Steve, you got fast and real good advice already but just a couple of things to
add for those who are thinking about strength at the transom. You are going to
tab the transom in on the inside (and outside) with tape anyway if you follow
the instructiones, but keep in mind it is a part that gets, well, sharp shocks
to be sure. Beach launchers like me should be aware that hitting the beach with
the rudder can have consequences for the transom. If your beach is a lee shore
more often than not, you are going to have to contend with waves at launch
(don't pack the rudder cassette too tight) and screaming returns that can also
impact on the gudgeons and transom if you bailout too late. For that reason a
lot of dinghies in other classes screw the lower gudgeon into the gudgeon
spacing block rather than bolt it right through, sacrificing the block and the
top pintle/gudgeon rather than splitting the transom. I'm going to bolt mine
right through as per the instructions though. I have plenty of practice bailing
out in time already.
Another way to strengthen the transom.
While it has not been recommended in "the book" it is possible to put the
hybrid cloth on a bias inside the hull so that it has most of both kinds of the
fibers traversing the joint with the transom. Cut the hybrid on an angle at the
gunwale to avoid wastage as it drapes off the roll. ( I suspended the roll on a
line running fore and aft next to the hull when I was cutting the cloth. If you
flip over or rotate (180 degrees) the next part of the hybrid off the roll it
will match the gunwale angle further up and so on, until you are complete. The
offcuts at the pointy end and or above the transom line can be used to fill
any small triangles in the back corner.
For my own transom I used hybrid on the inside when I made it. (vac bagged) so
I have a double layer that is very stiff now.
Also Steve It helps to make sure the chine and transom joints have a nice
radius so that the cloth sits in there well, especially in the arse end where
the chines are steep. I used the finger radius method with the goop leftover
from filling defects on the inside. I had quite a few edge defects to fill,
but not as many staple holes in my boat. If there are bubbles after its all set
then you can remove them with a stanley knife or a profile sander and patch
them. Don't worry what it looks like. I have a couple that I repaired and used
peel ply over the patch so that the patch edges would be smooth. Cut Kevlar
patch edges tend to be fuzzy and ugly.
A tip on strengthening butt joints.
Hybrid tape is very expensive for what it is and bias hybrid tape is hideously
expensive. If you want to make your own hybrid tape to tab things in here or
there, or for construction, roll some broad hybrid cloth out over a flat bench
and use narrow 1/4 or 1/2 inch masking tape strips in parallel across the
cloth to define strips of whatever width you need (across, so the ends will be
stitched). Follow a single weft strand to keep the strips straight. Press it
down well. Then cut the strips out down the middle of the tape with hybrid
shears. The tape will hold the strands at the edges together. The resulting
strips can then be wound around things or used in tabbing parts down. Where its
going to show I put the masking tape on the inside of the tab and usually get a
good visible edge effect, especially if I keep the edges held down with peel
ply (as I mentioned above). If the tab is not showing, or sometimes when I feel
like it, I leave the tape on the outside and wet the hybrid from the back for a
stronger bond right to the edge. Using colored "time tape" (NYCSkiffs.com) on
the outside makes a striking effect of delimiting the tabbed joins with a
rainbow of color possibilities. But most significantly, having tape on the
edges of a strip of hybrid allows you pull the tape in opposite directions so
that the fibers are on a bias (the tape is narrower then) and if the tape is to
cross a joint then all the fibers contribute to the strength of the joint by
crossing the corner rather than just 50% of the fibers in a regular woven tape
tab.
BTW if your shears are getting tired and you having great trouble getting the
bloody hybrid to cut, loosing your temper, feeling helpless or hopeless, no
time to go get new shears in the middle of a hot lay-up, then tape one or both
sides across where you want to cut and afterwards send me a beer for saving
your arse.
Float those bubble cares away.
My method to remove bubbles is to bend the flexible green squeegees from Sweet
so that a broad flat surface can apply a lot of pressure and be pulled across
the glass. You can hear the bubbles being forced through the glass as they pop
on the other side. This usually works 100% for me. If applying resin on top of
glass, work in small patches and do that patch before moving on to its
neighbor. Don't put resin all over the part in one thick spread and hope to get
the excess off and bubbles out so easily.
Christian and Robert both mentioned the soak up method I think. I use this a
lot when I use clear glass and want parts that have no blemishes. This method
works very well for small parts where the glass cloth is of a manageable size
(not wider than your arm span). Paint the part first with resin with a brush
or roller before you place the cloth. This allows you to get a much better
control of resin across the part, then lay the cloth over the part. You will
have no bubbles (unless you pick up the glass) as the resin filling the cloth
drives out the bubbles. With practice you will be able to get just the right
amount of resin to wet out the cloth but if too much or too little use the
squeegee on top and redistribute resin. Make sure to roll up your glass in a
clean and debris free way so you wont have to pick it up to remove a boulder of
something that got underneath. Debris always makes bubbles appear and these
are inevitably impossible to remove or reoccur over and over before gelling
sets in.
Sensei says Wax on Wax Off.
Dry cedar absorbs a lot of resin, so does endgrain materials but does not add
much strength. Its clear that having the glass close to the core with a little
as possible waste resin under it is the best situation. So to control more
precisely the amount of resin I add to the lay-up, I often paint or roll on,
and immediately wipe off with some rags, the base coat of resin. Wait just a
bit for it to begin to gel (so that no additional resin will soak in) before
placing the glass on top. A wet but slightly tacky gelling surface is good,
really well gelled surface is too tacky to move the glass if you need to and
past tacky is not giving a chemical bond. Pick up the rags from the floor after
your done (or leave them there forever) and feel how much waste resin you saved
from soaking in!! I think this method makes a lighter product but not enough
resin is left on the surface to push out the bubbles so its not a soak up
method as described above. Remove small bubbles by applying pressure with the
squeegee though as I described above. If you have saved resin weight you can
then afford to reinforce joints liberally to stay near the target weight but
then with added stiffness. Its all good.
Enjoy building
Yay, I am finally going sailing this weekend !!! (but in Sweet Caroline,
Christian's boat ). I am fearing that the only way I can win my bet with Mr
Rasmussen is to buy Rogers first boat at the auction!
Greg
----- Original Message -----
From: Steve Nichols
To: Swiftsolo
Sent: Tuesday, July 26, 2005 10:14 PM
Subject: RE: Bubbles in S-Glass layup
Guys,
Thanks for your assistance, the bubbles are only really small so I am not
going to worry about it. I was just pissed about the first real flaw in
building the boat.
At least I know now and the area where it happened isn't critical.
I will apply the lessons learned and the advice I have received on the
visible part of the transom in the next few days.
Cheers,
Steve
-----Original Message-----
From: Christian Rasmussen [mailto:Christian@xxxxxxxxxxxxx]
Sent: Wednesday, 27 July 2005 9:40 AM
To: Steve Nichols
Cc: Swiftsolo
Subject: Re: Bubbles in S-Glass layup
You are not alone in this. I went through it and it can be very frustrating
to get some of the tiny
bubbles out of the sglass. In fact I have seen S-glass advetised with a note
warning that it
should not be used for cosmetic areas due to the tight knits. Unless you have
a lot of dime size
bubbles I wouldn't worry about it. If you want to redo, then sand it off and
try again. BTW, you can
also use hybrid on the inside of the transom. Rules do not prohibit this.
Some things that will help.
- Make sure the resin viscosity is high. This means that the room/resin
should be warm
when applying it and while it cures. There is big different between the 65
and 85 degrees. I did
mine in the winter, so it added to my frustrations.
2. A roller can be pretty good, but the small bubbles has to be squeegeed
out. And make sure you stay with it.
the cedar is really bad at outgassing late in the curing stage. To that
effect make sure that you have "coated"
the wood with resin prior to doing the glass. But you dont want to coat it so
much that you add a lot of weight. Greg Ryan has a patent pending technique he
calls "on-off" which I am sure he has described somewhere in the archives.
Rumors are, he copied it from a scene in the movie "Karate Kid" :)
Christian
- Make sure its warm wher
Steve Nichols wrote:
I made my first major mistake during construction last night. Holy .... that
s-glass is hard to wet out. This was my first go with s-glass on the inside of
the transom and I was maybe a little casual as I had no problems with the
hybrid when doing the bulkheads. I think I applied too much resin at once as I
couldn't get rid of all the bubbles with the squeegee before the resin had gone
off slightly which made it impossible to do.
Do I need to ditch this piece and start again? The bubbles won't be visible
as it is the inside of the transom but have I compromised the strength too much
doing this?
Any tips to prevent a repeat performance?
Cheers
Steve
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