Some advice on costing

Discussion in 'Fiberglass and Composite Boat Building' started by pleasedontsink, Mar 24, 2016.

  1. pleasedontsink
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    pleasedontsink Junior Member

    I will do just that. Thanks heaps Jamie. You have helped so much.
    Fantasticity will be at 100% when I hop in for my first float.
     
  2. Jamie Kennedy
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    Jamie Kennedy Senior Member

    That makes sense. That's something I can relate to.
    I will be launching very soon for my first float of the season.
     
  3. pleasedontsink
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    pleasedontsink Junior Member

    Just a question on the male mould I will be making. I want to see if I have this right.
    I would sand it smooth. Prime it and seal it. (what is the best product for this?). Then I would use durabuild? and then wax it heaps of times then use a release agent?
    Or... would I finish it in a tooling gelcoat which I then sand to really fine and wax it and then put release agent. Bearing in mind I would like to use this mould many times hopefully.

    Cheers.
     
  4. gonzo
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    gonzo Senior Member

    Sanding is not enough for a good finish. You will need to buff and polish, then wax. Otherwise, the sanding marks will show through. The finish, before waxing, should be like a mirror.
     
  5. Jamie Kennedy
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    Jamie Kennedy Senior Member

    I asked my brother about the salt water at high temperatures, because I was curious. He said the high temperature was an issue, but the salt water wasn't, at least not as far as the fibreglass was concerned. He said hot fresh water could actually be worse than hot salt water, although he did say that certain additives, like say chlorine, without the sodium, can be a problem.

    They built a few for shipment down to the USA, from where he is in Nova Scotia. The customer did specify using Vinylester Resin, rather than Polyester Resin. That might be something to look into and consider whether it is necessary or worth the extra cost. I don't think it adds much cost over polyester. Not sure how it effects gelcoat, whether it involves a different gelcoat, or whether the same gelcoat is compatable with both.

    In their case they used one of their regular molds they use for tanks. It was 4' x 8' with a depth of 18". Not sure if that was water depth or full tank height. I was a little surprised that it had to be 4 feet by 8 feet, but I suppose when people are relaxing and go for full sensory depravation I suppose it is nice to be able to reach out and not touch the sides. Interesting stuff.

    So you might look into someone local that builds tanks. They might already have a mold that can be adapted. I forgot to ask and I can't remember from last time I was in Fred's shop, but I imagine these have to be male molds for tanks. For someone that builds tanks to make you a male mold for your purpose, they would only need to make a female mold from one of their tanks, and then adapt that to what you require.

    How would I do it myself, off the top of my head without asking Fred or Gonzo?
    1. make and test some small scale prototypes, of tanks and molds, to figure out what I want. these can be simple mockups on a small scale in just paper and tape.
    2. find out how much I need to angle the sides so the tank will slip off of the mold.
    3. find out how much I want to round the corners and edges to make the tank easy to clean, as well as to make it eaiser to maintain the male mold and have the tank slip off.
    4. decide how I want to reinforce the tank, especially on the top edge on the long side.
    5. maybe the sides need to go out from the top, and down again, meaning that the mold will be male in the middle, but female around the outside edges.
    6. build another prototype, but 1/4 to 1/3 size, using the same materials that you will use for your mold and tank, perhaps 1/3 to 1/2 as thick, and reinforced as you intend to reinforce your mold and tank. Test it with water, and give it a few good kicks.
    7. Do another cost analysis before going all in.

    But this is just me. Someone like Fred or Gonzo could skip a lot of this because they already have the experience from similar or very similar projects. Cheers.
     
  6. pleasedontsink
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    pleasedontsink Junior Member

    Hmmmm. the plot thickens. Thanks Gonzo and Jamie. I will definitely look into vinylester then and do some research on gelcoats. The tank most definitely has to have Chlorine or Bromide as a disinfectant. The tank runs a water temp of around 35.5 deg C.
    I will check some info on tanks but I presumed (probably wrong) that the standard tanks would have the gelcoat finish on the outside where I need it on the inside. The outside of my tank will be covered with insulation and panelling so outside finish is not a problem.
    With regard to the sides they will be a female mould. they will have a flange around 100mm or so. This will need to be a female mould. The problem I envisage is that the sides need to be straight so that the wall are straight. Will this will be hard to get out of the mould. Would I have to build a mould that can be pulled apart to remove the product or would a 100mm straight sided flange be ok to remove the product?

    Cheers.
     
  7. Stumble
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    Stumble Senior Member

    A hot brine is probably the single worst thing I can think of in term of likelihood of blistering. Absent some full scale tests I would really suggest going with epoxy instead. The premium price will very possibly come back to pay for itself in reduced warranty work.

    High temperatures increase the likelihood of blistering, as does the increased osmotic preassure from a high salinity solution. In my eyes this almost demands epoxy construction.
     
  8. pleasedontsink
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    pleasedontsink Junior Member

    Righto. Great. Thanks Stumble. I will have a look into this. Is there any difference in techniques used for expoxy vs fiberglass? excuse my ignorance here.
     
  9. ondarvr
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    ondarvr Senior Member

    35.5 C isn't an issue, and salt water is less aggressive than pure fresh water, distilled water is the worst.

    Use a swimming pool gel coat if you can get one, they are very similar to marine gel coats, a VE barrier coat and VE skin coat will further help prevent blistering, to the point where it shouldn't be a problem. A male mold is what you want to use.

    Why do the sides need to be vertical? A slight taper is normal and needed, especially on a male mold.
     
  10. pleasedontsink
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    pleasedontsink Junior Member

    Hi Ondarvr,

    OK great. I will look into pool and spa gelcoats. Thanks.

    The tub itself is a male mould and so is the roof. This will have tapered sides. The top of the tub will have a 100mm lip or flange and the walls will have a 100mm flange that bolt together. This flange will need to be square or there will be a gap in between the walls or the walls will not be square due to the angle not being 90 degrees. I can upload a drawing if this is not clear.
    As the walls need gelcoat on the inside and the flange is on the outside of the tank it will mean a female mould. It will basically be a flat sheet with the female bit being the 100mm flange. will I be able to remove this ok from the mould if they are square 90 degrees?

    Cheers.
     
  11. gonzo
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    gonzo Senior Member

    That would be a male mold if you want the inside to be the good finished side. The male goes inside the female. That means that since the cavity is what you want to look best, the male will be male.
     
  12. pleasedontsink
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    pleasedontsink Junior Member

    Hi Gonzo,
    Yep male definitely for the tub but the walls is different. The inside of the room on the walls is the good finished side but the wall sections meet flush with each other on the flanges. The flanges are bolted together from the outside of the room. So looking from the inside you just see seams where the panels meet. From the outside (rough side) you can see the flanges all bolted together.
     
  13. gonzo
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    gonzo Senior Member

    The mold will look like a flat plate with a block on top.
     
  14. pleasedontsink
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    pleasedontsink Junior Member

    Sorry Gonzo I can't visualize what you mean.
    I have attached a drawing I made showing the tank to avoid any confusion.
    The way I see it the tank sides would have to be a female mould to have the gelcoat on the inside and the flanges at 90 degrees and bolted together on the outside.
    The drawing shows the tank from the outside and I have drawn the bolts for clarity.
    I am probably wrong but I just can't see what you mean in my head. If the mould was male the flanges would be pointing inwards inside the tank.

    Cheers.
     

    Attached Files:


  15. ondarvr
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    ondarvr Senior Member

    not hard to build
     
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