Can someone please help???

[ihsan]

I have been given this lamination schedule for this 12 ft. FRP boat. This is what it says;


Hull:

20-24 mills Artic White NPG ISO Gelcoat
2 oz chop skin coat
18-08 bulk lamination with overlap in keel
Transom same as shell but with additional;
18-08 overlap 3" on bottom
1/4" coosa board core
2-layer 18-08 over core

Deck:

20-24 mills Arctic White NPG ISO Gelcoat
2 oz chop skin coat
18-08 bulk lamination
1/4" core on all flats
1/2" coosa board reinforcements at hardware attachment points
3 oz chop over core

Deck perimeter foamed with 2lb free rise urethane foam (Clearance provided at hatch openings and hardware attachment points)


I don't understand what they mean by "20-24 mills" for the gelcoat, "18-08 bulk lamination". i don't get what these numbers are. Can someone please help me out on this one? Or can someone try to translate this lamination schedule?

Also, is it possible to make a lamination schedule from using only fiberglass hand laid mat and resin method?

Kind Regards,

Ihsan from Indonesia

[marshmat]

"20-24 mil" refers to the thickness of the sprayed gelcoat.
"18-08 bulk lamination" is a weird one, I've never seen a notation like that. Usually a laminate schedule will be something like "3 layers 18oz roving" or something to that effect. I would contact the person you got this schedule from to confirm what this means. I suspect this refers to an 18oz roving with 8 yarns per inch but it's hard to say for sure.
The deck laminate is very heavy on the crappy chopped mat and the suggestion to use a core at hardware mounts is a bad one (places where holes will go through the sandwich should be done in solid fibreglass, or else water will seep through and get into the core). I prefer seeing veil instead of mat/chop against a gelcoat in both hull and deck, but chop is cheaper and so that's what they tend to do. Chop/mat is not strong at all, it's a filler layer and I don't like seeing it on its own anywhere.
Hopefully someone else can say for sure what those numbers mean.

[ondarvr]

18-08 is a nitted fabric, 18 oz. biax with a 3/4 oz. matt stitched to it.

[Eric Sponberg]

20-24 mils means 0.020-0.024 inches. That is, 20 thousands to 24 thousands of an inch. 0.001 is one one-thousandth of an inch = 1 mil.

18-08 is indeed a knitted (usually, but sometimes can be woven) biaxial (0/90 deg fiber orientation) fiberglass fabric with 3/4 ounce mat stitched to one side of it. The 18 refers to the weight of the biaxial fabric of 18 ounces per square yard, and the 08 refers to the weight of mat which is 0.75 ounces per square foot. The industry for some reason does not like to use decimal points or more than 2 digits if they can help it, so they made rounded the 0.75 ounces to 0.8. Hence the designation: 18-08.

Interestingly, a double-bias fiberglass material of similar construction is 17-08. The double bias fabric (=45/-45 deg fiber orientation) is 17 ounces per square yard, and again, the mat is 0.75 ounces per square foot. You cannot tell from the designation that 17-08 is indeed a double-bias material. That is why in a proper fiberglass specification, the writing should be clear about the fiber orientation. It should say 18-08 biax or 17-08 double bias (or 17-08 DB).

Eric