Sheerline and glassing

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Grumple
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Sheerline and glassing

Post by Grumple » Fri Jun 26, 2015 10:21 am

Hey guys,

Just a quick question...I've seen others say that they leave the sheer line cut pretty rough (ie extra 1/2" or so) to be trimmed down flush with the gunwales later, after glassing, etc. I plan to do this too in general, but at the center of my canoe I aligned my first strip such that there is just barely any waste area once I've trimmed off the bead off, and didn't add any extra (yet) to create this area.

Is this extra 'waste area' needed for a clean edge where the fiberglass ends?

I guess another way of putting this question would be, is it possible to keep a nice, clean finish when glassing at the edge of the sheer line cut? Any issues with the glass wanting to lift off, etc, for the first __ distance?

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Jim Dodd
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Re: Sheerline and glassing

Post by Jim Dodd » Fri Jun 26, 2015 12:53 pm

I have little trouble with the outside.
But the inside, where the cloth lays over the shearline, can be a difficult situation. Shortly after I have the inside wetted out, I trim the wet cloth, with an old, but sharp pair of scissors, the excess cloth. Then make sure the cloth is against the hull. This should take care of any air pockets that may form near the shearline.

Jim
Keep your paddle wet and your seat dry!

JesseP
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Re: Sheerline and glassing

Post by JesseP » Fri Jun 26, 2015 12:59 pm

Hey Grumple, I haven't started glassing yet, but when I started stripping mine my first strip was lined up with the shearline at the center station and continued that way until about station 4.5 where the shearline started curving. I guess what I'm saying is... are you sure you need to trim your shearline at the center station? if it is only a little off the shearline, say 1/8" or so and level across the strips I would leave it and and only worry about the shearline at the stern and bow. You should have cutouts on your station molds indicating where the shearline should start on each mold.
I'm up to my torch.

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Grumple
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Re: Sheerline and glassing

Post by Grumple » Fri Jun 26, 2015 2:07 pm

Hi Jesse,

Yeah that was my thinking too when I lined up my first strips. I really left just enough to trim off the bead flush with gunwales.

I can't find it, but I'm sure I saw a comment from Jim Dodd(?) not too long ago about how he likes to have extra waste strip beyond the line...I could have sworn it was something to do with the fiberglass tending to get a bit messy, etc, near the edges.

Anyway, I'm not overly worried, but figured now was as good a time as any to get some opinions. :safety glasses

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Patricks Dad
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Re: Sheerline and glassing

Post by Patricks Dad » Fri Jun 26, 2015 9:31 pm

I always trim my sheerline within 1/4" of the final place (usually within 1/8"). As Jim notes, glassing the outside is easy (unless you have lots of tumblehome). The trick is to keep an eye on the glass as the epoxy sets up. Once you have everything on, there is a tendency to say to yourself "Whew! glad that's done" and leave the shop for a few hours while you wait for the 2nd coat. Don't just leave it. keep looking at your wonderful work every 30 minutes or so to make sure you have no bubbles or places along the sheerline where the glass has separated from the hull. If you keep an eye on it, even a stubborn spot can be "cured" into submission.

Also as Jim notes, glassing the inside is a bit more difficult where the weight of any excess glass may pull it away from the hull. Here too it's important to keep an eye on things as it sets up. I don't trim the glass flush with the hull until after the first coat is ready for a 2nd coat (it should be just pack tacky and easy to cut with a sharp razor knife - a 5 minute job before staring the 2nd coat - If you wait until just before the 3rd coat it will be much harder to cut - if you cut too soon, it can be a gooey mess). If your glass is cut reasonably close in the first place, the tendency for the glass to separate from the hull will be minimal (but keep any eye on it every 30 minutes after you have finished so you catch anything anyway). And don't just glance at the hull from a distance. Scan every inch along the sheerline to look for any places where there might be a separation (which may be filled with epoxy and not really obvious). It's also helpful to have another pair of eyes take a look on your behalf (If you have a pal mixing epoxy while you work, they can do this job too).

And don't just look at the sheerline. Look at every square inch for any signs of bubbles or wrinkles (the inside is more critical than the outside because on the outside the glass tends to want to stretch out over the hull - on the inside it tends to want to slump from it's own weight or be pulled away fro the bottom by an overly aggressive squeegee).

enjoy!
Randy Pfeifer
(847) 341-0618
Randy.Pfeifer1@gmail.com

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Jim Dodd
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Re: Sheerline and glassing

Post by Jim Dodd » Fri Jun 26, 2015 10:28 pm

Well put Randy !
Never leave until the epoxy is very near set!!
I did that once !
A stitch in time saves nine !

Jim
Keep your paddle wet and your seat dry!

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Grumple
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Re: Sheerline and glassing

Post by Grumple » Mon Jun 29, 2015 11:23 am

Thank guys. That is an excellent description of the process, Randy.

Just a quick follow-on question...if you initially leave roughly 1/4" - 1/8" past the sheer line when trimming, how/when do you later bring it down exactly to the line?

I've been following the book, and I've drawn my sheer lines on the outside, prior to installing outer stem/fairing the hull. I assume I'll sand off my drawn lines when I fair the hull though. Are you just not drawing your sheer line until after fairing the hull to avoid losing it?

In the book Ted does the sheer line cut prior out adding the outer stem/fairing the hull. He seems to trim right down to the real line, and then glues his inner gunwales slightly below that edge before planing flush. I guess doing it this way he doesn't need care if his drawn lines get sanded off (as long as he keeps a consistent amount of the sheer line above the gunwale along entire length when installing it).

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Patricks Dad
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Re: Sheerline and glassing

Post by Patricks Dad » Mon Jun 29, 2015 1:21 pm

.if you initially leave roughly 1/4" - 1/8" past the sheer line when trimming, how/when do you later bring it down exactly to the line?
Once I have installed the gunwales (leaving a bit of the hull sticking out), I simply sand it flat with a belt sander (I didn't used to consider a belt sander to be a "fine woodworking" tool but it works great). You could also use any other aggressive sander. In either case finish with a finish with a fine sanding to make the joint between the hull and both gunwales perfect (this will also fix an slight mis-alignment between the inwale and the outwale).
Randy Pfeifer
(847) 341-0618
Randy.Pfeifer1@gmail.com

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Grumple
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Re: Sheerline and glassing

Post by Grumple » Mon Jun 29, 2015 3:23 pm

Ok so you must still have your reference lines/marks to know exactly where to put the gunwales then if not using the rough edge you cut?

I.e. do you wait and mark the real sheer line location on the outside of hull after you are done sanding?

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Patricks Dad
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Re: Sheerline and glassing

Post by Patricks Dad » Mon Jun 29, 2015 5:04 pm

I use the rough cut edge (minus a bit - ~1/8"). The gunwales will make their own fair curve and if it's off a bit it won't matter. I do try hard to make sure both sides are the same so it won't look goofy when you stand back and look at both sides at once.
Randy Pfeifer
(847) 341-0618
Randy.Pfeifer1@gmail.com

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Grumple
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Re: Sheerline and glassing

Post by Grumple » Tue Jun 30, 2015 12:12 pm

Perfect, thanks! I was kind of hoping that's what you'd say!

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