fiberglass hull thickness

Discussion in 'Boat Design' started by Gianf1041, Dec 18, 2019.

  1. Gianf1041
    Joined: Sep 2018
    Posts: 58
    Likes: 4, Points: 8
    Location: italy

    Gianf1041 Junior Member

    How much could an 8 mt fiberglass hull with an average thickness of 20 mm weigh?
     
  2. fallguy
    Joined: Dec 2016
    Posts: 2,981
    Likes: 331, Points: 83, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    A lot!

    Solid frp of 3/4" is thicker than needed for an 8 meter hull.
     
  3. rxcomposite
    Joined: Jan 2005
    Posts: 2,087
    Likes: 216, Points: 63, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    Relax. It could be only 1/16" wide.
     
    Doug Halsey likes this.
  4. Gianf1041
    Joined: Sep 2018
    Posts: 58
    Likes: 4, Points: 8
    Location: italy

    Gianf1041 Junior Member

    Gulp! ......... 1/16 "of an inch is about 1.6 mm ..........; to understand ....... 20 mm around the bottom to arrive at about 9-8 mm of the sides ........ it is only a rough evaluation to set a project start ............. 7mm foam core or structural felt, biaxial fabric 8 -5-3 layers, resin, gel coat ...... just to get about 8 mm of the sides.
    Maybe I'm exaggerating ??
     
  5. ondarvr
    Joined: Dec 2005
    Posts: 2,270
    Likes: 235, Points: 63, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    The weight of a laminate can be quickly estimated

    Every 1/8” thick square foot of laminate will weigh approximately one pound.

    So multiply the square footage by the number of 1/8” inches of laminate.

    1 square foot at 1” thick would weigh approximately 8 lbs.
     
  6. Gianf1041
    Joined: Sep 2018
    Posts: 58
    Likes: 4, Points: 8
    Location: italy

    Gianf1041 Junior Member

    Thank you for your suggestion !
     
  7. rxcomposite
    Joined: Jan 2005
    Posts: 2,087
    Likes: 216, Points: 63, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    You are not exaggerating. You simply did not provide information that you know. You did not even mentioned that it is a cored laminate that is why it is so thick. You also know the layup schedule but you did not post.
    It is simple but tedious. For every layer of roving or biax, the ratio is 1:1, that is for every kilo of glass you use, you use 1 kilo of resin. Chopped mat ratio 1:2.3. For every kilo of glass you use, multiply that by 2.3 to find the amount of resin. Since fibers are sold in unit weight per square meter, you will be able to calculate how much the laminate will weigh when the resin and the fiber is added together.

    Say you will use 600 gr/m2 of WR for the first layer, that will be 0.6 kg/m2. You will use the same amount of resin so, 0.6 + 0.6 = 1.2 kg/m2.
    For CSM, say 600 gr/m2 (0.6 kg/m2). To find resin weight, multiply 0.6kg by 2.3=1.38. Add the two so it is 0.6 + 1.38= 1.98 kg/m2.
    Foam is sold by its density. Say 100 kg/cu meter. To find how much a 7mm foam will weigh, slice the 1 meter (1,000 mm) high foam every 7 mm. 1,000mm/7mm= 143 parts. That means 100 kg of foam/143 slice = 0.699 kg per slice/per m2.

    Gel coat thickness vary but 700 kg/m2 is pretty standard. So 0.7 kg/m2.

    Since you have different thicknesses for bottom and sides, you must find the total area first for each.
    Multiply the unit weight of the WR LAMINATE by the number of layer x area (bottom or sides)
    Multiply the unit weight of the CSM LAMINATE by the number of layer x area
    Multiply the unit weight of the FOAM x area
    Multiply the unit weight of the Gel coat x area

    Add everything.
     
    Last edited: Dec 19, 2019
    Pammie, bajansailor and fallguy like this.
  8. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,486
    Likes: 470, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    This is a fairly simple calculation, at the basic level of analysis for the purposes of a 'project", reading the initial post I thought it was a case of someone trying to work out the weight of an existing boat.
     
  9. fallguy
    Joined: Dec 2016
    Posts: 2,981
    Likes: 331, Points: 83, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I was trying to prime the pump and get him to spill the scantlings is all.
     
    rxcomposite likes this.
  10. Gianf1041
    Joined: Sep 2018
    Posts: 58
    Likes: 4, Points: 8
    Location: italy

    Gianf1041 Junior Member

    It is not an existing boat but it is a beginning of a project ......... to have a basic starting point, then I will develop the project with more precise calculations. Thank you all for your technical support.
     
  11. Gianf1041
    Joined: Sep 2018
    Posts: 58
    Likes: 4, Points: 8
    Location: italy

    Gianf1041 Junior Member

    Let's say that the idea is the sandwich with a balsa or foam core .......... let's say 7mm, + two sides respectively 6mm + 6mm x 8-10 layers of impregnated biaxial fabric with a thickness of about 20mm.
     
  12. Gianf1041
    Joined: Sep 2018
    Posts: 58
    Likes: 4, Points: 8
    Location: italy

    Gianf1041 Junior Member

    we say that approximate weight bare boat + deck + deckhouse .......... less than 500 kg tot. ???
     
  13. BlueBell
    Joined: May 2017
    Posts: 1,131
    Likes: 193, Points: 63
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    This reminds me of the most refined question from the late PAR:

    "How long is a piece of string?"
     
    fallguy and bajansailor like this.
  14. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,486
    Likes: 470, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Way too light, that calculation has gone wrong.
     

  15. ondarvr
    Joined: Dec 2005
    Posts: 2,270
    Likes: 235, Points: 63, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    Without knowing any actual dimensions, my quick estimate would be in the 1,850 pound (839 kg) range for a solid 13mm laminate for just the hull. No core, no stringers or other structures.

    It could easily go up from there depending on the exact dimensions.
     
    Last edited: Dec 20, 2019
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.