coosa stringers

[KJM]

I'm wondering if stringers made from coosa would need to be completely glassed over? I'm thinking just stick them in the grooves left by the old removed stringers with thickened resin and then tabbed in at the join with the hull, up a few inches and call it done. Maybe stick the floor onto this with pl premium, since i've heard that Coosa don't hold screws real good. The floor will be plywood glassed over top and bottom. No pour in foam floatation, maybe pop bottles or something to allow ant water to drain freely. Any thoughts on the stringers being glassed in?

 

[AShipShow]

Coosa is not nearly as stiff as wood or plywood...
I took a quick glance at the test data from the coosa website and it states that the modulus of elasticity is 265,000psi for their strongest material (bluewater 26).. If you use their nautical line, its as low as 70,000psi.
Modulus of elasticity is basically a measure of a materials stiffness.
Plywood is about 1,000,000psi. So even the stiffest coosa is only 1/4 of plywood.

Then looking at purely ultimate strength (which is a materials resistance to fracturing/failing), the STRONGEST coosa board is 5,200psi where plywood is on average about the same.

So to summarize it, plywood and coosa will fail at about the same stress.. However to put it in perspective, if you have a plank of coosa and an identical plank of plywood and clamp it to a table at one end, and put a weight (say a gallon of paint) at the other end, the coosa will bend 4 times more (at a minimum) than the plywood.

So basically, the answer is no, you can't just use coosa for your stringers.. You will need to encapsulate them in glass just like you would with wood, but actually, you would need even more fiberglass than you would with a wood stringer.

 

[Scott Danforth]

coosa is a material that spaces out fiberglass and doesnt add as much strength like wood does

if you are replacing wood with coosa, you need to go thicker on your fiberglass than you would have had to do with wood

so to answer your question, yes, you need to do a better job fiberglassing coosa than you would wood.

and no, pop bottles will not work for flotation. the plastic breaks down too much and you end up sinking. also, the pour in foam is somewhat structural to provide rigidity to your boat.

 

[KJM]

Ok, no shortcuts and lots of fiberglass.

 

[AShipShow]

Nope... if you're honestly concerned about rotten stringers/weight... I would recommend doing molded fiberglass stringers... If I ever do another boat, I think thats the route I'm going to go...

It would be pretty simple... you could use foam or wood as a mold and coat them with epoxy to seal them and then wax, and then layup your stringers over top running them long and then trim them to the correct shape when you are done just like you would a piece of plywood or 2X material.

 

[Scott Danforth]

Nope... if you're honestly concerned about rotten stringers/weight... I would recommend doing molded fiberglass stringers... If I ever do another boat, I think thats the route I'm going to go...

It would be pretty simple... you could use foam or wood as a mold and coat them with epoxy to seal them and then wax, and then layup your stringers over top running them long and then trim them to the correct shape when you are done just like you would a piece of plywood or 2X material.

just buy a boat with engineered stringer tubs...... then you only need to deal with the stress cracks and the plexus joints failing about year 20.

 

[AShipShow]

just buy a boat with engineered stringer tubs...... then you only need to deal with the stress cracks and the plexus joints failing about year 20.

Thats cuz "engineered" got in the hands of the finance department and a proper structure would cost too much, but they still get to market it as a rot-proof design...

I completely agree that its not the most cost effective way to do it... I would only do it for the experience of doing it... Kinda like Ted with his vacuum resin injected swim platform.. definitely not the most cost effective method, but dang-it it was cool

 

[KJM]

Nope... if you're honestly concerned about rotten stringers/weight... I would recommend doing molded fiberglass stringers... If I ever do another boat, I think thats the route I'm going to go...

It would be pretty simple... you could use foam or wood as a mold and coat them with epoxy to seal them and then wax, and then layup your stringers over top running them long and then trim them to the correct shape when you are done just like you would a piece of plywood or 2X material.

So i make the stringer outside the boat from fiberglass, then remove the core and have a pure fiberglass stringer thats hollow in the middle? Thats interesting, I wonder how much fiberglass that would take? I could use the cooza for the deck or splashwell.

 

[KJM]

" and no, pop bottles will not work for flotation. the plastic breaks down too much and you end up sinking. also, the pour in foam is somewhat structural to provide rigidity to your boat." Scott I know this has been talked about before with some for and some against, but do you know of any specific occasions that the plastic broke down? I read somewhere that old plastic oil containers were better because they are made of more resistant plastic and fit in better because they are somewhat square. I really don't like foam as it will eventually always get wet IMO. No matter how well you seal the floor i think water will always find a way in after some years.

 

[Scott Danforth]

I have 5 year old plastic oil cans on the shelf in my garage that all broke down and leaked due to exposure to 95 degree heat.

I have 33 year old flotation foam that is just as dry today as the day it was sprayed under my gunwales and cap

if foam gets wet, you didnt encapsulate properly

or you drilled a hole and didnt seal it.

there was also discussions years ago about using pool noodles....... those break down in 6 months vs years for proper marine foam.

no mater what you use, in 15-20 years something will break down and someone will be re-restoring it.