Posted by: Paul Goodwin on March 24, 2005 at 08:46:53:
In Reply to: Re: Uni-glass sideboard reenforcement posted by Bob on March 23, 2005 at 17:01:07:
Actually, I would disagree with Bob's recommendation.
Here's my reasoning:
The forces that cause a side panel to split are not just
from rigging and/or sailing loads. If these loads were
the sole cause the panel wouldn't split near the setback
but closer to the front of the cockpit, and DN side panels
almost always split between the seatback and the knees.
What precipitates a split is the impact from the skipper
slammimg into the side (generally during a collision or
spinout on rough ice). The crack starts on the inside
of the side panel due to tension loads perpendicular
to the grain.
The most efficient way to counter these loads is to
reinforce the wood against the specific failure mode.
Uni-directional glass is perfect for this, and should
be applied perpendicular to the grain on the inside
surface of the wood. Placing the glass in the middle
of the side panel will significantly degrade the
reinforcement potential of the glass.
Woven cloth or biaxial cloth will have some percentage
(usually 50%) of the glass fibers in a direction that
provides no benefit. The cloth could be used on the
bias (45 degrees to the wood grain), but this still
provides only 70% of the strength of uni at 90 degrees.
Also, make sure you run the glass all the way to the
bottom edge of the side board, not just to the cockpit
floor. The highest stress in the side panel is right
above the joint with the cockpit floor - if the glass
stops here, it just increases the stress. If a fillet
is added between the side panel and cockpit floor and
the glass is run out onto the floor for some distance
this will make a strong joint, but it's not as good
as running the glass all the way down to the bottom
of the panel.
As far as weight of uni glass, there aren't a lot of
choices. Try to find something around 8 ounce/sq.yd.
www.fiberglast.com has 7 oz uni glass (actually 80x18
plain weave), 38" wide for $15 /yd. I haven't used
this particular material, but it sounds like a good
choice.