or freezing my a... off in the shop (there will be plenty physical work left to be done to counter the lazy moments). What sort of details can be integrated to the model to be cut? Not only frames basic shape but also all the notches for stringers (if there are some), limber holes, you can add the lids, sides and baffles of integral tanks, all the flat shaped plates such as cockpit sides, cabin top sides (than have the holes for portholes already cut out), chain locker ...

    I believe it is even worth it for a one off boat. It isn't because you're only building one that you won't have to measure twice. Remember, “measure twice, cut once”. Cad modelling the boat is like building it once before getting to the real thing. Many paper plans I have have seen I would rather call “concept plans”, leaving a lot of what I consider design work to the builder. A good computer designed model gives out all the details and measurements you need to build your boat, it shouldn't leave you scratching your head in the shop, using cardboard to fit out steel. It is much easier to correct an error on a virtual model than on the real thing. Misfits do show up in CAD but don't cost material, sweat and swear. To me the time spent modelling a “one off boat” is only time I take away from dicking around in the shop.

    Once you start assembling your giant jig saw puzzle not only you're working with very precised cut parts but they also offer precise reference points to help assemble it. If you have athwart ship parts cut as well as longitudinal parts, fitting them together will be a good indicator of the precision of your assembly. If you have the computer model you can use some odd notch to notch distances to verify square or parallelism with diagonal distances picked out of the 3d drawing.

    As for the cost, I have found that because the charge for materials from the NC shop I deal with (big industrial shop) is bulk (they buy there steel on rolls) and lower than what I can get my steel for, the incremental cost of steel and cutting minus the waste, compared to me purchasing the steel is to be laughed at and well worth a precise jigsaw puzzle.

    All this said, yes it takes a long time to draw it all and yes it takes a good forward vision of the project to detail it but a little extra time at the design truly can save a lot on the long run. I do have CAD training and that makes it more strait forward for me but you may not be designing your boat and wondering if it's worth purchasing cutting files. I think it is all worth it. Now the level of detailing may not be the same from a designer to an other and you want to make sure you only pay for what you get. You could expect the cost of very complete and detailed files to be quite pricier than an outline of frames. You can expect the cost of files for a one off to be much pricier than the files of a commonly built boat. Drawing it all out takes time, time is money. Same for building the boat, shop time is even more money. Simple for me, I would never bother building a metal boat without having CNC cut frame.

    Cheers,

    Murielle
     
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  11. Brent Swain
    Joined: Mar 2002
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    Brent Swain Member

    The avoidance of shrinkage is a huge advantage for flat panels like deck, wheelhouse and cabinsides etc, and definitlely speeds up assembly ,as does cutting with plasma ,which as the same advantage. For an origami hull more shrinkage in the hull plates can be an advantage, as it results in more compound curve in your topsides. The cuts on an origami hull are extremely simple, so the chance of screwups is minimal, and slight differences are simply a matter of pulling the edges together, not a problem.
    Whether to go CNC or torch is a tossup, depending on how much it costs and on's budget. An origami 36 only takes a day to cut all the plate, anyway.
    For scraping off slag on torch cut edges, I find that taking a big piece of half inch plate with a sheared edge and scraping the slag off with that is far easier than grinding it off. It's amazing how quickly and easily it can be scraped off.
    If you tip your cutting torch away from the piece you want to keep, toward the scrap, all the slag blows off onto the scrap , leaving the keeper amazingly slag free. Try it.
    With the wastage on an origami boat being around 2% I dont think wastage is an issue. It can be thrown in for ballast , costing less than lead, then lead melted around it. Or it can be made into anchors , woodstove, etc. If there is a lot of wastage, the builder or the designer didn't do his homework, or the designer hasn't got his hands dirty building his designs.
    Brent
     
  12. Mastadon
    Joined: Jul 2009
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    Mastadon Junior Member

    Alright, thank you all for those replies. The reason I asked is because Ive been looking at a few designers that offer either a kit with cnc cut and formed parts or a design package with the cut files. For one 25' sportfish the cost of these two options is $2500 for the design package and $26000 for the kit. So Im just trying to figure whether or not I have the skills to build from the design and hopefully save some loot or if I should buck up for the kit and avoid disaster.

    Murielle, you have got me thinking that it may be worth purchasing the design package and shopping around for a CNC supplier.

    Next question: How much forming is involved with an aluminum skin-on-frame build and what is the best tool for the job?
     
  13. Wynand N
    Joined: Oct 2004
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    Wynand N Retired Steelboatbuilder

    Brent, if theflame is well adjusted, correct speed used, there should be no slag to be removed.
    That said, I assume you use propane gas instead of acetylene - the construction of that type of cutting nozzle (two piece) lends itself to this problem where one is stuck with residue slag on the bottom of cut.

    BTW, that tip on cutting away; I found the opposite true - if one bevel plate, the slag, if any, tend to stick to the work piece and not the off cut..
     
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  14. apex1

    apex1 Guest

    Pro, no need to comment....................

    Go for a proper cut (if possible laser cut, bevelled to weld and held in one plate to make assembling easier). One plate leaves the offcuts on your bill, but having it precut is the same bill, just not having the plates convenient to transport.
    If a kit is ten times the basic design price, let us ask if the basic design kit was worth the money!?
    Or did I misunderstand kit? Is that including material?

    Where is Lund? Is it far away from civilisation? In the real world we can get cnc a 100 tonnes boat whithin 8 hrs. cut, marked and bent to spec.s and right on the truck at a tad above material cost from local "specialists"

    Murielle pointed the main advantages out.
    I just tried to make clear, there are pretty obvious ways to save money. When a yard does it that way, why would one amateur try to make it another way? Save money? how?

    Think about that, please.

    Regards
    Richard
     

  15. TeddyDiver
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    TeddyDiver Gollywobbler

    Southern Sweden..quite famous university..
     
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