layers of glass

[rockyrude]

First off, happy holidays to all of you generous folks out there without whom there'd be a lot of struggling folks.
I'm trying to be clear on the number of layers of 'glass over my stringers. If I read correctly, you all are doing one layer of 1 1/2 oz mat first then one layer of roving over it. Is this good enough or should there be another layer or two over it?
Thanks

 

[Bondo]

Re: layers of glass

Ayuh,.....

The Mat gives you the Adhesion required,+ the Roving provides the Strength.......

No Reason to over due it.........

 

[BillP]

Re: layers of glass

What size boat and motor is it? That might be ok for a 14' skiff with 15hp kicker but on an 18' with 100hp you could have problems.

 

[rockyrude]

Re: layers of glass

Sorry 'bout that, '70 18' airslot rated to 135 hp

 

[BillP]

Re: layers of glass

Sorry 'bout that, '70 18' airslot rated to 135 hp

That be a Wellcraft Airslot? That's a big, bulky, heavy boat for it's length that has plenty of bottom pounding power. You are wanting to use one layer each of standard 1.5oz mat and 18 oz woven roven? A bit light in my opinion...it's probably about half of what the factory did.

 

[rockyrude]

Re: layers of glass

Thanks, from what you are saying I should go at least two layers of each alternating right? Should I use heavier mat?

 

[ondarvr]

Re: layers of glass

Mat doesn't add much strength, so going heavier won't make much of a difference.

 

[seabasser]

Re: layers of glass

mat provides very little stregnth, if you haven't already bought the mat i would get 3/4 ounce it's easier to work with and gives the correct surface for the roven. do the project once and do it right, alternate layers of mat and roven three times so you don't have to worry about doing it again. don't worry about too much weight it won't add 100 lbs to the boat, that won't make much of a difference in the grand scheme of things.

 

[BillP]

Re: layers of glass

Mat doesn't add much strength, so going heavier won't make much of a difference.

I can't believe people say mat doesn't add much strength. Yes it's weaker than woven roven in tensile strength. How much less is where a resin rep should be able to post accurate calculations that show the difference.

Mat may be weaker but adding two layers of 1.5 mat to two layers of 18oz woven roven will make a huge difference. Anyone who doubts that should do a few samples...layup a square ft of each and do a physical distruction on them. Mat also has other important characteristics...that's why 99.99% of the boats made use the stuff. It's random strands give a uniform strength in all directions...stiffness. Mat has higher compressive strength when pushed to the failure point than roven woven. Mat has less tenancy to delaminate in multiple layers than woven roven. Mat conforms to irregular surfaces better. Mat gives better bonding between layers of woven roven (cloths delaminate easier without mat in between). This is the stuff some folks don't seem consider when bashing mat use.

bp

 

[seabasser]

Re: layers of glass

mat does add stregnth, but not campared to roven...or nytex (sp) i would rather use my resin on stringers with the roven rather than a heavy mat, laying flat on a deck is something completely different, a couple layers of mat is plenty.

 

[ondarvr]

Re: layers of glass

BillP

I think you're reading far too much into what I said, I didn't say mat is worthless and that it doesn't have it's place in a laminate schedule. I said it won't add much strength in this application, if he want's the laminate to be stronger, he can switch to 24 oz roving, or a biax type product, adding another layer of mat will make it heavier and stiffer without the same gain in strength.

 

[BillP]

Re: layers of glass

BillP

I think you're reading far too much into what I said, I didn't say mat is worthless and that it doesn't have it's place in a laminate schedule. I said it won't add much strength in this application, if he want's the laminate to be stronger, he can switch to 24 oz roving, or a biax type product, adding another layer of mat will make it heavier and stiffer without the same gain in strength.

I might be reading too much into it but I strongly disagree that one layer of 1.5 mat won't make a significant increase in strength...not as much as woven roven but still much stronger (I don't know how to do the math though)...and empiracle tests show that. Regardless, doubling the laminate schedule will double the strength no matter how you slice it...and 4 layers is in the structural ball park. There are other ways for sure but bulking up with old tech mat and woven roven is good for novices. It's how most old boats were built. Bulk gives better chances of sealing water out. Bulk also reduces flex without adding stringers, etc, etc.

 

[Robj]

Re: layers of glass

When I replace my stringers on my 18' Excel this past spring, I was suprised to find that the OEM only used matt on the original stringer install. So matt definitely add strength, but not as much when used with WR.

Have a great day,

Rob.

 

[BillP]

Re: layers of glass

When I replace my stringers on my 18' Excel this past spring, I was suprised to find that the OEM only used matt on the original stringer install. So matt definitely add strength, but not as much when used with WR.

Have a great day,

Rob.

Mat or chopper (gun) for stringers was common back in the 1950s & 60s. Not spoken of yet is that stringers with floors sitting on them take less lamination structure than stringers that don't have the floor sitting on them. Part of the stress is taken up by the floor when tied to the stringer. Its something to consider when rebuilding.

bp

 

[Robj]

Re: layers of glass

BillP,

That Excel is a 1992 and all they used was matt to install the stringers. You are correct about the floor adding strength to the stringer, it is kind of like an "I" beam, the hull is one flange of the I and the floor is the other flange. Makes it much stronger.

Have a great day

Rob.