Fiberglass lay up Schedules

So long time lurker and first time poster. I don't want to start start any forum wars here; but I have been looking at a lot of what people have been posting about lay up schedules for new stringers. I have seen a few of the posters tend to run with multiple layers of CSM its my guess, and then biax mat over the top. Is there a particular logic behind going with the CSM? It would seem it would be less labor intensive to say do 3 layers of 1708 vs 6 layers of CSM? But I am no expert. Im just looking to educate myself as I am about to glass some stringers in myself and was planning to do 3 layers of 1708 with CSM over top to seal them in! But got me second guessing reading a couple other threads. Thanks for the help in advance.

CSM = chopped strand mat. Had to look up that acronym.

I can't think of any memorable rebuilds where mat was the primary fiberglass used. Often, it is used in conjunction with cloth. The layups I gravitate towards use a lot of cloth for a few reasons- it has the highest strength to weight, it is thin and easy to work with, uses relatively little resin (per layer), and multiple thin layers is usually much stronger than fewer thick ones. Mixing in a layer or 2 of mat and/or biax (a combination of mat and cloth, where the cloth weave is usually oriented at 45 deg) adds strength in more directions and compliments the cloth nicely- but I don't prefer it as a primary material. Primarily due to its thickness- it doesn't go around corners well and it soaks up a lot of resin so each layer goes fairly slow.

Here are some photos of the project, its a ski supreme, but hopefully a stepping stone to a CC before too long.

https://photos.app.goo.gl/TEEiBghqxj4s5AUX2

[URL= ][/URL}https://photos.app.goo.gl/QnYflwPZvYs6zi7I2

Weight rating between cloth and mat are not comparable for some reason... 1.5oz mat is an order of magnitude thicker than typical cloth (4-8oz).

Many boats built with poly and it should be plenty strong, but boy is it harder to work with compared with epoxy. Hardener ratio (1% vs 1:3) and fumes are 2 big downsides... have had some problems with getting poly and vinyl to cure. Epoxy is always super easy, very tolerant to imperfect mix ratios, etc.

the reason CSM does not take to curves and such when used with Epoxy resins is that CSM was originally designed to be used with Poly or Vinyl Ester resins and not epoxy. the binder powder or substrate that holds all the chopped strands together, does not dissolve when used with Epoxy like it does with the poly or vinyl ester resins.. It works just fine on flat surfaces when mixed with epoxy, but if you try to drape it over stringers and such it can be a chore to get it flattened out. CSM when used with poly or vinylester resins will turn clear when they are wetted out as the binder dissolves, It remains more Opaque when used with Epoxy. There are CSM products designed to be used with Epoxy, but most are made for Polyester or Vinylester resins.

The stringers and floor supports in my 87 BFN has about 4" of the roven mat up the side of the floor supports and a couple up and over the two main stringers closest to the keel, and that's it. The floor supports and the two pieces of plywood that form the sides of the bilge (some people call these secondary stringers in a BFN) were not completely wrapped at all (the bilge side was covered with some kind of epoxy but no cloth). Of course that's why I'm scooping them out a mush now 30 year later. The two main stringers are completely covered with the roven mat, and are surprisingly in pretty good shape.

I was just describing the factory configuration on my boat. BFN's have a considerably different underfloor construction that a SN.

I will run a couple of layers of 1708 tabbing on the hull and sides of the secondary stringers (the boards on either side of the bilge) and all the floor supports and bulkheads as far forward as the battery box (I'm not going any further forward than that) and then a couple of overlapping layers over the tops to completely encapsulate the wood. All of the wood from the bulkhead behind the battery box aft is getting replaced In my BFN all of the stringers and bulkeads are 3/8" plywood with some 5/8" floor boards forward of the motor box and down the sides of the motor box with some 5/8" strapping that runs on top of the floor supports between the motor box and the sides of the hull. Then foam is placed under these stringers and leveled off at the top level of the stringers. Then theres fiberglass cloth on top of all of that forming the floor and sealing the foam and wood in place. I will used a combination of CSM and 1708 on top of the floorboards and stringers to build the floor up to its finished height. Oh, and I'm using Epoxy resin not Polyester resin.

It will be a bit better than what the factory did and I'm not going to be here in another 30 or so years when it might need to be done again.

Weight rating between the two cloth and CSM to not line up because cloth is given in sq yards vs mat being given in sq ft.   CSM also uses more weight of resin per fabric weight (2x what cloth takes) so it is generally builds bulk quick.

Epoxy over cloth (even large weaves) is not going to delaminate if done anywhere near properly.   

The binders in typical CSM do make it harder to work with epoxy for sure... I am still working off of a roll of epoxy specific CSM from back when it was available..   

You can any of these resins and reinforcements work - but it may take more time and money and end up a bit heavier than a careful selection of materials.

I also like the epoxy, I reglassed a crushed engine cover and it was very easy to work with.