Estimating man-hours for hull welding

Discussion in 'Metal Boat Building' started by makobuilders, Jan 17, 2015.

  1. makobuilders
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    makobuilders Member

    What are some rough guidelines for welding up a steel hull with CNC cut parts? I assume this would be on a hrs-per-pound basis or similar.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Generally quoted in man hours/tonne..or similar units.

    It can range from 300 manhrs/tonne (experts and good quality yard) to 1500 manhours/tonne (inexperienced or poor quality yard). It all depends upon the experience of the yard the facilities in the yard and the general infrastructure.
     
  3. makobuilders
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    makobuilders Member

    Is this estimate including laying out the lines and cutting the steel, or specifically for welding up?
     
  4. waikikin
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    waikikin Senior Member

    There's plenty of variables in there, you can have heavily plated with sparce framing....... or lightly plated with much more framing & intersections..

    You could go broke using one generic per tonne rate unless there's heaps & heaps of fat in the multiplier & then you could be feeling relaxed & have nothing on the floor to build....

    To me it would be better to have an idea of the cutting cost on a material plus linial meter rate per LM cut plus some factor for waste/transport & handling then a fabrication cost dependent on complexity then a weld out cost again related to complexity, LM, process.

    Facilities such as cranage & shelter for the build will affect the time & ease of fabrication as will chosen/specified welding process plus as Ad Hoc mentioned the skill & motivation of staff, plus the best are often harder to attract to a project as they are sought after & looked after.......

    Facilities vary from a paddock with nothing to weatherproof shelter with magnificent cranes & process/equipment that delivers high production & deposition rates.....

    The vessel style & size have not been indicated.... yacht, tug, barge, ship?

    Makobuild, you need to work this out for yourself, as Ad Hoc succinctly put it depends & no one but you knows what vessels & facilities you are aiming at or have, or do you have the perspective of a client/customer?


    All the best in your endeavours from Jeff
     
  5. gonzo
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    gonzo Senior Member

    You could not use a "per pound" estimate and be realistic. A small boat has many more hours per pound than a large supertanker. A better estimate would use total length of welds, multiplied by the number of passes for each weld. They would then need a correction factor for vertical and overhead, which take longer.
     
  6. TANSL
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    TANSL Senior Member

    All shipyards that I have known, and have been many, have their scales to estimate the cost of steel woorks and they all are in hours per ton (not per pound). These data are so realistic that is with them that shipyards make their offers to potential customers. Depend, of course, inter alia, vessel type, material, etc.
    You can make an initial estimate of the total weight of steel but weld estimating meters, horizontal, vertical, .... would be crazy. Can not estimate the cnc length cutting, empty movement, marking movements, etc. Nor can estimate the dead time, time for transport of material, or several other factors. That is why they have fixed rates that include all that.
    I'm not having that data to offer them to makobuilders.
     
  7. waikikin
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    waikikin Senior Member

    I concur,

    given that Makobuilders interest on the forum to date seems to relate to & around 45-50' trawlers these are in the boat range. A tonne rate will relate back to a function of all the processes used to manufacture including scheduling, management, transport, stores... just very unlikely that firms will give the breakdown away.
    Some marketers of steel kits & plans in the "boat" size range will offer optimistic estimates & "histories" of construction times of their product, best taken with a grain of salt.

    Jeff.
     
  8. TANSL
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    TANSL Senior Member

    I seem to understand that makobuilders also refers to times for cnc cutting and probably need some other time studies. In any case, the costs of welding, without more, is not going to give an idea of the cost of the steel of his boat as there are other associated costs that make welding represents only a small% of the total.
    If the boat is so small that it can estimate the costs of welding, better do a detailed time study, a study of material wasted, etc., etc .. In this I agree with you. But again, the cost of welding do not think it will be helpful to the OP.
    But hey, if makobuilders tell us what he needs, maybe we can stop giving "opinions" (not all with some base) and start giving specifics.
     
  9. gonzo
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    gonzo Senior Member

    He is very clear on what he wants: "What are some rough guidelines for welding up a steel hull with CNC cut parts?". The cost per ton only works on similar vessels. You can't compare a 30 foot trawler to a 1000 foot tanker.
     
  10. TANSL
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    TANSL Senior Member

    No one wants to compare small boats with oil carriers. I do not understand why you do not realize that's not the point. What I say is that measuring total welding of a boat, find out the throat of each weld, find out the layers that each welding leads, apply the minutes / meter depending on the position in which it is solder, apply a correction depending on the type of machine welding is used, etc. etc. etc., is really stupid.
    I'm sure if you think about it, you'll agree.
     
  11. makobuilders
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    makobuilders Member

    Yes the application is for a small steel trawler approximately 45 +/- feet. I work here in building construction, with excellent steel suppliers and fabricators. So access to pre-primed, CNC cut parts is a no-brainer. We have certified welders, unfortunately working at much lower productivity rates than back in the US, but at least their work output is predictable. The challenge that I'm facing though, is that although I can estimate for "building" construction, I'm trying to apply this to a future boat construction.

    Welding up a small boat is more about handling, positioning and making multiple small welds for distortion control. It makes sense that the productivity per ton (or lb) would be much lower than welding up heavy beams with long weld beads.

    Perhaps someone who has welded up a boat in the 35-60 foot range could chime in on how many man-hours were needed for a hull of "X" many tons steel.

    But my interest is in the fitting and welding, not the CNC cutting.

    Thank you.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    makobuilders

    Unfortunately there is no magic bullet here. Since each manhrs/tonne is different for steel as it is for ally or composite. Not only that, to add to this mix, difference in hull design. Thus the manhrs/tonne for a monohull would be different to that of a SWATH for example. And to add more variables, as also noted above and by yourself, whether the vessel is say a 10m hull or a 50m hull again, changes the variables.

    You can only work with what you know, like all engineering problems. This is no different. Your "model" of estimating needs validating and verifying. Only you can do that with your yard and facilities, each is unique.

    At one point many years ago i spent several months collating data form my yard on different designs and materials and establishing weld lengths and construction hours. From that i wrote a simple program to give me a quick first estimate of weld lengths and man-hours. Once delving into this it becomes very apparent that fabricating in steel is very different form aluminium and the size and hull design all play important roles in terms of hours spent fabricating; even though very obvious.

    Thus take what you know, then create simple sample test pieces and see how long each takes to make, us that as a basis and refine your 'model' as you acquire more data.

    This is why, certainly in the good old days, the estimator was as important as the chief NA. The estimator kept all his data very close to himself and a very good one was worth their weight in gold. Since no one thanks you for an under estimate project on terms of time or costs and you lose money, similarly if over estimated and losing the contract. Just as with the design, in terms of its speed and displacement etc. no magic bullet...just experience and lots of data.
     
  13. gonzo
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    gonzo Senior Member

    There is another very important thing to consider: what is the accuracy of the parts?
     
  14. waikikin
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    waikikin Senior Member

    Link Check

    http://www.bruceroberts.com/public/HTML/V495-1.htm
     

  15. waikikin
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    waikikin Senior Member

    Makobuilders, OK the link is good.... sometimes weird stuff happens there!
    http://www.bruceroberts.com/public/HTML/V495-1.htm

    That link is my old work mate & myself fabricating an Almarine/roberts/BR Australia kit, there was issues with the supply such as mis-matched thickness port to stb, wrong keel option supplied, wrong cockpit option supplied amongst some other minor issues, this will explain pre primed plating & plate in mill scale as seen to pics.
    During build the dispute of design ownership & general uncoolness added to the vibe... I digress but setting the scene,
    The build/fab was done roughly around/after the time of Sydney 2000 Olympics & tech stock crash.. more digression but just tuning my memory;)
    The below is not quite a trawler but similar in length, probably lighter plating: this is the closest representation I could remember, I try not to do that stuff anymore.......... wiser, richer, older/worn out maybe..
    The "Bermuda 485"(Same? as) kit was cut in Holland, delivery took some time, supplied plating issues were either locally cnc recut or recut to manual development & templating by myself, this supply was reimbursed in good faith by the Australian reseller:)
    I cant remember the fabricated weight but would be maybe be around 7-8 tonne, fin keel was 6mm, bottom plating 6, radius chine 5, topsides 4, deck & cabin mix of 3,4, 5. Tanks were included as separate drop in units to between frames, also water tight bulkhead "option" was filled in & stiffeners beyond kit supply at points, there was some rework/extra framing to skeg.
    The kit was generally good in fit up with framing & stringers profiled & notched etc, also there was whitish scribes to plating for framing & stringer intersections, on the recut/new cut material measurement sufficed, there was a 16-18mm shortfall in matching topsides to radius plates & a round bar of around 20/25mm inserted to tangent exterior plating. The supplied welding schedule apart from framing was to weld oustide only of plating, as builders this was unacceptable & inside welded out also. Memory fades but somewhere between 800-1200 meters of weld rings a bell. At around 1800 hours(total) tech stock crash hit & perspective of client adjusted to new circumstance, the vessels steelwork was all in place & probably 60-70% welded out. "Discussions" with owner included deposition rates to structure... a matter of perspective, my machine could squirt around 14-16 meters per hour at the setting & travel required but realistically acheived about 3+ mph with the sequence, grind out of every cold start & moving around to limit heat, my work mate & I would match efforts side to side & swap sides also, he also did tankage as the better qualified/experienced. After negotiations work continued & all mild steel work, lifting of vessel & fitup & weldout of keel fabrication I think we were at about 2200 hours total, this included tankage & all mild steel work complete, it had been proposed to fit a fair bit of stainless as wear points/sponson landing etc, from memory only the traveller landing was applied in staino as the rest of the shiny stuff never fronted due to diminishing funds of the client. The vessel was supplied with a hardstand adjustable cradle beyond the low set building jig supplied with the kit. Supervision of loading & delivery to another yard local to the owner ensued . At a later date this client communicated apologies & had some independent assessment of the works that came back very favourable, this was no surprise to us having been working well & fairly... also as soon as there was a whisper of issue we had a surveyor come in to assess the works .......
    As it was our agreements were on a handshake for supply of labour plus consumables & an allowance for site costs & the client got a well fabricated structure at a reasonable cost...
    Regards from Jeff
     
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