Permanent frames - alternatives

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Tor
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Permanent frames - alternatives

Post by Tor » Mon Feb 25, 2008 7:54 am

I'm building the DK touring canoe out of 4mm ply.

I've been a little dubious regarding the frames that sit towards the middle if the boat. They're not going to be easy to fix in place whilst all the stitches go in and the internals of the canoe are going to be messed up with the ~50mm intrusion.

As I messed up and cut one side at too low an angle I need to remake them. What effect do you think I would have if I made them from 25mm by 8 or 10mm Cedar (wood of choice for the gunwhales). Making and fitting then so that the 25mm side would be bonded to the boat. The piece across the boat would probably be 25x50mm and built under the gunwhales.

Hope this makes some sense, any comments gratefully accepted.

Thanks,

Tor.

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Post by hairymick » Mon Feb 25, 2008 9:30 am

G'day Tor,

Are you usng western red cedar or surian for the gunwhales?

Either way, I am not sure it is the best choice. (Very weak) Might I suggest Hoop pine or similar.

I haven't seen the plans for this boat so I am not sure what you are refering to by permanent frames. Can,t help there. sorry.
Regards,
Mick

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Post by jem » Mon Feb 25, 2008 11:00 am

Morten designed that canoe with those frames being a part of the hull. I'd say you might be better off making them to the specified size.
-Matt. Designer.

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Post by Boatplans.dk » Mon Feb 25, 2008 3:31 pm

Hi Tor,

You could change the size of the frames but you will have to observe some basic mechanic before doing so. Let's say you reduce the height (50 mm) to the half, 25 mm, you will then have to make the thickness 8 times larger in order to get the same moment of inertia for the frame. If you reduce the height to 10 mm you will have to make it 125 times thicker. This example is somewhat simplified since the hull panels will contribute to the overall stiffness of the frame, but as an estimate the above figures will do.

Another possibility is to add more frames that are lower. This will also be possible but then the different hull panels will have to be calculated again with the new frame spacing in order to calculate the new frame height, but as the above figures show it will be difficult to reduce the height significant.

My own experience is that the frames are not a problem when canoeing. In fact I often find it helpful with the partition of the canoe when securing equipment and gear in the canoe, but that is a matter of opinion :)
Morten Olesen - Boatplans.dk
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Post by Tor » Tue Feb 26, 2008 6:55 am

:P you pose arguments using logic, physic and maths. What hope have I got?

Well looks like another piece of ply is required I'll probably get a bit of 6mm for these bits.

I put the top section on tonight (couldn't wait for the frame - which I'll struggle to fit once I've made them at the weekend) and it's looking like a canoe now, just hope I can get the damn thing through the door.

Mick, yes I was going to use western red, y 'know light, water tolerant etc...
back to the drawing board then.

thanks for your words of advice (instructions not to be silly).

Tor

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