overlaps

im soon to be putting in 2 layers of 600/300 combi mat in to my build.

now when putting in a layer how much of an overlap should there be from 1 piece to the next.

when you put one sheet down and lay the next sheet to it what should the overlap be? 50mm?

probably a silly question can i butt the sheets together and when i put next layer on top put the next sheet over the join making sure the join is in the centre of the sheet on top and so on.

what i want to avoid is the slightly raised lump you get which is caused by the overlap.

 

50mm is about right, what are you building, hull, deck, furniture ?

Some manufactures cloths have a feathered edge, it may be worth a bit of research.
You can butt and overlap by about 200mm but it will not be as strong, since we have no idea what you are making, thats your call.
Another way round it is to use layers of uni which of course can be laid along side one another.

 

im building my new hull.







im sure the combi mat ive got coming dosesn't have a feathered edge on it.

what is the UNI you mentioned?

 

Laying up a hull the overlaps will give you defacto ribs, don't worry about it.
Unidirectional, could be laid at 0-90 in two layers, but with strakes involved I wouldn't bother.
For your hull I would increase the overlap to 75mm.

 

thanks for that mate.

i will also be adding PU foam ribs glassed over through out the hull for added strength.

i'll try and get the overlaps in places where the ribs are going to be.

im not worried about under the deck about the overlaps causing lumps.

just down either side where people can see the finish i want it as smooth as possible without and lumps caused by overlapping the combi mat.

 

Then why not run the cloth front to back with an overlap in the first chine where it joins the bottom laminate running across the boat ?
Voila ! No visible joins !

 

i have thought about that.

once i get the second layer of csm on i'll decide which way to go.

im doing this on my own so has got to be the easiest way of doing it so i know i won't have the resin going off on me.

 

Garry, ^^^^ exactly what I was thinking of b4 RedR wrote it ,

if your topsides especially are done longtitudinaly any print from laps is much less issue, maybe you can slit the fabric to suit, I've sometimes used some builders film to do a fabric layout on the job..... a few felt tip pen spots mark the way. If you're on your own you could slit your fabric to do the bottom & tunnel in 620mm or so widths or whatever suits, if you get some run out on the longti laps a bandage will fix it.
Continuity of fiber is king in composites, if as you alluded to butt the fabric you would need another layer to actually achieve your layup, on occasion I have done it on double bias(45/45) sheathing jobs but have laid 3 instead of 2 with generous staggering of plies, the object was to eliminate laps that had to be faired out but came at cost of an extra layer.

Jeff.

 

my problem is i don't really have the room to lay the cloth out flat so i can cut it in one long length.

if i were to butt the cloths together i would be putting another layer over the top by overlapping by half a sheet at a time.

i may go down the overlapping route of 75mm if i can space it all right so that when my ribs go in they are on top of the overlap.

i want to put ribs in at every 600mm centres and seeing the cloth is 1250mm wide it should work out ok but until i measure it all i won't know for sure.

 

Garry,
to slit your fabric all you need is a couple of of bits of 1,1/4"/32mm pipe, also get some pvc storm pipe to hold your slit lengths on... use a length of masking tape to hold the fbric to the pvc. Stitched fabrics hate over handling & especially folding. you need to set up a fabric rack to hang your rolls on & another pipe to transfer to.

Jeff.

 

With anything other than uni you should overlap even though you will be following with more layers because you do n0t have continuity of fiber in one direction. For this reason i prefer uni for big parts and save the axials for tabbing and repair work. That said most people just use axials and overlap and it works just fine, just not as good imho. I don't feel you need huge overlaps, just equal to a scarf joint, so perhaps 12 times the glass thickness so really 25mm would be plenty, its just easier to maintain a bigger lap during a wet layup.

Steve.

 

thanks guys for your info.

i have been over and measured it up and i can put the combi on and over lap by 50mm and then fit my ribs every 610mm centres which will then hide all the overlap joints in the combi mat.

so it looks like i will be going with the above once the 2 rolls of combi are delivered.