fiberglass hull layup

D

Dave Archer

New member
How many layers??? I am building a 15' fiberglass duck boat with a shallow vee hull, 10% dead rise. In the past I have built layout boats and a scull boat. I am building a one-off fiberglass boat using a male plug. I will reinforce the inside later, but I wonder how many alternating layers of mat and woven roving to use initially. I want to avoid excess and unnecessary weight. I am considering three layers of mat (1.5 oz) with two layers of woven (.025). Any thoughts?

PS- If I go with the three mat and two roven woving, I will grind and fair the hull and then finish it off with a heavy cloth. My worry is that if I have 3 and 2 layers it might be a bit floppy. I will be joining a top deck after the hull in reinforced. I don't want to lose the shape, although I know I can add spreader bars. I just think that going with four mat and three roven woving may be too much weight.
 
Dave,
does your floor have any contour to it? If you look at the bottom of most of the commercial boats, they have built in runners. These help limit flexing of the hull.

With the boats I built, we had a mold rather than plug and the layers from outside in consisted of: gel coat, 2 layers of mat, layer of heavy woven roving. It's been a while, so I don't remember the exact weight. These are small, Kara sized boats for hunting flooded ag fields and such. I did build runners into the mold and the floor is pretty stiff once you connect the deck portion to the hull. There is about 12" between the runners and it still flexes some along that span when running with a small motor.

My buddy has a different boat he built where he doubled the fiberglass layers, (2x mat, roving, 2x mat, roving) and you don't want to lift it up. He runs over small saplings with that boat and it doesn't seem to phase it. It has a single keelson down the middle and is wider than mine. He still has some flex to the bottom of his boat, but it's been well used for over a decade now with no major problems that I know of.

Scott
 
What oz. weight is the woven roving? I would use knitted biaxle glass over the woven roving. If it were me I would use two layers 1810 biaxle which has a light layer of mat on the back first then two to three layers of mat. The mat will give you material to grind off to fair the hull. A lot depends on the shape of the hull.
 
Scott, thanks for sharing. In addition to two bulkheads, I will have support ribs every two feet, which will give a good measure of stiffness and support. I plan on using plastic deck planks (Trex) cut down to size. They are heavy, but when cut to size won't be too much of a factor. They really bond well to resin, and I won't have to worry about rot. (I should say my son won't have to worry about rot!) This morning I reviewed a book on hand, and it reminded me that hulls can be over built. I only need a 1/4" thickness for a fifteen foot boat, given the structural support. I also plan on adding three keelsons to the outside of the hull for protection and strength. But I am left with the same question. How thick will the hull be if I add three layers of mat and two layers of woven roving?

If I use three layers of mat at .025 and two layers of woven roving at .045, the total is 0.165. That's a far cry from my goal of .250 or a quarter of an inch. So how much bulk and thickness is being added with the resin?

Thinking out loud! Maybe I should completely finish the hull, including the three keelsons. My design for the male plug is set up that the mold is designed to flip over for the deck and top. In other words, my stations ribs, and the shared joining edge, cover the design for both top and bottom plug. This way my top piece will join the bottom piece with little adjustment. HOWEVER, years ago I had a boat hull that did not retain it shape, when I attempted to line up the top piece with the hull. I had built the bottom hull too light and the shape morphed when I took it off the plug! BUT if I go to four layers of mat and three woven roving I have PERHAPS added more expense and strength than I needed. See what I mean? (Money is a factor too.)
 
Tom, thank you for replying. I am unfamiliar with 1810 biaxle so I will look it up. The mat I will use is 1.5 oz and the woven roving is 18 0z. The hull is a slight vee. I just don't know how much polyester resin adds to the bulk or thickness of mat and WR. Already, I think I screwed up on the actual thickness of the two products so I will check. The salesman this morning said he could not give me a rule of thumb and that I would have to decide on my own or consult an engineer -- yeah, right!
 
Dave,
Personally & professionally, I'm not a fan of woven roving.
My preference instead is 1708 by Knytex. It's a biaxial cloth with 3/4 oz. CSM (chopped strand mat) on the back and it's sewn. It wets out well, handles easily, gives great strength and squeegees nicely.
On our layout boat, we use one layer of 3 oz. CSM and one layer of 1708 and it gives plenty of strength but you do want to alternate the CSM & 1708.

Your layup schedule will depend upon what you want in thickness & strength.
Lou
 
My Fuzzy Math: OK, I checked the Fiberglast site again. 1.5 oz mat is .060 and 18 oz woven roving is .025. (I don't understand how mat is thicker than WR.) At any rate, if I used three layers of mat, encompassing two layers of woven roving, I end up with .23 thickness. If I add a final coat of 10 oz fabric at .014 I end up with a total of 0.244 thickness, which is close to 1/4-inch, which I think will be fine. I still do not know how much polyester resin adds to the thickness. Any final thoughts?

Could I go 2 mat + 1 woven roving + two mat like someone suggested? That would give me .265. It would save some money, but again I do not know if I should stick to two layers of woven roving for added strength. Dang! This is driving me nuts.
 
1 layer of 1.5 mat will yeld aprox. 1/16 in. 1810 is two layers of glass strands one knitted on top of the other. Most are 0/90 orientation. The 1708 is plus or minus 45 which is stronger then 0/90 It's also twice the price of 0/90 mostly because it's in short supply. I think to keep the price up. Any type of biaxle is several times stronger then woven roving. Wovenroving is used very little anymore in boat building because you can get better strength to weight with biaxles. Given the support your planning in a female mold I would put in one layer of mat and two biaxle done. In your case the extra mat would be for fairing the outside of the hull. The amount of extra mat will depend on how smooth your layup is. Tom.
 
Dave,
I would recommend either using 2 oz. CSM or 3 oz. CSM. It's much easier to work with and the 3 oz. can be pre-wetted and contoured much better. We abandoned 1.5 oz. over 10 years ago.
The 1708 that we use is outstanding but, of course, expensive. It is 45/45 bias and is called biaxial (meaning on 2 axis)...not biaxle. ;) small point.
Lou
 
Spelling never was my strong piont. I do think for someone that may not have done a lot of layup that pre wetting 3oz. glass could end up being quite a mess and also add un wanted weight if you don't know what your doing. 1.5 + 1.5 yelds 3.0 and the resin to glass ratio can be much more easily controlled. Another thing to keep in mind is the resin that he is using. If your buying resin by the gal. it most likely has had fumed silica added to prevent sagging which makes it harder to wetout the glass adding more weight. Try to buy resin for in mold layup. It won't have all that added crap that you don't need. Tom.
 
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I want to thank Tom Ayers and Lou Tisch. The information that you two have provided is so valuable to me. As an amateur I have so many knowledge gaps. Working with a ten foot layout boat is not as critical as moving up to a 15-foot boat. I have been aware of changes in this field, but I cling to old habits, especially when confronted with tech articles I don't understand. I am not too concerned with the wetting out process. I will have two other workers besides myself, and I have enough experience to avoid the PANIC stages of layout. I will be using resin sold in bulk from a hot tub manufacturer down the road so hopefully it will not have the non-sagging elements. If either of you find yourself reading this last post, could you answer one more question?

When you wet out this 1708 CSM, do you have any problems with the threads poking up and not laying flat. I will be laying up one half of the boat at a time. My CSM will be pre-cut and I will have extra resin ready to just add catalyst. I will have plenty of paint rollers and metal rollers and bristle brushes ready. Does this 1708 create special problems with bubbles or blisters or material sticking up?

If you feel comfortable recommending a supplier, I would appreciate that information. I have used Fiberglast in the past, but they perhaps use a different company for their CSM biaxel material.

Hey, guys, thank you so very much!
 
Dave,
When wetting out the 1708, you wet out the CSM side and that presses into the previous layer. Follow that with good rollers and then squeegee with plastic squeegees to remove the excess resin and lay the biaxial down into the resin/CSM mixture. That gives a nice surface. If you want smoother, lay down a later of 1.5 oz. CSM and follow that with a light weight cloth and squeegee into place. That will be easy to fill and sand for your final outside lamination. When squeegeed down, most of the cloths are very manageable.

I use a formulated laminating resin for all our layup and we buy everything in drums from our resin to foam to acetone. The CSM, 1708 & cloth is purchase in 300-600 pound rolls. We buy from wholesale suppliers and they don't sell retail.

There is one retailer that I use for some stuff and we've been friends for 30 years. I did a bunch of boat repair with one of the owners (that would be previous owner as he's dead now) and still use them today. Their place is East Pointe Fiberglass ( epfiber.com) and ask for Jerry or Darlene and tell them I sent you. They'll take good care of you but I don't know how they stack up pricewise to some of the other suppliers mentioned.

I don't like laying up one side of a boat complete and then the other side as you aren't really "knitting" everything together at the keel on that small of a boat. We lay down a layer of 3 oz. CSM and roll that in on one side and then go to the other side and lay down a later of 3 oz. CSM and roll that down. We follow that with a layer on each side of the 1708 and roll and squeegee. On a boat (or mold) the size you're doing, I'd lay down a second layer of each and make sure it's not toooooo hot. Let that set and cure. Go in and do some sanding and then begin your layup schedule again with CSM and 1708 until satisfied.

When wetting out, we use a large/full 4" brush (spreads easier with that) and often use a 4" (sometimes larger) paint roller for applying resin. This also helps roll stuff down as you're wetting it out.

Your last statement about CSM biaxial is a bit confusing. CSM is different than biaxial.
Holler with more questions and good luck.
Lou

=======================================
When you wet out this 1708 CSM, do you have any problems with the threads poking up and not laying flat. I will be laying up one half of the boat at a time. My CSM will be pre-cut and I will have extra resin ready to just add catalyst. I will have plenty of paint rollers and metal rollers and bristle brushes ready. Does this 1708 create special problems with bubbles or blisters or material sticking up?

If you feel comfortable recommending a supplier, I would appreciate that information. I have used Fiberglast in the past, but they perhaps use a different company for their CSM biaxel material.

Hey, guys, thank you so very much!
 
Dave,
When wetting out the 1708, you wet out the CSM side and that presses into the previous layer. Follow that with good rollers and then squeegee with plastic squeegees to remove the excess resin and lay the biaxial down into the resin/CSM mixture. That gives a nice surface. If you want smoother, lay down a later of 1.5 oz. CSM and follow that with a light weight cloth and squeegee into place. That will be easy to fill and sand for your final outside lamination. When squeegeed down, most of the cloths are very manageable.

I use a formulated laminating resin for all our layup and we buy everything in drums from our resin to foam to acetone. The CSM, 1708 & cloth is purchase in 300-600 pound rolls. We buy from wholesale suppliers and they don't sell retail.

There is one retailer that I use for some stuff and we've been friends for 30 years. I did a bunch of boat repair with one of the owners (that would be previous owner as he's dead now) and still use them today. Their place is East Pointe Fiberglass ( http://epfiber.com) and ask for Jerry or Darlene and tell them I sent you. They'll take good care of you but I don't know how they stack up pricewise to some of the other suppliers mentioned.

I don't like laying up one side of a boat complete and then the other side as you aren't really "knitting" everything together at the keel on that small of a boat. We lay down a layer of 3 oz. CSM and roll that in on one side and then go to the other side and lay down a later of 3 oz. CSM and roll that down. We follow that with a layer on each side of the 1708 and roll and squeegee. On a boat (or mold) the size you're doing, I'd lay down a second layer of each and make sure it's not toooooo hot. Let that set and cure. Go in and do some sanding and then begin your layup schedule again with CSM and 1708 until satisfied.

When wetting out, we use a large/full 4" brush (spreads easier with that) and often use a 4" (sometimes larger) paint roller for applying resin. This also helps roll stuff down as you're wetting it out.

Your last statement about CSM biaxial is a bit confusing. CSM is different than biaxial.
Holler with more questions and good luck.
Lou

=======================================
When you wet out this 1708 CSM, do you have any problems with the threads poking up and not laying flat. I will be laying up one half of the boat at a time. My CSM will be pre-cut and I will have extra resin ready to just add catalyst. I will have plenty of paint rollers and metal rollers and bristle brushes ready. Does this 1708 create special problems with bubbles or blisters or material sticking up?

If you feel comfortable recommending a supplier, I would appreciate that information. I have used Fiberglast in the past, but they perhaps use a different company for their CSM biaxel material.

Hey, guys, thank you so very much!
Click to expand...


Tom/Lou, thanks for taking the time. I enjoyed learning your perspectives on the process!

T
 
Tod,
Thanks, happy to help.


Dave,
Couple other quick thoughts.
1. When laying up one side and then the other as I indicated, be sure to overlap sufficiently past the keel. 6" overlap is a good starting point. Roll this overlap a bunch to "meld" the pieces together.

2. We use a catalyst that is 30% less reactive at the front end but then cures completely at the back end of the reaction. I don't recall the brand name of the catalyst but I know it's "DDM-30". When doing a hull layup, it gives you a lot more working time than the regular catalyst.

3. We add (or purchase already added) a red dye to our catalyst. This has several advantages, primary of which is that you always know if a bucket of resin is catalyzed or not. If it's RED, it's hot. If it's not RED, it's not hot. If it's not RED...do NOT laminate with it...it will never cure for you. ;) It merely removes one possible error from the equation.

Later,
Lou
 
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Ok I'll give my thoughts. Two in. overlap is plenty. I personally like to stager the seams leaving no need to overplap much. If you have laminate rollers that have shallow grooves you can remove all the air and compress the layup. I don't use paint rollers as I spray on the resin. In your case I would use the short nap pink 1in. x6in. rollers from Home Depot. You can work the resin in well leaving little rolling with the laminate rollers. I also use the red catalist. I use ddm9 or highpoint 90 catalist at 1.25 to 1.50 percent with 30 min. marine grade resin. I don't like the 30 catalist because of a narrow trim wondow compared to ddm9. I hate grinding where you shouldn't have to. Every manufacturer has there way of doing things and each thinks his is the best way to go. Good Luck.

Tom.
 
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