Builders' Forum Archives
Posted by Laszlo on Aug 28, 2007
The basic reason for glassing on both sides, whether it's a repair or not, is that it makes the hull a true composite structure which is much stronger than wood alone, or wood glassed on just one side.
In the glass/wood/glass composite, the glass fibers provide tensile strength while the wood provides compressive strength. The thickness of the wood core also provides stiffness by separating the glass layers. The whole is so much stronger than the sum of the parts that there is no real reason not to glass both sides. While some may feel that the extra glass adds too much weight, for 4 oz glass it comes to less than 7 oz per square yard (with unfilled weave).
When a boat impacts a rock, the rock tries to forces the hull material to bend inwards. If the material's critical bending radius is exceeded, its fibers break and the hull cracks or even breaks.
In a composite structure, as the hull bends inward the inner layer of glass resists stretching and fights to keep the hull flat. The wood resists the compression caused by the point of the rock. The epoxy in the outer layer of glass resists the compression caused by the hull wrapping around the rock. All three layers work to keep the hull flat, which prevent cracking & breaking.
For CLC boats which do not glass the inside, you end up with a web of wood glassed on the outside suspended between composite beams (the seams which are glassed inside & out). This is also a pretty stiff structure, so none of us need to worry about our boats folding up under us unless we really abuse them. But those who haven't put the deck on yet may want to consider the benefits of a layer of glass on the entire inside.
In Response to: Re: Oops! by Jim E on Aug 26, 2007