Wood Spar Scantlings

[Old Salt]

I know we have beat the building of wooden spars to death...but what about design charictoristics? How do you determine the flex of a birdsmouth homebuilt mast as compared to an aluminum? I would hate to go through the process only to find out that it is too limber or stiff.

Are there any books that deal with design issues? We can find scantling figures in most any boat building book for hull thickness. What about spars???

[mmd]

There are several books that give "rules of thumb" for spar scantlings - "Gaff Rig" by John Leather and "Skene's Elements" by Kinney come to mind - but to get hard numbers, one is relegated to a good text on Strength of Materials and a wood data book as prerequisited to some good ol' engineering calculations. ;)

[Art Read]

Well... While we're at it... Suppose one built up a solid spar from three laminations of epoxed Sitka Spruce and in the rounding/sanding process managed to ahhh... er... round and sand a little "too much"? :eek:

I'm not talking about a huge discrepancy, but I wonder how much "extra" strength is designed into the "rule of thumb" scantlings. At this point, I doubt I'll start over. Hell, it's just a daysailor. If the spar goes "galley west" in the first big blow, I'll just chalk it up as an (almost) full sized mock-up and build the next one with a little extra "meat" before tapering and rounding. ;)