Floor/stringer repair: how far?

David F wrote: Wrong again. Woven roving has the same strenght in two directions (at least), not just one.

it has strength in two directions only the direction of the weave so anything at an angle to the weave is significantly weaker, that's why most are layed at a 45 degree angle to each layer as it's built up to give strength in all directions not just axilly to the weave.

the strength is gained in how it is laided down and the directions that the weave is when laid down in relation to each layer, So if the cloth or direction of it is always laid down in the same direction then you are going to have a very weak cross-section and have strength in one direction only, and the type of cloth, fiberglass, kelvar, carbon, greatly effects the overal strength as well.

Ok 79, you will notice that I said CC uses woven roving in the hulls. Yes, it is bi-directional, so is cloth! However, in my '93 SN, woven roving was not used in the floor due to the thin cross section of the floor. You cannot get 1/8 to 3/16 thickness of any real strength by using heavy woven roving. You need a laminated composite system that builds thickness. Thus with thin sections/laminates you need to use light weight materials. What part of this is not making sense? Remember, TRBenj was asking about his floor, NOT his hull.

Oh, and by the way, the hull on my '93 had altenating layers of woven roving and mat. Always starting and finishing with mat (or it could have been chopped via a gun). If you start with cloth of woven roving, the pattern will telegraph through the gelcoat.

Nice work Tim. That thing will be mint in no time... wanna trade? (when you're done)

CC's site doesn't support your argument either, I would suggest you read their section under craftsmanship and notice they state bi-directional and woven not cloth and make specific reference about how the material is layed down to provide strength.

79...

You are just wrong this time. Woven Roving is a fiberglass cloth. Woven Roving is generally used when describing heavy weight cloth. Here is a typical description (not mine):

"Woven Roving cloth is a collection of specific numbers of untwisted continuous filaments. Fiberglass woven roving is basically a heavier version of fiberglass cloth. Due to higher fiber content, woven roving's lamination has excellent tensile strength and impact-resistant property. As woven roving easily wets out, provides great tensile and flexural strength, it is often used between layers of fiberglass mat in laminates. It can also be used with chopped strand mat to fabricate large size objects, such as boat, vehicle components, pressure tank, house, etc."

Woven Roving will yeild a lighter weight than "cloth" due to less resin being used to wet it out. However, this ligher weight makes it also more flexible...not good for the floor of our boats. CC does not use Woven Roving for the floor construction (they do for the hull) because they want stiffness and less thickness than woven roving can provide. basically the mat/cloth alternating layers will provide greater stiffness and more strength in a 1/8" to 3-16" laminate than can be had with woven roving.

Of course, how can I possibly know what I am talking about...oh wait, I spent 9 months working with the stuff!

TRBenj: Take my advice and stay away from the heavier woven rovings when intalling your floor. And alternate between mat and cloth for the best bending and shear strength.

Cloth and woven roving are basically the same thing. Cloth term being used when describing light weight material.

Either is fine, you will just need to more layers when using cloth, but the final thickness is what determines strength, not the weight of individual layers. Definatley use mat between each layer of cloth (or woven roving). The mat adds strength in the direction/planes that the woven is weakest. the mat also helps gaurd against the woven delaminating from each other.

The only caveat I have not mentioned in awhile is that when using epoxy resin, you must use mat designed for epoxy (it is sewn together, not bonded together). Epoxy will not dislove the bonding agent used in regular mat.

Tim,

Looks good. I didn't get nearly as far on mine this weekend as I had planned. I wasted my entire Saturday skiing .

I wouldn't worry about that 8-lb foam compressing. I contacted MWCC and they told me the factory used 2-lb foam.

TRBeng:

I simply use Life Boat Caulk on screws when screwing in the fiberglass only floor. I coat the screw liberally with sealant and install. Personally, I would avoid glueing the screw in with epoxy resin as sure enough, you will need to get it out one day.

79Nautique:

CC has been laying the fiberglass floor directly over the foam for many years...still do it that way. It works fine. However, I have seen impact fatique on several boats. Basically, the floor gets soft where people repeating jump in the boat on the same spot of the floor. Doing quick and dirty math, 8lb foam will support about 285 lbs from a size 12 foot. People that weigh more than 285 usually have an even bigger foot. Like I said quick and dirty, could be way off. But, jumping in the boat on one foot can exceed this weight calculation.

Yep, I agree with you on this 79N..., but since it is already done, I think the epoxy/fiberglass composite will perform ok even spanning the 5200. The Composite is flexible and strong enough to handle any potential tendency for movement.

TRBenj: Just keep an eye out on this area. If you are up to it, I would grind off the glass work, remove the 5200 and reglass after creating a fillet of thickened epoxy resin.

You can thicken epoxy resin with saw dust, chopped glass, talc powder, micro spheres, etc...should be consistency of peanut butter.

Again, I do not think there is much stress on the bulkhead, so you are probably ok as is.

not sure if I would have used the 5200 to glue that piece in, the resin isn't going to bond to the 5200 so now you have created a pocket that is flexable and over time it will crack the resin covering it then you'll have a path for the water to rot out the wood you installed, You should have left out the 5200 roughed up the old fiberglass to get a good bond then glassed it in like you did.
Other than that it looks pretty good.

One otherthing I hope you are going to put some wood over that foam before you glass over it. Otherwise you wont have a good anchor point for the seats and over a very short period of time the floor will get soft unless you are going to add 3/4" of fiberglass over it.

Absolutely amazing. All the more reason to fly out there for a ride one of these days!

Thanks DavidF! Youre right- the 5200 makes a nice fillet for the glass on the bulkhead. Its secured in there a lot better than it was from the factory, so I think its good to go. The only other critical area in the bilge that I can think of is where the main stringers meet the hull- thats really the only other joint, right? Good call on the fasteners. On the screws in the rear, I predrilled the holes, filled them with epoxy, screwed everything down and then coated the top. I plan on doing the same for the screws on the front floor section (1 at a time).

This project is taking me a little longer than I would have liked, but its coming out pretty decent, I think. I sure dont want to be doing this repair again any time soon!

Update: This weekend I made a little bit of progress. I coated the stringer and flooring with epoxy resin prior to installing. I dried out the area underneath the battery box, made a new drain for it, then sealed up the bulkhead with 3M-5200. I then fiberglassed the new stringer in with 3 layers of glass (mat/cloth/mat). I also glassed the bulhead in place. I then poured the foam and trimmed it flat with an angle grinder. Its starting to look like a floor again! All that is left is to glass everything down. Many thanks to DavidF and marks for all the great tips and advice! Pics:

Tim,

US Composites has a FAQ that answers your question. Yes, you can do multiple layers but need to wait 15 to 20 minutes between them.

http://www.shopmaninc.com/faq_foam.html#7