stand-along bait tank build

Discussion in 'Fiberglass and Composite Boat Building' started by Michael Ward, Dec 19, 2017.

  1. Michael Ward
    Joined: Dec 2017
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    Location: Mebane, NC

    Michael Ward New Member

    New to the forum - looks like a lot of great expertise here which I hope that I can learn from, and hopefully share back to over time as well.

    I am preparing to build a couple of stand-alone insulated bait tanks with a central filtration / recirculation stack- one with a target bait holding area of 50 gal and the other around 100. This will be a circular tank with exterior dimensions of approx 30" & 40" diameter respectively.

    Currently the thinking is to build a "core" column and base from foam boat (have access to a CNC and the thought was to cut out portions of a circle on the CNC and fit/stack them) - and then glass the interior/exterior, sand it then shoot with gelcoat. It will then be topped off with a Starboard lid, secured to the tank.

    A few questions:
    - recommendation on layup schedule/thickness for the interior/exterior
    - do we need to coat the foam board with anything specific before starting the glassing to prevent the foam from melting, etc?
    - other advice?

    These will be one-off tanks so I do not see the value in creating a plug, then mold then finished product. I would consider creating a plug and casting the finished tank over it - but with the two walls and insulated tank this would mean two plugs, twice the work - vs just glassing over the foamboard itself - however, I am wondering if we will be able to get a quality finish on the gel-coat by glassing over the foam then shooting the gel - not that is has to be totally perfect or pretty though I'd want the inside to be a smooth as possible just to keep it clean (and ideally the outside as well).
     
  2. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Going to be really hard to glass the inside.

    Sorry, but I think a plug is easier; even with the foam cutouts perhaps stacked later.

    So; you cutout the circles and stack them for the plug and then glass the plug and then put the exterior 'rings' onto the plug with some 'glue' between the glass and the foam rings. When done; you release and the inside laminate is real nice.

    That is what I would do.

    Glass must be 17oz min to avoid pinhole leakage if you ask me. But for 100 gallons; you might need a calc done for a strength min.
     
  3. IronPrice
    Joined: Jul 2017
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    Location: NZ

    IronPrice Senior Member

    I can't offer any advice at all on the composite of things but ... am I reading correctly that you are planning to build each tank out of a disc with rings stacked on top to form the walls?

    Could you CNC machine steps into the top surface of the discs and both surfaces of the rings so they will interlock when stacked. That would make it easier to assemble and it will hold together more easily while you are laminating.

    Just an idea that occurred to me when reading. I know nothing.
     
  4. Michael Ward
    Joined: Dec 2017
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    Location: Mebane, NC

    Michael Ward New Member

    correct - our thought is to cut portions of circles (1/4 or 1/3) and assemble them as rings - then stack to form the "core" - would probably to a "tab/slot" on the pieces so they register/lock together. Your suggestion fo some form of alignment groove on the top/bottom is not a bad one either....
     
  5. jorgepease
    Joined: Feb 2012
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    Location: Florida

    jorgepease Senior Member

    you can also laminate some thin skins on a nice surface, then glue them in place, save you some fairing time and get you a perfect finish.
     
  6. Michael Ward
    Joined: Dec 2017
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    Location: Mebane, NC

    Michael Ward New Member

    Fallguy - thanks for the input - I keep coming back to something similar as well - I can see the benefit of doing a plug for the interior - when I first starting looking at this I was thinking I needed to make a plug then mold then finished piece - but as this is effectively a one-off making a disposable plug for the interior may be the way to go - I can see it being a lot easier to get a good finish on the plug and the shoot it with gelcoat - then I have options on the exterior "shell" - either paint or gel-coat the exterior.

    On the 17 oz min.... newbie question here - but is this the total lay-up - or does it refer to a specific type / weight of material?
     
  7. AusShipwright
    Joined: Aug 2016
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    Location: Australia

    AusShipwright Junior Member

    I think the male mould is the way to go but a lot of material would be wasted cutting the rings out of foam if I understand you correctly.

    I would cut 4 panels and form the foam over the cylinder. You might need to apply some heat to help manipulate the foam. Can add extra strips around the outside for a stiffer wall.

    What lamination method do you plan on using?

    Be sure to add some taper to the mould to ensure clean release of the product
     
    fallguy likes this.
  8. Michael Ward
    Joined: Dec 2017
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    Location: Mebane, NC

    Michael Ward New Member

    To minimize waste on the foam we would not cut out full rings, but portions of the circles - most likely 1/4 of the circle, so that we could more efficiently use the foam sheet without the waste of the material inside each ring.

    As to the lamination method - other than patching a few holes on my center console, I'm very new to all this so I'm very open to recommendations/suggestions...
     
  9. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    How big is the cutterhead/kerf on the cnc?

    I'd make the circle cuts and stack full circles for the plug. And cut the rings from the same reference. Make your plug; then glue the rings back onto the mould with flox n balloons. Epoxy:Cabosil:balloons:cotton 1-1-1-1. You can glue the panels together with loose peanut butter epoxy n cabosil and a 1/8 vee trowel each panel. Just mix it all with slow epoxy and probably take it slow to avoid exotherm if you have a big cutterhead. Use 2" polystyrene. For 36" tank height; you need 17 circles n rings and a bottom circle. But that is pretty high. The sheets are like 26 bucks each. For a 24" outside diameter; you get 8 rings n circles per sheet. That is a super cheap tank. Not sure how the gallons work out...your job; not mine. The ring dimension is all about r-value. Three inches thick would be lots.

    17 oz is a fabric-lighter fabric might leak; but not anywhere for a leak to go really if you bond all the rings well enough.
     
  10. AusShipwright
    Joined: Aug 2016
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    Location: Australia

    AusShipwright Junior Member

    How would you finish the internals to prevent water permeating into the foam? As the OP mentioned he is fairly new to the process so I wouldn’t rely on thickened epoxy resin as a back-up to make it water- tight.

    I’ve only built tanks with vinylester resin due to the advantage of using a gel coat barrier and tissue or 225 gsm mat skin. This way there is minimal extra prep time with a proper schedule

    Michael if you are not so worried about the finish then you could just build a jig to support the circle pieces of foam you plan to use, glass the externals, pop off the jig and then glass the internal and give a good flowcoat.
     
  11. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    lotsa ways to skin this cat
    as long as the chemicals don't melt the polystyrene
    the plug mold method would have a nicer finish and I didn't mention how to build the plug. However, the plug is a cylinder and it is a one off, so there is no need for the csm to do anything other than hold the fabric steady unless you add the bottom into the plug.
    if he doesn't care about the internal finish; then your way would be best
    if he wants a smooth inside tank with gelcoat; then he needs to use a plug I'd say, adding the rings back onto the plug can be done as I described
    kind regards
     
  12. pauloman
    Joined: Jun 2010
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    Location: New Hampshire

    pauloman Epoxy Vendor

    use epoxy which will bond to the foam without damaging it - and no smell. Then paint the epoxy in whatever color you want. Lots of epoxy options - from Basic No Blush marine epoxy to Water Gard 300 white/blue epoxy paint (a barrier coat epoxy usually) -
     
  13. fallguy
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    fallguy Senior Member

    1F2DB223-54C1-4D54-8A37-C842BB921B05.jpeg You can blue tint the epoxy for a paintless option, but no uv protection. This one is a blue gelcoat.
     
    Last edited: Jan 15, 2018

  14. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You can gel coat over epoxy, you can paint the epoxy or tint it. Rather than rings and keys or other form of step/alignment arrangement I'd just do sections, say 1/4 or whatever size your CNC table can manage. These a circular tanks, so alignment of the foam isn't difficult nor necessary. Keying also isn't necessary, as the foam is just a core. The laminate bears the loading and after the core lightly glued together and is faired to it's desired shape, alignment arrangements are just a convenience thing during core assembly. Given the size of these tanks, you'd be wise to have a laminate schedule worked out for you, unless you prefer them to be extra heavy or worse, burst open. The math isn't hard, though a good understanding of the physics and material properties is necessary.
     
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