Fairing a Fiberglass & Epoxy Encapsulated Boat

[Don Maurer]

I am building a plywood boat that will be encapsulated in fiberglass and epoxy. There is a slight hollow on one side of the bow section, so I need to do some fairing with epoxy and microballoons. This is my first fiberglass and epoxy boat that has required fairing. My question is do you apply the microballoons and epoxy under the fiberglass or after the fiberglass has been applied? If it is applied under the glass, you maintain an abrasion resistant surface, but if it cracks or crumbles for any reason it would require a major repair. On the other hand if it is applied over the glass it would be an easy repair but would also be subject to damage from abrasion. So what say ye? Which method works best?

[pipefitter]

Is it enough of a hollow that a piece of contour cut, saturated glass cloth could be fit in taking out the need for filler? You would be better off if you replaced the depth with cloth and just use a skim coat of putty before your fill coats of epoxy go on. And yes it is better to fair under the glass if you have to, or at least under the final couple coats of epoxy. Check to see if the hollow can be preglassed before the main cloth goes on. How deep is this hollow spot? Best to get the hull as fair as possible before the glass goes on to save from sanding into the fibers of your cloth when trying to blend it in.

[paladin]

Dunno how big your boat is...but if it's plywood I will assume that you're using glass because of cost....If you assume 10 oz cloth...my defender industries catalog lists 10 oz glass at the same price as Xynole fabric, at less than half the weight, same price per yard and it's more abrasion and ding resistant......

[Cuyahoga Chuck]

The answer depends on the design. By keeping it to yourself you are making our analysis harder.
If the boat is a glass/plywood composite such as Bateau offers the glass has to be applied directly to the wood because hull strength comes from the glass/plywood sandwich. You don't want anything between the two.
From my perspective , even if the glass is applied as an add-on, anti-abrasive layer I would still put the fairing coat on last.
One thing to beware of is the idea that every hollow is a candidate for fairing. I went that route once and it was destined to be an overweight mess so I took all the filler out, slit a seam and worked the hollow out. It was definitely worth the effort.

[Don Maurer]

The boat is a Pocketship by Chesapeake Light Craft. Actually, it is a 1/8 scale model of a Pocketship that I am building first to work out any difficulties before I start the full size boat. It is a plywood/fiberglass composite construction. The hollow on the model is about 3/32" to 1/8" deep to match the other side. Obviously on the model it doesn't matter how the repair is made, but since the point of building the model is to work out problems, I thought I would ask how best to handle this on the full size boat. Thanks for the answers so far. I hadn't though of filling the hollow with more fiberglass. That could add a lot of weight if the hollow were very deep, but maybe Xynole would be a better option in that case?