Composite High Speed Boat Structural Hull Bottom Grid

Discussion in 'Boat Design' started by an2reir, Sep 28, 2021.

  1. an2reir
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    an2reir fifty boat designs

    Greetings from France I wish you all a great autumn
    I did recently design a high speed stepped hull motor boat speed 60 knots
    and I think people tend to appreciate my work we do as we speak have some preliminary orders
    Now I am planning to build a batch of 10 boats as fast as possible
    I did design the hull structural bottom grid as this attached
    I would appreciate your feedback in regards what you consider as an acceptable building time for a vacuum infused boat bottom grid like this
    The building sequence should be sort of like follows:
    1. Cutting of fiberglass fabric batches
    Typically we made drum rollers of fiberglass fabric material in the working perimeter and we cut by hand with the correct scissors the operation was done by the team of laminators
    Should I cut by CNC? Best to cut by hand?
    2. Cleaning of the mold 8 hours X 2 laminators + foreman laminator
    3. Apply mold release agent 8hrs x X 2 laminators + foreman laminator
    4. Apply the gelcoat 8 hrs X 2 laminators + foreman laminator
    5. Apply the strata of fiberglass or carbon 16 hrs X 2 laminators + foreman laminator
    6. Prepare the vacuum infusion 8 hrs x X 2 laminators + foreman laminator
    7. Make the vacuum infusion x X 2 laminators + foreman laminator
    8. Demoulding 8 hrs x X 2 laminators + foreman laminator
    9. Cut the edges 8 hrs x X 2 laminators + foreman laminator
    Total should be less than two weeks per team 2 laminators + foreman laminator

    What did I forget? Is 10 working days a building time that is compatible with your experience?

    I am thinking to make my forward section of the structural liner to substitute the forward section of stringers + transversal floors by the the module of structural components interior of the cabin that includes cabin sole and bed vertical surface

    Any opinions on that?Thank you in advance for yours answers.

    Structure Fond  Hull.jpg
     
    Last edited: Sep 30, 2021
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  2. fallguy
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    fallguy Senior Member

    @ondarvr has some relevant experience that may help you

    I don't have much to offer, but..

    I hope you are using electric scissors! No way would I do that by hand.

    Patterning is important. If you make patterns, it will save you time measuring which is slow and error prone. All the fabrics I use here I mark real well with sharpies which way is up and or forward, port/star as needed to avoid confusion later.

    Here is a fancy cutter.
    Cordless Fiberglass Cutter – LBI Fiberglass Products https://www.lbifiberglass.com/product/cordless-fiberglass-cutter/

    Here is the one I use.

    [US$84.99 17% OFF] Potable Electric Scissor Auto Cutter Power-driven Shears Household Industrially Cloth Power Tools from Tools on banggood.com https://m.banggood.com/Potable-Electric-Scissor-Auto-Cutter-Power-driven-Shears-Household-Industrially-Cloth-p-1300951.html

    Sorry, but not qualified to comment more.
     
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  3. an2reir
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    an2reir fifty boat designs

    nimbus bottom  structure  1.jpg Thank you @fallguy electric sciossors what a very good tip ! At present we cut the fiberglass by 2D CNC by an external contractor but I think it does take too long from make the patterns to send to the contractor to have them cut and to receive the fabric batches

    I am wondering how long this process of laminating the structural grid takes other boat builders ???? more precisely does it take others less than my calculated time of 10 working days by two laminators + foreman

    Thank you in advance for yours answers.
     
    Last edited: Sep 30, 2021
  4. fallguy
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    fallguy Senior Member

    If you had cutting setup, during times when people were not able to work; others could cut glass. For example, if you are edge trimming; the foreman standing there may be wasteful and so he could decide to go cut glass if the crew well understands the work. So, glass cutting could be backfilled some..or done during less critical phases. Or if only one gelcoat gun; one man can be cutting. But be careful of having someone cut glass during critical operations. No reason to have a failure because someone is cutting.

    I would say some of your estimates might be high. Cleaning the mould at 24 man hours seems a bit much. My experience is on much smaller moulds, though. I was able to use compressed air and the pva just blew off. Some small surface defects would seem allowable on an inside grid below decks, so getting 24 hours for cleaning and 24 hours for waxing may adjust downward for some quality reductions. What you don't want is sticking, of course. So, no trading off crew or reduction of quality waxing or release application.

    Try to be patient and see if others post any replies. It is mostly out of my league, but we'll keep you to the top with my annoying chatter.
     
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  5. an2reir
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    an2reir fifty boat designs


    Thank you @fallguy your kind feedback is most welcome and appreciated. Today has started the beautiful La Rochelle Boat Show Le Grand Pavois and come Saturday I plan to visit and will also ask the question directly to some of the France boatbuilders over there

    Thank you in advance for yours answers.
     
    Last edited: Sep 30, 2021
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  6. ondarvr
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    ondarvr Senior Member

    The time it takes for each step can vary a great deal depending on the exact design of the part and skill of the workers.

    Gel coating the parts could take as little as 2 hours if you spray, rolling and brushing will take longer.

    Mold prep shouldn't take that much time. And possibly much less after the first couple of parts.

    If all you plan to build is the hull and stringer grid, two weeks would be relatively easy. After these components the build gets much slower and more detailed.
     
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  7. rxcomposite
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    rxcomposite Senior Member

    Are you familiar with PERT-CPM method or at least the use of the software MS Project?

    If you are familiar with manufacturing, you can arrange a horizontal workflow diagram and from there you can refine it so that you can make parallel operations and support group to speed things up and increase efficiency. Manhours/Manloading becomes part of the study.

    For example, you can do simultaneous Hull Lamination, Grill stiffener lamination, and Deck lamination. When you finish the hull, the grillage is finished at the same time and is ready for mating/assembly. When you finish the hull, the deck is ready to meet the hull. All along you have support group supplying the laminators with cut parts and catalyzed resin Just in Time (JIT).
     
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  8. rxcomposite
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    rxcomposite Senior Member

    Example of horizontal workflow is Mold Prep-Gel Coat Spray- 1st layer lamination, 2nd....., stiffener/bulkhead assy-curing(zero manpower)- demoulding-trimming- deck to hull assembly. Allotting manpower base on productivity rate to meet a set time to finish. Add the manpower allocated for each station and you get a daily manpower total.

    There are industry standards for productivity and hope other members can pitch in.
     
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  9. an2reir
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    an2reir fifty boat designs

    Greetings from France thank you for your feedback wich is most welcome I do wish you a good weekend. Thanks @ondarvr for your feedback from what you kindly wrote it appears if I take 10 working days for the building of the structural grid alone the time of 10 working days for two laminators and one foreman would be perhaps more than sufficient.
    Thank you @rxcomposite I confess I will make myself familiar with the PERT-CPM method and to the use of the software MS Project ASAP following your kind input.
    At this stage I did design my stepped hull and I did the planing and speed predictions with Orca Savitsky and I am preparing to do the CFD simulations with the CFD software Simerics as my target speed is 55- 60 knots and in the meantime I try to determine what would be the best approach to the design of the structural Grid costwise and timewise for example these folks from Cigarette Boats they choose to have a structural grid made in preformed polyurethane stiffeners and I do see here the longitudinal stiffeners are very high going just to the inferior surface of the cockpit . I just wonder may that be the case that instead of paying say 50000 EUR for the structural grid mold we just choose the approach of building the bottom grid in preformed stringers and preformed transversal frames and do the wet layup lamination on top?
    Preformed stringers.jpg
     
    Last edited: Oct 1, 2021
  10. rxcomposite
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    rxcomposite Senior Member

    60 knots Holy cow. What is the length of your boat?

    Last time I did stress analysis, the average at midship is 150 kN/m2 and rises up to 360 on the bow, slamming at 50 knots.

    How did you do your stress analysis? What is the governing rule you followed?

    Sorry could not comment on grid arrangement.
     

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  11. an2reir
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    an2reir fifty boat designs

    Hi @rxcomposite thanks for your feedback! LOA = 13.6 m . Thanks for the table of pressure on high speed boat . I am working on the 3D CAD model for the FEA simulations ; I will use two FEA software : Hypermesh and Scan& Solve in Rhino 7 . I will comply to ISO standards and ABS standards.
    There are a number of options for laying out the bottom grid one is the bottom grid made in mold and hatsections another is the grid made in preformed polyurethane stringers and another kind of structural stringer appears to be this one made in CNC cut flat panels that are being laminated on the marble and that would be capped on top with unidirectional carbon fiber like this attached image raidisseurs type Gurit&.jpg . I think I need to do the PERT-CPM method analysis for all three and compare the results
     
  12. ondarvr
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    ondarvr Senior Member

    The stringers grids made on a separate mold and dropped in place are much faster and more uniform for rapid production.

    The pre-cut foam stringer grids are cheaper short term, but add time and labor to each build. The more hulls you build the less cost effective it is.

    Neither method is wrong, it's up to you to decide which method meets your budget and production goals.
     
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  13. philSweet
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    philSweet Senior Member

    Have you considered prepregs made from aircraft scrap? It wouldn't work if you needed to make 1000s. But if you could adapt your glass patterns to nest in the scrap pieces from aircraft, that should save time and money, and a set of ten would seem to be in the right scale of things.

    An acquaintance in the Florida Keys did this. He designed an entire small boat around Boeing scrap prepregs, and was knocking them out like muffins as the stuff was delivered. He could build a small dingy in 45 minutes total. Built 4 per day - two in the morning before going to work, and two in the afternoon after getting home from work. Then fold everything up and still park his car in the garage at night.

    It's hard to say about the labor hours without knowing the labor rates. Our laminator was from the mountains above Acapulco. He slept in a corner of one of the containers we used to store molds in. He worked about 12 hours/day for 11 months then went home for a month each year. He could build the mold for that grid and do all the laminating. It might take him a week to pop one of those out. That would have cost us about $200 in labor. Similarly, you can get laminators for about $300/month in the free trade zone of the Dominican Republic. If they built 10 in three months, you'd be into it for about $250 each once everything was squared away. Of course, getting them shipped back is another problem. One of my coworkers has a son in Long Beach. He has been taking photos of the container ships stacked up at the port. Some of them have been there for six months at anchor outside the port.
     
  14. rxcomposite
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    rxcomposite Senior Member

    Most new builders learn by the seat of their pants. For those who wants to plan, a Gantt chart is the easiest way of planning. Graphing horizontally when a project will start or stop.

    For your need and a desire to plan ahead and study the process, a PERT CPM is the way to go. It is the Start and END of simultaneous process. Sort of multitasking.

    This is a must for series production.
     

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  15. rxcomposite
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    rxcomposite Senior Member

    Yup. We throw a lot of stuff away. See, I built a plug out of scraps Diab HT Foam.

    One enterprising guy started building model boats out of scrap prepregs. Then graduated to model airplanes as the cast away stuff is only 9 mils thick.
     

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