Stringer placement and fiberglass questions

[61mysteryboat]

I am going to be replacing the wood stringers in a fiberglass boat. I have the old stringers removed and the bottom of the hull sanded down. I am going to have to lay an additional layer of fiberglass on to the bottom of the hull before I place the stringers. ( I ended up sanding into some of the old woven roving in order to get the old stringers out). My question is whether to use waxed or unwaxed resin when laying the fiberglass. I will be placing the stringers in a bedding Compound on top of that layer. If I use unwaxed resin will be bedding compound adhere to it. If I use the waxed resin I would end up sanding out a lot of that area in order to tab the stringers in place. I will be using loctite pl to set the stringers in and then filleting the wood to hull with pb. Any advice? Thanks.

 

[DeepBlue2010]

No wax on this layer at all. PL will stick to unwaxed resin just fine and even if it doesn't, the point is not to glue the stringers to the hull... it is to provide a gap between the stringer and the hull to avoid a hard spot. PL is just providing a filler for this gap so you don't end up with an air pocket during glassing.

Wax will add extra risk when you start fiberglassing the stringer tot he hull

 

[61mysteryboat]

Ahhh. Makes sense. Thanks for the help.

 

[Woodonglass]

Uhmmm if the hull is not ultra thin I see no reason to go to the time and expense to add another layer of glass. Sanding into the old RW is NOT an issue, in fact this should be done to ensure proper adhereance of the new resin/glass. NOTE: If you use PL as your bedding material, I'd strongly advice you NOT to lay any glass for a minimum of 72 hours. It takes that long for it the stop "Out-Gassing". Also polyester resin doesn't like adhering to it very well. PB is a better choice You may find this helpful...http://forums.iboats.com/forum/boat...r-flamingo-splashed-w-pics/page42#post5550980

 

[tpenfield]

Got any pictures to share? We love pictures It may also help with responses.

 

[61mysteryboat]

How thick can pb be placed between the hull and the stringers There are a lot of undulations in the hull. When placing the stringers there are some gaps that are as large as 3/8".

 

[ondarvr]

Depending on how you make it, up to several inches thick, your 3/8" is fine. It serves no purpose other than being a spacer.

And unless you sanded of a great deal of glass there's no needed to put more down, you're already going to be adding more when putting the stringers in.

 

[61mysteryboat]

As always, thanks for the info. Love being able to pick everyone's brain. Better than any boat building book.

 

[61mysteryboat]

Fiberglass layup time frame?

I am going to be replacing all of the stringers in my 18' StarCraft. The stringers have been built and consist of two stringers running the length of the boat and eight cross stringers. They are half lapped together. This creates a grid work of 21 squares. I am going to bed them to the hull with pb. My question is how long I have to get them bed and tabbed. This will be a long layup and I am concerned that I won't be able to get everything set in time to do a wet on wet layup. I will prep everything I can and have the fiberglass precut to fit but I'm sure I won't be able to move fast enough to get it all layed up in time. The thought if this makes my butt pucker. Please help!

 

[gm280]

61, those are all very good questions and I can understand what you are wanting to know and why.

First, manufacture all the parts well ahead of time and fit everything to verify everything fits without any issues. Then figure out how things can be installed in portions or segments. In other words see if you could break up the entire layup into manageable sections. Rarely does anybody lay the entire stringer and brace rib structural framework at one time. So segment it up so that you can simple add on to the previously installed structure at a later time. It sounds iffy, but it does work well if you approach it from that mindset when building the framework you can do it perfectly as well.

I say all that because once you mix the PB and start polyestering (probably not even a word) things, there is only so much time before things kick off and set up. You can play with that kick time somewhat by the amount of MEKP and the temperatures and humidity. But it is so much easier and less stressful to lay up sections instead of rushing to get everything install before it kicks. That is when problems show up and too many times cutting things out because of mistakes.

So approach your structual items with sectional design in mind and post pictures along the way for everybody to see what you are seeing and dealing with. There are ton of very qualitifed folks on these forums that have done such things before and know how to guide you for your project as well. JMHO

 

[61mysteryboat]

That sounds like a great idea. If I end up running into an area where I will need to lay out more glass later, is it as simple as just sanding that area, cleaning with acetone and laying more glass over that?

 

[DeepBlue2010]

The cross members are not stringers, these are bulkheads. Is my understanding correct that you want to build the "grid" and fiberglass it as one piece. If so, this is not how the process normally go. The stringers and glassed first (these are the ones that go from bow to stern) and then the bulkheads are glassed one by one.

When you do a wet on wet layup, you get chemical bond between layers except the very first layer which get a mechanical bond with the existing laminate (the hull)

You can do your layups on two sessions and still get chemical bond even after the resin hardens because hard to touch doesn't necessary means fully cured. Few hours between laminates are not enough for full cure; but as of how much time exactly between laminating sessions before the chemical bond window closes, I am not really sure but I am calling on our expert on the subject ondarvr to chime in.

 

[ondarvr]

The time frame can vary by resin type and ambient conditions. The shortest time frame resins can sit for a few days before needing to be prepped again for a good bond, this assumes it's indoors and no UV light has hit it. Other resins can go a few weeks. I'm not saying you should leave it sit this long, only that you have time to work on it bit by bit, no need to worry if you come back the next day continue glassing.

 

[61mysteryboat]

That is reassuring. I thank everybody for your input. Now I can relax a bit.

 

[jbcurt00]

Got any pictures to share? We love pictures It may also help with responses.

Bump ^^^

Pix?

Is this the Starcraft you started a new ropic about installing a pre-fabbed stringer grid?
http://forums.iboats.com/forum/boat...l-repair/10282007-fiberglass-layup-time-frame

 

[jbcurt00]

Is this the same boat you started a stringer replacement topic about?
http://forums.iboats.com/forum/boat...-repair/10279061-stringer-placement-questions

Same question: got pix?

IIRC, DeepBlue, many Starcrafts had a pre-fab hollow stringer grid originally, and it would have been laid up out of the hull and installed as a system grid. Not sure if this SC was made this way, but it could have been.

Is the cap off the boat?

 

[61mysteryboat]

That's me. I'll post some pix when I get to a PC

 

[tpenfield]

Mix small batches of resin as you go . . .it will take a long time to do all the tabbing, so a single batch will harden before your eyes.

 

[Woodonglass]

Make a stringer holder like this...

from scraps of 1x4. You only need two and it will hold them in place while you're doing the layup. Much easier IMHO.

 

[61mysteryboat]

. This is a photo of the stringers I am replacing in my boat. The previous stringers had rotted out. These may not be built in a traditional manner, but I built them exactly how they were done at the factory. They had half lap joints with brass screws holding them at the intersections. screw heads were on the bottom so I know they had been assembled prior to glassing. only difference is that I glued joints with pl.