Resin choice

If the epoxy bed is tapered (fillet) under and around the stringers, it'll be fine, though you could just as easily use a length of foam (also tapered) or a bead of polyurethane. I've taken to using polyurethane, because it's easy and quick, with lots of working time, but it's slightly more expensive than epoxy. You're just providing a transition from the vertical sides of the stringer to the hull shell, so the fabrics will not kink, bunch or ***** and moan about the hard turn.

 

The gap is around 1/4 to 1/2. I was able to grind down the glass back to the hull on the inside of the stringers but i was only able to take off the stringer lip on the out side due to the really thick inner liner so it is still about two inches high where they poured the inside liner. When you look at the location for the stringer you see the hull on the bottom and most of the inside and a 2 inch high wall on the out side so the fillet would be higher than the bed so to speak. Thanks

 

would look like this. Thanks Par!!

 

What ever it takes, so the fabric can transition from vertical to hull shell.

 

Thanks Par. I am good with the fillet's and the reason/need........just trying to understand the bed and if epoxy being so hard will cause issues. I tried to research the bedding material and it seems there are many camps, nothing, foam, PL, cut to fit/ lay on the hull, epoxy PB. Really hate the idea of nothing so that H20 has a easy route to travel and air to rot. Looks like some do not like the idea of anything hard under the stringer, some like something flexable and it seems like a hugh job to get the stringer to fit within 1/16. I like the epoxy PB but do not waht to have other issues

 

What the foam, bead of polyurethane or glob of epoxy all do, is eliminate stress risers. Simply put, picture a hull shell with a stiff, perpendicular bulkhead, touching it. The hull shell has a specific stiffness along the general area, but becomes dramatically stiffer right at the point the bulkhead butts against the hull. This can lead to stress concentrations along this line (where the bulkhead lands), because the density of the hull shell rises very quickly in this area. Surrounding laminate where the bulkhead isn't touching, is still of the same stiffness, but under the bulkhead, it's less forgiving, so the laminate can crack, oil can, etc. along the bulkhead/hull shell interface line. Again this is because the hull shell has a "hard point" along the interface, where loads will "hinge" around the contact are.

To ease this, you can make the transition from hull shell to bulkhead interface wider and gradual, typically with a fillet and tabbing. If you picture a strain traveling along the hull, reaching the fillet, the hull shell slowly gets thicker, then transitions to the bulkhead, then reverses on the other side, gradually getting thinner, back to the hull shell thickness. This lets loads spread out along the hull shell and the wider foot print of the bulkhead makes a less dramatic impact on the shell shell density.

Foam and polyurethane ease point loading (stress risers) by holding the bulkhead off the hull shell and transmitting the stresses through the tabbing alone. The same thing occurs, as the hull shell density slowly increases (along the tabbing) then decreases after passing the bulkhead (or what ever). This is one reason you stagger the tabbing. An epoxy bed and fillet does the same thing, except fills the void under the bulkhead with a hard, well tapered transition piece (think of it as a flange to spread loads). Both approaches work.

 

On to another issue. I have large void on the port side of the stringer where they made the fillet for the stringer. Can i pour epoxy into it or do i need to spend the day grinding back to the hull?

 

Maybe a few pictures will help. I had to make a pair of engine stringers and a floor a few years ago. I used foam as a form and 1708 bi-axle mat. You'll notice wood inserts in the stringers. These were inserted so that I'd have something to bolt the engine beds to (compression). If I had to do it again I'd just use woven roving but these came out fine. You live and learn.

1. Floor going in. Fillets not in yet. Fillets can be cut from scrap.

2. Floor partially glassed in.

3. Stringers going in. First layer of glass goes on. I used foam wedges to help create the fillets on either side of the stringers. You need to know the dead rise of the hull. Once you know that it's pretty easy to cut the stringers for correct fit as well as the wedges for the fillets. It all has to do with complimentary angles. Finally that high school geometry comes in handy! Once the wedges are stuck down I started laying up the mat. As I added layers the mat settled into a nice gentle radius.

4. Just another angle on the stringers.

5&6. What I ended up with. I painted the area with bilge paint after these photos were taken.

As I said before use woven roving rather than mat. PAR can tell you more about that if you need to know. He straightened me out on that years ago. The engine has been in for a few years now as I've continued work on other parts of the boat. This was the first big glassing project I did after disassembling the boat. Use slow hardener and carefully get your new parts in the correct positions. You'll mix fairly large batches of resin, all depending on how large your pieces of cloth get. As far as the question you just posted regarding the grooves in the hull where the old stringers/fillets were I'd say this. You need to get them even so that you can place your new parts in the proper position. I don't think they need to be ground off flush but they shouldn't interfere with the new parts going in. Filling them some shouldn't hurt

 

If bonding new fabrics to old laminate, you need to heavily tooth (scratch) the surface. This just means you run a 60 or 80 grit disk over the area and fill as desired. Bart's photos show the filiits and other pieces (foam, wood, etc.) making the transition from vertical elements to the hull shell.

 

Thanks!! The problem is where the old glass on the starboard side has a large void along the stringer area that I can pry up with a screw driver.....so to speak. It looks like it is about 12 inches long along the stringer and about six inches from the stringer bed toward the outside. I have the stringer cut, fitted and ready to bed but with the loose glass it did not make sense to bond it to loose glass. Can i drill a hole and try epoxy or do I need to remove the glass back to the hull.......alot of grinding if you look at the pic

 

missinginaction, great info and thanks

 

Just scuff it up with 60 - 80 grit and then fill with thickened goo. You'll get a pretty good bond to the resin that's there and you don't need to be down to mat for this.

 

It is worse than first thought. The MFG stringer glass is loose along the out side of the old stringer bed, about half the length of the stringer and about 6 inches in.......drill and pour epoxy and hope for the best or just man up and grind it all out to the hull.......man it is really thick? Thanks!!

 

Think I already answered my own question..........grind it out.......looks like they had putty 8 inches out from the bed........did not stick. I plan to leave the inside for now and just grind down a strip about three inches to the hull along the bed. Thanks

 

Have the two stringers up in place and held by supports . Can I leave the stringers up and shoot the PL under them? Thanks