Why were/are masts and spars tapered?

[achuck49]

Can someone explain to me why masts and spars were/are tapered in the first place?  Couldn't a builder just find a piece of wood that was the correct diameter and use that instead of going through the expense and trouble of tapering that same piece?

 

Just an idle question that keeps rattling around in my head.

 

Chuck Aldrich

[jud]

Weight and because of that weight and the deflection forces diminishing as you go out from the center allowed for reducing the weight without hurting function. Or could be like Grandad, he liked to stand on the sunny side of the barn out of the wind and whittle a tooth pick from a much bigger piece.

jud

[trippwj]

Two reasons really. First, the natural tree trunk had some taper but, more importantly, weight. According to R. C. Anderson, as the length of masts and yards increased, there was a need to keep the center of mass lower and along the centerline of the ship. By tapering, the strength was retained but the total mass/weight was reduced and kept lower (masts) and centered (yards). Resulted in greater stability.

[mspringer]

Jud, thanks for the visual of Grandad...which is what I called mine.  I got his image doing that very thing.  Grandad is also what my granddaughters call me.

 

Mark

[Doreltomin]

I would say the question is not just about weight. As Jud says, just think about the distribution of a force acting laterally on the mast. It acts just like one arm of a bow or more precisely like a cantilever with one end free and the other anchored securely on the deck. See:

 

http://en.wikipedia.org/wiki/Cantilever

 

Without goind too deep into structural analysis, the point is that the stress accumulates at the bottom of the mast, so the mast has to be thicker there to withstand the stress.

 

If instead of being tapered, it would have been straight, that would mean it would surely break at the foot because the ratio between its strength and the forces applied to it would have been the worst at this point. 

 

Now think again of one arm of the Archer's bow: it is also tapered from the tip to the middle for the same reason: to have a constant ratio between its strength and the forces applied to it, otherwise any irregularity would mean it would surely break under stress. 

 

Hope this helps!

Edited June 15, 2014 by Doreltomin

[HIPEXEC]

Trees are naturally tapered.

[trippwj]

Interesting stuff. The mechanics and dynamics factors are probably unintended benefits, since the vast majority of early shipwrights that developed the concept of tapering had little or no training in mechanics and often very little math. Worth a look at Anderson's books on Rigging in the days of the sprit sail topmost for his historical analysis.

[testazyk]

I never thought to wonder why--glad you asked the question!