Hull fairing questions

Discussion in 'Boatbuilding' started by laukejas, Nov 2, 2020.

  1. laukejas
    Joined: Feb 2012
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    laukejas Senior Member

    Well, crap. I have 57 sqft on the topside of the boat, and 71 sqft on the bottom. Together that's going to be almost 9 pounds of epoxy... Goddamit. I guess it is time to order a new batch. This is crazy... I don't remember using up so much stuff on my last boat.

    Yes, true for the temperature. That is why I brought 4 heaters into my workshop today, and set them on full blast. 2 kilowats each. Closed down the door, stuffed rags into every ventilation hole. After 3 hours of running these heaters, I managed to raise the temperature of my workshop from 48°F to 57°F. I also used a heatgun to pre-heat my epoxy batches to ~85°F. Not the same as heating up the boat, but the best I could do under the circumstances. The resin was liquid enough, I suppose, not much thicker than usual. Well, I guss I'll just have to suck it up and endure the expense and weight of the boat.
     
  2. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    what glass weight?

    14.2 yards of 6 oz is 85 oz
    Or 85 oz of epoxy by wt or 76 oz by volume
    Really gonna be hard to use at 100% in those low temps. The resin thickens instantly when it hits the boat. But be safe. Carbon monoxide kills. You would be better off heating under the boat with plastic to the floor perhaps.
     
  3. laukejas
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    laukejas Senior Member

    I am using 5oz cloth. I do have a monoxide detector installed in my garage, so I think it should warn me if it goes to dangerous levels.
     
  4. wet feet
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    wet feet Senior Member

    I don't think you are doing yourself any favours by trying to use notched spreaders at this stage.The fairness of the surfaces was dealt with before you added the glass cloth.All you really need to do is to sand down the ridges where the cloth overlaps and fill the weave of the cloth.If you try to use notched spreaders you inevitably have to go back and fill any grooves that are left-which means another mix of epoxy and another session of spreading it-followed by another session of sanding it.A smooth plastic spreader is all you should need for final filling and then maybe you can give it all a coat of high build primer.Sadly,these are all fairly expensive substances and they don't work well or rapidly when temperatures are low.
     
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  5. fallguy
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    fallguy Senior Member

    You have to raise ambient temperatures and the epoxy temps to keep use down to around 100% of glass weight.

    128 sqft
    14.3 sqyds
    @5 oz per yard
    72 oz glass
    72 oz epoxy plus add 14.3 oz for substrate(usually I add 2x)
    Or
    87 oz epoxy by wt at warm temperatures. Or 78 liquid oz at zero roller loss.

    But you have to find a way to warm the place up or you'll start going up by factors of somewhere around 1% per degree (in my experience). Try pushing cold honey around..
     
  6. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    A trick I've used is putting a small electric heater IN the boat and closing it up.
    Check your surface temperature before commencing though.
    As for the epoxy, keep it in the house and mix it there so it's nice
    and warm and gets the chemical reaction going in earnest.

    Challenging working in cold weather with epoxy.
     
  7. laukejas
    Joined: Feb 2012
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    laukejas Senior Member

    You are correct. Problem is, how do I fill that weave reliably? Going over the cloth with a spreader and thickened epoxy doesn't give a good result. The weave either doesn't get completely filled, or it gets overfilled. Very hard to control the layer thickness. Using a notched trowel I am building a bit of excess, but when I fill these grooves, I can be sure that the weave is also completely filled. And I have a small reserve for sanding, so I don't sanding into cloth, which will be painful and also ruin the finish when I paint these areas. I 3D-printed a notched trowel with teeth just 0.5mm high, so the these grooves are very shallow.

    I tried that today. Covered the boat with plastic sheets down to the floor, and put all of my heaters inside. Let them run for 3 hours before starting any work. When I removed the sheets, boat was very warm. Warmer than my hand. I guess 104°F at least. However, it cooled down in like 15 minutes. I barely had the time to cover 2 or 3 square feet with epoxy before the boat was cold again, and epoxy was like cold honey again. I guess my boat just doesn't have enough mass to hold thermal energy...

    In any case, I did the final 2 coats on that cloth today. First with notched trowel, and 10 hours later, filled them in with a spreader. It got a bit messy, especially around fillets and rounded edges, but I purposefully tried to be wrong on the plus side. Once I start sanding, I don't want to discover that I left some areas without enough epoxy and then I'll have to re-fill them and wait another week... I hope that one sanding will be enough after this.

    [​IMG]
    [​IMG]
    [​IMG]

    I tried really hard not to leave any places where I would fail to fill in the grooves left by the notched trowel, but they are extremely difficult to find. I went 5 times after the initial filling, hunting down for these spots and filling them in, and yet the photos reveal that there are still some left where I should have added more epoxy... And in other places I might have added too much. I just don't understand how to be consistent about it. I spent 6 damn hours at this, and yet I can't do any better result.
     
  8. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Your work looks good for one who has only been floating fairing compound for a few days.

    When you get to 60 hours you might be at the point where you will be sanding off less than half of the compound you put on

    At 600. Hours of experience you will only need to remove 25% of the applied compound.

    This is a learned skill that takes a while to perfect
     
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  9. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    very true, I am building a 10m powercat and the first hull took like 60 days and the second hull took like a month or less and the 2nd hull looks and is much better
     
  10. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Inside, not outside the boat, inside the hull, and leave the heater turned on while, and after, you're working!
    But, you need a temperature controlled heater, or at a minimum, an overheat shut-off.
    Don't use too much heat or it may catch fire and that would really spoil your day.
    Reread my previous post above.
     
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  11. fallguy
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    fallguy Senior Member

    Even a plastic enclosure around the boat would heat up more for relatively low $$. You can use 1x2 wood strips and staple the plastic to them and then screw them to the ceiling. This is how you build a cheap painting tent as well. You are basically reducing the building size. The heater can go under the boat and plastic around the bottom, but not as good as a tent. Heat loss is highest up; so you can also double the plastic on the ceiling it it is super high or open above.

    I have a friend in Alaska that uses a double plastic wall system for his boat area.
     

  12. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    The plastic tent is a good way to improve the work area for better cure times in cold weather.Even a light bulb inside a plastic tent creates enough heat to make a difference.When you have concluded the filling and fairing will the paint be sprayed or brushed?
     
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