Doing all the fill coats on the bottom before turning it over allows all the coats to go on wet-on-wet, which saves a lot of time, and a whole lot of sanding. The overlap at the sheer is no big deal. Feather the edge a bit with a scraper or some sandpaper if you want, before applying the deck glass. Overlap the glass at the sheer, and sand that all smooth when all the deck fill coats are done.

Old Yeller

I would second Old Yeller's post with one exception.  I found that after applying the first coat on the deck, before it sets up hard I could sand or plane the edge of the fiberglass smooth very easily and the fill layers really smooth it out.  If you wait untill all layers are on, it may be harder to smooth the edge.

You must work neater than me, Ed. I've usually got enough fill coat globs along the bottom edge that it needs quite a bit of sanding anyway before the deck glass goes on. Either way, it's no big deal.

Old Yeller

by doing the hull first you develop the experience of wet out and sanding in an area where any mistakes are less visible.  this way you can then bring that experience and confidence to the deck/topsides.

examples of things you will learn and develop confidence in are:

- how to wet out cloth and sort out issues like floating/too much epoxy or not enough epoxy and never getting the glass to actually become transluscent/clear (which, after that kind of mistake, you will usually not be able to make it transluscent by another coat of epoxy).

- how to sand broad areas of the hull to a final finish and or use a cabinet scraper without scraping into the wood or sanding through the cloth.

a wise builder on another site consistently finds a way to suggest to me when i am doing something for the first time....to find a way to do it on the bottom or inconspicuous place first.

fwiw...i also agree with old yeller.....you woud be most fortunate to have an edge clean enough to want to put another layer on it without some kind of fairing/clean up activity first.  it's a lot harder to clean up multiple layers of cloth...so you may not save yourself much time in the end. 

one last note on weight....which you mentioned. 

first, the amount of weight saving is probably trivial.  that said, however, absent using vacume bagging, which uses vacume pressure to compress the cloth/epoxy and minimize the epoxy to cloth ratio (minimum amount of epoxy to completely wet out the cloth and bind it to the adjacent layer), i think you probably end up with a heavier structure when you apply multiple layers at a time without taking the time to fill and sand back the prior layer. 

because you are applying multiple layers without sanding down the high spots on the lower layer (and you don't have pressure to force the upper cloth down tightly into the lower cloth, you will have more space between the layers that is just filled with epoxy (because the first layer didn't get sanded smooth to take the excess off the high spots before the new layer was put on). 

so i am pretty confident that sanding/cleaning up the lower surface first before moving onto the next layer results in a better cloth to epoxy ratio than doing it all at one time.  and the less epoxy, to the extent you have wet out the cloth completely, is lighter, and often stronger, than the same amount of cloth with bunch of excess epoxy.

again, all this is in the context of doing this with gravity being the only pressure.  when you can use a vacume system or another way to apply pressure, multiple layers at a time is more efficient because you will have enough pressure to distort the adjacent cloth layers to nest togther with the least excess space.

best

howard

Thanks Mr. Yeller, Ed, and Howard for all your insight and taking the time for a detailed reply.  I see the best way to move forward is by following the directions.  Imagine that!!!!   However.......... now I know the why.   

Tom