modifications to gf 16 new build

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levicitus
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Re: modifications to gf 16 new build

Post by levicitus » Sat Feb 25, 2012 5:09 pm

does anyone know how much rocker should be in the bottom? I noticed after I got the bottom zip tied to sides and flipped her over the transom was off the jig all the way a foot shy of the mid seat rear frame. Is this normal? I don't want to glass anything till i hear back. If it was there before I didn't notice as the bow was supported .b happy



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Cracker Larry
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Re: modifications to gf 16 new build

Post by Cracker Larry » Sat Feb 25, 2012 5:16 pm

There should be no rocker from the transom the the rear frame of the center seat. It's a flat run.
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levicitus
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Re: modifications to gf 16 new build

Post by levicitus » Sat Feb 25, 2012 6:53 pm

larry thanks for your comment. Have any ideas where to look first?

TRC886
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Re: modifications to gf 16 new build

Post by TRC886 » Sat Feb 25, 2012 9:29 pm

Is the bow heavy and lifting the transom up off of the jig? What happens when you pull the transom down to touch the jig, or jack the bow up until the transom touches? Does the bottom sit flat on the jig, from the transom to the center seat, then? If so, you're in good shape. If not, you need to fix it before going any further.

levicitus
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Re: modifications to gf 16 new build

Post by levicitus » Sat Feb 25, 2012 10:15 pm

Thanks for the reply. The bottom lays flat on jig with some pushing down on transom, feels slightly heavy in the nose. I'll check some measurements tomorrow. Maybe take bottom off. I had to use the ties to shift the bottom around somewhat when I laced it on. Will post tomorrow and try to get pics in. Thanks for your help.

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Re: modifications to gf 16 new build

Post by robbiro » Sun Feb 26, 2012 11:29 pm

I had to prop the nose of my GF up on a small red cooler to get the rear bottom to lay flat on my work surface.
Seem to remember that someone used some screws to hold the rear down on his jig while he did all fo the interior filets and taping. I remember that CL was in the conversation about this, but I do not remember at this time who the builder was. This did seem to do the trick.
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jacquesmm
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Re: modifications to gf 16 new build

Post by jacquesmm » Mon Feb 27, 2012 9:59 am

When you assemble, the hull panels tend to pull the bow away from the center.
There are several ways to prevent that.
The best way is to assemble as in the building notes and use the forward deck to pull the bow back.
Another method is to pull the transom back with a line or a tackle.
The plans give the total length, don't let the boat be longer than that.
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travis_in_alaska
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Re: modifications to gf 16 new build

Post by travis_in_alaska » Mon Feb 27, 2012 2:33 pm

I had to support the bow end as well. Another big help for me when getting the geometry correct was watching the centerline. Mark the midpoint on the bottom of each frame, and draw a centerline on your building jig. Wiggle stuff around to get all the frames to line up their midpoints to the centerline.

I kept having one side of the rear of the boat trying to lift off the jig. I thought it was a problem with the shape of my transom, but it turned out I just needed to do the midpoint thing, then everything came together very nicely.

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Re: modifications to gf 16 new build

Post by jacquesmm » Mon Feb 27, 2012 2:39 pm

Yes, the plywood sometimes has a mind of his own. One side may pull more than the other, symmetry is not automatic.
As said above, line up your centerline and before glassing, check the diagonals.
The distance from the bow port side corner to the transom port side corner must match the opposite diagonal.
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Cracker Larry
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Re: modifications to gf 16 new build

Post by Cracker Larry » Mon Feb 27, 2012 6:51 pm

I support the bow end and clamp or screw down the rear section flat to the building platform, and keep it in that position until it is glassed solidly in position. I've built a few GFs and they all want to rocker if you don't keep the rear flat and force the bow up. Screws, clamps, ratchet straps, whatever it takes. Keep the back half of the boat straight and let the bow go where it wants. Then prop it a little higher. If you prop up the bow a little it helps to force the stern flat and lets the sides flare nicely :wink:

This is a GF16..

Image

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And a GF12 behaves the same way. Prop up the bow and the rear section will be forced flat, If it isn't flat, run a ratchet strap around it and pull it down. Then start gluing it.

Image

Keep it supported in this position as much as possible throughout the taping and glassing.

Image
Completed GF12 X 2, GF16, OD18, FS18, GF5, GF18, CL6
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