light weight lay up

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

lay up

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