1971 Flatback

[LilRichard]

Ok, this weekend, ahead of our first tropical storm, I managed to get my inner layers of glass laid in the transom.  Here is a pic of the entire transom:



Here is a semi-close up:



As you might guess from the numbers written on the glass, I laid up four layers of 1808, then added some extra tabbing in the corners just to be ultra-safe.  Last I finished off with two layers of 1.5 oz mat.

Her is a pic of the back of the transom, where I wrapped one layer of 1808 around the back.  Note the air bubbles at the very bottom... those will have to be ground out.  No fun.



I'm going to take a couple of weeks off of the boat... I have a big race to prep for in July.  However I will be getting ready to do the stringers soon!

[JimCt]

Great progress!!!  That transom will outlast all of us.

It's interesting to see the stringer difference between the AS boats and Makos.  AS stringers are massive compared the Mako system.

[LilRichard]

Alrighty, given the cooling weather here in FL, I have gotten back to the boat.  Here is the removal of the stringers:







And here is the pile of foam and glass:



At this point, I am trying to figure out my next steps.  the front stringers (in front of the compartment with the windows) seem to be secure- but at this point, do I just remove ALL the stringers?  I think the anwer is yes... your thoughts?

Also- I have two options- using something like divynicell (like shine did), or using a lighter foam (10 lb) with more glass (four layers of 1808+) like Tommy at Hammerhead does.  Thoughts?  Mr Wart?

[Shine]

If the front part of the stringers are bonded well to the hull, maybe not.  The question is how do you make certain you tie them together with the new stringers.  It might not be easy with that shape.   You have gone this far, I would take them out and go with continuos stringers.

As for stringer construction, either way will work.  I prefer for the core to participate in the structure (true composite sandwich) vs. just using it as a form for the all glass stringers.  This method also gives more space under the sole for compartments.

If you go the trapazoid PU foam route, there is no need to use heavy foam like 10 lb.  The foam is only there to be a form.  Most of the preformed stringers used in production boats are only 2 lb density – you push your finger right through them.  Its only there as a mold, once the glass is laid, its only flotation.

Cooler weather means we should all make serious progress over the next few months

Joel

[LilRichard]

So the boat is slowly picking up momentum again... finished removing all but the front of the starboard stringer this weekend... and I am picking up materials to begin constructing the new stringers with over the next few weeks.

Here is the remainder of the stringers coming out:



I am glad to be almost done with this!



So the plan is to use 2" 3lb poly foam to build my stringers.  Not positive on the layup structure yet, but I am thinking either 3 layers of 2415 or 3 layers of 1808.  From what I hear, the 1808 has more strength for the weight, but there may be something to be said about nearly 75oz of material too.  Either way, I will be beginning the shaping of the foam this weekend.

Any thoughts - tips - etc are always appreciated.

[Shine]

one is 44% mat by weight the other (2415) is 63% so your right about that.

That also does not account for Biaxial being stronger be equal weight over Roving by 20%  - that means the 24 oz. roving has roughly the strength of 19 oz. of Biaxial (24 x 80%).  

make a little test to see if your resin dissolves the foam it can happen

have you thought about making a plywood trapezoid mold to pour the foam into?  I was considering that for our boat

[LilRichard]

I had thought about doing the foam molds, but decided to go with the grid system that I see a lot of folks doing, and I think the rectangular stringers would be easier to work with in that fashion.

I will continue to ponder my 1808 vs 2415 decision... heading back your direction again.

[Shine]

What is "my direction"

[LilRichard]

Meaning using 1808...

I was just impressed by what the gentleman at FGCI demostrated to me- he gave me a laminated sheet with 2 layers of 1808, and then a similar sheet laminated with 2 layers of 2415.  Obviously the 1808 was thinner due to less mat, but it was also less stiff.  His point was that for stringers, the more material the better, due to increased (longitudinal) stiffness.

But then hearing your input (and I think Mr. Wartman also commented on it before), I am thinking about sticking with 1808.

[Tim/GA]

I went with the original trapezoid stringer system on mine but after I got to building the forms I realized I might as well incorporate them into the stringer itself.  I was using 1/4 luan for the forms so my layup ended up being: inside the "form" 1 layer of 1708 biaxial, then the 1/4 luan form, then 1 layer of 1708 biaxial.  This part was done outside of the boat.  Next the stringers were installed in the boat using 2 progressively larger tabs of 1708 "tape" and then 2 more layers of 1708 over the whole stringer and each extending further out from the tabbing.  The final layer literally reaches across the bottom of the hull and part way up the outer stringer on one side and to the middle of the hull on the other and slightly overlaps the final layer from the other side.  The stringers ended up with the 1/4 luan and 4 layers of 1708 (plus the added strength of the trap. shape).   I will say this about the shape of the stringers, they do take up space and make running the rigging tubes harder though.

[Shine]

A laminated sheet does not well represent a stringer.  If the guy gave you 78 oz. of plain mat (same as 2 layer 2415), it would feel just as stiff on a small sample.  

with the 24 oz roving, only 12 oz. are running the warp direction - lengthwise.

[Shine]

One last thing, Tim has a good point:  The shape of the stringers are also very important in giving stiffness.  Imagine plain aluminum sheet, now bend it into corrugated panels - instant stiffness with no additional weight.  Come to think of it, the original trapezoid stringer shape looks a lot like corrugated sheet metal.  you have wonder if thats what they were thinking 40 years ago, pretty smart?

[LilRichard]

I am getting strung out... here is a pic of me fitting my 3lb foam board for the stringer core.  I managed to get both of the longitudinal stringers cut today.  Hope to glass these in this coming weekend.  



I have decided to use two layers of 1808 with a layer of 2415 in the middle for a little extra glass.

You all enjoy the meeting at Shell Island... I will be thinking of you all while I am grinding and glassing.

[RickK]

You all enjoy the meeting at Shell Island... I will be thinking of you all while I am grinding and glassing.

Thinking ahead, she'll be just broken in by next years gathering - looking good 8)

[warthog5]

I've seen the stringer's cut in AS's and Mako's like this from the factory. I have a BIG time problem with it. It's piss poor engineering.

The hole should be cut in the dead center of the stringer. If there is not enough room for a round hole then make it oval.

Look at the chopped out section for the fuel/vent line in the right stringer.