Fiberglass schedule

[ujc]

Hey guys, Working on a stringer/bulkhead replacement and wanted to know what would I need as a schedule using epoxy. The old innner stringer glass was
2 layers of 18oz WR
2 layers of 2 oz csm......all VE.

Old Bulkhead.
1 layer of 18oz WR
1 layer of 2 oz csm

Was looking at using DB170?

 

[Woodonglass]

Re: Fiberglass schedule

Is there a particular reason you're using Epoxy? How do you know its all VE?? What boat? What Year? Got pics?

 

[ujc]

Re: Fiberglass schedule

The boat is a 1999 Crownline 29 Express. Had the boat surveyed and found the issue so I knew it was bad and what was needed. This boat has had some stringer repairs before performed by a boat yard using VE. I have a freind that works on airplanes /model rockets and has all the 635 US Composites epoxy and slow hardner i need so epoxy it is. Now I need to figure out what Glass i need to use that will give me the same strength and stiffness as before.

Thanks Wood

 

[Woodonglass]

Re: Fiberglass schedule

Alrighty then!!! All you need is 1700 biax. Two layers and it'll be a TANK!!!! The combination of the Epoxy (stronger than VE) and the 17 oz Biax (MUCH stronger than woven roving) will really make her bullet proof!!! Baby sit the epoxy and when it's just setting up and getting sticky lay the next layer of cloth. This wet on wet layering will give you a much better bond.

 

[ujc]

Re: Fiberglass schedule

Thanks Wood!! WOW!!!! Now that is thin Two layers of 17 seems alittle flexible. Will I get the stiffness from the stringers being tied together?
The old stuff was really really stiff and I mean stiff. Thanks again for the help and support!!!

 

[Georgesalmon]

Re: Fiberglass schedule

Considering stiffness, more acurately called flex. During the change of many from woven roving to the stiched material there were some problems with stiffness and lamanate schedules were changed or other ways found to reduce the the flexural needs such as making the stringers closer, more bulkheads, etc. The stiched materials are thinner and use less resin to wet out properly. Sooooo,,if you changing a laminate schedule from 18oz WR to 17oz biax you'll need to use a little more of that biax to get the same thickness thus the same flexural modulus as you had with the WR. As to the actual strength comparison ounce for ounce I would have to agree.

 

[Woodonglass]

Re: Fiberglass schedule

Yup, two layers of 17 oz biax with epoxy should give you what you're looking for.

 

[ujc]

Re: Fiberglass schedule

Thank you for the replies!! We did a test patch with 2 layers of 17 oz DB and it is really flexible compared to the old glass? The test panel came out at 1.5 MM thickness compared to the old stuff at 10MM and as hard as a wedding.........well its reaaly rock soild. From what I have read it sounds like with epoxy, the total thickness can be reduced from 1/3 of the old glass? Should I add something else to the mix or what are we missing.

 

[Georgesalmon]

Re: Fiberglass schedule

If you want the same stiffness then you have to increase thickness. No other way short of changing materials. Also, epoxy is not as "hard" as the original poly or vinylester resins. Thats part of the reason epoxy is "stronger". Epoxy has a higher elongation and will bend more before it breaks sort of. I don't know if 1/3 is the right number but it certailny could be in terms of tensile strength however to get the flexural modulus back you just have to use more material to get it thicker.

 

[ujc]

Re: Fiberglass schedule

Would I will need the same stiffness or will I gain enough when its all tied together. My plan is to use 4 layers of 17 oz DB.......but if I need the stiffness, then it looks like 10 layers or use 1708 or something? Thanks for the help

 

[Woodonglass]

Re: Fiberglass schedule

What boat are we working on and what section?

 

[ujc]

Re: Fiberglass schedule

Hey Wood!! The boat is a 1999 Crownline 29 Express twin engine I/O, engine stringers.

 

[Georgesalmon]

Re: Fiberglass schedule

Problem here might be that even though your using epoxy for the repair/replacement you still have that "other" resin under everything. So if the hull was made needing the stiffness it had then it would still need that or smaller flat panel sections. Your repair will certainly be strong enough the way your going about it. But underneath the repairs you still have what was there in the first place. The epoxy repairs are strong but under them is the original hull which did not have the high flexural modulus that epoxy has. So when the hull flexes the epoxy will do fine but the poly or vinylester will also flex and it could crack or break. Arn't you already repairing a crack in the bottom? If I had to guess I would say you will still be OK but guessing on a boat hull can be a disaster. Should you find yourself caught in a big storm,,,,well enough said. As always just my opinion and I have been wrong before,,,,

 

[Woodonglass]

Re: Fiberglass schedule

Well, I shoulda dun this in the first place instead of surmising so much. Post up some pics of the boat and the repairs. GS makes some valid points especially since this is a Larger Craft. OOPS would be a much better resource for you. I'll PM him and ask him to drop in for a "Look See" Get those pics posted so he can "See" what you're doin.

 

[ondarvr]

Re: Fiberglass schedule

When changing from polyester or VE and using mat and roving, to epoxy and biax some things need to be considered.
The thickness (cross section) of the laminate provides the stiffness for side deflection. So in a hull side the mat and roving laminate would appear to be stronger because the deflection (flex) when pushing in on the hull side would be less even though the epoxy and biax laminate would be stronger, this is frequently the case when switching to biax type products even when using polyester. The reason is the lower resin content and higher strength result in a thinner and lighter laminate when using biax compared to CSM, It is even more common in closed mold applications were the resin content is reduced even further. This is more of a perception of strength thing than a structural issue.

In an application like a stringer, the side deflection (flex) is not something that is really a factor like it would be in a hull side. It is very common to increase the cross section (possibly with a core) of flat semi flexible surfaces to simulate a more typical CSM and roving laminate. In a vertical application the height of the stringer combined with the direction of the fibers in the Biax make the stringer very stiff in this direction, so adding thickness to increase the stiffness isn?t needed to the same degree.

 

[ujc]

Re: Fiberglass schedule

Thanks Guys!! Here are a few pic's of what we are working with. The concern is with the amount of tabbing that was removed the factory applied......around 12 inches out from the sides of the stringer, so I have removed a ton of really stiff material . The factory had the first layer of thick CSM then 2 layers of 18 oz WR (one on top of the other) then topped with a really heavy layer of CSM (Total 10/12 mm)
The wood has been glued in with epoxy 1/4 inch off the hull with nothing under them sp far. We did coat the bottoms and sides with three coats of epoxy, at this point the sides have nothing on them. We plan to us either PL or PB under the stringer then epoxy filet before glassing............once i get a game plan for the joint/hull area.

 

[Woodonglass]

Re: Fiberglass schedule

Thanks, ondarvr, for such an informative explanation of the variations between the two layups. This makes total sense. Thanks again for the education. That's why this is the Boat Restoration University!!!!

 

[ujc]

Re: Fiberglass schedule

Thanks Guys!! This is a great place to learn from some of the best!! I think I am good with the glass for the stringer sides now. Only question remaining would be the amount of stiff glass that was removed from the joint and hull area since it was so much. Mabe Wood can get get OOPS or someone to drop in. Thanks again

 

[Woodonglass]

Re: Fiberglass schedule

I sent OOPS a PM. Hopefully he will stop by. I'm thinkin you might want to lay a couple of layers of 1708 down on the hull first and then do the stringer motor mount installs. That way the hull gets reinforced both with the pre layers and the tabbing of the stringers and MM's. By the way, ondarvr has been in the Fiberglass business for decades and really knows his stuff!!

 

[ujc]

Re: Fiberglass schedule

Yes he is....has a way of explaining a problem that even I can understand And have learned alot from reading your post also.
Have been reading about not using 1708 with epoxy but I am also thinking that is what i may need also......maybe someone will show me the correct way. Thanks Wood you have been a great help!!