Resin choice

PAR, What type of polyurethane are you using to bed with, PL?

 

mcdc,

If i am not mistaken, I believe that PAR uses epoxy to make his fillets to bed with and to fillet out all 90 degree corners. After reading all of his threads, seems chopped fiber with a thickening agent like cabosil or fumed silica is the key.....using PL will create hard spots between the stringer and the hull (not good). He has a few other threads that specify what type of fiberglass to use. Hope this helps

 

Question, the old glass is 2 heavy woven and CSM on the engine stringer. The tab area is 17 to 20mm and the sides and top are 7 to 10mm. How many layers of 1700 do in need to use. Have read 3 layers of 1700 was a bit of over kill and have read to recreate the old thickness. Thanks

 

Applying more material then necessary isn't a bad thing in most cases, as manufactures often tend to not use enough. The general "recreate" idea is to save some material costs.

I use both epoxy and polyurethane to bed bulkheads, stringers etc., depending on hull shell thickness and general application. If the structure is cored or the hull shell relatively thin, I use a bead of polyurethane or foam, as it offers some "squish" and the loads are picked up solely by the tabbing, eliminating the any hard spots. If the hull shell is heavy, then I'll use epoxy tapered out into a fillet for the transitions, as it's not as important and a little cheaper, because epoxy costs less then polyurethane. Both are applied the same way, creating a bed and tapered ramp so the perpendicular elements, have their tabbing transition spread out, over a wide area and lets the fabric lay down nice.

 

Will 3 to 4 layers of 1700 work for the sides and 5 on the tab........hate to build back as it was with the mfg having 20 mm thickness in tab and 10 mm on the sides of the stringer.....will take a ton of 1700. Also do I need the glass on the side of the stringer covering the tab or just go from the bottom up and when you tab do you go smaller to larger? Thanks PAR you and the guys are a great help!

 

Since the stringers are bedded in PB, can I skip the tab and start the full lam? First one starting over the top and extending out 2 inches, then the second one out 3 inches, then out 4 ect? Thanks

 

PAR... what would you suggest for a type of mat to use? I know you were talking alot about the straight double bias material because it is great in stength and usability as well as resin savings. What weight would i possibly use? I am having to bed in my new stringers and redo the entire transom along with some hull slices that were somehow put there by a crazy sawzall blade..lol your information is greatly appreciated as always...anyone have any suggestions on the best and cheapest place to buy my resin and supplies?

 

I'm not sure I understand your question Mcdc.

Vanilla, Mat isn't necessary nor desirable in an epoxy laminate.

Holes in the hull are handled just like any other type of repair; grind back to good 'glass, tapering the edges all around, fill with fabric until it's just below the surrounding surface, then fair it up with a light weight compound.

 

Par, I had planned to tape the stringers once bedded. I think since i am going to bed in PB, I will skip the tape and start the full glass when I bed and fillet today. First layer starting at the top and running down the stringer and out 2 inches on the hull, Next one starting over the the top and down on the hull 4 inches and so on?

VG Call US Comp

 

I usually do it the other way around with the largest overlap first, followed by progressively shorter one, but it can be done both ways.

 

This is how I was taught this sort of joint should be constructed, not the other way around, so that one layer of reinforcement doesn't see the whole secondary bond line. Assuming I understand the original post correctly.

 

That's one way to look at it FishStretcher and a common attitude as well, particularly among polyester laminators (justly so). My logic is you have to assume good techniques and a continuous, solid bond with the substrate is better than a broken one, with epoxy. I'm not so worried about the mechanical bond with epoxy, but with polyester I would and will reverse my tabbing layering preferences, for the very reason you state. With polyester you do have to worry about the secondary bond and relying on just the first layer, could lead to catastrophic failure, so I would go little to big in these cases. You can get an argument with reasonable debate on either side of the coin. With epoxy, I want as big a contact patch as I can get. With polyester, I want as many contact patches as I can get.

 

Thanks Guys.... Par you have really kept up with my post and helped me out, and I wanted to say thanks again!! If you follow West System, they will tell you to place the long one in and work back. I Glued the bulk heads in along with the front and rear of the engine stringersi in today. Hope to shoot the PB under the strigers and create the fillets in the morning....start glassing. Have US Comp epoxy and med hardner due to the falling temps.....wish i had the slow since the temps will be back up.

 

A six pack will do . . .

It's usually much easier to increase temperatures if using a slow hardener, then hurry up using a regular speed hardener in warm temperatures.

Other advantages to working long to short in the laminate stack, is fairing and trapped air. If the laminate stack is staggered from small to large, the edges of the preceding layer can trap air along it, as the next attempts to conform over it. Secondly, the big to small layering technique, permits much easier fairing as the ridges in the laminate are naturally tapered and an over grinding situation only dings the edges of the layers, rather then eating up a whole top layer if done the other way around.

Again, this has been hotly debated over the years, but epoxy laminates are different then polyester, both physically and in application.

 

Based on my experience PAR's right about trapping air as you go from short to long on the laminations/tabbing. As an amateur and especially if you've never done this type of work before the longer you have to work/think the better off you will be. You don't want to make mistakes here.

One thing I don't see mentioned. As an amateur this is going to be a gooey job no matter how you do it. Please have plenty of protective gear. I used gloves, tyvek suits (with the boots to cover my feet), safety glasses and ventilate the area as you work. You'll be glad you did.