Resin choice

Discussion in 'Materials' started by mcdc, Jun 15, 2012.

  1. mcdc
    Joined: May 2012
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    mcdc Junior Member

    I have the stringers in with 8 total layers of DB170. That includes 4 tab/tape layers and 4 full covers all staggered ......One full cover layer and one tab layer, another full and another tab ect.
    Question with removing so much buildup from the hull area (from the stringer out one foot on the hull that had came loose) should i be worried about flex since the epoxy lam has so much more flex than the factory glass.
    Thanks to all for the help!!
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    In addition to the tabbing and localized reinforcements added to the boat, you also must replace the laminate that has been ground away. I'm not sure I understand the areas you're concerned with, but generally the hard turns the fabrics make, as they tab things down, stiffens the whole nicely. Also, before making any assessments about stiffness, wait a full week before testing things. Epoxy cures to within 80% - 90% of it's finial stiffness and hardness in 24 hours, but will continue to cure for about a week, assuming sufficient temperatures to permit it. You can speed this up by raising the temperature for several hours, to say 130 degrees. This post curing will also make the epoxy tougher. I post cure all structural laminates when I can. A kerosine heater is good for this, though you have to be careful you don't set things on fire. I usually build a tent with a thermometer located near the work. A flap like vent at the top of the tent, lets out heat and I size this by trial and error, just keeping an eye on the thermometer and moving the flap until I can maintain the temperature.

    I wouldn't be all that worried about it. You appear to have more than sufficient material in the repair.
     
  3. mcdc
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    mcdc Junior Member

    Thanks Par!! The area of concern is the area of thick buildup the factory had that was removed along the stringer 10 inches out on the hull. They set the stringers in place, created the filet and then layed the glass across the stringers and floor in one shot. Looks like where they created thefilet, they wiped the filler across the hull floor about 10 inches, and that is what came up......about 1/2 inch thick.
    So the question is , what glass is needed to replace 1/2 factory glass ( 2 layers WR and 2 layers of CSM) Thanks Par
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Quite often on production build, a lot of excess resin is left in the boat. It should be rolled out, but sometimes it's just left in a pool. Two layers of roving (weight?) and CSM (weight?) can range considerably in thickness. I'd estimate you have 3/16" (at least) in biax and epoxy down now, but it's hard to tell, not being able to see what you have. For example two layers of 2415 fabmat (24 ounces of roving and 1.5 ounces of mat, per layer) is only slightly more then an 1/8" assuming reasonable resin/fiber ratios. Even a 4020 stitch mat (40 ounces roving, 2 ounces mat, times 2) is going to be a wee bit less than .25"
     
  5. mcdc
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    mcdc Junior Member

    Thanks Par!!! I did several test panels before I started and they all are running 1/4 of an inch....all five. I kept all the glass that was removed and it all checks around 1/2 inch in the hull area and around the bottom of the stringer....of course there are areas that are full of resin and are much thicker.....the stringer sides are a about 1/4 of an inch.........sound like I need a few more layers on the bottom????
    Just so I will know, what would you suggest if I had used VE instead for a schedule......looking at 1/2 on the bottom of the hull and 1/4 or so on the sides? Thanks Par!! Have learned a ton!!
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You can add some more material if you like, but the 1/4" on the stringer sides is an indication of what the laminate probably was supposed to be. These would be areas that get lots of "ironing" with a roller during the layup. The fillets and tabbing on the hull shell are often a place where the excess resin just pools up, making it thicker (and more brittle) then needs to be. Toss some more tabbing on, just to be sure and call it a day. Grab a beer, you've earned it. I don't spec out polyester or vinylester very often, so I'd be guessing, without running some numbers.

    I'm showing .03" per layer of 45/45 17 ounce biax assuming good hand wetout, saturation and squeegeed tight with epoxy, slightly less with polyester. My estimate of 3/16" on your current laminate and your subsequent report of 1/4" test laminates, suggests you might be a little resin rich (not unusual), but still right in the ball park. Two more layers will add a touch over a 1/16" more material, which is more then the thinnest of the original laminate, but less then the thickest.
     

  7. mcdc
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    mcdc Junior Member

    10-4, will add two more layers and go have a beer or three.......need to find a smaller boat for a project this is not one to learn so much on for the first epoxy job. Thanks Par!! and everyone else that helped me get this far!! Will post some pics soon, still have a ton of work to do!!
     
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