Re: Fiberglass experts step forward please
I have a hypothetical question as to the ?finished? thickness of fiberglass; I don?t believe I have seen it addressed before and maybe there won?t be an exact answer, but here goes.
Hypothetically, I have a 4? x 4? sheet of ?? AB plywood. I have sealed it with a coat of resin. I am going to properly wet out and lay a layer of 1708 plus a layer of 1-1/2 oz. CSM over the surface. Anyone have any idea how much will be added to the final thickness of the ?? plywood? For example: let?s say I need to or want to increase the thickness by 1/8? to say 7/8? overall. This is just for general information?.I am not there yet. Thanks everyone.
Dan
You are basically spot on with your increase in thickness, that is assuming you do this to both sides of the plywood, as the nominal finished thickness of one layer of 1.5 Ounce CSM, {which by the way should be laid down prior to the 1708}, and one layer of 1708 are equivalent to approximately 1/16-3/32" thick...which also shrink slightly as it cures and as it ages over time...that is one of the reasons why the lams should not be overly resin rich, because as the resin shrinks, it cracks...
Remember, too, that the amount of pressure you apply when rolling the bubbles out of the lamination can affect the finished thickness to a certain degree.
Think of fiberglass cloth as being made of microscopically hollow tubes of glass fibers, that absorb the resin and become "filled", which is what creates the transparency...the amount of applied pressure can push some of the resin out of those "tubes" of glass and make them flatter as opposed to rounder...
I am talking about really minute differences that don't really apply to most of our boats. See Below...*
Another school of thought, which is valid, is that you do not need to apply a layer of CSM prior to applying the 1708 since it already has a 3/4 ounce layer of CSM bonded to it...this method would be closer to your desired finished thickness of 7/8"
I prefer the overkill method and almost always use a layer of 1.5 oz. CSM first, then the 1708.
In most boat related scenarios, 1/8"-1/4" variance is really not considered anything to worry about...
*Except in really high end, racing specific, high performance hulls where this is something to be concerned with...in most average pleasure type boats, the only places you will find a need for really close tolerances are the transom of an inboard/outboard [somewhere in the neighborhood of 1/8"-1/4" of tolerance] or the mechanical systems [such as engines and drives components where the tolerances are gauged in thousandths or 10 thousandths of inches]...
Heck, I have seen high end luxury yachts, that when viewed in dry dock are no where near symmetrical...they can have strakes on the bottom of the hull that are almost an inch of difference in their trajectory, from one side to the other...
