Good advice, thanks. But ...I'm from Oregon and don't know what you mean by
'a 4" wide oregon'. Do people outside the state call one of our woods
'oregon' instead of by the species name? I think I remember Douglas Fir
being called Oregon fir somewhere ...or maybe it was Hemlock. Do you happen
to know? I'm curious...

Brian


"rude" wrote in message
...
After using hundreds of kilos of fairing material on boats, the most
important thing is that the boat hull start out fair!!

Make far more effort on your hull lines and construction to save a HUGE
amount of work fairing it.

TIP: get in contact with a plasterer...use the same tools and techniques
as
wall plasterers (houses).

TIP: Use a sanding board at least twice as long as you think you need.
Always sand @ 45 degress to main planes (fore/aft Keel/sheer), but have
the
sanding board aligned with the longest plane (fore/aft). You will need at
least two or three boards for one hull, stiffer ones for the straighter
bits
and bendy ones for the curvier bits. These need to be just right so they
contact the hull properly when sanding.

TIP: Make the sanding boards out of something LIGHT!. You will have
"Arny"
arms after a few weeks of using boards made out of plywood or similar. A
nice piece of 4" wide oregon run through a thicknesser to about 3/8" makes
a
nice board, for the middle of the boat about 3 feet long is a minimum.

Unidirectional and woven fabrics are usually very accurate in thickness,
use
this to your advantage and make sure your overlaps are straight and even.
If
possible, make your overlaps along the hull, not across it. It is far
easier
to fair join in the bow/stern plane than the keel/sheer plane. Think of
the
'glass material as plywood for the same reasons...you wouldn't have a lap
join going around a hull would you?

There are a number of reasons for using vacuum process for reinforced
plastics (ie fibreglass):

1. It removes any excess resin from the fabric, to save weight
2. It (in theory anyway) should give you an even thickness in laminate,
particularly when using uni or woven fabrics, further helping with your
fairing
3. It (with the right amount of vacuum) will give the best
reinforcement/resin ratio (ask your resin supplier and/or reinforcement
supplier for this info).
4. It should leave no voids due to even pressure (from the atmosphere) on
all areas being vacuumed.

Make test pieces first to trial your process, laminate thickness and to
make
sure your resin system is actually suited to a vacuum process (I have seen
some that are not!).

TIP: Don't get sucked in by "brandname" vacuum bits and pieces for your
bagging process. Use cheap window glazing material (pliable double sided
stuff), this works brilliant on bags. Use heavy (200 micron+) clear poly
film (building supply - hardware store), test it to make sure it doesn't
LEAK! - Buy small bits first.

TIP: Make sure the hull part you are vacuuming will support a vacuum. If
there are any leaks from behind the timber/foam/laminate structure, the
vacuum will suck the resin right out of the reinforcing. TEST it first!

With practice and testing, vacuuming processes are very simple and
extremely
effective.

Good luck and have fun.

Rod.

"Pete" wrote in message
...
On average, how thick is the putty fairing layer over the mat on a
strip planked hull? I guess it may depend on whether vacuum bags were
used (that's a question too - what's the general consensus on vacuum
bagging a hull?; what are the gains 'cos it looks like loads of
work?).

I'm just trying to cut the molds from the designers lofting templates
and I want to know how much to reduce the size of them by, to allow
for the overall hull thickness. But I also need to order the right
amount of filler too.

The glass suppliers have told me that two layers of 500g m² mat of uni
directional rovings laid at 90° add up to about 0.75mm after layup -
sorry about the metric measurements for the Americans, I haven't a
clue how many ounces/yd² that is - which sounds negiligble to me, but
I have read somewhere of around 3mm or just over 1/8 inch may be
fairing filler.

This sounds a lot to me (after my many attempts at plastering over
defects, I feel that the more you put on, the worse things get). It
seems to me that if easily sanded fairing is used it must be a bit
soft, so would the minimum necessary be used?

I'm talking epoxy here BTW, and I'm assuming that I will make a
reasonable job of laying up the mat .............. hmmm, I can hear
the gods of Famous and Doomed Last Words stirring from their slumber
already.......

TTFN
Pete