light weight lay up

[nordvindcrew]

I have a mold of a 16' 8" rowing boat that I took off a boat that I designed and built. I pulled one boat out of the mold. The lay up is 3 layers of fiberglass mat and polyester resin. I didn't use any gel coat in the mold, and had a lot of pin holes to fill before the hull was painted ( a lot of work ). the resulting boat preforms well but is quite heavy ( about 180 lbs.) I race in open water events, and weight and strength are both important. Any help on a lighter lay up that is not too technically demanding would be a great help

[jimslade]

One layer of 1810, one layer of 1/2 inch nida core. one layer of 1810 glass. light and strong.

[nordvindcrew]

To jimslade, I'm an absolute beginner at this. actually, I was amazed I even got the mold done and a boat out of it, let alone a pretty good boat that rows fast and wins races. To get to my point, I have no idea what 1810 or nida core is, and how difficult they are to work with. If I can figure how to do it, I'll post a photo of the hull for general info. thanks

[marshmat]

Nord, there are two reasons I can think of why your boat is so heavy. One is chop-strand mat, the other is that you're new to composites.
CSM is weak, porous, absorbs a lot of resin and is by far the heaviest fibreglass for a given weight. Cloths are far lighter for the same strength.
New builders almost always use far more resin than needed. If you find yourself using more resin than glass by weight, you're probably adding a lot of extra resin that isn't making things any stronger. The trick is to use just enough resin to fully bond the cloth layers together, without any excess resin.
Core materials are tricky. They can be really beneficial, but I'd suggest you get some practice with simple laminates and vacuum-bagging before you go all gung-ho on coring.

[nordvindcrew]

Marshmat, Thanks, I think the lay up was pretty good on the resin to glass ratio. We rolled it very thoroughly as the mat and resin went in. the final thickness was just over 1/8". Cloth, maybe a more sophisticated variety, was what I had in mind. Coring and vacum bagging are something I need to learn a lot more about before I try It. The real culprit on the weight issue was the extras aded to the hul:flotation tanks, floorboards and thwarts. I built them all much too heavy. That part is easy to fix, especially if I start with a much lighter hull.

[jimslade]

1810 is fiberglass that has 18 oz of woving glass with 1 oz of mat. nidacore is a coring material. google nidacores website. they have alot of info. I use nidacore for floors, almost anything that used wood.

[JR-Shine]

One layer of 1810, one layer of 1/2 inch nida core. one layer of 1810 glass. light and strong.

You could come close to cutting the weight of the hull in half. I would even try 1208 or maybe just DB1700 (17 oz. biax with no mat). Either way a composite sandwich is going to be a big upgrade:)

Joel

[marshmat]

Nord, it's perfectly normal to overbuild the first boat... all production builders do this from time to time. Once you see how she handles, then it becomes a lot easier to see where weight can be lost.
A cored sandwich will give you a stronger and lighter hull, yes, but definitely practice on small stuff first. Vac bagging isn't hard, just tedious. The bagging materials themselves will only be a couple hundred bucks for your whole boat; the cost is in the labour it takes to form and seal the bag. (High-elongation films like Airtech Stretchlon can cut the bag-makig time by half, if you want to give bagging a try.)

[frosh]

I would think that for a one person rowboat, any PVC foam core of 10mm and one layer of 13 oz biaxial fibreglass outside, and one layer of 13 oz. double bias inside should be enough. Use epoxy resin and definitely vacuum bag with bleeder cloth to absorb excess resin. It is worth while using the slurry technique to seal the foam core first, which should save a few lbs of resin also. There is a thread on slurries in the forum. Thwarts, floorboards etc can be of selected very light pieces of Western Red Cedar with one layer of woven carbon reinforcing on the under surface to resist bending of the timber under load.
Could weigh in under 80lb depending hull dimensions, (beam and freeboard), and stronger than your first attempt. :)

[marshmat]

If you're interested in vac bagging, which I think could be really beneficial if you want to build more of these boats, check out http://airtechonline.com/ They're busy, but they have a huge range of bagging supplies and are very helpful in selecting appropriate films and breathers for any particular project. Bagging supplies aren't expensive; a 200-foot roll of a really good bagging film or release film might run you $150 and bleeder cloths are around $50 per 25 yards. It's amazing how much stronger and lighter parts can be with this kind of technique.

[nordvindcrew]

Ok, we did the new boat ( see designing a fast rowboat ) in a lighter layup and cut a lot of weight out of it. Vacume bagging still scares us. how about something like bi-axial cloth as some one suggested? any way to do a cored hull without bagging it? I'll be doing another varient of the boat next year as a 17' sail boat (battened sails, ketch rig?) so there's another opportunity to stretch our skill level. That will be the fifth varient of the original stitch and tape 9' plywood dinghy we built 12 years ago. Keeps the family tree growing.

[JRL]

Vacume bagging still scares us. how about something like bi-axial cloth as some one suggested? any way to do a cored hull without bagging it?

Vacuum bagging is an option, more than a necessity when using a core.

I like JR-Shines idea. Biax, no mat, with a PVC core.

And since you said your new.....Fully wetting out heavier cloths can be a little time consuming.

What I like to do is lay down some painters plastic on the floor. Wet out the plastic with resin. Lay the cloth on top of it. Then add more resin to the cloth. Roll the air out of it fully. Then peel it off the plastic and form it into the mold. This will help you keep tons of extra resin out of your layup (and prevent puddling). Its easier to get the air out of a 17, 18, 24 oz cloth when its laying flat on the ground.

[marshmat]

Vac bagging is not mandatory, no. If done properly (not actually that hard), it will result in a lighter and stronger part with minimal excess resin and very few if any air voids. Air voids between core and skin are what really kill a lot of cored boats, hence why bagging is so helpful.
A light biaxial (two unidirectional layers stitched together) is easy to wet out and gives you more engineering options than woven cloths or rovings, plus it's a bit more efficient on the resin. Heavy bi- or multi-axial cloths, though, are a real pain to wet out and the technique JRL describes will make the work easier and more reliable.
Wetting out from the bottom- lay down resin, press cloth into it, let resin soak in on its own, then once it's nearly saturated squeegee the last few drops in from the top side- almost always results in a more thorough wet-out and better resin penetration into the yarns than you get by squishing gobs of resin in from the top. Once an air bubble is trapped under a top-wetted cloth you'll never get the entire bubble out; better to let them float out on their own as the resin wicks up from below.

[nordvindcrew]

food for thought, still need a lot of info about bagging, ie: how do you hold all the laminations in place in the mold through the lay up and bagging, also, how do you retard the resin to give enough time to get everything done?

[KnottyBuoyz]

food for thought, still need a lot of info about bagging, ie: how do you hold all the laminations in place in the mold through the lay up and bagging If you're working on a horizontal surface you have gravity on your side. If you're working on a vertical surface it's a little more tricky. Pre-coating the surface and pre-wetting the fabrics will help hold them in place. If you're working upside down well that's a whole other story. If worse comes to worse there's always Raptor Staples.

, also, how do you retard the resin to give enough time to get everything done?Use a slower curing resin or do your lay ups first thing in the morning when it's cooler. You can chill your resins before mixing to give yourself more time. A large boat hull will require more hands. One or more mixing and one or more spreading.

Vacuum bagging is pretty simple but as you noticed you have a shorter window with which to lay up your fabrics and get it bagged before the resin kicks. It can be done though. Look up resin infusion which has alot of similarities to bagging but has the benefit of a virtually unlimited lay up time before you have to mix resin.

[JRL]

Look up resin infusion which has alot of similarities to bagging but has the benefit of a virtually unlimited lay up time before you have to mix resin.
I second that one. I cant believe I shy-ed away from it at one point. Now its the only thing I want to do.

Bagging for me is fun only because I find it challenging (to get air free, bridge free parts). And another problem with bagging is that the good information cant be freely given over the internet. Ive seen a few guys giving up some of boeings layup procedures on here. Not my cup of tea.

[Jimbo1490]

JRL,
You on the right track, but with one little addition, you can wet out the cloth PERFECTLY with no excess resin whatever. The trick is to lay down a piece 2-4 mil clear plastic film on the floor. You want it bigger than the piece of glass cloth you will be wetting out. Lay the dry cloth on the plastic then pour a puddle of resin in the middle of it. Then lay a second identical piece of plastic right on top. Now squeegee the puddle of resin around until all of the cloth is wetted out. Peel the topmost piece of plastic off, then lift the wet cloth and bottom plastic film together and place it where it goes in the mold. Squeegee the air out then peel of the plastic. This method saves both time and resin. You do tend to use a bit of plastic film, though.

Jimbo

[JRL]

JRL,
You on the right track, but with one little addition, you can wet out the cloth PERFECTLY with no excess resin whatever. The trick is to lay down a piece 2-4 mil clear plastic film on the floor. You want it bigger than the piece of glass cloth you will be wetting out. Lay the dry cloth on the plastic then pour a puddle of resin in the middle of it. Then lay a second identical piece of plastic right on top. Now squeegee the puddle of resin around until all of the cloth is wetted out. Peel the topmost piece of plastic off, then lift the wet cloth and bottom plastic film together and place it where it goes in the mold. Squeegee the air out then peel of the plastic. This method saves both time and resin. You do tend to use a bit of plastic film, though.

Jimbo
I actually saw a write up about that method. It was for wet layup vacuum bagging. I think it was a PDF file from perdue. Although for vacuum bagging that method has the potential to trap a lot of air between layers.

What you mentioned is the best method no doubt. And atleast plastic is cheaper than resin.

[keith66]

I would be tempted to go for what we call combi mat which is Biaxial stiched to a layer of CSM its resin to reinforcement weight ratio is 1;1 as opposed to CSM's 2.5-1
result instant 50% weight saving on resin and better stiffness.
I have used it and it wets out real easy. You could incororate coremat into panels on the interior this is an easy to use core on the roll that is useful for small applications and does not need vacumm bagging.

[marshmat]

I've never really associated combi-mat with lightweight.... I've always thought of it as being more of a resin-efficient thickness builder. In terms of strength/weight, the biax alone is far better; the stitched-on mat is just there to add thickness, as I understand it. Great stuff for when you need a quick, fairly strong buildup in a hull bottom laminate though.

[keith66]

The stiched biaxial/CSM combination mat has most of its weight in the biaxial, as i understand it the CSM is there to improve the bond between layers.
When i was at college we were told never to laminate rovings or cloths together unless there was a layer of CSM between them.
The reason for this was rovings were more prone to delamination, having spent many years doing some heavy duty GRP repairs i reckon there is a lot of truth in this.

[marshmat]

That is a problem with heavy rovings, yes... without something to cross-link the roving layers you get a very resin-rich layer between sheets of roving, which is vulnerable to peeling apart. With thin cloths or uni/mult-axials, though, the layers of fabric nest tightly enough that this isn't a problem, especially if it's vac bagged. For a bulk hand layup where you don't have as much control over the inter-layer thickness, though, a small bit of random strand could help with this problem.

[nordvindcrew]

OK, so if I decide to go with biaxial and core material or something similar, it can be done without bagging? My next question is how to deal with chines. If you look on my thread "Designing a fast rowboat", there are pictures that show our latest boat. The chines are not as evident as they will be when the boat is painted, but you should be able to see what the general shape is. currently, we lay up each panel (3 per side ) from stem to stern with an overlap going from 1/2" to 1-1/2" wide as we laminate the three layers. all laminations are overlapped in the keel area from 1" to 3'. Later, we add a couple of more layers of mat inside the chines and keel to provide fore and aft stiffness to the hull and protect from wear and collisions with rocks and other boats. right now total hull weight is about 86 pounds with flotation compartments, floorboards and gunnels to still go in. Hope to have finished weight of 140 pounds, maybe more, hopefully less, depending on what wood we decide on for the Gunnels. The gunnels have to be very strong to maintain the hull shape and to stand up to the strain we put on the oarlocks pulling 9'-4" oars