To: baidarka@lists.intelenet.net
From: Bram van der Sluys <bvdsluys@direct.ca>
Subject: Re: [baidarka] to peg or not to peg
Message-Id: <E0ycMNe-0002fa-00@jack.direct.ca>
Date: Wed, 20 May 1998 20:50:58 -0700
At 11:50 AM 20/05/98 EDT, you wrote:
>Hi there~
>
>Having survived engineering school with my humanity intact, I thought I'd
>give my two cents on the peg vs screw vs lashing inquiry.
>
>>From a basic "Strength of Materials" point of view, ANY material removed
>from the gunwales acts to weaken their resistance to the bending moment
>existing along their length. At the deck beam cross sections the mortise
>cut has already removed 1/4 to1/3 of the material, so it seems to me that
>in the interest of maintaining flexibility and strength , lashing is the
>way to go.
>
>If holes are going to be drilled through the gunwale (ie for pegging),
>they should be through the mid-point with the axis of the hole(s)
>perpendicular to the bend of the gunwale. This places them along the
>"neutral axis" where, in theory, no bending stress exists ( stress
>increases linearly with distance from the mid-point: inboard =max
>compression; outboard=max tension).
>
>Screws seem like a bad choice because their threads are going to "work"
>the wood as the frame flexes, possibly initiating a crack in the gunwale
>or the deck beam tenon.
>
>Well, that's one opinion. I wonder if anyone has done a 3D frame analysis
>on the baidarka. The joints get worked in so many ways that it would be
>difficult to account for all the loadings.
>
>Regards,
>
>Jeff
Hi also:
I would also like to comment on the above analysis.
a) a peg removes even more material than a screw (unless you use #14's or
bigger) and unless glued in place will work and create sress points equally
well. If the peg is glued than one may as well glue the whole joint.
b) consider the wood removed for lashing holes, do they not add up to more
than a single screw, probably.
c) the fixity of the deck beam joint to the gunwales has very little to do
with overall gunwale flexibity, thus glued, lashed, screwed or all of the
above doesn't make a hill of beans difference except that I wouldn't use
screws by themselves.
d) as for modelling 3-D it's not the load thats difficult, it's modelling
the various joint freedoms. The load remains reasonably the same regardless
of hull configuration.
good luck in your engineering endeavors!
Regards
Bram