mixing kevlar with glass matt and rovings in a lamination.

Foam cored hull.

 

Kevlar is strong in tension and weak in compression.

With a single skin this means the kevlar would be on the inside. Under tension

My composites knowledge is basic. A foam core sandwich panel is normally a balanced laminate..same skin scantlings each side. So if kevlar is used it would be on both skins.

It would be unwise to change your laminate schedule without approval.

 

Think logical

PUNTURE RESISTANACE puncture is coming from the outside towards the inside . SO WHY WOULD YOU HAVE THE MATERIAL THATS RESISTING THE PUNTURE THE FURTHEREST PLACE AWAY FROM WHATEVER IS DOING THE PUNTUREING ??? YOU MIGHT AS WELL JUST LEAVE IT ON THE ROLL AND CARRY IT WITH YOU IN THE BOAT !!
IS 2013 GOING TO BE YET ANOTHER OF THOSE YEARS LIKE LAST YEAR ????

 

Have approval, I dont need the kevlar to add strength, that has been added by replaceing the mat with more biax , only need the kevlar for puncture resistance. Rick

 

thinking logical !!

I know !! but my question is why have the material thats there to resist punturing at the furtherest place away from the object thats punching a hole in the hull !! it dosent make any sense at all !! Your tryng to stop or slow the object from not only punturing a hole but stop or slow the rest of the laminate from getting ripped to shreads .
Would you use a protective paint on the back of a panel or on the front where its doing good ?? Is my logic so hard or to simple to undestand ?? personally i would be making sure the rest of the glass layers were in a shedding mode as well so it will be helping to deflect damage away .

 

So you vote for the kevlar to go on the out side of the hull tunnels? That was the way I was going untill PAR said put it inside, got me confused now. Rick

 

Basically the only real purpose of the Kevlar is to keep the damaged area intact rather than creating an actual hole, on the inside it will do this, it would do it on the outside too. With cored structures the skins tend to be strong enough for sailing loads but puncture fairly easily because the skins are thin, a core with high compressive strength such as end grain balsa would would get more benefit from having kevlar as the very inside layer than a ductile core like foam which tend to absorb impacts better. Ignoring any additional "strength" kevlar may bring to the table, the very properties that everyone despises when working with the stuff is what makes it useful in keeping a damaged area of hull from actually becoming a hole but rather contains it as a crushed area that may keep a lot of water out and buy you time to stem the flow. Persoally i wouldnt bother since its not factored in as part of the structural laminat it is extra weight, even more so if you put another layer of glass over it so you dont have to sand it as has been suggested. Its a bit like back in the 70s lots of production catamarans like the Prouts, Mac 36 and others came with masthead floats but people took them off because they were detrimental to performance and the boats capsized so rarely.

Steve.

 

I have weight savings from removeing the mat from the schedule, I already have the kevlar . My plan has been to put the kevlar on as the first outside layer with two layers of biax for next two layers all wet on wet so it will weight the kevlar down and absorb excess epoxy off the kevlar. Rick

 

My present build is a conversion of a surf boat lifeboat hull into a sailer. As such I have to live with what I am given to work with. On my prev. conversions and again on this one I am using pairs of SS keel bolts that are bent inward and welded to a longitudional SS pipe once they pass thru the bottom of the boat. Thus each pair forms a cross sectional triange of strength against transverse loading plus what I term my ballast cage.
However due to access restrictions (existing excellent shaft tube which I do not want to disturb) I have to live with three existing longitudionally centered bolts to use as my skeg keel bolts. Thus I can not set up pairs of bolts to form triangles for good transverse strength in the skeg. I have figured out a way around this by using a welded up cage of SS flatplate and webs but I thought I would add to it's strength by laminating Kevlar into the skegs skin thus forming a cross sectional wrap giving strength similar to what pairs of keel bolts forming triangles would. Thus my origional query on Kevlar in the lamination. However having read the subsequent posts I am going to look in other directions. Possibly S glass or some other special purpose glass fiber.

 

S glass has a a tensile strength of around 128,000psi, kevlar 90,000psi, standard E glass is 15,000, this is why i like S glass in uni form.

Steve.

 

Thanks Steve-- looks like I'll have to bone up on working with S glass and next track down a supply. I'm visiting the local FRP/ boatbuilding supply tomorrow to pick up sanding disc for the Porter Cable and the Metabo so will check on S glass stock. Don't have high hopes but one never knows

 

Those numbers a bit away, S glass is about 50% better compared to E..

 

I think your numbers are drastically wrong.

This is a basic comparison wit e-glass as the standard/baseline and rated as 1.



This gives numbers, but not in psi.




It's surprisingly hard to find any charts or tables for comparative tensile strengths. I don't particularly trust those charts I posted, as the first shows kevlar and s-glass the same, but the second chart doesn't. Never the less, your numbers of 128,000 vs. 15,000 aren't right.

Here's an MPa to psi or psi to MPa converter...
http://www.chapelsteel.com/mpa-psi.html



I found this one for foams that I'm posting for no particular reason, other than someone might find it useful.

 

UIM already have test procedures for safety cells
Google it
Its all about impact protection

 

S Glass still looks pretty dam good for my requirements but I still have some 2 months to gather info. However, Thanks guys for all the good info including the foam chart. ---Geo.