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Old 07-15-2008   #1
lhowemt's Avatar
at my house, Montana
Paddling Since: 2020
Join Date: Apr 2007
Posts: 4,347
Double Rail frame design

OK you frame designers out there, I am putting together a double rail from out of NRS parts, and am looking for some detailed feedback.

New boat, 14', 80" total width, 20" tubes. I am not using metal as a platform connecting the double rails.


1) Should I have both rails touching the tubes? It seems so since 3 cross bars will only connect to that inner tube.

2) Width between the outer bars, width between the inner bars? I'm thinking 66 and 54, but would like a bit more space betwen the rails (this gives only 6").

3) If you think I can get wider than 6", what dimensions would you adjust from my base proposal?

4) Thinking of having one small cross bar connecting the side rails, just for torsional stability and strength, what do you think?

I'm checking with NRS, but don't think they do any double rails.


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Old 07-15-2008   #2
Chip's Avatar
SE, Wyoming
Paddling Since: 1986
Join Date: Apr 2007
Posts: 1,098
6 inches between the rails is a good fit on a 20-inch tube, with the top centerline of the tube down the middle. I'd guess you'll mount the NRS LowPro fittings on the rails, so you can adjust the distance between them pretty easily while the overall length is fixed.

If you've got 1 or 2 crossmembers (for seat & gear bays) between the inner rails, you shouldn't need further crossbraces between the side rails.

But one cheap dodge is to buy some NRS U-bolts (used in the LowePro joints and oarstands) and mount plywood decks between the rails, that give you a place to step and also provide bracing.

Click image for larger version

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Here are some wood decks on a steel double-rail frame (with corners from Cambridge Welding). I use cheap u-bolts from the local hardware, but the NRS version fits their aluminum tubing. Use washers, countersunk into the wood, and acorn nuts to cover the threads.

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