98 Pathfinder Stringer Job

[Cracker Larry]

Another question if I may. I see the stringer sections are 8' long, how are they spliced together without creating hard spots, or increasing the stringer height at the splice points?

My interest in this system is two-fold. I may have some applications for it in my own builds, but as a surveyor it is important that I fully understand it's properties, capabilities, limitations and proper use. When I run across it in the field, and I'm sure I will sometime soon, I need to be able to make an accurate and informed decision to be fair to my clients, whether they be sellers, buyers, insurance companies or lending institutions. A mistake on my part could cost someone, including me, a lot of money.

Thanks!

[Chisox]

Another question if I may. I see the stringer sections are 8' long, how are they spliced together without creating hard spots, or increasing the stringer height at the splice points?

My interest in this system is two-fold. I may have some applications for it in my own builds, but as a surveyor it is important that I fully understand it's properties, capabilities, limitations and proper use. When I run across it in the field, and I'm sure I will sometime soon, I need to be able to make an accurate and informed decision to be fair to my clients, whether they be sellers, buyers, insurance companies or lending institutions. A mistake on my part could cost someone, including me, a lot of money.

Thanks!

Now that is definitely a question for Scott!

[slewit]

Another question if I may. I see the stringer sections are 8' long, how are they spliced together without creating hard spots, or increasing the stringer height at the splice points?

My interest in this system is two-fold. I may have some applications for it in my own builds, but as a surveyor it is important that I fully understand it's properties, capabilities, limitations and proper use. When I run across it in the field, and I'm sure I will sometime soon, I need to be able to make an accurate and informed decision to be fair to my clients, whether they be sellers, buyers, insurance companies or lending institutions. A mistake on my part could cost someone, including me, a lot of money.

Thanks!

Hi Larry

Good question. Splices are treated very similar to interconnections between bulkheads and stringers.

You want to butt the two stringer segments together. You then need to place a layer of glass overlapping the joint onto both stringer segments. ABYC/Structural Composites and ACMA/CCT (both training programs for composites) Rule of thumb for E-Glass and boats is we want a minimum of 2-3" of overlap at the seams. This overlap rule applies not only to stringers and bulkheads but for tie ins and fabric layers.

The fibers are doing the bulk of the load bearing. What we need to do is have an effective way to transfer the loads from one fabric layer to another. The overlap provides this transition. Loads transfer from one fabric layer to another at the overlap via the resin interface. This is why we need the generous overlap so that we do not over stress the resin bond. If the overlap was too short, lets say only 1/4 or 1/2 inch, it could put too much load on the resin bond and it could delaminate (break).

I also get the question on what about the gap between the two segments. The gap is not a problem as long as it is not so large that the glass overlay can buckle into the gap. Think of scored core or spaces between sheets of core. In sandwich construction many times the scoring is just void (a problem for water migration but not loads). If you want to eliminate the gap you can putty the segments together at the foam.

large boat w/preform stringers. Segments were sized so workers could easly handle the preforms. Tabbing ties part together.

Same 2-3" overlap rule apples to stringer to bulkhead, stringer to hull and bulkhead to hull connections. The tabs on the preforms provide the overlap onto the hull. This overlap allows loads to travel into the stringer.

As to the hardspot caused by the overlap, this is not an issue in these applications. The laminate will be twice as thick in the overlap area, but we are still only going from 24 oz to 48 oz of glass. Conventional grid stringer systems typically have much more glass. This extra material is not to carry boat loads but for processing purposes. The grid is laminated on a mold and needs to have ample structure to be demolded, trimmed, jigged and craned into the boat, bonded or laminated into position. Many builders then post inject foam. So in this case the grid needs more added thickness so that it does not distort when the foam is injected.

The Prisma process is a total reversal of the grid process. Here we line pressure rated tools with Dry fabrics and inject the foam. Once the foam cures you have a nice strong lightweight preform, glass attached ready to install into the boat. So this allows the builder to put only the material needed for the structural loads into the boat. This saves time, weight and cost.

I dont want to tout that our products are the only way to build boats, it is not. Many boats use a wide variety of structural systems with great results. We are one of several options. Our process is a bit unique and works well for many, but not for all. We are finding that as the industry moves to closed mold process the preform is more and more the missing link that allows the builder to infuse or VARTM (Vacuum Assisted Resin Transfer Molding) structure into the part.

I hope this answered your question.

Also on your professional work, our sister company Structural Composites Inc may be able to assist you when you see a job that has those risks that can keep you awake at night. Here we provide independent laboratory testing, Expert Support, Design and Engineering, and ABYC Composites Training. Happy to help if we can provide value, if we cannot do what you need we can refer you to someone who can help.

Have a great Weekend... Raining cats and Dogs today in Melbourne Florida.

Scott

[Cracker Larry]

Excellent reply Scott, thank you for taking the time. I'm looking forward to the samples and I'll follow up further.

35 degrees and windy in Savannah, GA this morning!

[slewit]

Excellent reply Scott, thank you for taking the time. I'm looking forward to the samples and I'll follow up further.

35 degrees and windy in Savannah, GA this morning!

Thanks Larry glad that made sense.

Better in Fla today.. Sunny and starting to warm; 64 now.

Your sample set was sent out Friday via UPS. You will find some small beam segments, T-Mat, Prisma glass samples and literature. If you see a shape you are interested in I can send you some larger samples.

To wet out Prisma, flip the product over and back wet the T-Mat backing on the bottom and tabs of the preform. Then flip over into position. I recommend back wetting all knit fabrics. Much better to be pushing resin (and air) up though the reinforcement then trying to push resin down. Wetting the laminate surface prior to laying the material helps even more. Picture you are doing a large stringer. So now you would wet down the entire top of the preform and let the resin just soak into the fabric (you dont have to chase air bubbles on the preform as the foam is expanded into the inside T-Mat layer). You can brush or squeegee resin in if you like. While the resin is soaking on the preform, this is when you work the tabbing. You want to roll out the tabbing--

The job of a laminator is not just getting rid of entrapped air it is 1)properly place the reinforcement 2) properly saturate the reinforcement 3) properly consolidate and remove air and 4) properly cure the laminate.

While you work the tabs resin soaks into the Prisma. The glass fabric becomes nearly clear and you can see the foam of the preform. Too dry- White fibers.. Too wet- Glossy finish.

With E-Glass knit fabrics in hand layup you should not see any white fibers, it should be clear or nearly clear when properly saturated. When cured you would still be able to feel the texture of the fiber bundles. Adding additional resin past this point 1) increases weight and cost 2) increases laminate cracking (puddles of resin) 3) causes excess exotherm (heat of cure) and 4) shows poor workmanship

. In my class one technique recommend to boat builders who like to use a lot of resin is to leave a section of the boat dry while wetting out the bulk of the area. Backwet and use a bit of extra resin as that speeds the wetout process. Then take that excess resin and transfer it via a fuzzy roller to the reserved dry section of the boat. I find that builders who do this get nice quality laminates without wasting resin.

I will be in Gulfport, MS Mon-Wed teaching the ABYC CBBC (Composite Boat Builder Certification) so the above was good practice for me. I will be at one of the large shipbuilders doing DOD composites. I should be able to get on line at night, time allowing.

FYI- ABYC is looking at doing an open CBBC class 1Q 2010 for those that may be interested in learning more about composite boat building. I will post the date on Reelboating when they set it.

abyc class desc.doc

Have a great Sunday !

Scott

[Cracker Larry]

Excellent information Scott, thanks.

[slewit]

Excellent information Scott, thanks.

Hi Larry

Hope you had a good week.

Just wondering if the samples made it to you yet?

Thanks

Scott

[Cracker Larry]

Yes they did Scott, thank you very much. I haven't had time to really check them out yet but I will next week. What I've seen looks real good.

Larry

[slewit]

Thanks to Chris Peters for the photo’s of his repair job on his 1998 Pathfinder boat.

Chris’s boat was damaged in a trailer related accident. The result was he needed to replace the stringer system in the mid section of the boat.

Here the deck has been removed, exposing the hull.

Nice job removing the old stringers and getting ready to prep the laminate

New Prisma Stringers are laid into position.

Note how new Prisma preform stringers match up to the undamaged stringers. They are ready for wet out.

Wet Out Stringers. Note how you can tell it is wet out as you now see though the Prisma Glass

Great Choice selecting Epoxy for the Repair !

Notice how nicely the Prisma beam contours to the hull bottom.

Giving it that final roll to make sure its perfect !

Nice work Chris !

Thank you

Scott

I have more pictures of the Pathfinder that Chris is working on. He has now reattached the Deck to the new Prisma Stringers.

Here Chris has poured foam on the outboard side of the stringers.

From Chris "I used West Systems Cab O Sil to get the desired height of the deck from stringers"1/2 inch". I let the cabosil dry without the deck on and sanded it down with a belt sander. After a couple of dry fits "flush" I mixed up more cabosil and set the deck into place. Just got done grinding the edge "as shown" and used bi axel tape with west systems epoxy. Im not a boat builder but I am confident that the it will ride better than new. Ill have more pictures In a week or two."

Nice work Chris !

Scott

[wiley]

Great posts, Scott!