Why NOT attach the hull to the stringers and bulk heads?

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Stuff4Toys
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Why NOT attach the hull to the stringers and bulk heads?

Post by Stuff4Toys » Mon Oct 03, 2011 9:28 pm

Reading through the instructions while building our FS 18 [ viewtopic.php?f=2&t=27322 ] we noticed that it's recommended that we NOT attach the side and bottom panels to the stringers and bulkheads until after the outside is complete. Then NOT to press the stringers in and cause the boat shape to conform to the stringer shape.

Other kits I have looked at, you create the super structure first and attach the panels to it. These instructions say glue the frame in afterwards and fill the gaps.

Anyone have any different ideas?
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D2Maine
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Re: Why NOT attach the hull to the stringers and bulk heads?

Post by D2Maine » Mon Oct 03, 2011 11:03 pm

nm
Last edited by D2Maine on Fri Feb 17, 2012 11:14 am, edited 1 time in total.

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Re: Why NOT attach the hull to the stringers and bulk heads?

Post by gstanfield » Mon Oct 03, 2011 11:13 pm

Hopefully you'll get a response from one of the bateau guys tomorrow, but here's my guess (NOTE< only a guess) I'm thinking that by making the hull a complete structure and then adding the framework later that you will have made for a stronger hull that is not forced into shape, but rather is MADE to shape. Then by adding the framework in afterwards you'll have less chance of creating "hard spots".

Just my guess though. I've been wrong before :wink:

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Re: Why NOT attach the hull to the stringers and bulk heads?

Post by gk108 » Tue Oct 04, 2011 12:05 am

In addition to what is said above, with this method, you get a more fair hull shape. Plywood always bends at different rates, depending on species, local temps and humidity. This way, the plywood takes its own natural bend and then it's held there by the taped seams. You'll be surprised at how closely the frames and stringers will fit. In most cases, builders end up with just enough gap between the frames and the skin to get a nice thin layer of epoxy putty between them. That is the ideal. Sometimes a shim here and there will help achieve that gap. Pulling the hull skin tight to the frames after taping will deform the hull and result in less than optimum strength in the tabbed joints.
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Re: Why NOT attach the hull to the stringers and bulk heads?

Post by sitandfish » Tue Oct 04, 2011 12:21 am

Stuff4Toys wrote:...Other kits I have looked at...
You are right that "other" kits are different. You should follow this method. :wink:

Reading through the "How To" entitled What is the difference between our building material and others? should help you understand some of the difference. Here is part of of it.

"Plywood cored composite can be considered advanced stitch and glue. The building material may look similar to first generation stitch and glue but while the framing is identical, the hull skin is different. In plywood cored composites, the panels are a true composite sandwich."
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Re: Why NOT attach the hull to the stringers and bulk heads?

Post by cali123 » Tue Oct 04, 2011 1:21 am

When I started stitching my XF20, I noticed right away that the plywood wanted to be fair on its own. Any time I tried to fasten a panel with a couple of screws, I would create a wave where the screw was. When the hull was stiched ,fair, and level, I tabbed the stringers and frames with some glass mat and polyester resin to help maintain the shape. I think that this helped to hold the shape while I glassed and faired the bottom and sides. It also strengthened the hull for the flip. I removed all of the polyester before I glassed the inside. When I installed the stringers, the fit was excellent. When I installed the frames, the fit was awful. If I had it to do over, I would try to not use screws for anything and I would definately build temporary frames out of MDF and then build the permenent frames to fit the hull shape.You should always try to follow what the designer suggests but use common sense along the way. Good luck.

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Re: Why NOT attach the hull to the stringers and bulk heads?

Post by Daddy » Tue Oct 04, 2011 8:44 am

Nina, for example, has a layer of biax glass on the inside as well as the outside of the hull. I would be impossible to achieve this kind of strength if the frames were in place before the glassing. This method is different and is part of the evolution of composite boat building. One more step forward.
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Re: Why NOT attach the hull to the stringers and bulk heads?

Post by jacquesmm » Tue Oct 04, 2011 9:14 am

The above posts give a correct answer: the hull shape is defined by the plywood panels, not by the framing.

You compare two different building methods and materials:
- a plywood on frame boats is built . . . on frames. The frames shape the hull.
- our epoxy-ply composite boats are built from surfaces, the plywood panels shape the hull.
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Re: Why NOT attach the hull to the stringers and bulk heads?

Post by wadestep » Tue Oct 04, 2011 9:57 am

When putting the frames in after flipping, they fit so snugly that I had to force a space under them with nickles. Another way of saying the same thing as above is that the plywood of the hull shapes the boat, then you get the internal structural members to fit to the hull, rather than having the structural members form the shape, and fitting the ply to that.
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Re: Why NOT attach the hull to the stringers and bulk heads?

Post by Stuff4Toys » Tue Oct 04, 2011 10:16 am

The other boat is quite a bit larger and much more complex. Here's a pic.
Image
Image
Image
This boat is 24' long and nearly 10' wide so the super structure is much more complex.
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