Foam/Plywood boat plug construction ?s

Discussion in 'Boatbuilding' started by cla17, May 18, 2003.

  1. cla17
    Joined: May 2003
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    Location: San Diego, CA

    cla17 Junior Member

    Hello,

    Background:
    I am trying to build my dream 21'6" ski/wakeboard boat. I want to build a plug for an actual production style mold(I trying to build this into a business). I have some auto body and boat maintenance repair knowledge. I have had little experience with fiberglass and none with gelcoating.

    Situation:
    I have a design I want to build but and am on a budget(who isn't) and want to build a 2 part Poly foam and plywood plug. The plywood for support and the foam exterior shaped to the desired shell. I plan to use a Versi-Foam system to spray the foam, unless you someone knows of a better foam for shaping, but I don't know what tools I'm going to need to shape this stuff and how I am going to coat this foam to be able to lay-up a mold on it?

    Questions:
    - Is this the right foam(Versi-Foam) to use for this large project?

    - What tools am I going to need to shape this foam?

    - And what do I need to coat this foam in, to be able to lay-up a mold on it?

    Gratitude:
    Any advice is GREATLY appreciated and will garnish good karma, my eternal thanks, and a free ride on the finished product whenever you are in Sunny San Diego.

    Thanks,

    Chris Anthony

    Design pics:
    [​IMG]
    [​IMG]
    [​IMG]
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Are you talking about building a plug or a mold with plywood and foam?
     
  3. 8knots
    Joined: Feb 2002
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    Location: Wasilla Alaska

    8knots A little on the slow side

    Ideas...

    Chris
    I am not sure what versa-foam is But if it is the spray on eurathane type seen to insulate stuff it is of a fairly low density. I will guess about 3-5# per cubic foot. I spent a whole summer and several thousand dollars building the plug for my 19' sea kayak (That I too want to put to market) Yes... several thousand! I cut my stations out of 3/4" MDO plywood and built a 2' wide by 24' long table to set up the stations. I then strip planked the whole thing with 1/4" x 1/2" clear pine. Unfortunatly I read someplace that plaster of paris is good.. Forget it! way to much weight and sands terribly. So after that mess I popped all that junk off and broke out the bondo LOTS of bondo. It all worked out after too many hours of sanding. I would have layed up a few layers of 3/4 oz fiberglass mat over the pine to make the shape a little more rigid if I had it to do again. I will say that once you get it to the gel-coat stage fear not you are allmost there. When you shoot the first 2-3 layers of BLACK gel-coat and get to wet sanding you can really start to see the shape of your creation. Make sure you get plenty of build on those first few coats, you will likely need to get after it with say 120 grit then work your way down I learned that a little bit spent on sand paper will save you countless hours sanding. Just keep hosing her down with the gel then sand starting farly coarse even with surfacing agent (wax mixed into your gel-coat to help the surface cure harder so you can sand it without gumming up your paper)It will gum up a little. Anyway bla bla bla......Well I think looking at your drawings I would cut my hull stations set them up with a few battens and skin it with 10#1/2" PVC foam sheet (made for fiberglass laminate cores) maybe $60-75 for a 4' x 8' sheet then lay up some glass over the top start with mat then go into some 5oz cloth stay away from the roving I had a terrible time keeping it from Printing through to the surface after that you can skim coat the glass with a mixture of gel-coat and micro ballons or talc to the consistancy of say MAYO. dries quick and sands great then start with your gel-coat This is just my opinion but I promise you will love the foam in a sheet. Hope this will hope you a little. ;) 8Kts
     
  4. cla17
    Joined: May 2003
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    Location: San Diego, CA

    cla17 Junior Member

    Hello,

    Gonzo: I am trying to build the plug out of foam then of course its onto the mold. But, first things first :)

    8knots: Thanks for your reply. I appreciate the advice but should probably explain my thought process first. Vresi-Foam is:

    Versi-FoamĀ® System is the ultimate choice of special effects crews, artists, advertising agencies and scores of others for:

    Realistic theatrical, film and theme park special effects
    Sculptures
    Advertising specialties
    Indoor/Outdoor displays
    other applications limited only by the imagination!


    Here's why Versi-FoamĀ® System is one of the most remarkable art mediums of the 20th Century:
    Easily dispensed. Expands and dries in 60 seconds, workable in 30 seconds

    Moldable, sculptable and accepts virtually any finish material (paint, stains, lacquer).

    Rigid, lightweight but finished objects have appearance of great strength, solidarity. Foam has both flotation and structural enhancement properties.

    ---I copied that from the sales website. I have talked to a few people that say this foam is easy to shape and sturdy. It is also paintable and fillable. I was figuring I could spray this foam over a large, slightly smaller than real life, frame and then shape the foam to desired. Then paint and fill a necessary to make strong enough to lay-up a mold on it.

    - My main concerns are:

    --Will the foam structure be strong enough with just paint/fillers to properly lay-up a mold on?

    --What tools are best to use on this type of foam

    --And what kind of paint/fillers/fiberglass do I need to make this thing sturdy.

    I'm guessing I might be in uncharted territory here. This boat is a dream that is trying to be built on a budget so you can see the controversy there.

    Also I don't know what you mean by sanding the gel coats down? I though you just spray 1 gel coat, then a barrier coat, then a 1oz print through block then its just chop and bi-directional till your done. Do you have to sand after every coat? That would be a ever time consuming pursuit.

    Anyways any further advice/thoughts/comments are welcome and appreciated :)
     
  5. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    I think that building a wooden plug is easier. Your design can easily be built with laminated plywood over the molds. Carving it out of foam is possible but much more work. The shape you drew is almost developable, so triangular plywood panels will take the shape with little effort. I build custom boats and this method works fine. One of the advantages of wood is that you can plane it to shape. Also you can glue and screw pieces to modify the shape. A wooden prototype can be water tested too. It can prevent the extremely costly mistake of building a mold for a boat that handles terribly. Often, builders sell the prototype to offset the cost of production.
     
  6. 8knots
    Joined: Feb 2002
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    Location: Wasilla Alaska

    8knots A little on the slow side

    Chris
    You do not have to sand between coats as long as they are not farther apart that 24 hrs. this will ensure a chemical cross link between layers rather than a mechanical bond. I useda HVLP gravity fed spray gun to shoot my gel-coat. No matter what I did it would "orange peel" gel is not like anything you have shot before! This only matters in the plug as you are shooting the male side, It does not matter on the mold side. I would recomend getting a "cup gun" It is made to shoot gel-coat. I think they are about $100.00 and they use disposable paper cups. I have heard using one described as "A controlled pour" This is a great links page. Here are a few more I have used in the past. Good luck!
    8Kts


    http://www.composites-one.com/links.html
    http://www.fiberglasssupply.com/default.asp
    http://www.fibreglast.com
     
  7. cla17
    Joined: May 2003
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    Location: San Diego, CA

    cla17 Junior Member

    8knots: These links will be very helpful. I plan on buying a 2 quart pressure pot and a HVLP gun to spray my gel coats and I have a magnum chopper gun system coming for the lay-ups. But I wasn't planning on using gelcoat on my plug. I assumed a sturdy automotive paint would sufice for the plug finishing. Am I incorrect in this assumption? Well I guess it is not an assumption, I have read and seen video of auto paint being used on plugs but if it is better to gel coat your plug then by all means correct me :)

    Thanks
     
  8. Peter_T
    Joined: May 2003
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    Location: Gulf Coast

    Peter_T Junior Member

    This boat has a very full spoon bow from midship forward. How do you envision that you can ride clear of the advancing waves. The boat will be surfing along with the waves.

    For a wide body boat, suggest to take the buttocks at an angle like swim end barge. As the boat advance, you can expect water to follow the faired flow buttock or the streamline waterlines. Others white water with bow wave will be set up. For slow speed, this form offer high displacement and can be suitable for low speed.

    Your section show a chine step, but will be immersed in the water. This feature can offer roll resistance, but will increase resistance.

    It is a shallow boat. If depth is permitted, suggested to go for vee form than near flat bottom style. At least give a good rise of floor, so that the chine is just below the waterline. Then, take the chine up to the stem over the water to pick lift effect. The optimum chine crossing at the waterline is some what like forward of the forward quarter.

    If speed is not an issue, I will take back the comment.

    Peter
     
  9. cla17
    Joined: May 2003
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    cla17 Junior Member

    Peter_T: I appreciate your design advice but I feel I am in uncharted waters on this design. It has already changed 4 times since I made these drafts. I have abandoned the reverse chine in favor of a triple stepped spray reliefs on the stern. A lot like the new x-star and Super air nautique:
    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    I am not a design expert, so I don't fully understand the implications of different relief systems but it seems to work and I'm not trying to reinvent the wheel here so...I assume that these reliefs let the main planing surface ride lower, and with a heavier boat on top of that planing surface the displacement is greater and the wake is larger. The dead rise also seems to play a large role in wake shape. The more V the transom the more pyramid shaped the wake is the flatter it is the more of a kicker wake shape is formed but it also produces a trough on each side of the wake. If you have any other design input that would add to wake form, feel free to add.

    Thanks
     
  10. pjwalsh
    Joined: Mar 2003
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    Location: massachusetts

    pjwalsh Junior Member

    I would suggest finding your local composites supplier and developing a relationship with their outside sales representative - these guys are often very familiar with the processes their products are used for. See if you can find a copy of the "Cook Book" from Cook Composites and Polymers, this is a technical manual for their polyester products and has a lot of good information.

    Plugs are very often strip planked or plywood planked then glassed and faired. Sometimes the plug might be built of foam and used as a hull but this is not really very common - usually it is too expensive to build a plug that can become a hull - plugs and hulls have a whole separate set of requirements.

    I have heard of people using gel coat as the finishing material for plugs, but, having sanded gel coat before I would say this approach is for very small parts or folks who really like pain. I would recommend a product called Duratec. It is a vinyl ester gel coat that is designed to sand easily and take a smooth finish - it is specifically made for finishing plugs. I have had trouble getting HVLP guns to shoot gel coat effectively but it probably depends on the setup and users experience really (I have little experience with HVLP equipment).
     
  11. cla17
    Joined: May 2003
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    Location: San Diego, CA

    cla17 Junior Member

    pjwalsh: That is very good advice, and not something I really had in mind. Coming from sales I know that reps can be a great info resource. That is another issue I have to resolve. I don't know where to go for materials in the San Diego area. But I am really just gathering my though, formulating a plan and gathering the necessary equipment for this monumental task. But a Sales rep fits in nicely to my plan :) And I have heard of Duratec but haven't seen it used. I also have limited HVLP experience so this will be a fun one :)

    Thanks
     
  12. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Duratec sprays like an enamel. You can get application tips in the manufacturer's website. The Gugeon Bros. have a modified techinque in their site. The pics of the boats you send show something that is very interesting: there is a huge difference between a ski and a wakeboarding boat. Ski boats need a flat wake, wakeboarding a high steep one. Reverse chines and steps flatten the wake. A deep vee produce a large wake.
     
  13. cla17
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    Location: San Diego, CA

    cla17 Junior Member

    A V hull does produce a large wake but I think it is all about displacement. A V hull cuts the water and the wake spreads quickly. To give a rider a nice clean wake you need a realatively narrow flat planning hull that will plow a lot O water. The flatter the bottom the steeper the wake and larger the trough. The more V the hull the longer the wake transitions and the more pyramid the wake looks. It is kind of a comprimise to ge the perfect wake...
     
  14. Guest

    Guest Guest

    Cla...

    Not questioning your motives but what exactly do you want to accomplish by designing your own boat from scratch?

    If this is your first attempt to build a plug or mold for the first time I can tell you without any hesitation YOU WILL FAIL. If on the other hand you have previous experience you might have a 50% chance of making something different or interesting.

    When you see all those ski boats from MasterCraft, Nautique and others...what do you see that you either don't like or would like to improve upon.

    If trying to save money is your intent...You Won't.
    If improving design is your intent...You better know more than these designers.

    I am in the process of finish building and outboard waterski boat...why did I build it?

    1. They don't make them any more.
    2. Outboards offer better interior space compared to inboards
    3. I like going faster then the pathetic 45 mph top speed of today's ski boats.
    4. I hate the harsh ride traditional ski boats offer.

    My strong suggestion is not to build it from scratch...use an existing hull and modify its features...sorry for the long speech...good luck with whatever you decide to do.
     

  15. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    I'm glad you weren't around to advise the Wright brothers.
     
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