Why Isnt 1 Layer Of Mat And Roven Enough?

[mspring]

Why isnt one layer of mat and one layer of roven enough on stringers?

The boat is a fiberglass 20 footer with laminated 1/2 plywood to make 1" thick stringers, 3 stringers, one in the middle 14" at highest point and one on each side 8" at highest point.

 

[erikgreen]

Re: Why Isnt 1 Layer Of Mat And Roven Enough?

The layer count actually doesn't matter... what you're trying to do is acheive a certain thickness of glass, and therefore a certain amount of strength. Occasionally we also try to orient the glass fibers differently in multiple layers to ensure that the glass isn't weaker in any particular direction.

Those of us that are not marine architects or engineers cannot calculate the correct amount of reinforcement for a given hull design, so we have a lot of rules of thumb based on hull size and desired use that provide a large overage of strength.

Using these rules of thumb means our hulls are strong enough to take anything we throw at them in exchange for a slight increased materials cost and a small amount of weight.

A stringer failing in operation would likely damage the hull, would certainly require a major repair, and might possibly kill someone, so it's a trade-off that most of us are more than willing to make.

Erik

 

[ondarvr]

Re: Why Isnt 1 Layer Of Mat And Roven Enough?

Very good answer.

 

[BillP]

Re: Why Isnt 1 Layer Of Mat And Roven Enough?

I like that answer too and will add to it. One layer of mat and one of roven can/may be strong enough. There's a big difference in cloth weight to choose from and it can make or break the difference. Also, if the stringers are attached to the floor it turns into a box structure and requires less glass on the stringer to hull joint. The number and spacing of stringers makes a difference too. Lots of lightweight stringers with thin glass equal a couple heavy glassed stringers.

It's easier to over glass everything and not worry later.

bp

 

[oops!]

Re: Why Isnt 1 Layer Of Mat And Roven Enough?

erik stayed at a hoilday inn express last night....

 

[SnappingTurtle]

Re: Why Isnt 1 Layer Of Mat And Roven Enough?

erik stayed at a hoilday inn express last night....

... and where have you been?

Using these rules of thumb means our hulls are strong enough to take anything we throw at them in exchange for a slight increased materials cost and a small amount of weight.

Erik

A little over engineering goes a long way. Better too much as too little.

 

[reynold460]

Re: Why Isnt 1 Layer Of Mat And Roven Enough?

i have a 18' 1977 invader tri-hull i used only mat on that is all that was there to begin with and it lasted 30 years so i figured it was good enough least i hope so but the stringers are small less than 6 inches

 

[oops!]

Re: Why Isnt 1 Layer Of Mat And Roven Enough?

any glass is really strong......your probably thinking that the choppped look in your hull is matt........it isnt....its a chopper gun.....mat and resin and cat sprayed like paint.

but either way......fiberglass can be as strong as steel